Citation
CedarOrtega River Basin, Florida, restoration

Material Information

Title:
CedarOrtega River Basin, Florida, restoration an assessment of sediment trapping in the Cedar River : phase 2 final report
Series Title:
Cedar/Ortega River Basin, Florida, restoration
Creator:
Mehta, Ashish J
Hayter, E. J
Place of Publication:
Palatha FL
Publisher:
St. John River Water Management District
Publication Date:
Language:
English
Physical Description:
1 v. (various pagings) : col. ill., col. maps ; 28 cm.

Subjects

Subjects / Keywords:
Contaminated sediments -- Florida -- Cedar River ( lcsh )
Contaminated sediments -- Florida -- Ortega River ( lcsh )
Sediment control -- Florida -- Cedar River ( lcsh )
Sediment control -- Florida -- Ortega River ( lcsh )
Watershed restoration -- Florida -- Saint Johns River Watershed ( lcsh )
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bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references.
General Note:
"January 2004."
General Note:
"Special publication SJ2004-SP33"--Cover.
General Note:
"UFL/COEL-2004/001."
Statement of Responsibility:
by Ashish J. Mehta and Earl J. Hayter.

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University of Florida
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University of Florida
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Full Text
UFL/COEL-2004/001

CEDARIORTEGA RIVER BASIN, FLORIDA, RESTORATION: AN ASSESSMENT OF SEDIMENT TRAPPING IN THE CEDAR RIVER PHASE 2 FINAL REPORT
by
Ashish J. Mehta E. J. Hayter and
R. Kirby

January2004




UFL/COEL-2004/001

CEDAR/ORTEGA RIVER BASIN, FLORIDA, RESTORATION: AN ASSESSMENT
OF SEDIMENT TRAPPING IN THE CEDAR RIVER PHASE 2 FINAL REPORT
By
Ashish J. Mehta And

Earl J. Hayter
Submitted to:
St. Johns River Water Management District
Palatka, FL 32178-1429
Coastal and Oceanographic Engineering Program Department of Civil and Coastal Engineering University of Florida, Gainesville, FL 32611

February, 2004




SYNOPSIS
This report includes the findings of the study, "Remediation/Restoration of Cedar/Ortega Rivers. Phase 2: Scope of Work to Assess Fine Sediment Deposition, Erosion and Transport Rates and Evaluate Dredge Scenarios", carried out by the University of Florida
(UF) for the St. Johns River Water Management District (SJRWMD), Palatka, Florida. The project objective was to predict the rates of deposition, erosion and transport of fine sediment, to evaluate proposed remedial dredging works (e.g., sediment trap/channel dredging, computation of dredge volumes), and to develop management strategies in the lower Cedar/Ortega Rivers. This objective was met by carrying out physical measurements, modeling hydrodynamics and sediment transport, and evaluate present and future rates of sediment deposition, erosion and transport under selected remediation scenarios provided by SJRWMD.
We have examined both on-line and off-line sediment removal approaches, specifically off-line Wet Detention Systems and on-line dredged pits, as well as dredging and sand capping in the Cedar/Ortega River confluence area. Three assessment criteria have been used qualitatively to rank the 11 options; these criteria being removal of contaminated sediment from its source in upstream Cedar River, improved navigability in the confluence area and water quality.
We find that if the capture of contaminated sediment from upstream sources in Cedar River is the only or the main goal, one of the two off-line sites proposed by SJRWMD, preferably the one closer to the source of sediment, would be the preferred choice, provided the facility operates at very high, i.e, 80% removal efficiency. If improvement is navigation coupled with reduced resuspension of in situ material is additionally desired, selective dredging and sand capping in the Cedar/Ortega confluence area should be considered. If capping proves




to be costly, removal of the top layer of very soft mud from areas where boats regularly ply the waters may be further evaluated.
We would like to acknowledge the cooperation and assistance provided by Dr. Chandy John and Dr. Fred Morris of SJRWMD throughout the study. Principal contributors to the appendices of this report, Dr. Earl Hayter, Dr. Robert Kirby and Dr. John Land, and UF graduate students Vladimir Paramygin, Jason Gowland and Dan Stoddard are recognized. A noteworthy contribution independent of the present study was also made by visiting researcher Fernando Marvin. Prior contribution by graduate student Jianhua Jiang to Phase 1 of this study formed the basis for the design of the present Phase 2.




TABLE OF CONTENTS
SYN O PSIS ...................................................................................................................................... ii
TABLE O F CO N TENTS ............................................................................................................. iv
LIST O F FIG U RES ....................................................................................................................... V1
LIST O F TABLES ........................................................................................................................ ix
1. INTRO DU CTIO N ................................................................................................................... 1
1.1 Pream ble ....................................................................................................................... 1
1.2 O bjective ....................................................................................................................... 4
1.3 Tasks ............................................................................................................................. 6
1.3.1 Task 1: Assem bly of Existing D ata .................................................................... 6
1.3.2 Task 2: Samples for Engineering Characterization of Sediments ................... 6
1.3.3 Task 3: ADCf, Water Level and Salinity Measurements ................................. 6
1.3.4 Task 4. Sedim ent Load Rating Curves .............................................................. 7
1.3.5 Task 5: M odel Setup, Sim ulations and R esults ................................................. 7
1.3.6 Task 6. Run M odel Scenarios ............................................................................ 7
1.3.7 Task 7. D redging A lternatives Evaluation ........................................................ 8
2. OBSERVATIONS FROM FIELD INFORMATION .......................................................... 9
2.1 Pream ble ....................................................................................................................... 9
2.2 Bottom Sedim ent Sam pling ........................................................................................ 9
2.2.1 Cedar River .................................................................................................. 13
2.2.2 Ortega River .................................................................................................. 14
2.2.3 Inner Confluence Region ............................................................................ 15
2.2.4 Outer Confl uence Region ............................................................................ 16
iv




2.2.5 Data Statistics .............................................................................................. 17
2.3 Hydrographic M easurements ................................................................................... 18
2.4 Suspended Solids Content from Acoustic Profiling ............................................... 24
3. LABORATORY TESTING FOR SEDIMENT TRANSPORT ......................................... 30
3.1 Pream ble ..................................................................................................................... 30
3.2 Erosion and Settling Tests ........................................................................................ 30
3.3 Settling Velocity Algorithm ...................................................................................... 32
3.4 Consolidation ............................................................................................................. 35
4. SEDIM ENT REM EDIATION ............................................................................................. 37
4.1 Sediment Treatm ent Scenarios ................................................................................ 37
4.2 W et Detention Systems .............................................................................................. 41
4.3 Cedar River Sediment Trapping M odeling Results ............................................... 42
4.3.1 Cartesian Grid M odeling Results ................................................................ 42
4.3.2 Curvilinear-Orthogonal Grid M odeling Results ........................................ 43
4.3.2.1 Off-line Sediment Traps .................................................................. 46
4.3.2.2 On-line Sediment Traps .................................................................. 47
4.3.2.3 Results from Sediment Trap Simulations ...................................... 50
4.4 On-Line Alternative: Dredging in the Confluence Area ........................................ 56
4.5 Selective Dredging ..................................................................................................... 58
4.6 Selective Dredging and Capping .............................................................................. 59
5. ASSESSMENT OF REMEDIATION ALTERNATIVES ................................................. 60
5.1 Selected Alternatives/Options ................................................................................... 60
5.2 Qualitative Assessm ent ............................................................................................. 60
BIBLIOGRAPHY ........................................................................................................................ 64




Fig. No. Page No.
1.1 Regional map of the Lower St. Johns River basin ......................................................... 2
1.2 Cedar/Ortega River system and tributaries ..................................................................... 4
2.1 Bottom sediment-sampling sites in 1998. The region is conveniently
divided into four regions (from Appendix A) ................................................................ 9
2.2 Composition of area bottom sediment (from Appendix A) .......................................... 10
2.3 Moisture content distribution (from Appendix A) ....................................................... 11
2.4 Total solids distribution (from Appendix A) ................................................................ 11
2.5 Total organic carbon distribution (from Appendix A) ................................................. 12
2.6 Sedimentation rates (based on Donoghue, 1999) ......................................................... 12
2.7 Cedar/Ortega River data collection sites (from Appendix E) ...................................... 19
2.8 Simulated flood flow (depth-mean) velocity field during El Nino discharges
in the Cedar/Ortega system (after Marvdn, 2001) ........................................................ 19
2.9 Simulated ebb flow (depth-mean) velocity field during El Nino discharges
in the Cedar/Ortega system (after Marvdn, 2001) ....................................................... 20
2.10 Cumulative frequency distribution of Cedar River discharge ...................................... 22
2.11 Measured suspended sediment time-series at San Juan Rd. Bridge,
Cedar River, 01/09/94-02/11/95 ................................................................................... 23
2.12 Cumulative distribution of significant wave height (H,,,,,) at the mouth of the
Ortega during 02/10/01 to 04/25/01 (from Appendix E) .............................................. 24
2.13 Discharge relative to high water level at Ortega Main bridge (from Appendix Q ...... 26
2.14 Solids flux estimates corresponding to Figure 2.13 (from Appendix Q ..................... 27
2.15 Solids concentration estimates corresponding to Figures 2.13 and 2.14
(from A ppendix Q ....................................................................................................... 27
2.16 Rating curve of Stoddard compared with that of Marvdn (from Appendix F) ............ 28

LIST OF FIGURES




3.1 Map of Cedar and Ortega River sampling sites. Sites UFO Iare for the present
study; UF99 are from a previous sampling study (Mehta et al. 2000) ..................... 31
3.2 Composite plot of bed erosion rate versus bed shear stress (from Appendix B).
Note that for computational purposes, the first line, representing minor
"floc entrainm ent" is ignored ................................................................................... 31
3.3 Settling velocity variation with concentration data and best-fit of
Eq. 3.2. Peak velocity is 1.5x102 rn/s (from Appendix B) ..................................... 32
3.4 Floc growth with time measured and predicted for River Ems-Dollard
fine sediment (Winterwerp, 1998) (from Appendix E) .......................................... 34
3.5 Settling velocity calculation test results, and comparison with data of
Wolanski et al. (1992) using sediment from Townsville Harbor, Australia
(from A ppendix E) ................................................................................................... 34
3.6 Consolidation for initial conc. of 13.7 g/l (from Marvdn, 2000) ............................. 35
3.7 Consolidation for initial conc. of 24.3 g/l (from Marvdn, 2000) ............................. 36
4.1 Cedar/Ortega Rivers data collection and sediment off-line treatment
(Wet Detention System) alternative sites OFL-1 and OFL-2 proposed
by SJR W M D ................................................................................................................ 37
4.2 Sediment treatment facility alternatives in addition to those proposed by
SJR W M D ..................................................................................................................... 38
4.3 Cedar River bathymetry. Bottom elevations are in meters with reference
to N G V D ...................................................................................................................... 39
4.4 Bathymetry of the Ortega River (running north-south) at its confluence
with Cedar River (to left). Depths are in meters. Note the change in
map orientation with respect to Figure 4.3 .............................................................. 40
4.5 Schematic drawing of a Wet Detention System ...................................................... 42
4.6 Location of open water boundaries in the Cedar River modeling domain.
(from A ppendix G ) ................................................................................................. 45
4.7 Sediment pit or trap and, on the tide-mean basis, a removal defining
"streamline" separating material that deposits from that carried past the trap
(after G anju, 2001) ................................................................................................... 48
4.8 Removal ratios for ONL-1 (upper curve) and ONL-2 (lower curve) as
functions of Cedar River discharge (from Appendix F) ........................................... 49




4.9 Core thickness isopleths based on 1998 data (from Appendix E) ............................ 56
4.10 Isopleths in the confluence area (bounded by dashed lines). Dark circles
are 1998 core sites ................................................................................................... 57
4.11 Illustrative plot of bed density stratification in the confluence area ........................ 58




LIST OF TABLES

Table No. Page No.
2.1 Statistical values associated with bed sediment distribution (from Appendix E) ....17 2.2 Tide statistics for the study area (based on Appendix E)................................. 18
2.3 Current statistics at the mouth of the Ortega River (based on Appendix E)........... 21
2.4 Salinity statistics for the study area (based on Appendix E) ............................ 21
2.5 Confluence region concentrations on May 17, 2001 (from Appendix E).............. 22
2.6 Statistics based on measured TSS by SJRWMD during 01/09/94 02/11/95......... 23
3.1 Data from settling column tests with Ems-Dollard fine sediment
(from Appendix E)........................................................................... 33
4.1 Cedar River off-line sediment trapping scenarios (from Appendix G)................. 44
4.2 Cedar River on-line sediment trapping scenarios (from Appendix G) ................. 44
4.3 TSS removal efficiencies of treatment systems in Florida (after Harper, 1997) ....46 4.4 Results from off-line sediment trapping scenarios (from Appendix G)................ 52
4.5 Results from on-line sediment trapping scenarios (from Appendix G)................ 52
4.6 Percentage change in reach average net erosion (from Appendix G) .................. 53
5.1 Selected alternatives/options................................................................ 61
5.2 A summary assessment of remediation options for Cedar River sediment ............ 62
5.3 Ranking of options based on selected criteria............................................. 63




1 INTRODUCTION

1.1 Preamble
This report is the final technical report to be submitted to the St. Johns River Water Management District (SJRWMD) by the University of Florida (UF). It includes work carried out on the contract entitled "Remediation/Restoration of Cedar/Ortega Rivers. Phase 2: Scope of Work to Assess Fine Sediment Deposition, Erosion and Transport Rates and Evaluate Dredge Scenarios".
The Cedar/Ortega River basin is located west of the St. Johns River in south-central Duval County in northern Florida, and is an important tributary of the St. Johns River (Figs. 1.1 and 1.2). The Ortega River is the main tributary of the system, discharging approximately half of the total system's volume to the St. Johns River. The Cedar River is the second most important tributary, and there are three other secondary tributaries of the system (Fishing Creek, Butcher Pen Creek and Williamson Creek). The upstream portion of the Ortega River is known as McGirt's Creek. The creek lies within the Duval uplands physiographic province and flows generally north to south. The Ortega River continues this course until it reaches the Eastern Valley physiographic province, where the river gradually turns 180 degrees to a northnortheasterly course before reaching the St. John's River north of the Jacksonville Naval Air Station. A tributary, Big Fishweir Creek, joins the Ortega near its mouth (Figure 1.2).
The Cedar River is actually a major system itself. From its headwaters north of Interstate-10 and west of Interstate-295, this river flows southeast to its confluence with the Ortega River. Major tributaries to the Cedar River are Willis Branch, Williamson Creek, Butcher Pen Creek, and Fishing Creek. The tidal interface for the Ortega River is at Collins Road, while the tidal interface for the Cedar River is near Lane Ave. (These two and other road




Figure 1. 1 Regional map of the Lower St. Johns River basin.
locations are not highlighted in any drawings herein; they are found in road maps of the Jacksonville area.)




In the early 1990's, approximately one-third of the Cedar/Ortega River basin was residential, with commercial/industrial and vacant land comprising the other major land uses. Since then, vacant land has decreased significantly. The average annual rainfall in the Ortega/Cedar basin is approximately 132 cm and the major portion of it falls between June and September (Campbell et al., 1993). Water depths in the Ortega/Cedar basin study area range between 1 and 7 m, with the range in the Cedar River between 0.7 m and 4.3 m (NGVD). At the mouth of the Ortega River with St. Johns River, the semi-diurnal (M2) tide ranges from 0.14 m (neap tide) to 0.28 m (spring tide), having a mean of 0.19 m. The bottom and suspended sediment is mostly a mixture of clay, silt and organic matter, with occasional intrusions of sand. Typical suspended sediment concentration is approximately 15 mg/l; however, during storm runoff events it rises to as much as 105 mg/l. The dominant range of organic content was found to be 20-30%.
Remediation of contaminated sediment in the Cedar River has become a critical issue due to elevated concentration of PCBs (polychlorinated biphenyls) in the water system due to leeching of sediments and runoff from a fire at a chemical company in January 1984. The site was located approximately 0.6 km east of the Cedar River near the headwaters north of Interstate route 1-10 and adjacent to municipal storm drains and drainage ditches. The fire destroyed several tanks storing high concentrations (4,425 ppm) of PCB-laden oils and other materials. It is believed that a combination of damage to the storage tanks and the fire-fighting effort created a vehicle for the PCB to enter the Cedar River basin. (Environmental Protection Board, 1985). The surrounding groundwater and soil were sampled extensively in 1989 and the concentrations were still significantly above the regulated amount of 50 ppm.




Figure 1.2 Cedar/Ortega River system and tributaries.

1.2 Objective
As stated in the contract, the objective of this project was to predict the rates of deposition, erosion and transport of fine sediment, to evaluate proposed remedial dredging works (e.g., sediment trap/channel dredging, computation of dredge volumes), and to develop management strategies in the lower Cedar/Ortega Rivers. It was required to conduct physical measurements, set up and apply a numerical model, the Environmental Fluid Dynamics Code
4




(EFDC), to simulate hydrodynamics and sediment transport, and evaluate present and future
rates of sediment deposition, erosion and transport under selected remediation scenarios
provided by SJRWMD. Core and any related data already collected by SJRWMD were to be
used for sediment model calibration and validation and quantification of sediment fluxes to
from the lower Cedar/Ortega Rivers, and accumulation/depletion of sediment within this area.
Specific objectives of the contract were listed below.
1. To collect and analyze bottom sediment grab samples from 10 sites, including
Fishweir Creek, and to analyze these samples for erosion potential, settling rates and consolidation in the Coastal Engineering Laboratory of the University of Florida
UF).
2. To obtain continuous measurement of the water level (tide and waves), conductivity
and temperature (hence salinity) at three sites one in upstream Cedar River, the second in upstream Ortega River and the third at the mouth of the Ortega River where it joins with the main stem. In addition, continuous data on the current velocity are to be obtained at the Ortega River mouth using a moored Endeco cur-rent meter. These measurements are to be carried out over a period of one lunar
month, and are to be used to calibrate the circulation model.
3. To obtain current velocity and suspended solids concentration data at selected crosssections within the lower Cedar/Ortega Rivers using an Acoustic Doppler Current Profiler (ADCP) and synchronous bottle-sampling of water at these cross-sections.
The ADCP measurements are to be carried out twice, each time over a 13-hour duration covering the semi-diurnal tide. One 13-hour run should obtain "normal"
values of the current velocity and suspended solids concentration and the second
shall be run under "storm" conditions.
4. To carry out model calibration with one set of data, and to use a second set of data
for model validation.
5. To conduct model simulations to study circulation and sediment transport in the
Cedar and Ortega Rivers using EFDC to evaluate past, present and likely future
rates of sediment deposition, erosion and transport and depth-shoaling patterns.
6. To run model scenarios for dredging and provide results to be evaluated by the
District Project team.
7. To develop short and long term goals for dredging and sediment removal
management, and criteria for environmental enhancement (e.g., due to
sedimentation traps/basins).




8. To provide a critical evaluation of selected sediment remediation alternatives to be
provided by the District including the "no-action" alternative and suggest
recommended option(s).
1.3 Tasks
Seven tasks were assigned to accomplish the eight objectives given above. In what follows, these tasks and locations (Appendices A through H and other citations) in which they are reported are described.
1.3.1 Task 1: Assembly of Existing Data
In order to assemble the data required for the sediment transport modeling, a review of all available data related to the sedimentological regime of the rivers and their tributaries will be conducted.
The sedimentological regime of the rivers and tributaries is reviewed in Appendices A and E, and in Mehta et al. (2000).
1.3.2 Task 2: Samples for Engineering Characterization of Sediments
Ten surficial sediment samples will be collected to describe the present spatial distribution of sediment types. Selected fine-grained samples will be tested at UF's Coastal Engineering Laboratory to determine the erosion, deposition and consolidation properties of these sediments.
The erosion, deposition and consolidation properties of the river sediment are reported in Appendix B, and also in Appendix H.
1.3.3 Task 3: ADCP, Water Level and Salinity Measurements
Current velocities and suspended solids concentrations will be measured at selected cross-sections in the confluence of the Cedar/Ortega Rivers. Water and suspended sediment fluxes at these cross-sections will be calculated using the measured data.
ADCP and suspended sediment measurements as well sediment flux calculations are presented in Appendices C, D and E. Water level and conductivity/temperature data utilized for modeling are provided in Appendix E.




1.3.4 Task 4: Sediment Load Rating Curves
TSS-discharge rating curves will be developed, to the extent possible, at these crosssections. These rating curves should be used to determine sediment flux time series over the period of record.
The rating curves are presented in Mehta et al. (2000) and Appendix H, and revised in Appendix F. It is shown that both the original and the revise curves yield reasonable values of suspended sediment fluxes and deposition rates within the Cedar/Ortega River area, although the paucity of data leaves a degree of uncertainty that is difficult to quantify. Subsequently, SJRWMD supplied and required the use of rating relations at the heads of Cedar River and its tributaries (Williamson Creek, Butcher Pen Creek and Fishing Creek), derived from applications of the SWMM model. Predicted sediment concentrations based on these appear to be lower than those derived from the rating curve, as noted in Appendix E.
1.3.5 Task 5: Model Setup, Simulations and Results
Setup, calibrate, validate and run EFDC using measured tides, currents, river and tributary discharges and suspended solids concentrations for boundary conditions.
Exploratory modeling work related to sediment entrapment in the Cedar River and using EFDC is reported in Appendix E and expanded in Appendix G. Appendix E also summarizes the modeling framework including equations, grid development, boundary conditions and output.
1.3.6 Task 6: Run Model Scenarios
Run model scenarios to "assess likely short term (e.g., 1-3 years) and long term (e.g., a decade or longer) sedimentation rates based on historical trends and likely future scenarios with respect to the hydrologic/hydrodynamic regime of the rivers"~.
The above statement was further quantified during the study to include the examination of the impact of placing sediment traps at selected locations with three different removal efficiencies (i.e., 40%, 60%, 80%) on the net sediment flux out of the Cedar River. Exploratory work in this regard is described in Appendix E. Further work is reported in Appendix G.
7




1.3.7 Task 7: Dredging Alternatives Evaluation
Evaluate potential dredging alternatives for basin restoration.
Dredging alternatives of two types are considered off-line and on-line. Exploratory work related to off-line sediment entrapment systems prescribed by SJRWMD is carried out in Appendix E, and expanded in Appendix G. On-line entrapment was not initially prescribed; nevertheless, in Appendices E and F, the role of on-line trapping of sediment is examined as a remediation option, and five scenarios that involve the placement of at least one on-line (i.e., in-channel) sediment trap were simulated, the results of which are described in Appendix G.




2 OBSERVATIONS FROM FIELD INFORMATION

2.1 Preamble
In what follows, noteworthy findings from the analyses of (collected and procured) field data are provided. See also Appendices A, C, D and E.
2.2 Bottom Sediment Sampling
Figure 2.1 shows core-sampling sites for a 1998 survey (SJRWMD) of physical and chemical attributes of bed sediments in the Cedar/Ortega River system. The system can be separated aerially into four identifiable regions. Figure 2.2 gives distributions of clay, silt, sand and organic content (loss on ignition). Figures 2.3 and 2.4 respectively give distributions of moisture content and total solids. Figure 2.5 shows the distribution of total organic carbon and, finally, Figure 2.6 gives annual sedimentation rates (Appendix A).
'Nv 1998 sample sites
ADA
ReRegion
Figure 2.1 Bottom sediment-sampling sites in 1998. The region is conveniently divided
into four regions (from Appendix A).




Composition of area bottom sediment (from Appendix A).
10

Figure 2.2




Moisture (%)
-\
70~ 7
\ \ os
7.
II 2D5 I7
,o s 0o. To,
D42
iI. 17 .
,/
.20
/ /7
Figure 2.4 Total solids distribution (from Appendix A).
I I




Figure 2.5 Total organic carbon distribution (from Appendix A).

Figure 2.6 Sedimentation rates (based on Donoghue, 1999).




Data examination indicates that there is a limited input of inorganic sediment from the main-stem, although this has only penetrated into the outer confluent region. No clear evidence has emerged as to the extent of autochthonous, plankton sediment production or the breakdown products of in situ sea grass in the system. Human settlement within the last century has had a major impact on the types of sediment being input to the estuary and on the sedimentation rate.
2.2.1 Cedar River
With respect to the more minor, inorganic fraction of the sediment, the Cedar River (Region 1, Figure 2.1) deposits show the highest clay content in the entire system (18%). There is also a pronounced down-estuary decrease. This is consistent with a fluvial clay input. The silt content of the inorganic fraction is higher than the clay with a comparable down-estuary reduction, implying a similar detrital fluvial input. The sand fraction, in contrast, is low at the landward end and increases down-estuary. As far as the sediment as a whole is concerned, there is a much higher solids percentage, coupled with relatively low moisture content, again consistent with a significant detrital input from the watershed. The solids percentage decreases down-estuary and the moisture content rises. This implies a rising organic fraction in the downestuary direction. Consistent with these trends, the organic content of the upper Cedar River samples is amongst the lowest in the entire system and increases down-estuary. This is the reverse of the situation in the Ortega River, and may reflect the urbanization of the Cedar River watershed. In core samples sand layers occur only very occasionally, and when they do they are present as thin laminae. This confirms that, in spite of the level of urbanization, detrital sand is not a significant input. This is equally the case for Williamson and Butcher Pen Creeks. In contrast, there is a significant detrital sand input, represented as thick and multiple layers, being transported down Fishing Creek, and doubtless accounting for what is otherwise an anomalouslooking "high" in the sand fraction in the inner confluent region. The input must be terrestrial,




arising from recent deforestation, and it cannot be relict marine sand as it lies mainly in the shallowest parts of the sediment succession.
A further prominent anthropogenic input is that of wood chips. The level of wood chips in the cores from the upper reaches of the Cedar River is low. This probably reflects the fact that deforestation and urbanization of the Cedar River watershed is a relatively old feature. To complement this, the largest quantities of wood chips emanate from Williamson, Butcher Pen and Fishing Creeks and are abundant in the sediments of the lower reaches of the Cedar River, i.e., down-estuary of these three tributary creeks. A further anthropogenic input confined to the Cedar River is oil. Oily muck is interbedded with the wood chips and with the less common sand horizons. It is not possible to comment on whether there has been a single relatively large spill, or whether frequent or maybe semi-continuous low level hydrocarbon inputs occur. Finally, to complement the large-scale sand and wood chip inputs from Fishing Creek, bluegreen inorganic detrital clays were sampled at shallow depths in recent sediment material at the entrance to Fishing Creek. A tentative suggestion arising from this might be that in recent decades, deforestation and urbanization has focused not in the Cedar, but in it tributaries Williamson, Butcher Pen and Fishing Creeks. Fishing Creek seems to have some affinities in this respect with Big Fishweir Creek in the outer confluent region (as discussed later).
2.2.2 Ortega River
The sediments of this river (Region 3) show some distinctive features and pronounced contrasts with the Cedar and other zones within the study area. It is predominantly a detrital, organic-dominated sub-estuary at a less-developed stage of urbanization than the Cedar River. With regard to its inorganic fraction, it has very low clay and sand inputs and a mid-level silt input, with a strong down-estuary decrease. The sand content rises in the down-estuary direction. With respect to sediment as a whole, the Ortega has by far the highest moisture and




lowest total solids of anywhere in the system, again reflecting the major terrestrial organic input to the watershed basin. The total solids percentages show a down-estuary decrease. Consistent with this, the organic content is at a system-maximum and also decreases downestuary. Examination of core logs confirms the relative paucity of sand laminae. Where these are present they tend to occur deep in the sediment colum n. Wood chips are also less common than in the lower reaches of the Cedar and the inner confluent region. Where present they can be interbedded with the black finely divided mucks and the sand layers. These multiple-layered wood chip horizons are detectable in all sampled reaches of the Ortega and are presumed to reflect the onset of deforestation in this watershed as well.
2.2.3 Inner Confluence Region
The inorganic fraction in Region 4 shows an apparently anomalous, exceptionally low clay content, although the recent blue-green clays being input from Fishing Creek seem not to be represented in this suite of samples. In contrast, the silt content is extremely variable, although still generally low in level. There is no obvious reason for the high variability. The sand content is relatively high and variable (22-75%, but mainly 60-70%). The sand cannot originate down-estuary, as concentrations decrease into the outer confluent region, and it must be either relict marine sand or a detrital input from the tributary creeks. The high elevation of the sand layers in cores suggests a fluvial source due to recent anthropogenic changes. With respect to the "whole sediment" analyses, and in contrast with the high sand content, these sediments also have high moisture and low solids contents. They can best be described as predominantly sandy mucks. There is a suggestion of an association between the high moisture/low solids rich sediments and the left bank in the inner confluent region. This is very likely induced by the presence of the flow impediment provided by the large commercial marinas along this coast. A tongue of high organic-rich sediment is issuing from the Ortega and




is strongly evident in this region. It possibly indicates that the signature of Ortega type sediments is locally stronger than either that of Cedar or St. Johns River sediments. In vertical sections from the core logs, multiple sand layering is found to be well developed and widespread, but there are never more than 10 sand layers. The sand must be contributed from Fishing Creek during occasional high discharge events. Wood chips are frequently interbedded with the sand layers in these reaches. These are very likely input from Williamson, Butcher Pen and Fishing Creeks. The distribution of wood chips and the variability in the silt content might be consistent with the presence of a large stable eddy in this region (Mehta et al., 2000).
Measurements of sedimentation rate show a strong lateral variation, with relatively low values on the right bank, but high rates up to 20 nun/yr on the left bank amongst the marina developments. Mehta et al. (2000) show that this is consistent with the Ortega's potential to erode bottom sediment opposite to the marinas during high river discharge events.
2.2.4 Outer Confluence Region
The inorganic fraction of sediments in this area (Region 2) is elevated compared to values in the up-estuary direction back into the Cedar and Ortega, and probably reflects inputs from the main-stem. The silt content is elevated and relatively constant in this area, with a small degree of axial increase. Sand contents are generally low. Whole sediment analyses show levels and distributions very similar to the inner confluent region, i.e., the sediments have a high moisture concentration (>70%) and a low solids percentage. The maximum moisture and minimum solids contents are again found along the left bank, and probably linked with the marina developments. Lateral partitioning is further evident in the presence of a tongue of low moisture, high solids detrital sediments penetrating the right bank of this region from the mainstem. In cores, the pronounced lateral segregation is again detectable with multiple sand layering involving up to 15-20 sand horizons towards the right bank. The most seaward of these




cores is all sand. In contrast, there are commonly no sand layers along the left bank, and the maximum number of layers found is seven.
There is an unambiguous sand input from Big Fishweir Creek on the left bank at the confluence with the main-stem. In general, few wood chip horizons are to be found in outer confluent region core samples, consistent with input from the river watershed up-estuary. Core logs at sites in the entrance to Big Fishweir Creek consistently identify one of the components of the sediments as "woody". In spite of this consistency in description, it is not possible to confidently associate this non-specific term with the "wood chips" described from up-estuary sites, and thus, the provenance of this material must remain unknown.
Sedimentation rate measurements show the same lateral partitioning, with values in the range of 4-8 mm/yr along the right bank, rising to 20 mm/yr along the left. Whether these are linear sedimentation rates or, instead, whether surficial rates of sedimentation might be even higher, are also unknown.
2.2.5 Data Statistics
Table 2.1 summarizes the overall statistics of moisture content, organic content and solids content for the study area. We make particular reference to the organic content, which is high in the mean, and characteristically influences fine sediment transport in a complex manner. This complexity is especially due to the adhesive effect of mucopolysaccharides, and the binding effect of long-chain polymers (Mehta and Parchure, 2000).
Table 2.1 Statistical values associated with bed sediment distribution (from Appendix E)
Statistic Moisture content Organic content Solids content
MtaMsti
_______________(%) (%) (%)
Minimum 54 6 16
Maximum 84 51 46
Mean 76 21 24




2.3 Hydrographic Measurements
Sites at which data were collected during the study are shown in Figure 2.2. Tide, salinity, and temperature data were obtained at TG 1, TG2 and TG3, and tide, waves and current measurements were made at WGC. At the three transects shown, ADCP (RDI 1200 kHz Broadband Workhorse Acoustic Doppler Current Profiler, together with an on-line DGPS system) data on current velocity were obtained along with water samples and (Seapoint) optical backscatter sensor data for suspended solids. These three transects were traversed on May 17, 2001. Additional transects were traversed at other dates, as described later.
Depths (NGVD) within the area varied from 0.5 to 3 m with an average depth of just over 1 m. Depths in the Cedar River varied from 0.3 m to 1.5 m with an average of 0.5 m. From data collected during 09/29/00-10/18/01 using Infinities USA Inc. ultrasonic recorders, (semidiurnal) tide statistics given in Table 2.2 were obtained.
Table 2.2 Tide statistics for the study area (based on Appendix E) Cumulative percentile range (in)
Gage location
25 50 95 98
TG1 0.27 0.44 0.70 0.90
TG2 0.04 0.10 0.45 0.62
TG3 0.08 0.18 0.45 0.53
The observed variation of ranges reflects gage distances from the mouth of the Ortega. In general it is evident that the system is very much micro-tidal (< 2 m), and that the upstream reaches covered by the study are only weakly tidal. Such weakly tidal systems are substantially influenced by episodic runoff. Elsewhere (Mehta et al., 2000) it is shown that when the runoff is very high, as during the February 1998 El Nino event, flow in the entire system was directed downstream at all stages of tide (See Figures 2.8 and 2.9).




4>

/

rG3

Figure 2.7 Cedar/Ortega River data collection sites (from Appendix E).

Figure 2.8 Simulated flood flow (depth-mean) velocity field during El Nino
discharges in the Cedar/Ortega system (after Marvdn, 2001).
19

. .. 15t Bridge

~~~~Iiiii~ !!i!

Ortega River Bridge

v ul




15th Bdge
i~~~ . ... . . .. .
Ortega River Bridge
Figure 2.9 Simulated ebb flow (depth-mean) velocity field during El Nino discharges in the Cedar/Ortega system (after Marvdn, 2001).
Tidal current measurements were made initially with an Endeco tethered meter, and later using UF's P-U-V gage employing a Marsch-McBirney electromagnetic transducer. Statistics derived from the Endeco for the 02/05/01-03/08/01 period are given in Table 2.3. Magnitude-wise the 98 percentile value of 0.30 m/s is consistent with the tidal range at the mouth (Table 2.2). As a rule of thumb, when the current speed is less than -0.30 m/s, sediment resuspension is weak and the suspended load low. As shown elsewhere (Mehta et al., 2000), resuspension and transport of sediment is noteworthy only when runoff is high enough to generate velocities on the order of 0.5-1.0 m/s.
Statistics for the salinity values calculated from conductivity and temperature measurements (using Greenspan VEC-250 transducers) for the period 10/27/00-11/26/00 are given in Table 2.4. During the period of measurement the system was brackish, with very low salinities in the upper reach of the Ortega. Nevertheless, inasmuch as critical salinities for flocculation of clay minerals in water are quite low, on the order of 0.5-2 psu, it is evident, and




confirmed by observation, that the clayey material in suspension is flocculated, even as the floc properties are substantially modulated by organic matter.
Table 2.3 Current statistics at the mouth of the Ortega River (based on Appendix E)
Cumulative percentile Speed (m/s)
98 0.30
95 0.25
50 0.08
25 0.04
Table 2.4 Salinity statistics for the study area (based on Appendix E) Cumulative percentile value (psu)
Location
25 50 95 98
TG1 6.3 6.9 8.8 9.5
TG2 6.9 7.6 10.1 11.0
TG3 0.3 0.7 2.6 3.2
River discharge data from Cedar River for the period 03/01/97 to 10/22/98 are plotted on a cumulative basis in Figure 2.10. These imply typically very low values (< 5 m3/s 94% of the time and > 45 m3/s for only 0.16% of the time). The mean and maximum discharges are found to be 1.4 m3/s and 112 m3/s, respectively.
Tidal discharge measurements carried out using an ADCP on 05/17/01 (along the transects shown in Figure 2.2) revealed that due to the shallow nature of the estuary and the marginal performance of the ADCP in shallow waters, the data were found to have a somewhat qualitative significance. Nevertheless, Table 2.5 presents the analyzed data for the Cedar River transect; see Figure 2.7, in which this transect is located at the confluence of the Cedar and Ortega Rivers. Positive discharge is directed west, and negative is directed east. As shown later, these discharges are consistent with tidal forcing at the site.
Sediment samples collected during the 05/17/01 ADCP study (Table 2.5) indicated that with the exception of one "anomalous" value of 101 mg/i (sample no. 73), possibly due to its




0.01

0.1 1 10
Discharge (m3/s)

Figure 2.10 Cumulative frequency distribution of Cedar River discharge.
proximity to the bed, the sample range was 8 to 57 mg/I and the mean 20 mg/l, indicating a
characteristically very low suspended sediment concentration regime. These values are
comparable to those in Table 2.6 obtained by SJRWMD over a four-year period at Ortega
Bridge.
Table 2.5 Confluence region concentrations on May 17, 2001 (from Appendix E)
Sample Conc. Sample Conc. Sample Conc. Sample Conc.
no. (mg/1) no (mg/1) no (mg/1) no (mg/l)
1 14 21 33 41 15 61 16
2 17 22 17 42 14 62 15
3 16 23 19 43 18 63 16
4 17 24 16 44 12 64 20
5 8 25 14 45 19 65 15
6 22 26 16 46 37 66 15
7 14 27 17 47 13 67 14
8 13 28 17 48 17 68 16
9 35 29 16 49 16 69 16
10 23 30 13 50 19 70 26
11 15 31 14 51 17 71 15
12 15 32 14 52 21 72 14
13 20 33 13 53 16 73 101
14 15 34 17 54 18 74 19
15 14 35 18 55 13 75 17
16 15 36 17 56 13 76 16
17 19 37 17 57 16 77 15
18 16 38 15 58 15 78 57
19 13 39 11 59 16
20 27 40 11 60 16




Table 2.6 Statistics based on measured TSS by SJRWMD during 01/09/94-02/11/95 Maximum Minimum Mean
(mg/I) (mg/I) (mg/I)
Ortega Bridge 50 3 14
Ortega mouth 22 1 9
Timaquana Bridge (Ortega) 25 6 14
San Juan Bridge (Cedar) 105 4 21
The long term (01/9/94-02/11/95) data from Cedar River also reveal the significance of the episodic nature of sediment transport in this river, as seen from Figure 2.11, in which the measured time-series is plotted. Note that the TSS is typically less than 20 mg/I. During El Nino, however, it exceeded 100 mg/i. Any sediment remediation technique for this area must recognize this significant non-steadiness of sediment transport in the area.
120
100
E 80
.2
w 60
0 40
Q
C
0
o 20
0 i N c i N i i i Q i I N N i \ I
Figure 2.11 Measured suspended sediment time-series at San Juan Rd. Bridge, Cedar River, 01/09/94-02/11/95.
Wind record from the nearby Jacksonville Naval Air Station for the 01/01/95 12/31/98
period indicate that speeds of 3-5 m/s are common (61.7% of time). Significant directions are the 48o-720 (10.3%) and 1680-1920 (15.2%) sectors. During that period the highest speed recorded was 15 m/s from the 72o-96' sector. These data, taken along the main stem, must be interpreted with care when applying to the study area, especially because portions of the waterway reaches are flanked by trees, while others have been cleared and developed (see
Appendix E).




Wave data obtained using a Transmetrics Inc. pressure transducer at the mouth of the Ortega showed generally mild wave action. For example, during the 02/10/01 to 04/25/01 period, the wave modal period was found to be 2.0 s and the significant wave height only rarely exceeded 0.2 m (Figure 2.12).
100 90
80 .
70.
60
E 50.
4 0 . . . . . . . . .. . . . . . .... . . . . . . . . . . . .
3 0 . . .. . . . . . . . . . . . . . . . .
2 0 1 . . . . . . .. . . . . . . . . . .. . . . . . . . .
10
0 0.05 0.1 0.15 0.2 0.25 0 .3 0.35
HmO, m
Figure 2.12 Cumulative distribution of significant wave height (Hmo) at the mouth of the
Ortega during 02/10/01 to 04/25/01 (from Appendix E).
This mild climate is due to the limited wind fetches in the St. Johns River. Wave action in the Cedar River is believed to be even milder, and is unlikely to contribute much to sediment transport except possibly under severe conditions when comparatively large waves may break along the banks.
2.4 Suspended Solids Content from Acoustic Profiling
In addition to the May 17, 2001 survey, detailed acoustic profiling using the ADCP was carried out during October 2-3, 2000. The nine transects covered are shown in the inset of Figure 2.13. The ADCP was also to be run with the "Sediview" software, which permits simultaneous suspended solids data to be obtained without any alteration to the manufacturer's (RDI) hardware.




On the advice of RDI the ADCP came equipped to operate in "Mode 8", said by the manufacturer to be ideally suited to working in conditions of very weak currents in shallow water. Sediview is a DOS program and works with Transect software supplied by the equipment manufacturer. To calibrate the ADCP, the survey vessel was also equipped with salinity and temperature measuring instruments and a calibrated optical backscatter sensor for measuring suspended sediment concentration. These instruments were mounted on a watersampling bottle.
For the nine transects, estimates of suspended solids concentration are plotted in Figure 2.13. Very shallow water at transect 2 (Big Fishweir Creek) and transect 7 (Butcher Pen Creek) precluded data collection. In Figures 2.14 and 2.15, the corresponding estimates of discharge and solids flux, respectively, are plotted.
Observe that whereas tidal discharges during October 2-3, 2000 (Figure 2.4) were comparable to those on May 17, 2001 (Table 2.3), concentrations were generally higher on May 17, 2001 (mean 20 mg/l) than during October 2-3, 2000 (Figure 2.15, with a mean of -8 mg/1). This variability may result from the corresponding variation of river discharge, as seen from the concentration (C) versus discharge Q rating function in Figure 2.16. The data points are derived from long-term measurements at San Juan Bridge on Cedar River. Despite the evident data scatter, Stoddard (Appendix F) attempted to derive a plausible mean relationship. Marvdn's (2001) relationship (Appendix H) is based on a different analysis of the same data.
In general, the Cedar and Ortega Rivers are a challenging environment in which to measure suspended solids because of the consistently low solids concentrations. This makes calibration of both turbidity meters and ADCPs difficult because calibrations must be based on comparisons with water sample data that are inherently subject to errors at low concentrations. In addition, the unavoidable temporal and (particularly) spatial mismatching of three different




1502
1501

WS -ehrs -4hrs -2hts igh Water +2hrs -4hrs +4

* Line I Line 3 bne 4 Line 5

ULine6 V Lne8

asPM 2
bar one

, Road at
7 OOK
cooea "

SLine 9

Data from LiUne 2 not reported, Insuffcn water depth for meanngful mesuremems.

Sr jous R

DIscharge ma per second
- ..- .

Figure 2.13 Discharge relative to high water level at Ortega Main bridge (from
Appendix C).

'At n




1500
Solids flux, gr ms per seconI
1000
500 X
Xb 0
oT Ex

-500
-1000

-1500
-8hrs
Figure 2.14

-6hrs -4hrs -2hrs High Water +2hrs -4hrs +6hrs
Solids flux estimates corresponding to Figure 2.13 (from Appendix C).

11ii
Solids conce itration
mg/L
10
+x + x
9
- X v +
8 -*- -X X
7 X
6 - --- Mr
6
5.
4

-8hrs
Figure 2.15

-6hrs -4hrs -2hrs High Water +2hrs -4hrs +6hrs
Solids concentration estimates corresponding to Figures 2.13 and 2.14 (from Appendix C).

-0Y

qp




0.30 T
0.25 6x10-2Q28
0.20
0.15
S0.10 Band Averaged
0.1
= -----New Curve
U) 0.05 -" Marvan
] Raw Data
0.00,
0 10 20 30 40 50 60 70 80
River Discharge (m3/s)
Figure 2.16 Rating curve of Stoddard compared with that of Marvin (from Appendix F).
types of measurements (i.e., ADCP backscatter intensity, infrared backscatter intensity of the optical sensors, and gravimetric analysis of bottle samples) leads inevitably to scatter in comparisons between the results. Despite these difficulties, a satisfactory calibration has been achieved. Although scatter is evident in the comparison between Sediview concentration estimates and the water sample data, there is a high degree of correlation and the scattering lies within the expected range.
Measurements of discharge and solids flux were hampered by the shallow water and the presence of extensive fields of sea grass. The sea grass resulted in frequent loss of bottom track which meant that current data had to be referenced to GPS, rather than bottom track, using compass corrections determined for each line by comparing bottom track data with GPS data. A considerable amount of bed level editing was required in order to correct the bed levels and ensure that all valid measurement data were included in the estimates. There was clearly nothing that could be done about the shallow water, which resulted in significant proportions of the total discharge and flux estimates being based on estimated data. However, in future 28




surveys, the magnitude of this problem might be reduced by using the recently introduced ZeeHead ADCPs. Also, shorter time intervals between successive transects and sailing at a slower speed might provide more reliable data in future surveys.




3 LABORATORY TESTING FOR SEDIMENT TRANSPORT
3.1 Preamble
Noteworthy findings from the analysis of (collected and procured) laboratory data are provided here. See also Appendices B and E.
3.2 Erosion and Settling Tests
Laboratory tests were carried out on 20 grab samples obtained from locations identified in Figure 3.1 (Appendix B3). Figure 3.2 shows the erosion plot. It was found that, with the exception of two samples, which mainly consisted of sand, the remaining 18 samples had organic content ranging from 16 to 74%. For the organic-rich samples the erosion rate equation was prescribed as:
F_ = SNtc)(3.1) in which F_ is the erosion rate and *~ is the applied shear stress. Relative to this equation, the condition for the onset of significant erosion was characterized by the critical shear stress tce = 0.17 Pa. The corresponding erosion rate constant was 5_N = 3.5x10 4 kg/m2s Pa. These coefficients apply to beds with bulk densities ranging between 1,021 and 1,274 kg/in3, which are within the range of surficial sediment densities found in the study area.
Under quiescent conditions, the settling velocity, W, of fine-grained sediment is related to suspension concentration, C, according to:
aC' 32
W (b 2+ c2)(.2
In the present study (see Appendices B and E), a = 0.035, b = 2.0, n = 3.5 and m =2.75 were obtained, given settling velocity W, in rn/s and suspension concentration C in kg/in3. The characteristic peak settling velocity was found to be 1.5x10-2 rn/s (see Figure 3.3).




CEDAR RIVER

/J
.. 't 1
,# :. ......... .

3,35 3.349 3.348 3347
3.346 3.345 3.344 3343 3.342

ST JOHNS RIVER

1Q35
~7 2t~.
11

-. IF 1
6
C
(1
-, P F

xlO

Figure 3.1 Map of Cedar and Ortega River sampling sites. Sites UFOl are for the present
study; UF99 are from a previous sampling study (Mehta et al. 2000).

0.000 0.05D 0.100 0.150 0200 0.250 0.300 0.350 0.400 Q45
Shw Sess (Pa)
Figure 3.2 Composite plot of bed erosion rate versus bed shear stress (from Appendix B).
Note that for computational purposes, the first line, representing minor "floc
entrainment" is ignored.

3.351

ORTEGA RIVER

3.341

I I I




1.5E-2 -" z
1.AE-0X3
E M 7 1 II L I 1 I I
E
1.JE-04
St ii I I I L
1.M -0 i1 i I I I -I-;
C I I I I I I I I I
-1 j L I A I I A L
I I I I I I I I I I I I II I I I I I I
1.01E-07
0.1 1 10 100
Omcentwrion (kftfm)
Figure 3.3 Settling velocity variation with concentration data and best-fit of Eq. 3.2. Peak
velocity is 1.5x10-2 m/s (from Appendix B).
3.3 Settling Velocity Algorithm
A settling velocity algorithm was developed for incorporation in the Environmental Fluid Dynamics Code (EFDC) used herein for examining sediment remediation scenarios. This code for estuarine flows contains a three-dimensional, hydrostatic flow model, as well as a compatible sediment model. It uses either a Cartesian or curvilinear orthogonal coordinate system in the horizontal plane, and a stretched or sigma vertical coordinate that enables it to follow the bottom topography and free surface displacement. A level 2.5 turbulence closure scheme in the hydrodynamic model relates the turbulent viscosity and diffusivity to the turbulence intensity and a turbulence length scale. An equation of state relates density to pressure, salinity, temperature and suspended sediment concentration (Hamrick 1992; 1996).
The settling velocity algorithm calculates the settling velocity of the particles by accounting for the floc growth and breakup processes that occur for fine-grained sediment in estuarine and coastal waters due to different mechanisms. As a result, instead of using the settling velocity derived from measurements in a laboratory settling column in still water (Eq.




3.2) directly, the model, is merely calibrated using laboratory data. This enabled the settling velocity to be not only dependent on suspended sediment concentration, but also on flow turbulence, as characterized by the energy dissipation parameter G.
The model was validated against the floc size data of Winterwerp (1998) from two settling column tests using fine sediment from the Ems-Dollard River area in The Netherlands. Comparisons between simulations and data are shown in Figure 3.4. Values of concentration C and dissipation parameter used are given in Table 3. 1. Floc size is seen to grow with time until it reaches an equilibrium value (there is an equilibrium particle size for given concentration and dissipation parameter) and remains the same beyond that point. For Cedar River the dissipation parameter was estimated to range from 0.5 to 10 Hz (Appendix E). Table 3.1 Data from settling column tests with Ems-Dollard fine sediment (from Appendix E) TsNubrC G
Tes Nuber(kg/rn3) (Hz)
T-73 1.21 81.7
T-69 1.17 28.9
Wolanski et al, (1992) measured the settling of sediment obtained from Townsville Harbor, Australia in a Plexiglas cylinder of 10 cm internal diameter and 140 cm height. Turbulence could be generated in this column by oscillating 1 cm wide rings along the walls, spaced 2 cm apart. Two sets of data were obtained: in quiescent water, and with rings oscillating. Quiescent water can be characterized by very low values of dissipation parameterG. These data are compared in Figure 3.3 with model output. The simulated curve based on measurement in oscillating water indicates a reasonably good match with data points. However, measurements in quiescent water are not predicted as well. This is believed to be due to the fact that, the model does not perform well for low values of dissipation parameter G (i.e., in the absence of turbulence).




E
......... .. ... .. ;.!! ; "..... : : : :........ :..... : : : :
(D
1 0 c .. . .. . . . .
10, 102 103 104
Time, s
Figure 3.4 Floc growth with time measured and predicted for River Ems-Dollard fine
sediment (Winterwerp, 1998) (from Appendix E).
10c
.K .. ..
X, .. -. .. .....
XLab results (quiescent water) X X X
10 2): 2 . 2 . .. . ..) / -: -: . .. ..
10
.... ... I,..
X.
U) Lab results
2 (Max. velocity=0.09 m/Vs)
.0 ......
10- 100 10' 10,
Concentration gil
Figure 3.5 Settling velocity calculation test results, and comparison with data of Wolanski
et al. (1992) using sediment from Townsville Harbor, Australia (from Appendix
E).




3.4 Consolidation
Two tests on the self-weight consolidation of bottom material from the study area were carried out (Marvdn, 2001). In Figures 3.6 and 3.7, hindered, or collective settling can be observed during the first 10 to 15 (t -1 = 6-4 h-1) minutes, respectively. Note that h, is the initial height of suspension and h(t) is the instantaneous height. At this point, a transition to consolidation occurs which is related to the change from the first consolidating mode to the second mode. This transition point does not necessarily have to be the same in each case since it is expected to be a function of the initial concentration. Within the consolidation phase, three trend lines can be observed, which can result from a rearrangement of particles due to selfweight consolidation at discrete time intervals. As observed in Figure 3.7, the transition point for every phase occurs sooner than the corresponding times for the sample shown in Figure 3.6. This could be due to the higher self-weight at higher concentrations.
Figues36lCnodaon n forinal conettingo 37gl(rmM 20)




Consolidation

Hindered settling

2 4 6 8 10 12
1t hours 4 start
Figure 3.7 Consolidation for initial concentration of 24.3 g/l (from Marvin, 2000).




4 SEDIMENT REMEDIATION
4.1 Sediment Treatment Scenarios
Referring to Figure 4.1, the two off-line sediment treatment alternatives (OFL-1 and OFL-2) proposed by SJRWMD are seen to be in the upstream reach of the Cedar River. At the better of the two sites, a Wet Detention Systems (WDS) would be constructed with the objective to entrap contaminated sediment, off-line and especially during high flood events, from sources upstream of these facilities, thus intercepting the material well before it reaches the confluence area, where in has accumulated over the years.
Figure 4.1 Cedar/Ortega Rivers data collection and sediment off-line treatment (Wet
Detention System) alternative sites OFL-1 and OFL-2 proposed by SJRWMD.
Further alternatives investigated in this study are shown in Figure 4.2, and for reference purposes, the bathymetry of the study area is shown in Figures 4.3 and 4.4. The latter figure especially highlights the shallow waters in the confluence area. Note that OFL- 1 is located 37




Figure 4.2 Sediment treatment facility alternatives in addition to those proposed by SJRWMD.
north of OFL-2, beyond the sketch boundary (see Figure 4.2). Assuming the feasibility of its construction, a third off-line treatment site, OFL-3, is conveniently chosen to be downstream of Williamson Creek, which debouches sediment into Cedar River. Two on-line (i.e., in channel) sites, ONL-1 and ONL-2, located at sites (see Figure 4.2) where it may not be feasible to design WDS due to land requirements, are on-line sediment traps or pits into which sediment would be captured due to enhancement of settling as the flow velocity over the depressed bottom is reduced relative to the velocity away from the pit (Parchure et al., 2000). They are chosen to be downstream of Butcher Pen Creek, which also empties water and sediment into Cedar River. In Figure 4.2, CAC refers to sediment accumulation in the confluence area, and CB is the reference downstream flow boundary for the Cedar River at the confluence.




In what follows each of the above options will be examined separately. To that end, the following four general criteria may be selected as a basis for the examination: 1) A significant

Figure 4.3 Cedar River bathymetry. Bottom elevations are in meters with reference to NGVD.
reduction in sediment flux out of CB, 2) removal of accumulated sediment from critical sites in the confluence area, 3) sequestration of accumulated sediment at critical sites in the confluence area, and 4) improvement in navigation. The choice of the first three criteria is rationalized by the need to enhance water quality. Two water quality indices are commonly used in Florida's estuaries, both associated in part with water column turbidity via Secchi disc reading.
The Florida Water Quality Index (WQI) is used to quantify the quality of water. A higher WQI number indicates poorer water quality. This index is comprised of six categories 39

Cedar River with curvilinear grid
Bottom Elev
-2.316 Time: 30.00 .

I




Figure 4.4 Bathymetry of the Ortega River (running north-south) at its confluence with the
Cedar River (to left). Depths are in meters. Note the change in map orientation
with respect to Figure 4.3.
that include: (1) biological integrity including species diversity, (2) clarity of the water which can be tested through light penetration tests, turbidity analysis, total suspended solids tests, color determination, and Secchi disc depth tests, (3) dissolved oxygen in the water, (4) organic wastes which, for example, in the Loxahatchee River tend to accumulate in deep holes in the riverbed and become resuspended during a storm event or periods of heavy rain, (5) nutrients including nitrates, and (6) bacteria and specifically fecal coliform. Note that besides the Secchi disc value, WQI also depends on organic content.
The Florida Trophic State Index (TSI) includes four components in its attempt to quantify the water quality in a sample (Wanielista, 1978). The four indices include: (1) total nitrogen concentration, (2) total phosphorous concentration, (3) mean Secchi disc depth, and
(4) Chlorophyll A concentration. Increasing TSI implies poorer water quality.




Thus we note that both indices are contingent upon Secchi disc readings, hence to a degree on the suspended sediment load. We must note, however, that whereas these indices are meant for surface water quality, accumulation of contaminated sediment and associated pore water influence surface water quality in an indirect way. In other words, for the present analysis WQI and TSI can only be considered as indicators of the environmental state of the river system in a qualitative way.
The choice of navigation too must be considered in a qualitative sense, inasmuch as specific channel depth requirements have not been integral to the problem statement specified by SJRWMD.
4.2 Wet Detention Systems
In a WDS, by diverting river flow into a pond where flow velocities are small, a major portion of suspended sediments can be expected to settle out. Such systems can also be effective for storm water treatment when the bulk of the solids are carried with the first flush, as they can be intercepted and given a sufficient residence time to allow them to deposit. The concern for the Cedar River WDS is to provide as much treatment as possible; hence the effectiveness of the facility has been defined by the area available for constructing the facility. As we shall see later, this requirement also limits sites for its construction, hence sediment remediation based on this technique.
In its simplest form, WDS is a settling pond with weir inflow and outflow (Bedient and Huber, 2002) into which sediment is shunted out of the main stem river, as shown schematically in Figure 4.5. The length of the pond is determined by the depth of water and the sediment settling velocity (Sarikaya, 1977). Naturally, the peak flow velocity (or, better, associated bed shear stress) in the pond must be less than the critical velocity (or critical stress) for resuspension. Referring to Figure 3.2, for design purposes and for fine sediment, this stress




is equal to 0.17 Pa. For an assumed depth of 2 m and Manning's n = 0.020, the critical velocity would be about 0.5 m/s.

Figure 4.5 Schematic drawing of a Wet Detention System
4.3 Cedar River Sediment Trapping Modeling Results
4.3.1 Cartesian Grid Modeling Results
The results from Cedar River modeling performed by Paramygin (2002) using EFDC with a Cartesian grid are presented in Appendix E and summarized in this section. Model runs were carried out without and with the off-line sites in place for the selected efficiencies of 0%, 30%, 60% and 90%, in order to cover a wider range than the prescribed 40%, 60% and 80%. The model was run for three days, during May 16-18, 2001. Three output-control points (OFL2, OFL-3 and CB) were selected. OFL-2 and OFL-3, corresponding to the off-line sites, were placed just upstream of a site to measure sediment flux into the site, and CB was the control

Inflow Inflow




point just upstream of the downstream boundary, for monitoring trapping influence at the downstream end.
As discussed in Appendix E, it was found that the two sites (OFL-2 and OFL-3) would have a low effect on sediment transport at the lower end of the Cedar River individually and together, especially if removal efficiencies at the traps are not found to be high. The primary reason for this finding is that the majority of sediment load is derived from Williamson and Butcher Pen Creeks, rather than the Cedar River. However, this does not mean that either OFL2 or OFL-3 would be ineffective in capturing contaminated sediment from sources upstream of OFL-2, especially if these off-line sites can be operated at, say, 80% efficiency. An advantage both sites have is that the Cedar River sediment load is typically low (Appendix E and Table 4.2); hence it should be feasible to operate an effective containment system for a longer period without renewal in comparison with systems further downstream.
4.3.2 Curvilinear-Orthogonal Modeling Results
The results from the EFDC modeling using Curvilinear-Orthogonal grids, described in Appendix G, are summarized in this section. Using the boundary conditions generated by the Cedar-Ortega-St. Johns River (COSJR) model (see Appendix G), the 21 trapping scenarios defined in Tables 4.1 and 4.2 were run using the Cedar River (CR) model. The purpose of running these 21 scenarios was to allow for relative comparisons of the proposed remediation measures under varying hydrodynamic and sediment loading conditions. The 18 scenarios given in Table 4.1 involve simulation of the three off-line (i.e., sedimentation ponds) sediment traps, whereas the three scenarios given in Table 4.2 involve simulation of up to three on-line (i.e., in-channel) sediment traps. Each of the 21 scenarios was run for seven days during the COSJR model validation period.




Table 4.1 Cedar River off-line sediment trapping scenarios (from Appendix G)
Off Channel Trap Hydrodynamic/Sediment Conditions
Scenario efficiencies (%)
No. Downstream tide
OFL1 OFL2 OFL3 Wind CR inflow CR TSS D t i
BC
1 0 0 0 None 1 1 1
2 0 0 0 measured 1 1 1
3 40 0 0 None 1 1 1
4 60 0 0 None 1 1 1
5 80 0 0 None 1 1 1
6 40 40 0 None 1 1 1
7 80 80 0 None 1 1 1
8 40 40 40 None 1 1 1
9 80 80 80 None 1 1 1
10 40 40 40 measured 1 1 1
11 40 40 ONL3 measured 1 1 1
12 40 40 40 30 mph S 1 1 1
13 40 40 40 30 mph N 1 1 1
14 40 40 40 measured 1 1 1.5
15 40 40 40 measured 2.5 2.5 1
16 40 40 40 measured 5 5 1
17 40 40 40 measured 10 10 1
18 40 40 ONL3 measured 10 10 1
Table 4.2 Cedar River on-line sediment trapping scenarios (from Appendix G)
Scenario In Channel Trap Hydrodynamic/Sediment Conditions
No. Downstream tide
ONL3 ONLI ONL2 Wind CR inflow CR TSS BC
BC
19 yes 0 0 None 1 1 1
20 yes yes 0 None 1 1 1
21 yes yes yes None 1 1 1
The bathymetry of the CR modeling domain is shown in Figure 4.6. The horizontal
grid was curvilinear-orthogonal, and was five cells wide to represent the lateral variability in
flow and transported constituents, i.e., dissolved salt and sediment. To simulate the partially
stratified estuarine flow in the lower reach of the Cedar River, six vertical layers were used in
every computational cell. Also shown in Figure 4.6 are the locations of the six open water
boundaries (BC1 BC6) where boundary conditions were applied. The stage, salinity and
suspended sediment concentration boundary conditions at the downstream boundary (BC6)




Cedar River with curvilinear grid

Bottom Elev
-2.316 Time: 30.00 -.9
a, "A

Bc5

BC

B C'_-

Figure 4.6

Location of open water boundaries in the Cedar River modeling domain (from Appendix G).

were generated by the COSJR model. Time-variable freshwater inflows and suspended cohesive sediment concentrations were applied at the following locations: BC1 Cedar River; BC2 Williamson Creek; BC3 Butcher Pen Creek; BC4 Fishing Creek; BC5 Willis Branch. These time series were generated using the SWMM (Freeman 2001).

4 BC6




4.3.2.1 Off-line Sediment Traps
As seen in Table 4.1, each of the three off-line sites was tested with four assumed trapping efficiencies of 0% (no trapping), 40%, 60% and 80%. The last three were prescribed by the SJRWMD. The maximum efficiency (80%) is in part based on the estimated 85% for TSS (Total Suspended Solids) removal by WDS in Florida (see Table 4.3). For each scenario, the assumed sediment trapping (or removal) efficiency (0, 40, 60 or 80%) is given for each of the three proposed remediation sites. For scenarios 1 and 2, no sediment traps were simulated. These are considered the low-flow baseline cases. As seen in Table 4. 1, the difference between
Table 4.3 TSS removal efficiencies of treatment systems in Florida (after Harper, 1997)
Treatment system Estimated TSS removal efficiency(%
Dry Retention 60-98
Off-Line Retention/Detention 90
Wet Retention 85
Wet Detention 85
Wet Detention with Filtration 98
Dry Detention 70
Dry Detention with Filtration 60-70
Alum Treatment 90
these two scenarios is that in Scenario 1 wind was not included as a driving force, whereas in Scenario 2 the measured wind velocity at the NASJax weather station was used to calculate the (assumed) spatially constant wind-induced surface shear stress over the modeling domain.
The numbers in the "CR Inflow" ". .CR TSS" and "Downstream tide BC" columns in Table 4.1 indicate the factors the corresponding time series are multiplied by during the model run. For example, in Scenario 15, both the CR inflow time series and the CR TSS time series are multiplied by a factor of 2.5 to simulate a higher flow (and corresponding higher TSS) than that predicted by the SWMM. In Scenario 14, the downstream water surface elevation time




series (predicted by the COSJR model) is multiplied by a factor of 1.5 to simulate a tide with a 50% larger tidal range.
In Scenarios 3 9, the number of sediment traps and their efficiencies were systematically varied. The difference between Scenarios 8 and 10 is that wind was included as a driving force in Scenario 10, whereas it was not in Scenario 8. In Scenarios 12 17, in which three off-line traps with 40% sediment trapping efficiencies were represented, one or more of the driving forces were varied. The hydrodynamic/sediment boundary conditions changed in Scenarios 14 and 15 were described above. In Scenarios 16 and 17, the CR inflow and TSS time series were multiplied by factors of 5 and 10, respectively, to represent increasing flows and sediment loads from the watershed upstream of the upstream CR boundary. In Scenarios I11 and 18, the two upstream most off-line traps were represented along with the upstream most on-line trap (ONL-3). The latter is located at the same location as OFL-3. These two scenarios were run (with the difference between them indicated in Table 4.1) to investigate the use of both off-line and on-line traps.
Due to modeling related complications in representing the off-line sites as water bodies with channelized flow diverted into them, the representation of off-line treatment sites in the model was simplified. Accordingly, a function was implemented in EFDC that decreased the sediment flux bypassing the grid cell by a pre-defined percentage. The channel cross-section, where the treatment site would be located, was represented by model grid cells having such a sediment removal function, in terms of the percentage by which the effluent sediment load leaving the site is reduced with respect to the influent load entering the site.
4.3.2.2 On-line Sediment Traps
As an alternative to off-line treatment sites, it is instructive to examine the effects of online traps (see Figure 4.7 which shows a dredged pit). This is because along portions of the




Cedar River land is believed to be unavailable for an off-line facility. The general principle of such a trap have been examined in Appendix F based on the use of a depth-averaged model setup for the Cedar/Ortega River system in an independent study summarized in Appendix H.
Still water level
Remnoval
defining IInflow Velocity profile
"streamnline"4
Velocity profile in pit Inflow concentration profile Concentration profile in pit
Figure 4.7 Sediment pit or trap and, on the tide-mean basis, a removal defining "streamline" separating material that deposits from that carried past the trap
(after Ganju, 2001).
Formalizing the trap efficiency basis already introduced, we note that in the tidal situation the seaward edge of the trap will be the influent side during flood tide, and the effluent side during ebb tide, and vice versa for the landward edge. The sediment load q is calculated as: q = UCHAx (4.1)
where U is the local flow velocity and Ax is the cell width. The sediment load on each side of the trap yields sediment removal ratio R:
R -qe (4.2)
qi
where qi is the influent sediment load, and q, is the effluent sediment load. The removal ratio is averaged over a tidal cycle.
The locations of two of the on-line traps (ONL-1 and ONL-2) are shown in Figure 4.2. Both traps are selected 60 m (1 grid cell) wide by 300 m (5 grid cells) long with a surface area of 18,000 m2 and a (dredged) volume of 36,000 m3. The traps have an initial dredged depth of 2 m (below the ambient bed depth of 1.2 m at ONL-1 and 1.8 m at ONL-2). The traps have an




initial dredged depth of 2 m (below the ambient bed depth of 1.2 m at ONL-1 and ONL-3 and 1.8 m at ONL-2). These are considered sufficient to reduce the velocity in the river to allow measurable sediment to deposit. For example, at a river discharge of 3 m3/s and M2 tidal forcing, the mean velocity over ONL- 1 would be 0.13 m/s with the trap and 0.24 m/s without it, i.e., a 49% reduction in velocity over the trap.
Removal ratios were calculated only during periods of ebb tide flow through the ONL- 1 trap and are plotted against Cedar River discharge in Figure 4.8. These simulations, which assume a constant (time-independent) dredged depth for each trap, show that the removal ratio is maximum at a discharge of approximately 16.4 m3/s. It can be shown that as the discharge increases above its characteristic value, the flow increasingly becomes unidirectional, and R varies inversely with it (Baker et al., 1999). In contrast, as the discharge decreases below the characteristic value, the tidal influence increases and R decreases as the oscillating flow inhibits deposition in the pit (Appendix F).
The poorer performance by ONL-2 observed in Figure 4.8 can be partly attributed to the increased tidal action closer to the confluence of the Cedar and Ortega Rivers. ONL-1 performed more effectively due to more consistent flow direction and velocity since the location is well within the Cedar River.
0.4
0.3
:40.2 -IT
0 .
0.1 1 10 100
Discharge (m3/s)
Figure 4.8 Removal ratios for ONL- 1 (upper curve) and ONL-2 (lower curve) as functions of Cedar River discharge (from Appendix F).
49




The trapping efficiencies of ONL-1 and ONL-2, in accordance with Figure 4.8, are an artifact of the chosen dimensions of the traps. Also, the trap efficiency will decrease, rapidly at first and more slowly with time, as a first order rate function (Vincente, 1992). It can be accordingly shown that, for instance, considering the pit shoaling thickness equal to 90% of the initial pit depth, filling of the pit would occur in time t90% = 2.3/K, where K is a site-specific time-constant. In that connection, the above R-values merely indicate initial trap performance.
As an alternative approach, the EFDC application of Section 4.3 was extended (as described in Appendix G) to include the three on-line traps ONL-1, ONL-2 and ONL-3. The middle of the latter trap is located at OFL-3 (see Figure 4.2). As seen in Figure G.26, each online trap was three cells wide and had an initial bottom elevation 2 m lower than that of the surrounding cells. The lengths of ONL-1, ONL-2 and ONL-3 were 298 m, 287 m, and 319 m, respectively. Scenarios 11 and 18 in Table 4.1 and Scenarios 19 21 in Table 4.2 were run using one of more of these on-line traps.
In Table 4.5 the impact of treatment (load reduction) in the confluence area corresponds to 30% trapping efficiency at OFL-2 and OFL-3 (considering it to be realizable). It is evident that, from the point of view of intercepting sediment arriving in the confluence area: 1) OFL-2 is too far upstream to be effective, 2) OFL-3 is a better choice, and 3) OFL-3 coupled with ONL-1 is the most appropriate treatment scenario.
4.3.2.3 Results from Sediment Trap Simulations
For each of the 21 scenarios, net sediment fluxes, in units of grams per second (g/s), over the seven-day simulation at five transects along the CR were computed. The results are presented in the second through the sixth columns in Tables 4.4 and 4.5. The five transects, identified as TI T5 in Tables 4.4 and 4.5 and showed in Figure G.27, were located as follows: TI: immediately downstream of OFL-1; T2: immediately downstream of OFL-2; T3:




immediately downstream of OFL-3, which is located in the middle of ONL-3; T4: immediately downstream of ONL-1; and T5: immediately downstream of ONL-2. The last four columns in Tables 4.4 and 4.5 give the percentage decrease in the net downstream sediment flux at transects TI T4 relative to that for each of these transects calculated for Scenario 1 (the dashes in the first row of these last four columns indicate that the percentages were not calculated for these transects since the relative differences are meaningless for Scenario 1). The dashes in the last four columns in Table 4.4 for Scenarios 15 18 were not calculated since the changes in the boundary conditions for these scenarios nullified comparisons in terms of the relative net sediment fluxes. The negative sediment fluxes given under Ti and T4 in Table 4.5 indicate that the net flux increases at these transects relative to Scenario 1.
Percentage changes (relative to Scenario 1) in reach average bed elevation change for six reaches over the seven-day simulations are shown in Table 4.6. A positive percentage in this table indicates that there was more erosion in that reach than that which occurred in Scenario 1. The first reach, designated u/s Ti, extends from the upstream (u/s) boundary to T I, reach Ti T2 extends from Ti to T2, reach T2 T3 extends from T2 to T3, reach T3 T4 extends from T3 to T4, reach T4 T5 extends from T4 to T5, and reach T5 d/s extends from T5 to the downstream (dls) boundary. The actual reach average erosion (not the percentage change in reach average erosion) is given in Table 4.6 for reach T4 T5 since the reach average erosion for reach T4 T5 for Scenario 1 was zero, thus not allowing the percentage change to be calculated.
As seen by comparing the results for Scenarios 1 and 2 in Tables 4.4 4.6, the measured wind had no impact on net sediment fluxes or reach average erosion. The impact of adding OFL- 1 is seen for Scenarios 3 5 in Table 4.4. With increasing trap efficiency, the net sediment flux decreases at T I T3. As expected, the largest decreased occurred at T I as this




Table 4.4 Results from off-line sediment trapping scenarios (from Appendix G)
Scenario Net sediment flux (gls) at indicated transects Decrease in net sediment flux (%)
No. TI T2 T3 T4 T5 Ti T2 T3 T4
1 4.91 19.47 2.00 4.26 2.85
2 4.91 19.47 2.00 4.26 2.85 0 0 0 0
3 3.54 17.81 1.98 4.25 2.85 28 9 1 0.2
4 3.11 17.28 1.97 4.25 2.85 37 11 1.5 0.2
5 2.78 16.86 1.96 4.25 2.85 43 13 2 0.2
6 3.54 11.00 1.92 4.23 2.85 28 44 4 0.7
7 2.78 7.54 1.88 4.22 2.84 43 61 6 0.9
8 3.54 11.00 1.03 3.63 2.77 28 44 149 15
9 2.78 7.54 0.742 3.43 2.74 43 61 63 19
10 3.54 11.00 1.03 3.63 2.77 28 44 49 15
11 3.64 10.06 1.53 4.26 2.84 26 48 24 0.9
12 3.54 11.00 1.03 3.63 2.77 28 44 49 15
13 3.54 11.00 1.53 4.05 2.83 28 44 24 5
14 3.56 11.21 1.01 4.12 1.45 27 42 150 3
15 20.76 68.39 8.42 12.87 4.66
16 75.88 215.5 64.46 111.5 30.10
17 286.9 659.9 394.9 870.1 271.8
18 1278.8 638.7 382.1 11024 327.9 1-
Table 4.5 Results from on-line sediment trapping scenarios (from Appendix G)
Scenario Net sediment flux (g/s) at indicated transects Decrease in net sediment flux(%
No. TI T2 T3 T4 T5 Ti T2 T3 T4
19 5.05 18.46 1.57 4.28 2.84 -3 5 22 -0.5
20 5.04 18.54 1.59 4.02 2.95 -3 5 21 6
21 5.04 18.63 1.60 4.15 2.14 -3 4 20 3
transect was located immediately downstream of GEL- 1. Essentially no reduction in net
sediment flux occurred at T4. The results in Table 4.6 for these same three scenarios show that
the reach average net erosion increased with increasing trap efficiency for the three upstreammost reaches. The increase in the net erosion for these three reaches, possibly explained by the
decreasing suspended sediment concentrations (due to the increasing trap efficiencies) partially
counters the decrease in the net sediment flux noted above.
The impact of adding GFL-2 (in addition to GEL-i) is seen in Table 4.4 for Scenarios 6
and 7. The percentage decrease in the relative net sediment flux at T2 increases from 9% to
44% for Scenario 6 and from 13% to 61% for Scenario 7. Similar, though smaller, increases are
52




Table 4.6 Percentage change in reach average net erosion (from Appendix G) Scenario Change in Reach Average Net Erosion (%)
No. u/s-Ti Tl-T2 T2-T3 T3-T4 T4-T5 T5-d/s
I -2 0 0 0 0 0 0
3 0.6 8.4 9.8 0 0 0
4 0.9 10.8 13.0 0 0 0
5 1.2 12.7 15.4 0 0 0
6 0.6 14.0 53.1 0 0 0
7 1.2 19.9 75.3 0 0 0
8 0.6 14.0 53.2 0 0 0
9 1.2 19.9 75.5 0 0 0
10 0.6 14.0 53.2 0 0 0
11 17.0 21.9 16.8 -76.6 0 21.2
12 0.6 14.0 53.2 0 0 0
13 0.6 13.9 70.3 0 0 0
14 2.2 17.7 57.2 19.6 8.77 x 10-5 4.03 x 105
15 374 402 178 -1.85 x 103 5.79 x 10-5 823
16 1.03 x 103 1.20 x 103 695 -2.09 x 104 2.16 x 10-3 -9.52 x 10'
17 2.41 x 103 2.88 x 103 2.07 x 10' -7.08 x 104 1.51 x 10-2 -9.69 x 104
18 2.55 x 10' 3.00 x 103 2.33 x 103 -8.52 x 104 1.73 x 10-2 -1.17 x 105
19 16.1 6.9 -43.4 -76.6 0 21.2
20 16.1 7.6 -41.9 -29.8 0 37.4
21 15.9 8.4 -39.7 16.6 0 79.9
* the numbers in this column are the reach average bed elevation change (m)
noted at both T3 and T4 for both Scenarios. These results show that OFL-2 has a larger impact
on reducing the net sediment flux to the lower portion of the Cedar River than OFL- 1 by itself.
Also note that increasing the trapping efficiencies of both OFL-1 and OFL-2 from 40% to 80%
results in only a 17% decrease in the relative net sediment flux at T2, though the relative
decrease at T3 is 50%. Also as seen in Table 4.4, the net sediment flux at T4 decreases from
0.2% for Scenario 5 to 0.9% for Scenario 7. The additional increase in the reach average net
erosion is noted in Table 4.6 for Scenarios 6 and 7.
The impact of adding OFL-3 (in addition to OFL- 1 and OFL-2) is seen in Table 4.4 for
Scenarios 8 and 9. The percentage decrease in the net sediment flux at T3 increases from 4% to
49% for Scenario 8 and from 6% to 63% for Scenario 9. The percentage decrease in the net
sediment flux at T4 increases from 0.7% to 15% for Scenario 8 and from 0.9% to 19% for
Scenario 9. Thus, adding OFL-3 has a large impact in reducing the net sediment flux at both T3
53




and T4. Also note that increasing the trapping efficiencies for all three off-line traps from 40% to 80% results in a moderate 14% decrease in the net sediment flux at T3 and a minimal 4% decrease at T4. The reach average net erosion is essentially the same for Scenario 8 (in comparison to Scenario 6) and for Scenario 9 (in comparison to Scenario 7). Similar to the comparison between Scenarios 1 and 2, no change due to the measured wind is noted in Tables
4.4 or 4.6 between Scenarios 8 and 10.
In Scenario 11, the addition of ONL-3 instead of OFL-3 results in a 49% higher net sediment flux at T3 than that in Scenario 8, a 17% higher flux at T4, and a 3% higher flux at T5. The -76.6% change in net erosion given in Table 4.6 for Scenario 11 at reach T3 T4 is attributable to the deposition that occurs in ONL-3. Thus, using three off-line traps is more efficient at reducing the net sediment flux in the Cedar River than the use of two off-line traps and one on-line trap. Comparison of Scenarios 6 and 11 shows that the relative net sediment flux at T3 is reduced from 4% to 24% by the addition of ONL-3. The difference in the net fluxes at T4 is negligible.
Next, Scenarios 12 and 13 were compared with Scenario 8. As seen in Table 4.4, the results obtained for Scenario 8 (no wind) and Scenario 12 (constant 13.4 m/s (30 mph) Southerly wind over the seven-day simulation) were surprisingly identical. The constant 13.4 m/s Northerly wind simulated in Scenario 13 resulted in a 25% less relative decrease in the net sediment flux at T3, and a 10% less relative decrease in the net sediment flux at T4. Taken together, these three scenarios show that low to moderate winds (i.e., less than that during tropical storms) have an insignificant impact on the sedimentary regime in the relatively narrow and winding Cedar River.
Scenario 14 shows the impact that a 50% higher tidal range at the downstream boundary has on the net sediment flux in the Cedar River. A smaller decrease in net sediment flux occurs




at T4 in Scenario 14 (3%) than that in Scenario 8 (15%). Insignificant differences occur at the upstream transects. The biggest differences between these two scenarios are seen in Table 4.6, in which the higher tidal range at the downstream boundary results in reach average net erosion for the three downstream-most reaches, i.e., reaches T3 T4, T4 T5, and T5 dls. The latter is particularly significant in reach T5 dls.
Scenarios 15 17 simulate the impact of increasing both the flow and TSS boundary conditions at the upstream boundary of the Cedar River by factors of 2.5, 5 and 10, respectively. These three scenarios are compared to Scenario 8. As seen in Table 4.4, the net sediment fluxes at all five transects increase in proportion to the increase of inflow and TSS loads at the upstream boundary. Scenario 18 is identical to Scenario 17 except that an on-line trap is used at the location of OFL-3 instead of the off-line trap. The ONL-3 on-line trap results in higher net sediment fluxes at T4 and T5 than those obtained with the OFL-3 off-line trap. This same finding was obtained by comparing Scenarios 10 and 11.
The results for Scenarios 19 21 seen in Table 4.5 show that the only transect at which a significant reduction in the net sediment flux occurs is T3, which is located immediately downstream of ONL-3. Scenarios 11 and 19 show that the reductions in the net sediment flux at T3 is essentially the same. This indicates that OFL-1 and OFL-2 have minimal impact at T3.
To summarize the significant findings from the Cedar River modeling reported in Appendix G, more than one order of magnitude reductions in the net sediment fluxes at T3 and T4 were obtained using three off-line sediment traps as opposed to using just the two upstreammost off-line traps. The largest reduction (25%) in the net sediment flux at T5 was found using three on-line traps (Scenario 21). The largest reduction in the net sediment flux at T5 using online traps was seen to be only 4%.




4.4 On-Line Alternative: Dredging in the Confluence Area
Dredging soft sediment accumulated in the confluence area is an option that must be considered, inasmuch as it is this material that is contaminated, and has led to concern for water quality and accumulation of high levels of toxicity in local biota.
A measure of the thickness of the material in question can be estimated from the lengths of the bottom cores collected from the area, assuming that they were pushed down to the hard substrate below. If so, consider the soft sediment thickness isopleths in Figure 4.9.

Figure 4.9 Core thickness isopleths based on 1998 data (from Appendix E).




In Figure 4.10, the confluence region is enclosed within conveniently marked dashed lines. The mean thickness of the deposit here is about 1.85 m. Consequently, the volume of deposit in the area (-0.95 kmi2) is approximately 1.76x 106 M3 Assuming a mean wet bulk density of 1,200 kg/in3, corresponding to 21% organic matter (Table 2.1 and Appendix F), the total mass (solids + pore water) would be 2.11 xl10 metric tons, a very large value. Using the corresponding dry density of 300 kg/in3 (Appendix F), the (dry) solids mass would be 0.53x 106 metric tons. Now if we consider, for the sake of a practical illustration, that it may be feasible to identify critical areas for sediment removal by leaving out one-half the total area, the dredged mass would be lXlO6 metric tons, which is still large. It may therefore be necessary to look at dredging in the confluence area on a more selective basis.

Figure 4. 10 Isopleths in the confluence area (bounded by dashed lines). Dark circles
are 1998 core sites.




4.5 Selective Dredging
This process will be explored here on a qualitative basis with reference to Figure 4.11, which represents, in a general way, the bed structure in the confluence area. Under very high runoff conditions, such as occurred during El Nino in February of 1998, a few (up to 10 cm in selected locations, but generally 1-5 cm) centimeters of the very soft bottom mud may erode (Mehta et al., 2000). Since mud of this type cannot bear overburden unless the bed density is on the order of 1,300 kg/m3 (Mehta, 1991), from the point of view of navigation and stability of bottom mud, it appears reasonable to remove the -0.5 in thick top layer down to -1,300 kg/in3 density. If once again we assume that half the total area of 0.95 km2 needs to be dredged, we get a volume of 2.38x105 M3, or assuming the mean layer density to be 1,075 kg/m3, the mass would be 2.55x105 metric tons, which is more reasonable than the previous 1x106 metric tons.
Mean low water
Navigation depth =
1-2 rn Maximum draft + 0.6 m
Water 10
WResuspension may occur Vr s -1,005kg/m3 Resuspenslgn
potentially 5
mobile mud "- 1,300 kg/m
i.................... Minor resusp.ension
Soft mud
deposit
d-1,800 kg/m3
Harder bottom
Wet bulk density
Figure 4.11 Illustrative plot of bed density stratification in the confluence area.
The rationale for selective dredging can be for maintaining navigable depths for small craft. Assuming the maximum vessel draft to be 1.5 m, the depth can be 1.5 m + 0.6 m




(underkeel clearance) + 0.3 m (wave allowance) = 2.4 m, which would mean down to the hard bottom in the confluence area. ADCP based measurements in the confluence area and downstream (see Appendices C and D) suggest that bottom sediment resuspension due to boat traffic in the shallow zones is not minor. Thus, even for very shallow draft vessels, dredging to remove the top (-0.50 m; Fig. 4.11) soft layer down to a bulk density of 1,300 kg/m3 can be arguably important from the point of view of navigation and minimization of resuspension of very soft contaminated mud.
4.6 Selective Dredging and Capping
Sand capping of the bed after removal of the top -0.50 m should be considered, since it would have three advantages over the no-capping scenario:
1. It would prevent the freshly exposed surface of soft mud deposits (Figure 4.11) from
softening by wave induced liquefaction and by bioturbation, which may mean that the
top -10 cm of the surface would eventually become potentially mobile.
2. It would sequester the contaminated mud on a more or less permanent basis.
3. It would increase the depth of navigation due to consolidation by overburden.
Considering a 0.50 in thick cap and the mean density of the soft mud deposit underneath to increase from, say, 1,500 kg/m3 to 1,650 kg/m3, would decrease the thickness of the -1.5 m thick soft deposit to -1.4 m. In other words the bed level would lower by -10 cm at the end of the consolidation process. Considering the mean deposition rate in the
area to be -1 cm/year, this would mean a 10 year advantage in terms of navigation.




5 ASSESSMENT OF REMEDIATION ALTERNATIVES
5.1 Selected Alternatives/Options
The alternatives/options considered in Section 4 are summarized in Table 5.1. An assessment of the remedial measures for the Cedar River are summarized in Table 5.2. Their advantages/disadvantages are summarized in Table 5.3. In Table 5.2, the listed removal efficiency at the specified transect is calculated as the reduction in the net sediment flux at that transect over the seven-day simulation.
5.2 Qualitative Assessment
The following three criteria are considered for each remedial option on a qualitative basis:
1. Optimization of capture of contaminated sediment in transport;
2. Minimization of accumulation and navigability; and
3. Water quality (in terms of contamination of surface water).
In Table 5.3 the options have been ranked (1 = good, 0 = moderate, -1 = poor) according to each criterion, and the net values for all options are calculated.
Based on the evaluation in Table 5.3 it is noted that if the capture of contaminated sediment from upstream sources in Cedar River is the only or main goal, one of the two off-line sites proposed by SJRWMD, preferably the one closer to the source of sediment, i.e., OFL-1, would be the first choice, provided the facility operates at very high, e.g., -80% removal efficiency. If improvement in navigation coupled with reduced resuspension of in situ material is additionally desired, selective dredging and sand capping in the confluence area should be considered. If capping proves to be too costly, removal of the top layer of very soft mud from areas where boats regularly ply the waters may be further evaluated.




Table 5.1 Selected alternatives/options
No. Approach Description
1 No-action Maintain the system as is, with continued arrival of
contaminated sediment from Cedar River and its accumulation downstream, especially in the confluence area, at the rate of-10 mm/yr.
2 Off-line treatment: SJRWMD proposed Wet Detention System in the u/s reach of
up-reach at OFL-1 Cedar River meant to capture a significant fraction of the
contaminated material at its source.
3 Off-line treatment: SJRWMD proposed Wet Detention System in the u/s reach of
up-reach at OFL-2 Cedar River meant to capture a significant fraction of the
contaminated material close to its source. This facility would be d/s of OFL-1, but u/s of
Williamson Creek.
4 Off-line treatment: Treatment (e.g., Wet Detention System) between Williamson
mid-reach at OFL-3 Creek and Butcher Pen Creek.
5 Off-line treatments: Treatments (Wet Detention Systems) in the u/s reach of Cedar
up-reach at OFL-1 & OFL-2 River.
6 Off-line treatments: Treatments (Wet Detention Systems) in the u/s reach of Cedar
up-reach at OFL- 1 & OFL-2, River, and mid-reach between Williamson Creek and Butcher
and mid-reach at OFL-3 Pen Creek.
7 On-line entrapment: Treatment (dredged pit) between Butcher Pen creek and
mid-reach at ONL-1 Fishing Creek.
8 On-line entrapment: Treatment (dredged pit) between Butcher Pen Creek and
down-reach at ONL-2 Fishing Creek, downstream of ONL-1.
9 Off-line treatments up-reach at Treatments (Wet Detention Systems) u/s of Williamson Creek OFL-1 & OFL-2 and on-line combined with a dredged pit) between Williamson Creek and
treatment at ONL-3 Butcher Pen Creek.
10 Selective dredging at Dredging for navigation within the shallowest zone of the
confluence confluence.
11 Selective dredging and capping Dredging for navigation within the shallowest zone of the
at confluence confluence coupled with sand capping.




Table 5.2 A summary assessment of remediation options for Cedar River sediment
Opt. Approach Advantages Disadvantages
1 No-action System remains undisturbed Sediment accumulation at
confluence likely continue at present
rate (-10 mm/yr)
2 Off-line treatment: Capture contaminated sediment No impact on accumulation at upreach at OFL-1 close to its source; removal confluence; removal efficiency at T4 efficiency at T3 is 2% is 0%
3 Off-line treatment: Advantage over #2 in capturing No impact on accumulation at upreach at OFL-2 sediment due to d/s location; confluence; removal efficiency at T4 removal efficiency at T3 is 4% is 1%
4 Off-line treatment: Entrapment of sediment load is Off-line site location may be mid-reach at OFL-3 significant; removal efficiency at T3 difficult is 57% and at T4 is 18%
5 Off-line treatments: Entrapment of sediment load could Construction and maintenance of up-reach at be significant, provided both two facilities may be untenable
OFL-1 & OFL-2 facilities operate at high efficiencies; removal efficiency at T3 is 6% and
atT4 is 1%
6 Off-line treatments: Entrapment of sediment load could Construction and maintenance of at OFL-1, OFL-2 be very significant, provided both three facilities may be untenable
and OFL-3 facilities operate at high efficiencies;
removal efficiency at T3 is 63% and
at T4 is 19%
7 On-line entrapment: Entrapment of sediment load could Capital and maintenance dredging of mid-reach be significant depending on pit on-line trap containing contaminated
at ONL-1 design sediment could be problematic
8 On-line entrapment: Due to proximity to confluence, Capital and maintenance dredging of down-reach considerable advantage in on-line trap containing contaminated
at ONL-2 intercepting sediment load, if the sediment could be problematic
removal ratio can be optimized
9 Off-line treatments Entrapment of sediment load could Capital and maintenance dredging of at OFL-1 & OFL-2 be significant, depending on pit on-line trap containing contaminated
and on-line design and provided both off-line sediment could be problematic
at ONL-3 facilities operate at high efficiencies
10 Selective dredging Reduce in situ, mobile contaminated Dredging of contaminated hot-spots at confluence sediment and improve navigation could be environmentally problematic
11 Selective dredging Reduce in situ, mobile contaminated Dredging of hot-spots could be and capping at sediment and improve navigation; environmentally problematic; cost
confluence cap would sequester contaminated will be higher than dredging alone
material




Table 5.3 Ranking of options based on selected criteria Criterion
Option Capture of Improvement Water
contaminated Improvement WaterNet
sdi.nt in navigation quality Net
sediment
1. No-action -1 -1 -1 -3
2. OFL-1 1 -1 1 1
3. OFL-2 1 -1 1 1
4. OFL-3 1 -1 1 1
5. OFL-1 + OFL-2 1 -1 1 la
6. OFL-1 + OFL-2 + OFL-3 1 -1 1 la
7. ONL-1 1 0 0 1
8. ONL-2 1 0 0 1
9. OFL-1 + OFL-2 + ONL-3 1 0 1 2a
10. CAC dredging -1 1 0 0
11. CAC dredging + capping 0 1 0 1
a The cost of operating multiple facilities may negate part of the advantage.




BIBLIOGRAPHY

Baker, E. T., Milburn, H. B., and Tannant, D. A., 1999. Field assessment of sediment trap
efficiency under varying flow conditions. Journal of Marine Research, 46, 573-592.
Bedient, P. B., and Huber, W. C., 2002. Hydrology and Floodplain Analysis. 3rd ed., PrenticeHall, Upper Saddle River, NJ.
Campbell, D., Bergman, M., Brody, R., Keller, A., Livingston-Way, P., Morris, F., and
Watkins, B., 1993. Lower St. Johns river basin SWIM plan. St. Johns River Water
Management District, Palatka, FL.
Donohue, J. F., 1999. Investigation of historic sedimentation rates in the lower St. Johns River.
Technical Report, St. Johns River Water Management District, Palatka, FL.
Environmental Protection Board, 1985. Annual Environmental Status Report: Year Ending
September 30, 1985. Jacksonville, FL.
Freeman, R.J. 2001. Simulation of Total Suspended Solids Loads into the Cedar/Ortega River,
Duval County, Florida Using SWMM. St. Johns River Water Management District,
Palatka, Florida. Department of Water Resources Technical Memorandum No. 46.
Ganju, N. K., 2001. Trapping organic-rich fine sediment in an estuary. M.S. Thesis, University
of Florida, Gainesville, FL.
Harper, H. H., 1997. Pollutant removal efficiencies for typical stormwater management systems
in Florida. Proceedings of the Biennial Stormwater Research Conference, Southwest
Florida Water Management District, Tampa, FL, 6-19.
Hamrick, J. M., 1992. A three dimensional environmental fluid dynamics computer code:
Theoretical and computational aspects. Special Report No 317, Applied Marine Science
and Ocean Engineering, Virginia Institute of Marine Science, Gloucester Point, VA.
Hamrick, J. M., 1996. User's manual for environmental fluid dynamics computer code. Special
Report Special Report No 331, Applied Marine Science and Ocean Engineering,
Virginia Institute of Marine Science, Gloucester Point, VA.
Marvdn, F. G., 2001. A two-dimensional numerical transport model for organic-rich cohesive
sediments in estuarine waters. Ph.D. Thesis, Heriot-Watt University, Edinburgh, UK.
Mehta A. J., 1991. Understanding fluid mud in a dynamic environment. Geo-Marine Letters,
11, 113-118.
Mehta, A. J., Kirby, R., and Hayter, E. J., 2000. Ortega/Cedar River basin, Florida, restoration:
work plan to assess sediment-contaminant dynamics, Report UFL/COEL-99/019, Coastal and Oceanographic Engineering Department, University of Florida, Gainesville.
Mehta, A. J., and Parchure, T. M., 2000. Surface erosion of fine-grained sediment revisited. In:
Muddy Coast Dynamics and Resource Management, B. W. Flemming, M. T.
Delafontaine, and G. Liebezeit eds., Elsevier, Amsterdam, 55-74.




Paramygin, V., 2002. Sediment Trapping in a microtidal estuarine system. MS Thesis,
University of Florida, Department of Civil and Coastal Engineering.
Parchure, T. M., Brown, B., and McAdory, R. T., 2000. Design of sediment trap at Rollover
Pass, Texas. Report ERDC/CHL TR-00-23, U.S. Army Engineer Research and
Development Center, Vicksburg, MS.
Sarikaya, H. Z., 1977. Numerical modeling of discrete settling. Journal of the Hydraulics
Division ofASCE, 103(8), 866-876.
Vincente, C. M., 1992. Experimental dredged pit of Ka-Ho. Analysis of shoaling rates.
Proceedings of the International Conference on the Pearl River Estuary in the Surrounding Area of Macao, Vol. 2, Civil Engineering laboratory of Macao, Macao,
paper P6.4, 1 lp.
Winterwerp, J. C., 1998. A simple model for turbulence induced flocculation of cohesive
sediment. Journal of Hydraulic Research, 36(3), 309-326.
Wanielista, M. P., 1978. Stormwater Management. Ann Arbor Science, Ann Arbor, MI.
Wolanski, E., Gibbs, R., Ridd, P., Mehta A., 1992. Settling of ocean-dumped dredged material,
Townsville, Australia. Estuarine, Coastal and Shelf Science, 35, 473-489.




Appendix A

Appendix A
Sedimentary Regime of the-Lower Cedar/Ortega River System
and its Environs, Florida, Report
Ravensrodd Consultants Ltd.
6 Queen's Drive, Taunton Somerset TA1 4XW UK February 2002

University of Florida, Dept. of Civil and Coastal Engineering A-1




Appendix A
Contents
List of Figures ....................................................................................................................... A-3
List of Tables ........................................................................................................................ A-4
A l. THE LOW ER ST. JOHN S RIVER ............................................................................... A-5
A L I Sedim entary Regim e ........................................................................................... A -5
A 1.2 Linear Sedim entation Rate .................................................................................. A -5
A 1.3 Sedim ent Sources ................................................................................................ A -5
A2. SEDIMENTARY REGIME OF THE LOWER CEDAR AND ORTEGA RIVERS ... A-7
A2.1 D ata Sets and Background .................................................................................. A -7
A2.2 Grain Size V ariations .......................................................................................... A -8
A2.2.1 Clay ....................................................................................................... A -8
A2.2.2 Silt ......................................................................................................... A-8
A 2.2.3 Sand ..................................................................................................... A-13
A2.3 Other Physical and Chemical Properties of Bed Sediments ............................. A-13
A2.3.1 M oisture and Total Solids Content ...................................................... A -13
A 2.3.2 Total Organic Carbon/Organic % ........................................................ A -16
A2.4 Core Descriptions from the 1995 Cam paign .................................................... A -16
A 2.4.1 Clean Sand D istribution in Cores ........................................................ A -19
A 2.4.2 Core Stratigraphy ................................................................................ A -21
A2.5 InteT rotation ..................................................................................................... A -22
A 2.5.1 Cedar River .......................................................................................... A -22
A 2.5.2 Ortega River ........................................................................................ A-23
A 2.5.3 Inner Confluent Region ....................................................................... A -23
A 2.5.4 Outer Confluent Region ...................................................................... A -24
A3. IMPLICATIONS OF SEDIMENT REGIME FOR PCB
REMEDIATION AND SYSTEM RESTORATION .................................................. A-25
References ............................................................................................................................. A-26
A-2 University of Florida, Dept. of Civil and Coastal Engineering




Appendix A
List of Figures
Fig. Al Grab sampling sites for 1998 survey of physical and chemical attributes
of bed sediments in the Cedar & Ortega Rivers system ..................................... A-9
Fig. A2 Areal variation in percent clay in the 1998 suite of grab samples .................... A-10
Fig. A3 Areal variation in percent silt in the 1998 suite of grab samples ...................... A-11
Fig. A4 Areal variation in percent sand in the 1998 suite of grab samples ................... A- 12
Fig. A5 Areal variation in percent moisture content of bed sediments
from 1998 grab sampling survey ...................................................................... A-14
Fig. A6 Areal variation in percent solids content of bed sediments
from 1998 grab sampling survey ...................................................................... A-15
Fig. A7 Areal variation in percent total organic carbon (TOC) of bed sediments
from 1998 grab sampling survey ...................................................................... A-17
Fig. A8 Computer-contoured plot of areal variation in percent organic content
of bed sediments from 1998 grab sampling survey .......................................... A-18
Fig. A9 Sedimentation rate measurements for eight recent cores from the inner
and outer confluent regions of the Cedar/Ortega River system ........................ A-20

University of Florida, Dept. of Civil and Coastal Engineering A-3




Appendix A
List of Tables
Table A l Measurements of siltation rate for lower St. Johns River and
for Cedar River m outh ...................................................................................... A -6

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Appendix A
Al. The Lower St. Johns River
A1.1 Sedimentary Regime
A good perspective on the sedimentary regime in tidal reaches of the Cedar and
Ortega River System can be obtained from comparison with studies in adjacent reaches of the main stem of the St. Johns River (Cooper and Donoghue 1999). These authors applied a range of geochemical techniques-mainly 21Lead, "'Caesium, Carbon:Nitrogen Ratios, 13Carbon: 12Carbon Ratios, 13Carbon Solid-state, Natural Magnetic Remnance (NMR) Spectroscopy, and so-called "Biomarkers", distinctive organic molecules synthesised by plants or animals and incorporated into sediments. Cooper and Donoghue undertook multiple analyses on eight cores from the lower tidal reaches of the St. Johns River. The three most down-estuary cores, situated in the reaches to the south of and above of the confluence of the combined Cedar/Ortega River system, at Christopher Cove/Beauclerc Point, Mandarin Point and Doctors Lake, are especially relevant here.
The report is remarkably light in its overall description of the bulk sediment type, but it is presumed to be the dark colloidal, highly organic-rich mud, locally called "Muck". In the report the sediments are described as "overwhelmingly fine-grained, averaging 80% fines, unusually high in moisture content, averaging 79%, and in organic material, averaging 29% by weight", all leading to extremely low dry bulk densities, averaging 0.24g cm-3. This work, and another by Alexander et al. (1993), do, nevertheless, give some estimates of siltation rate, which may lead to an expectation for the Cedar/Ortega River system. Similarly, these same authors have investigated sediment sources in the St. Johns River.
A1.2 Linear Sedimentation Rate
In Table Al, siltation rates for the lower St. Johns River and Cedar River derived from Cooper and Donoghue (1999) and Alexander et al. (1993) here below summarized.
A1.3 Sediment Sources
The fractional contribution of marine and fluvially derived 137Cs in estuarine sediment are claimed by Mulholland and Olson (1972) to be distinguishable if marine and riverine 137Cs input concentrations are known. Applying the Mulholland and Olsen equation obtained for the Savannah River to these Cedar/Ortega samples leads to an estimate of 29% for the marine-derived portion in core Cs-127, compared to 20% in core 039. The precise sampling localities of neither core is known.
Further evidence for sediment sources in the St. Johns main stem may be taken from C:N ratios of cores from the 3 sites immediately up-estuary from the Cedar/Ortega Rivers. Elemental carbon should represent roughly 40% of the sedimentary organic fraction based on a chemical formula approximation for biomass of methanal (CH20)(CH20 Methanal/ Formaldehyde, a compound produced by the oxidation of methanol or by oxidation of ethane in the presence of a catalyst), although this number is usually significantly lower in sedimentary organic matter due to the complexity of biologically derived molecules. The
University of Florida, Dept. of Civil and Coastal Engineering A-5




Appendix A
Table Al. Measurements of siltation rate for lower St. Johns River and for Cedar River mouth
Excess 21Lead 137Caesium
Locality Core Sample Amount Core Sample Amount
No. (mm/yr) No. (mm/yr)
Christopher Cove 1 6.2 NA NA
2 9.3 NA NA
Mandarin Point 1 38.8 NA NA
2 25.0 NA NA
3 15.1 NA NA
Doctors Lake 1 10.3 NA NA
2 10.8 NA NA
3 13.5 NA NA
also Alexander et al. (1993) 1 11.0 1 9.0
Cedar River Mouth
Alexander et al. (1993) "039" 11.0 "039" -9.0/~12.0
Cs"127 2.13 dpm/g*
"039" 2.4 dpm/g*
Source: (Cooper and Donoghue 1999; Alexander et al. 1993). Note: NA = not applicable
*average surface concentration.
elemental carbon values at Christopher Cove, 6%, parallel lower combustible organic matter at the same site, 25-30%, (they reach about 40% at the most up-estuary sample sites in the St. Johns River). Mandarin Point values are intermediate between the down- and up-estuary extremes, lying at -8% elemental carbon and 30-35% combustible organic matter. C:N ratios for most of the cores were found to lie in the range 10-14:1 and do not vary significantly with depth. Such values are consistent with values in terrestrial soils and the surface sediments of lakes. The suggestion from this is of a mainly terrestrial source for the organics in these suites of cores.
Organic matter in sediments known to originate from higher terrestrial plants exhibit a functional grouping of stable Carbon isotopes, approximately 30-40% aliphatic (Aliphatic Compounds: methane derivatives of fatty compounds; open chain or ring carbon compounds not having aromatic properties), 20-30% aromatic (Aromatic Compounds. Compounds related to benzene. Ring compounds containing conjugated double bonds) and 20-30% heteroaliphatic. (Heteroaliphatic. Hetero-a prefix meaning other or different).
This contrasts with the typical distribution of carbon isotopes in brackish waterderived organics, which are reflected in the sedimentary biomass as 40-50% aliphatic, 1520% aromatic and 20-30% heteroaliphatic. The values detected in the St. Johns River cores are consistent with derivation from degraded higher plant (terrestrial) sources. Only at Mandarin Point and Christopher Cove did sediments with higher (marine/aquatic) stable carbon ratios make any contribution to the overall 13C isotope ratio pool.
When geochemical "biomarkers" were investigated in the suite of cores, the overwhelming feature in each is the predominance of higher molecular weight hydrocarbons, i.e., those containing 22-24 or more carbon atoms. This also reflects a strong terrestrial input
A-6 University of Florida, Dept. of Civil and Coastal Engineering




Appendix A
signal, since the alkanes and alcohols in plant waxes, the most prominent sources of hydrocarbons in terrestrially-derived sedimentary organic matter, are primarily in the 25-33 range (Tissot and Welte 1984). In contrast, hydrocarbons derived directly from planktonic algae are dominated by shorter alkanes in the 15-17 range. This is further evidence that organics in the St. Johns River sediments are mainly allochthonous and terrestrial, being derived from the catchment. Cooper and Donoghue further report ... "In spite of the overwhelming dominance of higher-molecular weight hydrocarbons, there are measurable quantities of hydrocarbons in the C16-C2o range. These most likely originate from planktonic algae". The presence of these shorter chain alkanes is consistent with a small contribution to the organic content of these sediments (.- 10-20%) from authigenic, aquatic sources. The ratios of the various fractions presented can be taken as reflecting their sources and it is suggested these ratios have not been significantly affected by diagenetic post-depositional changes.
The summary of important attributes of these main stem sediments is that their
sedimentary regime is a net and rapid depositional one, with a mean long-term average linear sedimentation rate for the 8 sites of 10.7 mm/yr. At all 8 sites the mass accumulation rate can be observed to have increased during the latter half of the Twentieth Century in some cases by a factor of 3 or more. Sand laminae are relatively common in the upper 40 cm sections of many cores, possibly as a result of deforestation followed by storms or floods in recent years. All 4 approaches adopted by Cooper and Donoghue for characterising sources and transformations of organic matter in sediments from the lower St. Johns River indicate that allochthonous, terrestrially-derived material from the watershed is the primary carbon source in these organic-rich sediments. There does not appear to be any significant historical change in sources or qualitative variation.
A2. Sedimentary Regime of the Lower Cedar and Ortega Rivers
A2.1 Data Sets and Background
Two data sets are available for appraisal. One was a set of 172 cores obtained
between 1993 and 1995 and subsequently analyzed and reported by Morgan & Eklund, Inc., in 1995. The history of deposition within the study area has been interpreted herein from core descriptions made at that time. A second set of 51 surface grab samples was obtained and a preliminary report submitted in 1998 by Battelle Ocean Sciences. Both grain size and geochemnical analyses were performed on this suite of samples. The geochemical analyses were variously subcontracted to Mote Marine Laboratory, Savannah Laboratories, etc.
The bed materials involved are locally referred to as "muck". Muck is defined as "black, fine-grained sediment with a high water content, composed of partly decomposed organic matter with a considerable amount of admixed silt and clay material".
The St. Johns River system, which the Cedar/Ortega are part of, has an unusually low gradient, dropping less than l1in from head to mouth (approx. 480 kin). It also has a low tidal range (about 30 cm at the Cedar/Ortega River mouth) and a channel often 6m below
University of Florida, Dept. of Civil and Coastal Engineering A-7




Appendix A
mean sea level. Normal river flows and the perturbation of these by the tides give rise to a gentle flow regime which is depositional/retentive for sediment during most normal circumstances. This largely explains the relative paucity of detrital mineral inputs. The system is, nevertheless, susceptible to wave stirring during windy spells, such as storms and the exceptional hurricane. Such disturbance might be expected to have a noticeable impact on bed sediments due to the unusually shallow nature of much of the system. Winnowing and segregation of sediment might be anticipated. Similarly, occasional high rainfall and run-off events occur, the consequences of which might also be detectable in the sediments. The physical properties of both surface sediment samples and cores have been investigated and plotted, leading to a comprehension of the bed sediment regime both really and with depth.
It turns out that the sediments of the Cedar/Ortega River system fall very readily into four quite distinct zones and they are best described in these. The zones are: the Cedar River, the Ortega River, the inner confluent region between Fishing Creek and Roosevelt Boulevard Narrows and finally the outer confluent region between Roosevelt Boulevard Narrows and the junction with the St. Johns River itself The minor tributary creeks, Big Fishweir Creek, Fishing Creek, Butcher Pen Creek and Williamson Creek, are considered within these zones (Figure A 1).
A2.2 Grain Size Variations
The areal variation of grain size of the inorganic fraction has been plotted from the 1998 data. These appear here as three maps based on % Clay, % Silt, % Sand (Figures A2, A3 and A4).
A2.2.1 Clay(< 2 gm)
There is very little clay in the system (Figure A2). The highest clay percentage in the entire data set, 18%, occurs at the innermost station in the Cedar River and there is a pronounced decreasing down-estuary gradient in the clay fraction. The Ortega has a uniform and low clay content, whereas the inner reach of the confluent region is an anomalouslooking zone of exceptionally low (mainly 1-2%) clay content. The outer confluent region is wholly separated from the elevated clay contents of the Cedar River, but clay contents are again slightly elevated (> 7.0%).
A2.2.2 Silt (> 2 ttrn < 62.5 Itm)
The silt content of bed sediments also shows distinctive area groupings (Figure A3). Both the Cedar and Ortega show values in the mid-levels (50-60%) and both show a pronounced decreasing down-estuary gradient to the inner confluent region. This, latter, zone is again apparently anomalous having both variable silt contents (25-7 1 %) but an extensive region of values significantly lower than elsewhere in the system (23-35%). Both the variability and the unusually low silt fraction in these reaches needs to be explained. The most pronounced feature of the silt distribution is the elevated and fairly constant quantities

A-8 University of Florida, Dept. of Civil and Coastal Engineering




Appendix A

1998 sample sites

Region 2

Region 3

Figure Al. Grab sampling sites for 1998 survey of physical and chemical attributes of bed
sediments in the Cedar & Ortega Rivers system (after Battelle, Mote Marine,
Savannah, etc.). The system can be separated areally into four distinctive
regions
University, of Florida, Dept. of Civil and Coastal Engineering A-9




Appendix A
Clay (%)
.6
18.3 ,
2 .4.
Figure A2. Areal variation in percent clay in the 1998 suite of grab samples. A detrital
input from the Cedar River catchment and especially low values in the
Cedar/Ortega confluence are evident
A-i 0 Unz'i'ersitv o Florida, ept.6o.ii ndCatlEniern

University, of Florida, Dept. of Civil and Coastal Engineering

A-10




Appendix A

Silt (%)
42.2
49.3 .
20 30 40 50 6
FigreA3.Aralvaratonin eren sit n he 99 siteofgrb smpes Threar
eleatd ales sgnfyng npts fomth Cda Rieran te ai2sem
Siltis he ain etrtalinogani inut nto he rtea. hereis zoe o
variable9. an5fe.eylwvlusi7h ea/reg ofunergo
Univrsiy olFloida Dep. o Civl ad Casta EnineeingA-4

A-1 1

UniversitY of Florida, Dept. of Civil and Coastal Engineering




Appendix A

Sand (%)

;.Of 'I

20 30 1 40 50 60 70

Figure A4.

Area[ variation in percent sand in the 1998 suite of grab samples. There are minor inputs from both the Cedar and Ortega but high inputs from Butcher Pen and Fishing Creek which are spread into the inner confluent reaches. Some sand also enters from the main stem

A-12

University of Florida, Dept. of Civil and Coastal Engineering




appendix A
in the outer confluent reaches extending from the main stem, (> 70-< 80%). There is some tendency for these zones of elevated silt content to be associated with the axial zone of the estuary.
A2.2.3 Sand (> 62.5 pm < 1000 gm)
The sand fractions of the inorganic portion of bed samples, naturally, mirrors the clay and silt fraction distribution (Figure A4). Unlike the fines, which show a down-estuary decrease in amount, the sand fraction increases down-estuary in both the Cedar and Ortega Rivers to reach a system maximum in the inner confluent region. This latter zone also shows the greatest area variability (22-75%). The sand content of the inorganic portion of much of this zone lies in the range 60-70%.
The sand content of the outer confluent region is the lowest anywhere in the system, generally ranging between 15 and 25%. Extreme values span 16-74%, with no obvious pattern.
A2.3 Other Physical and Chemical Properties of Bed Sediments
The 1998 grab samples have been subjected to further analyses. Samples have been analyzed for physical properties, such as moisture content, quoted in percentages, and for total % solids. (Obviously solids and moisture are reciprocals of each other). The samples have also been subjected to chemical analysis for total organic carbon and for organic content
(%). In the plots the data has mainly been contoured by hand. In areas of great topographic complexity and with relatively few sample points to describe a distribution, hand contouring avoids the anomalies a computer is unable to cater for.
A2.3.1 Moisture and Total Solids Content
Within the system the four regions described above are distinguishable. In respect of the related moisture and total solids percentages, there is a strong contrast between the sediments in the Ortega, coming in from the south, and those of the Cedar entering the confluent region from the north. The Ortega bed sediments have by far the highest moisture contents (Figure A5) and by the same token, the lowest total solids input (Figure A6). There appears to be an axial "tongue" of high moisture content sediments projecting from the Ortega River and into the inner confluent region off Fishing Creek. Unfortunately, there are only six axially placed samples in the Ortega such that any lateral and more extended longitudinal gradients cannot be determined. In contrast, the Cedar has much higher detrital solids percentage values in its inner reaches, as well as a pronounced down-estuary decrease. Similarly, the moisture content of the sediments of the inner reaches of the Cedar is virtually the lowest in the entire system.
The inner confluent region shows a broad zone of bed sediments with 73-79%
moisture and 20-27% solids. This contrasts markedly with the peak in sand content in bed sediments of this zone (Figure A4). Although the sample grid is wanting in this respect, there is a possible focussing of high moisture, low solids bed sediments on the left bank,

A- 10

University, of Florida, Dept. of Civil and Coastal Engineering




Appendix A

Moisture (%)
50 60 70 80 90
60,-'
80"'

75~i 1i 70 5 55
10
75 1 70

73

70
'6o 70
/ ~
j' .

Figure A5. Areal variation in percent moisture content of bed sediments from 1998 grab
sampling survey. The distinctive and high moisture content of Ortega River
samples and at marginal sites often coincident with marina developments in the
inner and outer confluent region is evident

A-i 4 University of Florida, Dept. of Civil and Loastal Lngineerrng

University of Florida, Dept. of Civil and Coastal Ezngineering

..... .. F w

A-14




Appendix A

Total solids (%)

10 20 30 40 50

40 30
20
20. 22
/19*o
24
20 27
7 22

'3 26 27.
26 21
21
S20
/*35/30

\* 40
30\- 27
*26 21 3040
20k- *
18 I 45
14 5
20 2 26 730
20." "- a .
22* 24
9 22
.2023 24*
- 22
9 20
21 21 1
21 2 19
22
s 20 6/
2

27
22
20
22
* 27

23

20
21/22 '
0

016

20
'-. r

/r
20+
17
r

Figure A6. Areal variation in percent solids content of bed sediments from 1998 grab
sampling survey. The highest solids contents occur in the Cedar River,
Butcher Pen and Fishing Creeks and at the meeting point with the main stem.
The Ortega River input is especially low in solids

University of Florida, Dept. of Civil and Coastal Engineering A-i 5

i

A-15

University of Florida, Dept. of Civil and Coastal Engineering




Appendix A
coincident with the flow impediment provided by commercial marina development in these reaches. The outer confluent region is not dissimilar to the inner region in respect of % moisture and solids. There is a broad zone where sediments show % moisture in the high 70s, low 80s in 1995. Particular features of this outer confluent zone are the high moisture/low total solids zones, again on the left bank co-extensive with marina developments. A separate and strong feature is an apparent tongue of low moisture %, high solids sediments apparently penetrating the system from the main stem direction.
A2.3.2 Total Organic Carbon/Organic %
As with % moisture and % solids, these analyses reflect directly the organic content of bed samples, as opposed to the inorganic fraction revealed in the grain size measurements. The results show some pronounced contrasts from the inorganic bed sediment plots and also some distinctive features. The Ortega River sediments have a significantly higher organic content than any others in the system (Figures A7 and A8), as well as a pronounced downestuary decrease.
There is also a tongue of relatively elevated organics fraction sediment, possibly
emerging from the Ortega and enriching sediments in the inner confluent region. This region thus exhibits the combination of unusually sandy bed sediments, which are also unusually organics-rich. In contrast, the innermost sediments in the Cedar River are amongst the lowest in the system in organics content and the analyses show a steady rise in organics in a down-estuary direction, the reverse of that in the Ortega.
The outer confluent region shows TOC % background values mainly in the 11-14% range. Organic content (%) shows a little more variability and a higher range, 16-24%. There is possibly some tendency for elevated organic values in more marginal sediments, especially along the left (northerly) bank coincident with the marinas. A tongue of low organic-rich sediments appears to be penetrating the system from the main stem along the outermost (down-estuary) line of samples.
A2.4 Core Descriptions from the 1995 Campaign (plus measurements of sedimentation rate)
The Morgan & Eklund, Inc., report from 1995 gives detailed and useful core logs and their positions. More recent, and still preliminary, determinations of sedimentation rate have been made available for 8 samples (Higman, pers com). The evaluation of the sedimentary regime has also benefited from advice from Dr. J. Higman, especially in respect of biological issues. The core logs and mapped distributions perm-it additional understandings of the area and depth variation of sediment characteristics.
In respect of sedimentation rate measurements using 210 Pb and 137 Cat the three
closest sampling localities of Cooper and Donoghue in the St. Johns River, rates normally in the range 9-12 mm/yr but rising at exceptional localities to 25-40 mm/yr have been determined. The measurement of core 0-39 from the Cedar River mouth gave 11.0 mm/yr.
A-i16 University of Florida, Dept. of Civil and Coastal Engineering




Appendix A

Total organic Carbon (%)

0 5 10

,J~f' '>~.S 13
/
If i

15 20 25 10 ] 110
2 5
15 20 25
10
15 13 2, I
02 12
1 13
"11 21
'13 1
13
6 14
/ 1
161
014 1
, 17

Figure A7. Areal variation in percent total organic carbon (TOC) of bed sediments from
1998 grab sampling survey. The especially high TOC of Ortega River samples,
spreading into the inner confluent region, as well as the low TOC at the
confluence with the main stem, is evident

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University, of Florida, Dept. of Civil and Coastal Engineering




Appendix A

Organic content (%)

CI

10 15 1 20 25 30

Figure A8. Computer-contoured plot of areal variation in percent organic content of bed
sediments from 1998 grab sampling survey. The most distinctive features are
the high organic content of the Ortega River input together with low organics
content of Roosevelt Narrows and the main stem confluence

A-i 8 Unii'ersitv of Florida, Dept. oJ CAVIL and Loastai ~ngineermg

University of Forida, Dept. of Civil and C~oastal E~ngineering

A-18




Appendix A
Figure A9 shows the sedimentation rate for these 8 latest cores, which are all more or less confined to the inner and outer confluent regions of the two rivers. It is evident that cores from the right bank and main stem confluence show accumulation rates ranging between 4 and 8 mmn/yr-almost half the value of the "normal" range of the few analyses available from the St. Johns River. There are three samples from the left bank of the confluent region, amongst or in close proximity to the commercial marinas. These have high and consistent sedimentation rates of about 20 mm/yr. though these are still half the maximum rates determined in adjacent sites in the main stem.
A2.4.1 Clean Sand Distribution in Cores
Detailed descriptions of 172 cores taken from the system in 1995 and extruded for examination have been studied. Sand admixed with silt, clay or the large organic muck fraction cannot be distinguished in laboratory descriptions, but clean sand laminae in mud cores are quite distinctive. Review of these core logs reveals that there is no sand in cores from the Ortega in the section immediately down-estuary of Collins Road Bridge, and virtually no sand in the lower reaches of the Ortega. Such sand layers as are occasionally recognized are invariably very thin and present at deep horizons in the core. A similar situation applies-to the Cedar River. Sand layers are present only occasionally, often singly in cores, and are thin.
Two cores from Williamson Creek show virtually no sand. Down-estuary from the Blanding Boulevard Bridge, multiple sand layers are common in Cedar River cores and in cores from Butcher Pen Creek. Fishing Creek appears to be exceptional, having either thick or multiple sand layers in all cores taken from it and in its entrance. Sand layers 0.5 and 2.0 cm thick are noted, for example. Several cores in the approaches to this creek have thick sand layers at their surface or in one case are all sand to 46 cm below the estuary bed.
In the lower Cedar River below the Blanding Boulevard Bridge, as mentioned above, not in the Ortega, but also in the inner confluent and outer confluent region of the estuaries, the cores show multiple sand layering. For the most part there are never more than 10 sand layers in cores up-estuary of Roosevelt Boulevard Bridge and they tend to be very thin. A local area with thicker sand layers is coincident with Roosevelt Boulevard Narrows.
The situation in the outer confluent region is developed to a greater degree. There is also a pronounced lateral variation in this zone. On the right bank the stratigraphic column in the mucks is characterized by multiple thin clean sand layers, generally exceeding 10. The most down-estuary sample on the right bank is entirely sand to 98 cm. In contrast, on the left bank, sand layers may be absent entirely, or present in low digit numbers 4, 2, 6, 7, etc. Big Fishweir Creek also has sand-rich sediments, the innermost core has all sand down to 13 cm, whereas others have multiple and thick clean sand layers. Muck sediments lying immediately off Big Fishweir Creek tend to have more sand layers, despite being on the left bank.

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Appendix A

8 mnM/y Region 2
1
4 mm/y
2 mm/y

19 mm/y

19 mm/y
5 mm/y

1 mm/y

Region 3

Figure A9. Sedimentation rate measurements for eight recent cores from the inner and
outer confluent regions of the Cedar/Ortega River system. The siltation rate
progressing at about four times the rate on the left compared to the right bank
seems not entirely explained by the flow impediments created by marinas

A-20

Universit, of Florida, Dept. of Civil and Coastal Engineering




Appendix A
A2.4.2 Core Stratigraphy
Study of the 172 detailed core logs permits further interpretation of the bed sediment regime in the Cedar/Ortega going back over perhaps 50 or 100 years or so. There has been a profound change in the sedimentary regime, which is evident in every core examined. It is difficult to envisage a natural regime change of such widespread extent in this benign system.
The lower horizons of most cores comprise material termed soupy muck, muddy
muck, etc. Frequently these muck sediments have had or still have living bivalves in them. The bivalves can never have been dense faunal communities as the mucks remain largely unbioturbated. The two most common species are the clam Rangia and the Dark False Mussel Mytolupis. The former is a filter-feeding organism which initially colonizes the bed surface, often as a result of massive "sets" of spat during occasional high salinity events. These can then survive a return to low salinity conditions. The Rangia individuals eventually burrow into the bed, reaching up to 15 cm below the bed/water interface. Mytolupis, on the other hand, is a filter-feeding, surface dwelling organism attaching itself to any available "hard ground" on the bottom. The shells of these organisms are recorded in cores as articulated pairs, as single individuals, as layers in life position or as reworked, disarticulated groups or zones. The existence of these disarticulated layers indicates occasional exceptional events in the past when the weak and soupy mucks were swept away and shelly material was left on the surface as a kind of "lag" deposit. A good example is to be found in Core Sample No 39D from the Cedar River, although such features are doubtless present throughout the system.
There is always a strong disconformity in the successions above which distinctly contrasted sediments occur. These upper deposits still involve mainly the finely divided black muck sediments, often with tree leaves swept in from the catchment, but these are inter-bedded with the sandy intercolations described above, and with other materials. The most widespread additional material is wood chippings or in some cases bark chippings. These can only arise due to tree felling or pruning operations. Wood chips and sand layers are frequently inter-bedded with the muck layers in cores, hinting at a penecontemporaneous input or source. The next most common material, widely evident but confined to the Cedar River is oil. The oil-rich sediments are sometimes buried under more recent uncontaminated mucks and at other times occur at or close to the surface of the riverbed. Presumably there must have been a spill at some time, or instead successive series of spills.
One sample close to the northern coastline in the outer confluent region contained an abundance of grass-cuttings, described as "yard grass" in the core descriptions. Another, close to the Blanding Road Bridge in the Cedar River, contained asphalt and rubble attributed to construction or destruction of a car park. Finally, two samples immediately of Fishing Creek are described as a blue-green sandy clay, in this case with associated leaf litter and roots, but seemingly attributed by the logger of the cores as derived from ancient Hawthorne Formation deposits. In both cases these occur at the top of the succession and are the most recent input material.
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Appendix A
Wood chips are present in cores right up towards the headwaters of the Ortega River and in places occur as multiple layers, indicative of repeated or intensive activity, but they are relatively uncommon compared to in the Cedar River. Wood chips are again relatively uncommon towards the headwaters of the Cedar River, but become very common in deposits in the lower Cedar River and at times with multiple layers from the reaches off Williamson Creek, Butcher Pen Creek and Fishing Creek, down-estuary. Wood chips are present in cores from the outer reaches of all three of these tributaries as well. Wood chips are also relatively common in the inner confluent region east of Roosevelt Boulevard Bridge. They are also present, but infrequently, in the sediments of the outer confluent region.
Sediments at the entrance to Big Fishweir Creek have layers within them, consistently with the enigmatic description "woody". It is unclear whether such materials should be regarded as having a natural or instead an anthropogenic input.
A2.5 Interpretation
The presentation of the results, above, shows that a pronounced and consistent areal and vertical variation in the sediment types is present.
The organic and inorganic sediments of the Cedar/Ortega River system are
allochthonous and originate very largely in their own catchment system. There is a limited input of inorganic sediment from the main stem, although this only penetrated into the outer confluent region. No clear evidence has emerged as to the extent of autochthonous, plankton sediment production or the breakdown products of in situ sea grass in the system. Human settlement within the last 100 years has had a major impact on the types of sediment being input and on the sedimentation rate.
A2.5.1 Cedar River
In respect of the more minor, inorganic fraction of the sediments, the Cedar River deposits show the highest clay content in the entire system (18%). There is also a pronounced down-estuary decrease. This is consistent with a fluvial clay input. The silt content of the inorganic fraction is higher than the clay with a comparable down-estuary reduction, implying a similar detrital fluvial input. The sand fraction, in contrast, is low at the landward end and rises down-estuary. As far as the whole sediment is concerned, there is a much higher solids percentage, coupled with a relatively low moisture content, again consistent with a significant detrital input from the catchment. The solids percentage decreases down-estuary and the moisture content rises. This implies a rising organic fraction in the down-estuary direction. Consistent with these trends, the organic content of the innermost Cedar River samples is amongst the lowest in the entire system and rises downestuary. This is the reverse of the situation in the Ortega River. It is suggested to reflect the urbanisation of the catchment. In core samples sand layers occur only very occasionally and when they do they are present as thin laminae. This confirms that, in spite of the level of urbanisation, detrital sand is not a significant input. This is, equally, the case for Williamson and Butcher Pen Creeks. In contrast, there is a significant detrital sand input, represented as thick and multiple layers, being discharged down Fishing Creek and doubtless accounting for

University of Flofida, Dept. of Civil and Coastal Engineertng

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Appendix A
what is otherwise an anomalous-looking "high" in the sand fraction in the inner confluent region. The input must be terrestrial, must arise from recent deforestation and it cannot be relict marine sand as it lies mainly in the shallowest parts of the sediment succession. A further prominent anthropogenic input is that of wood chips. The levels of wood chips in the cores from innermost reaches of the Cedar River is low. This probably reflects the fact that deforestation and urbanisation of the Cedar River catchment is a relatively old feature. To complement this the largest quantities of wood chips emanate from Williamson, Butcher Pen and Fishing Creeks and are abundant in the sediments of the lower reaches of the Cedar River, down-estuary of these three tributary creeks. A further anthropogenic input confined to the Cedar River is oil. Oily muck is interbedded with the wood chips and with the less common sand horizons. It is not possible to comment on whether there has been a single relatively large spill or instead whether frequent or maybe semi-continuous low level hydrocarbon inputs occur. Finally, to complement the large scale sand and wood chip inputs from Fishing Creek, blue-green inorganic, detrital clays were sampled at shallow depth in recent sediment material in the entrance to Fishing Creek. A tentative suggestion arising from this might be that in recent decades, deforestation and urbanisation has focussed not in the Cedar but in it tributaries-Williamson, Butcher Pen and Fishing Creeks. Fishing Creek seems to have some affinities in this respect with Big Fishweir Creek in the outer confluent region (see later).
A2.5.2 Ortega River
The sediments of this river show some highly distinctive features and pronounced
contrasts with the Cedar and other zones within the study area. It is predominantly a detrital, organic-dominated sub-estuary at a less-developed stage of urbanisation than the Cedar River. In respect of its inorganic fraction, it has a very low clay and sand input and a midlevel silt input, with a strong down-estuary decrease. The sand content rises in a downestuary direction. In respect of whole sediment physical and chemical analyses, the Ortega has by far the highest moisture and lowest total solids of anywhere in the system, again reflecting the major terrestrial organic input to the catchment basin. The total solids percentages show a down-estuary decrease. Consistent with this, the organic content is at a system-maximum and also decreases down-estuary. Examination of core logs confirms the relative paucity of sand laminae. Where these are present they tend to occur deep in the sediment column. Wood chips are also less common than in the lower reaches of the Cedar and the inner confluent region. Where present they can be interbedded with the black finely divided mucks and the sand layers. These multiple-layered wood chip horizons are detectable in all sampled reaches of the Ortega and are presumed to reflect the onset of deforestation in this catchment, too.
A2.5.3 Inner Confluent Region
The inorganic fraction shows an apparently anomalous, exceptionally low clay
content, although the recent blue-green clays being input from Fishing Creek seem not to be represented in this suite of samples. In contrast, the silt content is extremely variable, although still generally low in level. There is no obvious reason for the high variability. The sand content is relatively high and variable, (22-75%, but mainly 60-70%). The sand cannot
University of Florida, Dept. of Civil and Coastal Engineering A-23




Appendix A
originate down-estuary, as concentrations decrease into the outer confluent region, and it must be either relict marine sand or a detrital input from the tributary creeks. The high elevation of the sand layers in cores suggests a fluvial source due to recent anthropogenic changes. In respect of the "whole sediment" analyses, and in contrast with the high sand content, these sediments also have a high moisture and low solids content. They 'can best be described as predominantly sandy mucks. There is a suggestion of an association between the high moisture/low solids rich sediments and the left bank in the inner confluent region. Very likely this is induced by the presence of the flow impediment provided by the large commercial marinas along this coast. A tongue of high organic-rich sediment is issuing from the Ortega and is strongly evident in this region. Possibly it indicates that the signature of Ortega type sediments is locally stronger than either Cedar or St. Johns River sediments? In vertical sections from the core logs multiple sand layering is well developed and widespread but there are never more than 10 sand layers. The sand must be contributed from Fishing Creek during occasional high discharge events. Wood chips are frequently interbedded with the sand layers in these reaches. These are very likely input from Williamson, Butcher Pen and Fishing Creeks. The distribution of wood chips and the variability in the silt content might be consistent with the presence of a large stable eddy in this region, but this must be a speculation.
Measurements of sedimentation rate are available and show a strong lateral variation, with relatively low values on the right bank, but high rates up to 20 mm/yr on the left bank amongst the marina developments.
A2.5.4 Outer Confluent Region
The inorganic fraction of sediments in this region are elevated compared to values in the up-estuary direction back into the Cedar and Ortega and probably reflect inputs from the main stem of the St. Johns River. The silt content is elevated and relatively constant in area, with a small degree of axial increase. Sand contents are generally low. Whole sediment analyses show levels and distributions very similar to the inner confluent region, i.e., the sediments have a high moisture concentration (>70%) and a low solids percentage. The maximum moisture and minimum solids contents are again found on the left bank, linked with the marina developments. Lateral partitioning is further evident in the presence of a tongue of low moisture, high solids detrital sediments penetrating the right bank of this region from the main stem. In cores, the pronounced lateral segregation is again detectable with multiple sand layering involving up to 15-20 sand horizons towards the right bank. The most seawards of these cores is all sand. In contrast, on the left bank, there are commonly no sand layers and the maximum number found is 7.
There is an unambiguous sand input from Big Fishweir Creek on the left bank at the confluence with the main stem. In general, few wood chip horizons are to be found in outer confluent region core samples, consistent with input from the river catchment up-estuary. Core logs at sites in the entrance to Big Fishweir Creek consistently identify one of the components of the sediments as "woody". In spite of this consistency in description, it is not possible to confidently associate this non-specific term with the "wood chips" described from up-estuary sites and the provenance of this material must remain unknown.

University of Florida, Dept. of Civil and Coastal Engineering

A-24




Appendix A
Sedimentation rate measurements show the same lateral partitioning, with values in the range 4-8 mm/yr on the right bank, rising to 20 mm/yr on the left. Whether these are linear sedimentation rates or, instead, whether surficial rates of siltation might be even higher, is also unknown.
A3. Implications of Sediment Regime for PCB Remediation and System Restoration
Establishing the areal and vertical extent and the severity of PCB contamination of sediments has not been part of these contracted investigations. Nevertheless, a few guiding comments are possible. We are not aware of how widespread and severe the initial distribution of PCB contamination has been, nor whether significant amounts are still held up within the urban drainage system to be flushed into the Ortega River in the future. Neither are we aware of whether episodic events capable of entraining and further redistributing the PCB contaminated sediment have occurred since the spill. However, from recent Acoustic Doppler Current Profilers (ADCP) work, which is a component of this investigation, it is now well-established that recreation vessel propeller scour of the shallow and weak bed sediment throughout the system is a perpetual feature. Sediment flux calculations have proved a challenge, not least on grounds that, where boat tracks cross an ADCP traverse line, a large percentage of the sediment flux is that contained within the boat wake. These sedimentladen wakes are also very persistent. There is possible evidence that high-speed racing-type motorboats may be particularly effective in stirring sediments. An implication of this finding is likely to be that the PCB contaminated sediment has spread more widely in the system due to this unanticipated anthropogenic effect than would otherwise be the case. We have not investigated the extent to which PCB contaminated sediment may have become capped by more recent, hopefully less-severely contaminated sediment in the years since the spill. The extreme shallowness of the system and the frequency of traversing of broad swathes of the estuaries by recreational vessels suggests that PCB contaminated sediment may still be accessible or may even have been reworked from the most actively trafficked zones into quiet water areas. The ADCP work indicates that in the low flow situations which exist for the bulk of the time, axially-directed currents are weak, whereas the two-dimensional internal medium and small scale turbulent eddying is by comparison strong. Over a prolonged period this may have provided a mechanism for lateral mixing. It might be anticipated from this that the PCB contaminated sediment will be more widely distributed in the Cedar River, inner and outer confluent regions than might otherwise have been anticipated.
On the other hand, this investigation of the fabric of core samples indicates a
sedimentary system dominated by primary depositional structures. There are relatively few living organisms and winnowed shell layers are relatively uncommon. There is little evidence that soft-bodied invertebrates are any more successful than the shelly invertebrates in colonizing the bed deposits. This relative lack of bioturbation evidenced from the scarcity of the fauna and the apparent lack of secondary, biogenic structures in the sediments strongly suggests an inability to mix the PCB contaminated sediment deep into the underlying uncontaminated deposits.
University of Florida, Dept. of Civil and Coastal Engineering A-25