TIDAL INLET MANAGEMENT AT JUPITER INLET:
SECOND PROGRESS REPORT
I. SUMMARY OF PROGRESS IN COASTAL AND
ENVIRONMENTAL ENGINEERING STUDIES
A. J. Mehta, C. L. Montague and R. J. Thieke
II. ENVIRONMENTAL SEDIMENTOLOGY OF THE LOWER
LOXAHATCHEE RIVER ESTUARY AND JUPITER INLET
R. W. Faas
Jupiter Inlet District Commission
P.O. Box 73
Jupiter, Florida 33468-0073
REPORT DOCUMENTATION PAGE
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TIDAL INLET MANAGEMENT AT JUPITER INLET: October 1990
SECOND PROGRESS REPORT, PARTS I &II6.
7. Afuoer(s) 8. artar.ias OrsuMcastm *port so.
PART I: A. J. Mehta, C. L. Montague and R. J. Thieke UFL/COEL-90/010
PART II: R. W. Faas
9. Perfondla Orgmctsa.ts e a r Address 10. rroject/ auk/tL Onit go.
Coastal and Oceanographic Engineering Department
University of Florida 11. cocor or Cra No.
336 Weil Hall C89-002
Gainesville, FL 32611 13. Tp o mrt
2. Sposorlag Orgaliautale Ma au Address
Jupiter Inlet District Commission Second Progress Report
P.O. Box 73 r
Jupiter, Florida 33648-0073
IS. Supplementary Nloc
This report summarizes progress in the ongoing study on the management of
Jupiter Inlet, Florida during the period 4/6/90 through 10/5/90. The report is
divided into two parts, the first of which summarizes ongoing coastal engineering
and ecological studies and the second provides a full description of the bottom
sediment in the interior portion of the study area, with particular emphasis on
the flood shoal area west of the Florida East Coast Railroad bridge.
It is found that the flood shoal has been receiving sediment from a number
of sources including the littoral drift, fluvial material, and sediment derived
from localized erosion of the banks and the shallow bottom. Thus the existing
sand traps are shown to have been ineffective in catching all the littoral drift
sand, particularly the finer portions. Past and present trends suggest that the
shoal will continue to extend into the central basin of the Loxahatchee River
estuary until such a time that an internal sedimentary balance is achieved.
Continual changes in the size and shape of this shoal are of direct consequence
to the sedimentary budget for the interior of the inlet, navigation to and from
the upper regions of the river, and ecological management of the estuary.
Potentially conflicting management objectives in this region can pose serious
17. Origiator's Key words 1*. Availability Statemeat
19. U. S. Security Classif ot the report 20. U. S. Security Classit. of This Page 21. No. of Paes 22. Price
Unclassified Unclassified 79
questions for long term management of the lower end of the Loxahatchee River.
In a related context, a study of growth management and its relation to the
ongoing engineering and ecological impact studies is highly recommended.
Central to the matter of managing the problem of beach erosion,
sedimentation in the interior areas including the marinas, and maintenance of
the navigational channels in the interior, is the problem of excessive influx
of sediment from the littoral drift. Preliminary tracer experiments using dyed
sand suggest that there can be elemental conditions during which measurable
quantities of sand placed in the area of downdrift sand deficit reenter the
inlet, thus exacerbating the problem of sand influx in the area of the sand trap
and beyond. A passive modification of the inlet, e.g. jetty modification, may
reduce sand influx somewhat, but by itself, in the absence of an active means
of sand transfer, is not likely to achieve high efficiency in terms of minimizing
TIDAL INLET MANAGEMENT AT JUPITER INLET: SECOND PROGRESS REPORT
I. SUMMARY OF PROGRESS IN COASTAL AND
ENVIRONMENTAL ENGINEERING STUDIES
A. J. Mehta, C. L. Montague and R. J. Thieke
II. ENVIRONMENTAL SEDIMENTOLOGY OF THE LOWER LOXAHATCHEE RIVER
ESTUARY AND JUPITER INLET
R. W. Faas
Jupiter Inlet District Commission
P.O. Box 73
Jupiter, Florida 33468-0073
This report briefly summarizes progress made during the period
April 6 to October 5, 1990, and constitutes the second progress
report for the study. It is divided into two parts. The first part
only briefly considers the coastal and environmental engineering
aspects of the study with the exception of the sedimentological
investigation of the inlet interior, which is reported fully in the
second part. Special thanks are due to Prof. Frank Townsend for
providing necessary facilities for sediment grain size analysis.
Thanks are also due to Drs. Miao, Lin and Parchure for their
participation in different phases of the study.
TABLE OF CONTENTS
FOREWARD . . . .. . . ii
LIST OF FIGURES . . . .. . .. v
LIST OF TABLES . . . . ... . vii
SYNOPSIS . . . . ... . viii
I. SUMMARY OF PROGRESS IN COASTAL AND ENVIRONMENTAL
ENGINEERING ASSESSMENTS . . . 1
I: INTRODUCTION . . . . 1
II: COASTAL ENGINEERING ASSESSMENT. . ... 1
2.1 Sand Transport near the Inlet Mouth 1
2.1.1 Field Measurements: Sand Tracer
2.1.2 Modeling Longshore Transport Rates 3
2.2 Wave-Current Interaction in the Offshore
2.2.1 Modeling Wave-Current Field 4
2.2.2 Field Study of Wave-Current Field 6
2.3 Physical Modeling 6
2.4 Flood Shoal, Marina and Sand Trap
III: ENVIRONMENTAL ASSESSMENT . . . 7
3.1 Seagrass Mapping and Density Estimates 7
3.2 Experiments to Determine Seagrass
Sensitivity to Salinity Change 8
3.3 Mangroves Mapping and Density Estimates 8
3.3.1 Sea Turtle Nesting 10
3.3.2 Offshore Rocky Outcroppings 10
3.3 Salinity Intrusion 12
IV: CONCLUDING COMMENTS. .. . .... 12
V: REFERENCES . . . . 12
II. ENVIRONMENTAL SEDIMENTOLOTY OF THE LOWER LOXAHATCHEE
RIVER ESTUARY AND JUPITER INLET . . 1
I: SUMMARY ...... . . . 1
II: INTRODUCTION . . . . 2
III: THE PROBLEM . . . ... 2
IV: BACKGROUND . . . . 3
V: FIELD AND LABORATORY WORK .. . ... 3
VI: DATA ANALYSIS AND INTERPRETATION . . 4
6.1 Median Diameter Map 2 4
6.2 Coefficient of Sorting Map 3 5
6.3 Coefficient of Skewness Map 4 6
6.4 Sediment Distribution Map 5 7
6.5 Analysis of Vibracores 8
6.6 Summary of Vibracoring 9
VII: SEDIMENTARY TYPES AND SOURCES . . 9
VIII: PATTERNS OF SEDIMENT TRANSPORT . ... 12
IX: CONCLUSIONS . . . . ... 13
X: RECOMMENDATIONS FOR FUTURE WORK . .. 15
XI: REFERENCES . . . . ... 16
PLATE CAPTIONS . . . . ... . 18
MAP CAPTIONS . . . . ... . 26
I. Sample Descriptions . . . ... 32
II. Description of the Vibracores . ... 39
III. Sedimentary Data . . . ... 41
a. Table 1 Grain Size Parameters . .. 41
b. Table 2 Particle Size Conversion Chart
c. Table 3 Organic Matter Contents ..
LIST OF FIGURES
1. Flow diagram showing the inter-relationship between
inlet management choices, information required for
that purpose by JID, and technical issues and impacts
which require investigation .. . . 13
2. Technical issues, physical impact studies and
ecological impact studies for the inlet management
plan . . . . . . .14
3. Number of red grains and d50 of sand samples taken on
June 19, 1990 . . . .... .. 15
4. Number of green and d50 of sand samples taken on
June 19, 1990 . . . .... .. 16
5. March-April wave height roses for station off Jupiter
Inlet . . . . . ... .17
6a. Offshore bathymetry in March, 1979 . .. . 18
6b. Offshore bathymetry in August, 1979 .. . 19
6c. Recent bathymetry .... . . 20
7a. Numerically simulated 8 sec waves approaching Jupiter
Inlet and interacting with 0.5 m/sec ebb flow issuing
from the inlet . . ..... . 21
7b. Current circulation associated with simulation in
Fig. 7a. . . . .. . 22
8a. Southeast channel option for navigation . ... .23
8b. Southern channel option for navigation . ... 24
9. Physical model layout; the horizontal scale is 1:100
with a distortion of 2 . . . 25
10a. Current near U.S. 1 bridge . . ... 26
10b. Current in marina . . . ... 26
1. Textural classification of Loxahatchee Estuary and
Jupiter Inlet bottom samples (Shepard, 1954). Inset
shows the descriptive terms. Sixteen samples
(Appendix III Table 1) did not plot within the 'sand'
category and are shown on the diagram. These are
designated as 'mixed' samples in the text . .. 17
LIST OF TABLES
1. Effect of natural ebb shoal migration on wave height
(m) at the beach (corresponding to an incident wave
height of im) . .. . . 5
2. Seagrass biomass found per 15 cm diameter core
removed from various locations in the Loxahatchee
River Estuary and Intracoastal Waterway East of the
Railroad Bridge . .. . .. .... 9
3. Time in days for seagrass blades to turn brown in
various constant salinities. In 35 ppt seawater,
all remained green . . . . .. 10
4. Mangrove density and height estimates from various
locations in the intertidal zones of the Loxahatchee
River Estuary and Intracoastal Waterway East of the
Railroad Bridge . . . . 11
This report summarizes progress in the ongoing study on the
management of Jupiter Inlet, Florida during the period 4/6/90
through 10/5/90. The report is divided into two parts, the first
of which summarizes ongoing coastal engineering and ecological
studies and the second provides a full description of the bottom
sediment in the interior portion of the study area, with particular
emphasis on the flood shoal area west of the Florida East Coast
It is found that the flood shoal has been receiving sediment
from a number of sources including the littoral drift, fluvial
material, and sediment derived from localized erosion of the banks
and the shallow bottom. Thus the existing sand traps are shown to
have been ineffective in catching all the littoral drift sand,
particularly the finer portions. Past and present trends suggest
that the shoal will continue to extend into the central basin of
the Loxahatchee River estuary until such a time that an internal
sedimentary balance is achieved. Continual changes in the size and
shape of this shoal are of direct consequence to the sedimentary
budget for the interior of the inlet, navigation to and from the
upper regions of the river, and ecological management of the
estuary. Potentially conflicting management objectives in this
region can pose serious questions for long term management of the
lower end of the Loxahatchee River. In a related context, a study
of growth management and its relation to the ongoing engineering
and ecological impact studies is highly recommended.
Central to the matter of managing the problem of beach
erosion, sedimentation in the interior areas including the marinas,
and maintenance of the navigational channels in the interior, is
the problem of excessive influx of sediment from the littoral
drift. Preliminary tracer experiments using dyed sand suggest that
there can be elemental conditions during which measurable
quantities of sand placed in the area of downdrift sand deficit
reenter the inlet, thus exacerbating the problem of sand influx in
the area of the sand trap and beyond. A passive modification of the
inlet, e.g. jetty modification, may reduce sand influx somewhat,
but by itself, in the absence of an active means of sand transfer,
is not likely to achieve high efficiency in terms of minimizing the
PART I. SUMMARY OF PROGRESS IN COASTAL AND
ENVIRONMENTAL ENGINEERING ASSESSMENTS
The scope of the study from the perspective of the Jupiter
Inlet District (JID), gleaned from the Scope of Work, is shown in
Fig. 1, and is essentially self-explanatory. Presently, University
of Florida (UF) is focusing on item (A), namely information
required to develop a management plan (B) which, once developed,
should allow JID to make management choices (C). The various
components related to (A), including the technical issues and the
physical and ecological studies in progress, are shown in the flow
diagram of Fig. 2. These essentially follow the Scope of Work, as
elaborated in the first progress report (Mehta, Montague and
Parchure, 1990). From this diagram, the inter-relationship between
the various components is evident. Coastal engineering aspects and
environmental assessment are noted next.
II: COASTAL ENGINEERING ASSESSMENT
These studies can be conveniently divided into those in the
inlet exterior region and those in the interior.
2.1 Sand Transport Near the Inlet Mouth
The present progress in the study of sediment transport
patterns in the exterior portion of Jupiter Inlet and along the
south beach is discussed in two parts. The first part is comprised
of the results of two field experiments using sand tracers, and the
second part consists of the compilation of available wind and wave
data for the prediction and simulation of longshore sediment
2.1.1 Field Measurements: Sand Tracer Studies
To verify the ultimate fate of dredged sediments placed on the
south beach and to establish whether the south jetty is in fact
"leaking", two sand tracer studies were performed during June,
1990. Two lots of colored sand (red and green) were prepared with
the following grain size distributions to closely match the dredged
material placed on the south beach in May 1990:
15% of sand: d > 0.85 mm
70% of sand: 0.52 mm < d < 0.85 mm
15% of sand: 0.38 mm < d < 0.52 mm
On June 1, 1990, approximately 170 pounds of red sand was
placed in shallow water (roughly 3-5 feet deep) off the beach in
a region 20-40 yards south of the south jetty. The sand was placed
at low water slack at 1100, and hand samples were taken at various
locations over the six hour period of the incoming tide. The tidal
range for this period was approximately 2.1 feet (almost
minimum). The wind conditions were observed to be quite calm, with
no obvious swell and small (less than 0.5 foot high) wind waves.
Later analysis of the samples taken indicated that over the six
hour period no red sand was found more than 15 yards from the
initial placement site.
For the second study a robust "wind-sock" style sand trap was
designed to collect suspended sediment and withstand the expected
channel velocties of up to 5 ft/sec within the inlet itself. The
trap consisted of a fine mesh material attached to a 2 ft diameter
iron ring, which was secured to a pair of 3-inch diameter steel
pipes to be jetted into the sand channel bottom.
On June 18, 1990, 250 pounds of green sand was placed in
shallow water off the south beach. The following day, the sand trap
was installed by divers during low water slack at 1240. The trap
was placed within 30 feet of the south jetty, approximately 100
yards from the eastern end. Observed wave conditions were
significantly higher than in the June 1 study, with the predominant
direction from the southeast. The tidal range was approximately 3.2
feet, also significantly greater than the first test.
The sand trap was monitored during the incoming tide and was
observed by divers to withstand the maximum flood velocities
without difficulty. During the later portion of the flood tide
(1600-1830), hand bottom samples were taken at various points along
the possible sediment pathways. At 1840 the sand trap was removed
during high water slack.
Analysis revealed that 10 pounds of sand were captured in the
trap. Of this amount, 70 grains of green sand and 10 grains of red
sand were recovered. These numbers are deemed quite high when
considering the travel distance from the placement site to the trap
location. Red and green grains were also found in hand samples at
other locations (recall that the red sand was placed 18 days prior
to this experiment). The median diameter (d50) of all sand grains
in the trap was found to be 0.36 mm, which is smaller than that of
the material placed on the south beach. However the sand trap will
only collect material being transported in suspension. Locations
of the trap and positive samples (with number of grains found and
the median diameter of each sample) are given for the red sand in
Fig. 3 and the green sand in Fig. 4. Hand samples had an average
weight of 0.75 pound.
The results clearly show that sand is moving into the inlet
around the jetty from the south beach (i.e. the south jetty is
"leaking"). It is also likely that the time scale for such motion
is as short as two (or even one) tidal cycles, given the proper
conditions (moderate wave activity from the southeast and
relatively high tidal range). The surface currents observed during
the later drogue study also support this conclusion. Determining
the threshold conditions for such "leakage" in terms of tidal
range, wave height and direction will require further
investigation. Quantification of sediment transport rates
(particularly bedload transport) and sediment residence times under
such conditions is also beyond the scope of these preliminary
2.1.2 Modeling Longshore Transport Rates
In the context of providing a decision-making tool for the
evaluation of the nature and scheduling of potential sand bypassing
schemes, the quantification of both southward and northward
longshore transport rates and their frequency of occurrence is
crucial. To provide a useful statistical description of the
magnitude and direction of the transport, wind and wave data from
all available sources have been collected and are being evaluated.
A statistical wave hindcast model for calculation of longshore
transport is being combined with a "one-line" model for shoreline
evolution to provide a tool for the evaluation of sand bypassing
scenarios. Wave hindcast data are being compared with wave height
and direction obtained from a p-u-v wave gage located just offshore
of Jupiter Inlet.
Wave roses from this station for March and April, 1990 are
shown in Fig. 5. There is a significant amount of wave energy
tending to produce a northward longshore drift of sand (the
critical direction at Jupiter is approximately 2500) during both
March and April. Similar conditions were observed during the June
18-19 experiment and are believed to contribute to the transport
of sand around the south jetty into the inlet. Use of net annual
transport rates will not account for this effect. These conditions
must be properly accommodated, such as in the present statistical
description, to most appropriately evaluate inlet management
2.2 Wave-current Interaction in the Offshore Region
2.2.1 Modeling Wave-Current Field
The combined effects of waves and currents makes the inlet
exterior area a highly dynamic one, as manifested by perpetual
changes in the bottom topography in the area of the ebb shoal
(Figs. 6a,b). More recent bathymetry is shown in Fig. 6c. An
example of numerically simulated wave field in the presence of flow
issuing out of the inlet is shown in Fig. 7a. One of the important
effects which needs examination is in terms of flow circulation
patterns in the downdrift area; Fig. 7b illustrates the results.
Flow gyres set up in the area offshore of the inlet mouth and,
especially in the downdrift beach area of sand deficit have
implications for sand transport; this is an aspect which we plan
to examine in considerable further detail. Note also the shoreward
intrusion of water due to water level setup by waves.
The evident strength of this modeling approach is that it
enables investigation of the effects of any changes in bottom
topography on the resulting waves and currents. Thus it will be
possible to look at potential effects of ebb shoal dredging and
dredged offshore channels on beach stability using this model.
Following discussions with JID and individuals with first hand
experience in navigating through the entrance, it has been decided
to investigate two possible 10 ft deep and 100 ft wide dredged
channel orientations shown in Figs. 8a,b. The efficacy, dredging
requirements and any effects on the beach apropos these channels
will be examined using numerical modeling as well as physical
It is interesting to note that natural variations in the
offshore bathymetry can themselves cause significant changes in
wave action near the beach. Given the incident wave direction shown
in Figs. 6a and b, Table 1 gives the numerically calculated wave
heights at location A and 80 ft offshore of A, starting with 1 m
high incident waves. In both March and August 1979 bottom
conditions the waves were considerably lower at the beach than
offshore due to nearshore breaking; however, the wave height is
considerably greater in August than in March due to the combined
effects of wave shoaling and refraction.
Table 1. Effect of natural ebb shoal migration on wave height
(m) at the beach (corresponding to an incident wave
height of im).
Date A 80' Offshore of A
March, 1979 0.04 0.22
August, 1979 0.07 0.54
2.2.2 Field Study of Wave-Current Field
In order to examine actual flow patterns in the offshore area,
a research crew from UF performed an aerial photo study of current
dynamics near the inlet on August 14 and 15, 1990. The work
consisted of tracing free-motion styrofoam floats on the water
surface during ebb and flood tides. The float-tracing technique
was to take time series of aerial photos of floats, along with
several anchored sea buoys and beach targets as fixed reference
points, to determine the current direction and magnitude in the
flow field near the inlet. On the August 14, the current study was
concentrated at the flood tide stage. Six floats were first
released in the nearshore area close to the south side of the south
jetty, where erosion is significant. Deployments of floats in the
study were then repeated in the nearshore areas to the east and
north of the inlet, and then in further offshore areas. A total of
six deployments of floats were performed that day. During the float
study, waves with about two-feet height were coming consistently
from the southeast direction.
On the next day, the current study was performed for the ebb
tide stage. Three floats were first released just inside the inlet
entrance at about maximum ebb current. Three more deployments were
then conducted in the nearshore areas to the south, east, and north
of the inlet. During the float study, small southeast waves were
observed. After the field trip, float locations were identified and
converted into plane coordinates from the time series aerial
photos. The mapping of the aerial photo plane to the actual
horizontal plane is based on the linear transformation of the
coordinate system. The corrected float trajectory data will be
utilized to describe the current characteristics observed in the
2.3 Physical Modeling of the Exterior Region
The layout of the physical model covering the exterior area
is shown in Fig. 9. With respect to the two options for a 10 ft
deep offshore channel (Figs. 8a,b), the stability of these channels
against infilling (and hence maintenance dredging requirements),
as well as the effects of these channels on shoreline stability
will be examined in the physical model. Also, wave-induced
circulation in the area of downdrift erosion and its role in
tranporting nourished sand downdrift and updrift (into the inlet)
will be examined in the model.
2.4 Flood Shoal, Marina and Sand Trap Sedimentation
A complete analysis of the sedimentology inclusive of the area
of the flood shoal west of the Florida Eastcoast Railroad bridge
is given in Part II of this report.
The marinas east of the U.S. 1 bridge experience sedimentation
due to three reasons: 1) influx of sediment in the area from the
offshore area and from other sources (see Part II), 2) the location
of the marinas at a localized inner bend of the River (a natural
area for sedimentation), and 3) reduction in the flow by virtue of
the pilings as well as the shadow effect from the adjacent
shoreline. The drastic reduction in the current velocity becomes
evident when the velocity in Fig. 10a is compared with that in Fig.
The matter of efficiency of the existing sediment traps is
being examined through a numerical model which will encompass the
water area shown in Fig. 7, Part I, of the first progress report
(Mehta et al., 1990). This model is being calibrated with available
data (from SFWMD, USGS and UF), plus the data obtained in the
III: ENVIRONMENTAL ASSESSMENT
3.1 Seagrass Mapping and Density Estimates
A map of seagrasses east of the railroad bridge is 75%
completed in depth using aerial maps and ground-verification from
shore. Ground-verification was accomplished using a 50 ft grid
system along all shorelines east of the railroad bridge. The
remaining 25% must be assessed by boat and is scheduled for
completion in October 1990.
Accompanying the map is information about the general species
composition found in seagrass beds, relative density of seagrasses,
water depth, crude sediment type (shelly, muddy, etc.), and
location of features such as sand bars, channels and shallow
depressions. This information gives insight into the determinants
of the distribution of various seagrasses. We have found Halodule,
for example, on sand bars, and we have found Thalassia not only
subtidally but also in the intertidal zone in water-holding
Density of seagrass biomass by species and by leaf blades
(above-sediment) and roots and rhizomes (below-sediment) have been
determined in 12 test cores involving 6 major areas of seagrass
occurrence that are accessible from shore (Table 2). Additional
cores will be removed for testing from areas accessible by boat
during October 1990.
3.2 Experiments to Determine Seagrass Sensitivity to Salinity
Tests of the effects of sudden changes in salinity are being
run to help in an assessment of the possible effects of salinity
changes caused by inlet modification. This work is part of the
Master's thesis of Mr. Scott Fears. Survival of various seagrasses
was tested in rain water, tap water, and 15 ppt seawater (diluted
with rain water). Tests were repeated three times. Results are
shown in Table 3.
Additional tests are planned for the coming months. These
include comparative tests of Halodule, Thalassia, Syringodium, and
perhaps some species of algae in water of 0 ppt, 5 ppt, 15 ppt, 25
ppt, and 35 ppt salinity. Some tests of frequency and duration of
salinity change are also planned.
3.3 Mangroves Mapping and Density Estimates
A map of all mangrove areas east of the railroad bridge has
been developed from aerial photographs and ground verification.
Mangrove height and density has been estimated in several areas.
Seagrass biomass found per 15 cm diameter core
removed from various locations in the Loxahatchee
River Estuary and Intracoastal Waterway East of the
1. North bank, Right behind Jupiter Marine Center just east of US1
2. North Arm of Intracoastal Waterway, East side across from Coral
Cove Park. 3. North bank, west of Coast Guard Dock in very
4. South bank at Charley's Crab Restaurant, west of US1 bridge.
5. South bank, 35 m west of Charley's Crab Restaurant, 15 meters
6. Same as Location 2.
Table 3. Time in days for seagrass blades to turn
brown in various constant salinities. In
35 ppt seawater, all remained green.
Water Percent Elapsed
Species Type Brown Time (days)
Syringodium Rain water 90% 1
Tap water 90% 1
15 ppt 100% 2
Halodule Rain water 75% 1.5
Tap water 80% 1
15 ppt 100% 3
Thalassia Rain water 100% 3
Tap water 100% 2
15 ppt 100% 3
Some of this data is shown in Table 4. Additional sampling is
planned for October 1990.
3.3.1 Sea Turtle Nesting
Documentation of the beaches near Jupiter Inlet as among the
highest density sea turtle nesting beaches in North America is
available. Besides the literature referenced in our First Progress
Report (UFL/COEL-90/005), two local monitors of sea turtle nesting
have been identified: Mr. Jeff Lange and Ms. Mary Lou Jackson.
We have spoken to Ms. Jackson, who transplants sea turtle eggs for
the Jupiter Hilton and learned about the Hilton's sea turtle nest
program. We understand Mr. Lange is a local authority on nesting
in the area. We have observed sea turtle nesting and attempts to
nest on several occasions. We were impressed with how many
attempts fail apparently because the turtle does not like something
about the sights. This may be routine behavior on all of Florida's
nesting beaches. This is a question perhaps for Mr. Lange.
3.3.2 Offshore Rocky Outcroppings
The potential for inlet management impact on rocky
outcroppings and several reports from Continental Shelf Associates
have been reviewed in the First Progress Report. We have observed
the submerged rocky outcroppings north and south of the inlet on
Table 4. Mangrove density and height estimates from various
locations in the intertidal zones of the Loxahatchee
River Estuary and Intracoastal Waterway East of the
Eco Quadrat Size Rope Seed
No. Live Trees
No Red Black White Button Other
1 1 4 4 9 0 0 0 0
1 2 4 1 27 0 0 0 1
1 3 4 2 2 0 0 0 0
2 1 4 4 8 1 0 0 0
2 2 4 4 18 9 1 0 0
2 3 4 20 6 0 0 0 0
3 1 4 19 7 2 1 0 0
4 1 4 4 23 14 0 0 0
Trunk dia. of 3
No. Dead Trees Avg ht 1 2 3
Red Black White Button Other cm cm cm cm
Location of Mangrove Ecosystems:
1. South side of estuary, west of
2. Northernmost island in south arm
Charley's Crab restaurant to
3. Southernmost mangrove island in north arm of ICW.
4. Second southernmost mangrove island in north arm of ICW.
several occasions. The rocks are covered with macroalgal growth
and are used by a variety of reef fishes. After heavy, but not
particularly unusual weather during summer 1990, some of the
outcroppings were covered by sand and fish were absent. Within a
few weeks these same sites were re-exposed and fishes were present.
Apparently some if not all of the outcroppings in the area are
frequently covered and re-exposed by sand.
3.4 Salinity Intrusion
Salt transport from the ocean through the inlet and westward
under the railroad bridge will be indicated by the salinity model
now being developed. Salt transport under various inlet management
scenarios can be simulated and conclusions about the effect of
inlet management options drawn at that time.
IV. CONCLUDING COMMENTS
The thrust of the investigation at this stage is almost
entirely technical in nature, and is concerned with physical and
ecological impacts arising from four basic issues management of
downdrift erosion, navigational safety, sedimentation in the
Loxahatchee River, and potential impacts of ebb shoal dredging for
beach nourishment purposes. As outlined in Fig. 2, all the issues
dealt with in the Scope of Work, and in the first progress report,
will be accomodated within the rubric of these four basic issues.
An important aspect germane to the future needs of JID, but
outside the scope of this investigation, is that of growth
management. we recommend that a relevant study be initiated in this
respect, in which the impact of growth on physical, ecological, and
economic variables is compared to inlet management impact.
Mehta A.J., Montague C.L. and Parchure T.M. (1990). Tidal inlet
management at Jupiter Inlet, Florida. First Progress Report
(UFL/COEL-90/005), Coastal and Oceanographic Engineering
Department, University of Florida, Gainesnille.
Information Need to Develop
Management Plan : Technical
Issues and Associated
Physical and Ecological Impacts
Information Required by JID
for Inlet Management Plan:
Proposed Options and Impacts
Fig. 1. Flow diagram showing the inter-relationship between inlet
management choices, information required for that purpose
by JID, and technical issues and impacts which require
Fig. 2. Technical issues, physical impact studies and ecological impact studies for the inlet
10, 0.36 mm
1, 0.34 mm
2, 0.17 mm
L Sand trap 6
*. 170 pounds red sand
placed June 1 1990
0 100 200 300 ft:
*;.. 0 1, 0.47 mm
Fig. 3. Number of red grains and d50 of sand samples taken on June 19, 1990.
1 -,r4 9
70, 0.36 mm
2, 0.17 mm
0 1, 0.34 mm
0 100 200 300ft
! ",! 1
0 1, 0.56 mm
250 pounds green sand
placed June 18 1990
1, 0.42 mm
Fig. 4. Number of green and d50 of sand samples taken on June 19, 1990.
I I Hs <1m
=E 1m Hs < 2m
EIM 2m < Hs < 3m
0 Hs 2 3m
0 10% 20%
r= __ a
Fig. 5. March-April wave
height roses for station off
Fig. 6a. Offshore bathymetry in March, 1979.
--_---- --------- -------- -
- -- -- --- -- -------------'---------
Fig. 6b. Offshore bathymetry in August, 1979.
Fig. 6c. Recent bathymetry.
Fig. 7a. Numerically simulated 8 sec waves approaching Jupiter Inlet and interacting
with 0.5 m/sec ebb flow issuing from the inlet.
-- . I / ," ,e J --" \ t f . . . . . .
H . . . . .. .
e > 4 s I t \ t . . . .
__.. *. . . . . . .
Stl ...... ........... .
Shoreline I I
Su 32g. a.
Fig. 7b. Current circulation associated with simulation in Fig. 7a.
Fig. 8a. Southeast channel option for navigation.
--I---I-~-i-!-4- I-C-I--I-~-I-- -- I-C--
Fig. 8b. Southern channel option for navigation.
Fig. 9. Physical model layout; the horizontal scale is 1:100 with a distortion of 2.
-1.21 I I I 1 I I I ,
0.0 100 200 300 400
Current near U.S. 1 bridge.
Current in marina.
PART II. ENVIRONMENTAL SEDIMENTOLOGY OF THE LOWER LOXAHATCHEE
RIVER ESTUARY AND JUPITER INLET
The purpose of this work was twofold: 1) to develop a sediment
distribution map for the interior water area of Jupiter Inlet, and
2) to attempt to explain recent depositional trends for coarse and
fine-grained sediment fractions in the study area. An extensive
set of surface grab samples and five vibracore samples comprised
the material upon which this work was based. Sediment distribution
maps included sediment median diameters, sediment sorting, sediment
skewness (based on Trask parameters) and sediment texture (Shepard,
1954 classification). The bottom texture was quite coarse at the
inlet mouth and became progressively finer and less well-sorted
inland in the Loxahatchee Estuary. A prominent flood tidal delta
occurs in the estuarine embayment, at the confluence of the
Southwest, Northwest, and North Forks of the Loxahatchee River.
This wedge-shaped deposit, consisting of at least 80 cm of very
fine-grained, well-sorted sand, overlies a muddy, less well-sorted
substrate containing brackish-water fossils, and appears to be
extending itself into the Northwest Fork.
Several areas show significant sediment mixing and high
organic matter contents. Both the Southwest Fork and the reach
above Pennock Point in the Northwest Fork contain sediments having
organic matter contents in excess of 20% (dry weight basis). These
reaches could easily become anoxic if tidal circulation patterns
were to change and cause less well-oxygenated conditions.
Sediment appears to originate from two sources. On one hand,
sediment comes from the fluvial Loxahatchee, bypassing the
freshwater delta at the head of the tide, and working its way
seaward, probably during periods of increased runoff. On the other
hand sediment appears to be supplied from seaward, entering the
inlet from the longshore current system on flood tides. A lesser
ebb flow volume leaves some of this material within the estuary.
Fine-grained, well-sorted siliciclastic material appears to enter
the inlet when the longshore drift is from the north. Shelly sand,
distinctively different in appearance, appears to enter the inlet
when the longshore drift is from the south. Both sediment types
mix within the inlet, but only the siliciclastic sands are
transported into the estuary. A third source of sediment appears
to be coming from unprotected banks which are being undercut and
eroded by wave and boat wake energies.
Sediment is presently being retained and redistributed within
the estuary and these conditions are likely to persist for the
foreseeable future. If Global Warming is a valid scenario for the
future, then accelerated sea level rise will compound the present
adverse sedimentological effects in the Loxahatchee Estuary.
Jupiter Inlet is one of many small tidal inlets that have
developed in the eastern United States coast line to allow access
of small boats to the interior rivers, lagoons, and intracoastal
waterway system. These inlets have an erosion/deposition history,
most of which have been well documented, that often strongly
reflect a cultural influence. This project originated as part of
a comprehensive management plan for the Jupiter Inlet in Palm Beach
County, Florida, such plan to serve as a guideline for coastal
management for the next 25 years.
III: THE PROBLEM
This study focuses specifically upon the problem of excessive
sedimentation in the Loxahatchee River Estuary, in the region
adjacent to the convergence of the Northwest, Southwest, and North
Forks of the estuary. It is here that a significant flood tidal
delta has formed and impedes navigation. The project involves the
development of a sediment distribution map of a specified portion
of the estuary (based upon literature review and extensive bottom
sampling), and attempts to explain the observed distributional
The Jupiter Inlet and its immediate environment has a long
and rich history of change, extending back to 1892 when the St.
Lucie Inlet was artificially cut through the barrier island, about
10 km north of Jupiter. A recent comprehensive review of these
changes has been prepared by Dr. T. M. Parchure of the Coastal and
Oceanographic Engineering Department at the University of Florida.
It is presented as Part II., REVIEW OF LITERATURE AND DATA of the
April 1990 progress report (UFL/COEL-90/005) to the Jupiter Inlet
District Commission. It seems redundant to include that material
in this report inasmuch as it is readily available. Accordingly,
the reader is referred to that report for background information.
V: FIELD AND LABORATORY WORK
The field work consisted of two and a half days of bottom
sampling from a small boat, using an Ekman-type grab sampler for
soft fine-grained sediments and an Ekman bottom dredge for coarser
materials. Locations were chosen to provide thorough coverage, with
certain areas receiving greater attention. Positions were
determined by line of signt orientation on recognizable structures
and plotted directly on an enlarged set of aerial photographs from
which a base map was made (Map 1). Long cores (>1 meter) were taken
with a vibracorer, designed and manufactured by the University of
Florida (Kirby et al, 1989). Grab samples were collected,
photographed, described into a voice recorder on deck, and placed
in sample bags for analysis in the laboratory. The vibrcores were
taken, capped, and returned to the laboratory for further analysis.
In the laboratory, sand samples were rinsed free of salt water,
dried in a 1050C oven, and, using a Ro-Tap sieve shaker, each
sample was sieved through a nest of sieves (1/2 phi intervals) for
15 minutes. The amount remaining on each sieve was weighed and a
cumulative distribution curve was plotted. Sample statistics were
calculated according to Trask (1932). Mixed sediments (sizes
smaller than 62 microns) were analyzed first with a hydrometer,
then the residue sieved as above (Bowles, 1970). A cumulative curve
was constructed from which percentages of sand, silt and clay were
determined, the sample classified according to Shepard (1954), and
Trask estimators calculated, where applicable. Organic matter was
determined by loss-on-ignition in a 4000 C oven for 24 hours
VI: DATA ANALYSIS AND INTERPRETATION
Following the particle size distribution analyses of the
samples collected in the field, a set of maps were constructed,
based upon the particle size parameters, i.e., median diameter (in
phi units), sorting, skewness, and sediment texture (based upon the
classification of Shepard (1954). The central tendency estimators
used were those of Trask (1932), used primarily to facilitate
comparison with the work of Buckingham (1984). Median diameters
are reported in both millimeters and phi units (Appendix III, Table
1), but the map (Map No. 2) was constructed using the phi units as
textural contours. Sorting and skewness are ratios of quartile
measurements and are dimensionless numbers and are easily mappable.
Textural classification concentrates on fine discrimination within
the sand sized material, using the terms "very fine" (0.063 to 0.11
mm), fine sand" (0.13 to 0.21 mm), etc (Appendix III, Table 2).
When sediment became mixed with finer silt and clay-sized material,
they were mapped as "mixed" sediment, but classified more
descriptively in Figure 1.
6.1 Median Diameter Map 2
Median diameters (phi units) show several distinctly different
patterns through the estuary/inlet complex. Within the area
studied, two reaches of fine-grained sediments are observed, the
most obvious being the segment of the Southwest Fork extending
3000' from the entrance to the C-18 canal toward the main body of
the estuary. Sizes range from medium silt (6 phi 0.016 mm) to
fine sand (3 phi 0.125 mm) in this reach, the finer material
being concentrated toward the entrance to the canal. A second area
of fine-grained sediment occurs in the Northwest Fork, upstream
from Pennock Point. A patch of coarse silt (5 phi) is found in a
restricted area, approximately 2000 ft2, and appears sharply iso-
lated from the lower and upper portions of the estuary. Sands of
varying textures dominate the remainder of the map, falling into
the categories of fine to very fine sand (3 to 2 phi -0.125 to 0.25
mm). The central sand bar (flood tidal delta) is distinguished by
a coarsening to a medium sand (2 phi >0.25 mm) but exists as an
isolated textural island within a larger sea of finer grained
material. Coarsening occurs toward the mouth of the inlet, with
median diameters changing from 3 phi (0.125 mm at the southern
extension of the Intracoastal Waterway) to -1.2 phi (2.2 mm) within
the mouth of Jupiter Inlet. Fine sand (3 phi 0.125 mm) extends
up the North Fork of the Loxahatchee to the bridge at Tequesta
Drive, where it coarsens to a medium sand at 2 phi 0.025 mm.
6.2 Coefficient of Sorting Map 3
As expected, the degree of sorting of the sediment reflects
the size distribution of the sediment, e.g., the wider the
distribution, the poorer the sorting and the reverse. Two regions
of poorly sorted sediments are seen, one occurring in the Southwest
Fork of the Loxahatchee River, the other occurring in the Northwest
Fork. In the former, sorting coefficients greater than 4.0 result
from the incorporation of fine material derived from the C-18 canal
and the lack of significant tidal circulation in the reach (cul de
sac) which keeps the sediment in place. The latter region shows
sorting coefficients exceeding 5.0 located within the center of the
enlargement of the stream, between 26057' and 26057'30" N latitude
and 80007' and 80007'15' W longitude. The situation here seems quite
different from the preceding inasmuch as the reach experiences
normal tidal circulation. The abrupt occurrence of this material
appears related to the sediment trapping phenomenon and will be
discussed more fully in a later section. A third area of poorly
sorted sediments occurs in the Northwest Fork at the very top of
the mapped area. While not being of particular importance to this
work, it does signify additional influences of the estuarine
A dramatic change in sorting becomes very apparent below the
reach previously discussed and extending seaward through the Jupiter
Inlet. The remainder of the area is characterized by sediments
which show Trask sorting coefficients between 1.0 and 1.4. In order
to discern sorting differences, the area was contoured in 0.2
contour interval units. Thus, a qualitative aspect to sorting is
introduced to the map, e.g., a sediment with a 1.41 sorting
coefficient is less well sorted than a sediment with a 1.01 sorting
coefficient. However, the sorting interval between 1.0 and 1.4 is
still considered to represent a well-sorted sediment. Sorting
within the enlarged central portion of the Loxahatchee Estuary,
between 80006' and 80007'is well-sorted, with the best sorting
occurring in a belt parallel with the shorelines. The poorest
sorting of the sands occurs in the vicinity of the flood tidal
delta deposit (based on only one sample). Sorting decreases
somewhat east of the southern arm of the Intracoastal Waterway.
As shown on the map, a central band of sediment with coefficients
exceeding 1.4 extends to the month of Jupiter Inlet. The situation
is somewhat complicated by the fact that this bottom is composed
of a shelly sediment, derived from the erosion of the Anastasia
6.3 Coefficient of Skewness Map 4
Skewness is a measure of the asymmetry of a distribution.
Its significance to sedimentation processes has long been debated
and the jury is not yet in. Since skewness measures the abnormality
of the sediment distribution, i.e., does it have more fine- or more
coarse-grained particles than expected, it is presented here as an
aid to interpretation of sedimentary processes. The values used to
construct this map represent a semi-quantitative estimate of the
shape of the size distribution, based upon the central 50% (tails
of the distribution are not included in the Trask skewness
Two distinct fields of finely-skewed sediment occur west of a
line drawn north and south of Pennock Point in the Southwest and
Northwest arms of the Loxahatchee River. This boundary is very
sharp and must surely reflect the oceanographic conditions within
the estuary. The central portion of the estuary is characterized
by normally-skewed sediments, perhaps slightly dominated by a
coarse sediment mode. Normally-skewed sediment exists in the
northern Intracoastal Waterway and on the northern side of Jupiter
A strip of coarsely-skewed sediment extends from the north
bank of the Loxahatchee, from its intersection with the north
branch of the Intracoastal Waterway, through the central portion
of the Loxahatchee, and up the North Fork. This strip is quite
distinctive and is shown on the map. It seems unlikely that this
particular distribution would occur by chance in the sampling
scheme used. [note: the beginning of this strip coincides with the
erosion of the bank on the north branch of the Intracoastal
Waterway. It looks as if the fines have been winnowed out from the
North Fork and possibly deposited in the confluence with the main
stem, to be further transported up the main stem on flood tides].
6.4 Sediment Distribution Map 5
As noted earlier, the dominant sedimentary deposits within
the Loxahatchee-Jupiter Inlet system are sands. Coarse to medium
(0.25 to 0.84 mm) sands are found from the inlet mouth, extending
landwards to the southern extension of the Intracoastal Waterway.
Very fine- to fine-sands (0.063 to 0.21 mm) occupy the central
reach between the ICW and the divergence of the Northwest and
Southwest Forks from the central basin. A band of very fine- to
fine-sand occurs along the western shoreline of the Northwest Arm,
but mixed sediments fill the remainder of the channel. [note:
mixed sediments refers to the various clayey silts, silty clays and
SaSiCls that result from the Shepard Classification]. The eastern
portion of the map shows an obvious sediment gradient, with coarse
sand giving way to very fine sand within 2700 m of the inlet mouth.
Very fine sand dominates the interior basin of the estuary, merging
with the 'mixed' sediments occurring in both the lower Southwest
and upper Northwest Forks. The exception to the expected sediment
distribution occurs in the North Fork. Here, very fine-sand grades
into medium sand, thus reversing the expected distribution.
6.5 Analysis of Vibracores
Five vibracores were taken to provide some information
concerning the nature and thickness of the flood tidal delta
shoals. The general stratigraphy of each core is presented in
Appendix II. This stratigraphy is based upon examination in liner.
Core VC1A90 was taken in very shallow water (61 cm) on the
flat part of the shoal immediately east of the channel. This site
was selected specifically because the lobate, tongue-like shape of
the body seemed to state that it was a site of active accumulation
and apparent up-estuary migration. The core penetrated 81.3 cm of
fine sand and entered an underlying, dark brown silty sand with a
distinct shelly zone.
Core VC2A90 was taken in deeper water (1.2 m) from the up-
estuary terminus of the flood tidal delta. This also appeared to
be a site of active sediment accumulation and extension. It seemed
reasonable to expect that the core would penetrate a thin sand
layer migrating up-estuary over the present estuary bottom.
Although a short core (38.1 cm), it penetrated a 20.3 cm thick fine
sand layer overlying a dark brown, silty sand containing shell
Core VC3A90 was taken in shallow water (61 cm) from the
northern shoal of the flood tidal delta at the intersection of the
North Fork with the Northwest Fork of the Loxahatchee River. This
also appear to be an area of active accumulation and, in this case,
extension into the North Fork appears to be indicated. The core
penetrated 80 cm of fine sand, thus giving a minimum accumulation.
Core VC4A90 was taken in shallow water (61 cm) from the
southern shoal, directly across the deposit from the preceding core
site. It was taken from the delta-shaped deposit that appears to
be transferring sediment into the lower portion of the embayment.
The core penetrated 43.2 cm of fine sand before entering a dark
brown, silty sand (no shells were observed through the core liner).
Core VC5A90 was taken in deeper water (1.2 m) immediately
downslope of the preceding core. It penetrated 48.3 cm of fine sand
and endered a dark brown, silty sand containing shell fragments.
6.6 Summary of Vibracoring
Two clearly defined layers occur within the immediate region
of the flood tidal delta (FTD). The deposit is a composite feature,
showing evidence of very fine- to fine-grained sand accumulating
to considerable thickness (approximately 1.5 meter) in the
shallowest reach, thinning outward and toward the channel as the
deposit extends itself further up the estuary. This sand deposit
conformably overlies a silty sand which contains an abundance of
shells and most probably represents sediment which normally
accumulates on the bottom of the Loxahatchee Estuary. It is, in
fact, the bioturbated mud, described by Wanless et al, (1984) as
"homogenized organic-rich mud containing a small amount of sand"
which reflects intense bioturbation and forms the bottom of the
VII: SEDIMENTARY TYPES AND SOURCES
Examination of the various sediment samples (see Plates 1-
13) indicated that only two major sediment types are involved in
this study. On the one hand, we see several variations of
siliciclastic material, generally defined as very-fine, fine, and
medium grained sand. This material is composed of clean quartz
grains, low in organic matter, and often containing small amounts
(up to 3%) of calcium carbonate shell debris, generally small
fragments of thin-shelled molluscs, some complete juvenile
Macoma(?) clams, and some unidentifiable gastropods. Wanless et al,
 present a faunal listing of the shelly material and state
that they are representative of a shallow, brackish-water fauna.
Consequently, it is believed that material of this composition was
produced directly within the Loxahatchee River Estuary, perhaps as
sandy material which mixed with the brackish water fauna as it
worked its way down-estuary from the upper fresh-tidal reaches. In
general, this material is unimodal, with the modal diameter falling
between 110 to 150 microns (3.25 to 2.75 phi). This modal diameter
prevails in the upper portion of the estuary where mixed sediment
types occur, being quite distinctive in the size analysis.
Consequently, it appears that the same sand exists throughout the
estuary, being cleaner and more narrowly sorted in the lower
portion of the estuary than in the upper portion. There, because
of the estuarine circulation pattern which creates a sediment trap,
it becomes mixed with finer-grained material (organic matter,
diatom frustules, foraminiferal tests, and clay particles) to form
the mixed sediments, e.g., silty sands, sandy silts, and SaSiCls.
[note: this sediment is also found offshore]. The late Pleistocene
Pamlico Formation which covers older formations (Miami and
Anastasia) to thicknesses up to 60 feet (Hoffmeister, 1974) is a
likely source of sand for the Loxahatchee River. The offshore sand
may have had multiple sources, e.g., submerged early Holocene
beaches and dunes which are being transported shoreward as sea
level continues to rise. This would include the Pamlico Formation.
The second type of sediment is the coarse, shelly material,
which is found in the entrance to the Jupiter Inlet (Area B) and
in coastal waters on the south side of the inlet (Area C and Plate
1). This material appears to be derived from the Anastasia
(Pleistocene) Formation which comprises the bedrock from Palm Beach
to Jacksonville, Florida, and occurs offshore in numerous shallow
water outcrops. The formation is often called a 'coquina', being
composed nearly completely of fragmented calcium carbonate shell
material cemented by a siliceous or calcareous cement. The shell
fragments vary in size, are dominately molluscs, and usually have
a distinctive orange-reddish color which makes the material easily
recognizable (Plate 2). It is difficult to find a sediment sample
which does not contain some Anastasia fragments due to the ubiquity
of the formation within the region. However, the presence of local
underwater outcrops provides a significantly larger portion of
Anastasia material for the Jupiter Inlet (Area B) than for the
sediments in the Loxahatchee. Indeed, it is believed that samples
without Anastasia-derived material originated and were transported
within the fluvial/estuarine environment whereas those samples
containing recognizable Anastasia fragments represent material
eroded from the offshore outcrops which have been transported
inland on flood tide.
A third sediment type which has been found in minor amounts,
is the fine-grained, organic-rich deposit which accumulated in the
low energy, canal-linked arms of the estuary, specifically the
Southwest Fork of the Loxahatchee River. Classified as SaSiCl's,
clayey silts, and silty sands, they also occur in a restricted area
of the Northwest Fork above Pennock Point (Map 5). Organic matter
contents are varied, ranging from 2.23% (9A90) to 29.45% (27A90) -
APPENDIX III, Table 3. yet no evidence of anoxic conditions due to
oxidation of this material was observed during the sampling period.
It seems unlikely that such conditions could often occur due to the
shallow depths of the estuary and the vigorous tidal currents.
However, the energy levels in the Southwest Fork of the estuary
seem conducive to the development of anoxic bottom conditions and
it would not be unexpected to see such conditions occur during
Several local sources of sediment to the Loxahatchee River
were observed during this sampling period. Generally speaking, the
shoreline is well armored, with rip-rap and pilings installed to
prevent erosion of the shoreline (Plate 3). However, a significant
slope failure was occurring on the west side of the north bank of
the IntraCoastal Waterway (Plates 4 and 5). A second area of
significant erosion was the shoreline of Dubois Park, just inside
the Jupiter Inlet. These failures, operating over time, would
provide a substantial amount of sediment to be redistributed within
VIII: PATTERNS OF SEDIMENT TRANSPORT
Two general patterns of sediment movement seem to be operating
in this environment. 1) There is likely to be episodic movement of
sand from the fresh tidal portion of the Loxahatchee River to the
lower flood tidal delta where it becomes incorporated into the
deposit. Wanless et al, (1984) observed lenses and laminae of fine
sand in the mixed sediments of the middle estuary deposits. Their
hydrologic data indicates that near bottom current velocities
sufficient to transport sand-sized material up to 500 micron
diameters exist throughout the Northwest Fork. The fresh tidal
delta that exists at the head of the estuary contains 25% of sand
less than 200 micron in diameter. Storms and other meteorologic
events could winnow these finer sands out of the deposit and they
could be transported as suspended material down-estuary to the
flood tidal delta. 2) Two different sediment populations
(siliciclastic and shelly) are being transported from offshore into
the inlet. The siliciclastics are introduced on flood tide whenever
the longshore currents flow from north to south. These are clean,
very fine- to fine-grained, unimodal (0.11 to 0.15 mm) sands,
practically indistinguishable from those being carried down the
Loxahatchee River, except for a small amount of recognizable
Anastasia fragments in their coarse fraction. These sands can be
transported deeply into the estuary, probably as suspension load
(Wanless et al, 1984). Vibracores taken through the flood tidal
deposit reveal it to be a wedge-shaped deposit, tapering up-
estuary and composed of this siliciclastic material. This strongly
suggests that sediment is being introduced from the offshore
through the Jupiter Inlet.
Sediment derived from the Anastasia Formation is transported
into Jupiter Inlet as bedload and saltation load and is deposited
within the narrow channel of Area B. A few smaller shell fragments
may be carried into Area A on flood tides, but the majority of the
sediment is confined within the eastern part of Area B. Carrying
capacity of the flood tidal flow diminishes when it enters the
enlargement at the confluence of the North, Northwest and Southwest
Forks of the Loxahatchee River. Sediment is naturally deposited in
a flood tidal delta which is further modified by winds, surface
currents, and boat wakes. This process has been been occurring at
least since 1940 (McPherson et al, 1982).
The flood tidal delta which is located at the intersection of
the Southwest, Northwest, and North Forks of the Loxahatchee River
is extending itself into the mouth of the Northwest Fork, causing
shoaling and a general deterioration of the access channel for
small boat traffic. It is not absolutely clear where the sediment
is coming from, however, both the longshore sand transport system
and the fluvial transport system appear capable of making
significant contributions. Shoreline erosion offers an additional,
as yet unquantifiable contribution to the supply of sediment.
These conclusions are based upon the similarity of textural
parameters in the different deposits, the availability of
sufficient tidal energies to transport this material, and the
evidence of significant shoeline erosion in two specific areas.
Sediment maps show that sediment textures become finer up-
estuary, beginning as coarse sand/granules at the mouth of Jupiter
Inlet, grading into mixtures of sand, silt, and clay in the
Southwest Fork and above Pennock Point in the Northwest Fork.
Sediment is generally very well-sorted in the eastern and central
reach, becoming poorly sorted in the western portion of the
Northwest Fork and the Southwest Fork. This reflects the
availability of wind and tidal energy to rework and winnow the
material with less reworking occurring in the poorly sorted
reaches. The estuarine sediment trap occurs in the Northwest Fork,
above Pennock Point, and results in a reach dominated by mixed,
organic-rich sediment in the center with progressively better
sorting occurring along the shallow margins. Coarse and fine-
skewed reaches occur adjacent to each other in the central and
western portions of the mapped area. A band of coarsely-skewed
sediment 'appears' to outline a channel or pathway down the North
Fork into the main portion of the estuary. The Southwest Fork is
finely-skewed, the Northwest Fork above Pennock Point is also
finely-skewed. The central portion of the estuary is normally-
skewed, and, except for the strip down the center of the North Fork
and through the estuary to the north bank of the inlet, the
remainder is finely-skewed. It is noted that the flood tidal delta
is finely-skewed, possibly due to sea grasses which would tend to
retain fine-grained material due to a baffling effect.
Studies by Sonntag and McPherson (1984) indicate that tidal
flow into and out of the estuary is much greater than freshwater
flow from the tributaries. Measurements during the 1980 'wet'
season showed the freshwater inflow to be 1.15 x 105 m, only 1.5%
of the ebb tidal flow of 7.65 x 10 m3. The corresponding flood
tidal flow was 8.26 x 106 m3. During the study period, the
freshwater inflow per tidal cycle averaged about 2% of the average
tidal flow through Jupiter Inlet. While important in maintaining
the estuarine environment, increasing the magnitude of fresh water
flow in the Loxahatchee will have little effect on determining
sediment import or export. Further reduction of the freshwater flow
of the Loxahatchee River will occur as long as the present drought
conditions exist. It is concluded that the flood tidal delta will
continue to extend into the central basin of the estuary until such
time that the net ebb tidal volume exceeds the net flood tidal
volume and causes net ebb tidal sediment transport to occur.
Accelerated rise of sea level, occurring as a result of Global
Warming, will drive the estuarine circulation pattern toward a Type
A (salt-wedge) configuration, with the null point occurring farther
up-estuary. Thus, high density salt water capable of carrying
sediments will progress further up-estuary. The flood tidal delta,
so well-developed in the lower reaches of the estuarine
Loxahatchee, will continue to migrate up-estuary.
X: RECOMMENDATIONS FOR FUTURE WORK
In order to more fully understand the processes operating in
Jupiter Inlet and the Loxahatchee River, it is suggested that the
following projects be initiated. If the postulated Global Warming
event is really occurring, then we can can expect sea level to
increase between 4.8 to 17.1 cm by year 2000 (Hoffman, 1984). This
is an unprecedented rise in global sea level, undocumented in human
times, and can be expected to result in some immediate and dramatic
changes to the coastline. Some of the effects will include a loss
of coastal wetlands due to inability of marshes to match the rate
of sea level rise (Hackney and Cleary, 1987), significant shoreline
erosion and property losses arising from storms with increasing
duration accompanied by wave heights in excess of 5 m (Dolan, et
al, 1990), and an increase in the landward transport of sedimentary
material as the salt water prism moves up the estuary. The Jupiter
Inlet area will certainly be affected by these events.
1. We must begin a regular period of monitoring of sediment
accumulation. In particular, we must be able to assess the
seasonality effects (summer/winter storms) and periodic and
episodic meterologic events, e.g., Hurricane HUGO, on sediment
accumulation. This will require the installation and monitoring of
sediment traps, designed specifically for shallow water,
microtidal, episodically high energy, estuarine systems.
2. We must begin a program of sediment tracing, using
fluorescene dyed-particles which will indicate the direction of
sediment transport under various conditions of storms, tides, and
reduced or enhanced freshwater flow. Different colored tracers
should be used to differentiate the fresh tidal sand deposits from
the longshore sand deposits.
3. Assess the effectiveness of shoreline erosion by wind
waves and boat wakes in contributing to the supply of sediment
available for deposition in the flood tidal delta.
Bowles, J. E., 1970. Engineering properties of soils and their
measurement. McGraw-Hill, Inc., New York, 187 p.
Buckingham, W. T., 1984. Coastal engineering investigation of
Jupiter Inlet, Florida. UFL/COEL-84/004, 228 p.
Davies, B. E., 1974. Loss-on-ignition as an estimate of soil
organic matter. Soil Sci. Soc. Amer. Proc. 38, p. 150.
Dolan, R., D. L. Inman, and B. Hayden, 1990. The Atlantic coast
storm of March 1989. Jour. Coast. Res. 3, 721-725.
Hackney, C. T. and W. J. Cleary, 1987. Saltmarsh loss in
southeastern North Carolina lagoons: importance of sea level
rise and inlet dredging. Jour. Coast. Res. 3, 93-97.
Hoffman, J. S., 1984. Estimates of future sea level rise. Pages
79-103 in Greenhouse Effect and Sea Level Rise, M. C. Barth
and J. G. Titus, (eds). Van Nostrand-Reinhold Co., NY.
Hoffmeister, J. E., 1974. Land from the sea. Univ. of Miami
Press, Miami, FL, 143 p.
McPherson, B. F., Maryann Sabanskas, and W. A. Long. 1982.
Physical, hydrological and biological characteristics of the
Loxahatchee River Estuary, Florida. U.S.G.S. Water Resources
Parchure, T. M., 1990. II. Review of literature and data. In:
Tidal inlet management at Jupiter Inlet, Florida, UFL/COEL- 90/57
Shepard, F. P., 1954. Nomenclature based on sand-silt-clay ratios.
Jour. Sed. Pet. 24, 151-158.
Sonntag, W. H., and B. F. McPherson. 1984. Sediment
concentrations and loads in the Loxahatchee River estuary. Florida,
1980-1982. U.S.G.S. Water Resources Rpt. 84-4157.
Trask, P. D., 1932. Origin and environment of source sediments of
petroleum. Gulf Publ. Co., Houston, TX.
Wanless, H., V. Rossinsky, Jr., and B. J. McPherson, 1984.
Sedimentologic History of the Loxahatchee River Estuary, Florida.
U.S.G.S. Water Resources Rpt. 84-4120, 58 p.
Fig. 1. Textural classification of Loxahatchee Estuary and Jupiter Inlet bottom samples
(Shepard, 1954). Inset shows the descriptive terms. Sixteen samples (Appendix
III Table 1) did not plot within the 'sand' category and are shown on the
diagram. These are designated as 'mixed' samples in the text.
Plate 1 -
Plate 2 -
Dredged sample of lag shelly material from mouth of
Jupiter Inlet (12B90). This represents a high-energy
deposit of coarse shells derived from the Anastasia
Coarse shelly sand (10B90) from dredged pit in center of
channel immediately inside Jupiter Inlet. Orange-
colored shell fragments indicates derivation from the
Plate 3 Example of shoreline armoring using rip rap material.
Plate 4 -
Plate 5 -
Shoreline erosion slumping of west bank of the north
branch of the Intracoastal Waterway at its intersection
with Jupiter Inlet channel.
Large bank failure due to undercutting of bank along the
west side of the North branch of the Intracoastal
Plate 6 Mixed sediment (SaSiCl Figure 1) from center of
estuarine sediment trap in upper portion of Northeast
Plate 7 Coarse shelly sand with Anastasia-derived shell fragments
from northernmost sample from North Fork (21A90).
Plate 8 "Silty sand" (Figure 1) taken within the South Fork at
the eastern edge of "mixed sediment" (35A90).
Plate 9 Clean, well-sorted "fine" sand, typical of sediment found
in the open portion of the Loxahatchee Estuary in Area
Plate 10 Clean, well-sorted "very fine" sand with oyster shells
Plate 11 Clean, medium well-sorted "fine" sand with shell frag-
ments (possibly derived from the Anastasia Formation)
Plate 12 -
Northernmost sample of well-sorted fine-grained marine
sand. This is material which may be transported into
Jupiter Inlet by south flowing longshore currents
Plate 13 Marine sample immediately south of Jupiter Inlet mouth.
Composed primarily of shells derived from submerged
Map 1 Grab sample locations are shown by a closed circle,
vibracore locations are shown by closed triangles. Area
west of the railroad bridge is designated Area 'A'.
Area east of the railroad bridge, including the mouth
of Jupiter Inlet, is designated Area 'B'. Marine
samples come from Area 'C.
Map 2 Distribution of sediment median diameters, contoured in phi
units (see Appendix III Table 2 for conversion).
Since phi units bear an inverse relationship to metric
units, areas outlined by large phi values show fine-
grained material and low phi values show coarse-grained
material. Fine-grained material is found in patches in
the Northwest and Southwest Forks of the Loxahatchee
Estuary and on the flood tidal delta in the central
portion of the estuary. Median diametersincrease
generally from the center of the estuary through the
mouth of Jupiter Inlet.
Map 3 Distribution of Trask sorting coefficients. Several areas
of poorly-sorted sediment occur in the Northwest and
Southwest Forks and 1.0 unit contour intervals were used
to delineate these areas. The remainder of the estuary
and tidal inlet was contoured in 0.2 unit contour
intervals to emphasize small differences of sorting
within generally well-sorted material.
Map 4 Distribution of sediment skewness, e.g., degree of
abnormality of sediment distribution. Values less than
0.9 indicate an excess of material smaller than the
modal diameter (finely-skewed). Values greater than 1.1
indicate an excess of material larger than the modal
diameter (coarsely-skewed). Normal skew is shown by
values between 0.9 1.1. The Northwest and Southwest
Forks are finely-skewed and the central portion is
normally-skewed. A small patch of finely- skewed
sediment occurs off the entrance to the southern portion
of the Intracoastal Waterway, and a coarsely-skewed
region exists offshore to the south of the inlet mouth.
A band of coarsely-skewed sediment extends through the
North Fork eastward to the north branch of the
Map 5 Textural distribution of bottom sediment types, classified
according to Shepard (1954 Figure 1).
MAP 1 Sample Locations
0 500 1000 1500 meters
I I I I
MAP 2 Median Diameters
0 500 1000 1500 meters
I I I I
MAP 3 Sorting Coefficients
1000 1500 meters
MAP 4 Skewed Coefficent
0.9 -1.1 Normal Skewed
1000 1500 Meters
MAP 5 Sediment Textures
Very Fine Sand
4 4 *
1000 1500 Meters
I I I I
"A" DESIGNATES SAMPLES TAKEN WEST OF THE RAILROAD BRIDGE
1A90 Fine-grained sand very little material smaller than
fine sand size. a few fragments of shells, broken up into very
small shell fragments.
2A90 Dark brown to light gray to black, somewhat anoxic,
slightly silty. Lot of organic matter some large particles. No
sea grasses in this sample very fine grained silty material.
3A90 Mixture of fine sand and darker organic material. A
little bit coarser than the material found in the middle of the
channel. This is different in character from the sample from the
west side. This sample is much more organic rich, indicating that
some organic material is accumulating on the east side of the
4A90 Silty sand, quite organic, a few shells, I see no
particulate organic dark but not smelly. Not dissimilar from
5A90 Looks like 1A90. Quite clean, well-sorted, shell
fragments (picture taken).
6A90 Channel sample. (no description).
7A90 0.9 m of water. Coarsest sample I have seen. A nice
clean sand, overlain by a dark dirty sand layer an inch thick.
Small pieces of shell (picture). No significant shell
8A90 Clean, coarse sand less well sorted than previous
samples. Large abundance of shell fragments. Also appears to have
been a darker layer on the top of the material. Doesn't differ
greatly from previous sample.
9A90 Dark gray to black, highly organic silt no sandy
particles. Sea grass is here, roots, stems, pieces, and lot of
undecayed organic material. No worms, no living things in here.
Seems to have been a dark finer-grained layer up in the top. Some
pieces of decaying organic matter. Finer-grained than previous
samples on the west side of the Lox. finest grained so far.
10A90 1.8 m deep. Dk gray to dk brown silt. Lots of clay-
sized materials. Thixotropic gel-like. Not reduced, doesn't
smell, oxidizing. Organic rich-large particles. Yoghurt texture.
11A90 Dark-brown to dark gray muddy silt looks organic
with fluff on top thixotropic materials very similar to preceding
samples. 2.1 m depth.
12A90 Dark brown to gray, silt, sandy silt somewhat
thixotropic. Not different from the previous sample. No sea
grasses, no organisms. 2.1 m depth.
13A90 Sand, slightly reduced. Buff surface layer. Gray(?)
shell fragments no living organisms, no sea grasses. Medium
14A90 Dark brown to dk gray silt. Sopme organic fragments,
number of small fragments of carbonate. Very similar to 9 and
10A90. Thixotropic fluff layer on top. 1.5 m.
15A90 -Fine, thixotropic silt identical to previous sample.
There is a band of this material extending down the east side of
the Lox. 1.8 m.
16A90 Mixture of sand, silt, and clay. Coarser mixture than
previous two samples. Med. to dk brown color. Buff colored fluff
layer on the top. 2.3 m.
17A90 Gray mud, very fine small amounts of fine sand -
organic. 1.8 m.
18A90 Muddy sand sandier than preceding. Dk brown, some
carbonates mud blebs, but still a sand. (picture).
19A90 Muddy, dk brown to gray, muddy sand. Buff to orangy
covering over the surface. Minor carbonate. Medium grained small,
slightly cohesive sediment (picture). 2.4 m.
20A90 Clean, coarse to medium grained sand. Fairly-well
sorted, small (10%) of shell material. Some mottling of fine-
grained material (OM)-very siliciclastic deposit. No life. 1.2 m.
21A90 Coarse, shelly (more than any previous samples) very
coarse sand ( 1-1.5 mm mean dia. est.), 1.5 m.
22A90 Fine-grained sand, some mud, silty material in it.
Brown, different material from 21. Carbonate very light (5%).
23A90 Fine silty sand shells, dark brown same as 22.
24A90 Fine sand. Small amount of silt 8% carbonate
particles, dark streaks of organic matter no sea grasses looks
pretty much like previous sample., 1.2 m.
25A90 Coarse, shelly sand definite increase in amount of
shell-similar to sample 21., 1.5 m.
26A90 Coarse sand, identical to previous sample., 2.1 m.
27A90 Coarse,shelly sand identical with 25 and 26., 1.8 m.
28A90 Fine sand, silt and minimal shell material. Lots of
organic material quite dark. Mud dk brown to grayish-black with
flakes of organic matter. Very different from preceding samples.
Seems to mark some limit to the degree of mixing of the sediments
from two different sources. 1.8 m.
29A90 Sand some dk material overlain by 0.5 cm oxidized
material. Appear to be some vertical burrows, tubes. No grasses,
coarser than previous sample. 0.9 m deep. Reduced to some extent
due to gassy smell.
30A90 Very fine sand or a silt more of a silt than sand.
Dk brown, mottled, places with lighter brown material shells
(indigenous rather than reworked) 2.4 m (picture).
31A90 Fine-sand, mixed with variegated browns and grays -
appears it could have been layered. A few shell fragments with this
- some particulate organic matter. 1.2 m.
32A90 Silty sand or sandy silt dark brown small amount
of shelly material some organic matter little difference in
these last few samples 1.2 m.
33A90 Fine-grained sand or silty sand dk brown to gray,
small amt of shell -particulate organic no difference between
this and previous samples.
34A90 Dk brown to gray sand and silt little variation in
this area., 1.8 m.
35A90 1.5 m. Dk brown, silty clay/clayey silt. Soft -
definite textural change from previous material. Burrows obvious -
no grasses. Living razor clam shell material. Very rich dark
but well oxidized, almost clean sand, interbedded and surrounded
by darker silt. Organisms seem to have been inplace not
36A90 Dark brown to brownish-black silt very liquid,
remolded sample by sampling.
37A90 Dark brown, soupy silt no picture. 2.3 m, anoxic.
38A90 Dk brown,small amounts of carbonate -soupy silt, no
life. Slightly coarser than preceding sample.
39A90 Dk brown to dk gray silt. Quite organic, but not
producing gas after several days in.the bag. Clayey silt.
40A90 Fine, well-sorted, It brown sand. Contains minor percentage
(3-5%) shelly material. Contains organic matter, particulate
rootlets, etc. A clean, well-washed sand (no clay or silt
41A90 Clean, well-washed, fine-grained sand, containing
shell particles up to a few %. Sand is It brown, some organic
matter. Looks like sample 40A90.
42A90 1.5 m. No description lost sample?
43A90 1.5 m. Lt. brown, orangy, very-fine-grained sand.
Quite clean. Some organic fragments minor amount of shell
44A90 1.2 m. Very fine-grained, well-sorted sand containing
organic particulate material. Very minor amount of carbonate
material. Well-washed clean, no clay similar to sample 43A90.
45A90 1.4 m. Medium to coarse-grained, poorly sorted sand
containing significant quantities of shell fragments particularly
orange Anastasia type of shells, as well as indigeneous white
shelly material. No obvious organic material in here.
46A90 Collected on 4/19/90. Very well-sorted, fine-grained
silty sand. Dk brown to gray color, contains fragments of organic
matter allochthonous shell material definitely a silty sand or
a sandy silt.
47A90 Very fine-grained silty sand/sandy silt. Dk brown to
dk gray, organic rich material identical with 46A90.
48A90 Slightly coarser, silty sand, dk brown to dk gray
organic rich (not smelly). Carbonate particles (2%). Similar to
preceding samples, possibly slightly coarser.
49A90 No description lost?
50A90 Fine-grained silty sand coarser than the preceding
sample. Lt brown oxidized portion (all preceding samples beginning
with 46A90, had changed color during storage, becoming reduced and
darker in the plastic bag).
51A90 Fine sand, quite clean, well-sorted. Considerable
percentage of shells no obvious particulate organic matter.
This is quite different from the. preceding samples. A mixed
"B" DESIGNATES SAMPLES TAKEN EAST OF THE RAILROAD BRIDGE
1B90 Had difficulty taking a sample at this locality. The
dredged bounced over a hard bottom and several attempts had to be
made. "Either large rocks or a shell-covered bottom". Fine, very
clean, well-washed material -associated with large oyster shells.
Area is disturbed, looks very unlike the Anastasia formation. Lot
of shelly material well packed sand on the bottom.
2B90 Very grassy, fine silty sand. Second sample is a dk
brown to gray fine sand mixed with considerable amount of organic
matter. This makes it look like a mineral clay, but it is not.
Took picture of the weeds and sea grasses.
3B90 Medium grained sand, some coarse particles, increasing
number of shells poorly sorted, clean (no silt). Carbonates
probably 12% maybe. Could be Anastasia material.
4B90 Fine-grained sand, silty components. Large oyster
shells with expected increase in carbonate particles (picture).
5B90 Clean, medium grained, quite well-sorted sand. Large
shell fragments (8-12%). Nice fine-grained well-sorted sand.
6B90 Very-clean, medium grained, well-sorted sand. Taken at
15' up the Incracoastal Waterway. Shells occupy minor portion of
the sample. Took a picture. West bank of waterway is eroding and
could be providing the well-washed sands to the waterway. This
could be quite significant.
7B90 Fine-grained sand, well-sorted but not well washed -
It.gray rather than buff colored. No significant increase in
carbonate content. Some darker material which may represent either
organic matter or possibly some heavy minerals washed out of the
8B90 Med to coarse grained sand very shelly. brown with
orange flecks. Lots of carbonate material. Looks very much like
Anastasia some sea grass (Picture).
9B90 Very shelly sand controlled by the Anastasia
Formation. In fact, it looks like the Anastasia formation being
transported inward here. (Picture).
10B90 Coarse-grained, Anastasia derived sand greater
number of large shell fragments. 2.1 m.
11B90 Medium, well-sorted sand. Shell particles same size
as the other clastics. This was taken from the scour pit at 3.9 m.
Possibly represents material which is saltating through the system
at the present time.
12B90 Very coarse, shelly conglomeratic deposit 100% shell
material. Lag deposit consisting of mixed Anastasia and younger
"C" DESIGNATES OFFSHORE SAMPLES
1C90 Fine-to medium grained, light brown to gray sand. Some
carbonate particles in it. 1.5 m deep about 61 m off the beach.
Reminds me of some of the sands already seen up the Loxahatachee.
This is surprising since I expected to see some evidence of
derivation from the Anastasia. This is distinctly different.
2C90 Fine-grained, gray to It brown, very-well sorted sand.
A few shell fragments but not particularly significant.
3C90 Coarse grained, very shelly sample, taken from 2.7 m
of water. Anastasia-derived sediment. On the other side of the
jetty we find a totally different kind of sand very strange. I
suspect that this sample may represent erosion of the Anastasia
subcrops which we can see and from which we collected a sample.
Since this sample was taken immediately adjacent from the area
showing the greatest sand loss, it may represent a lag
concentration from which the fine material has been removed.
4C90 This sample is in the plastic bag.
5C90 Fine-grained, It brown to gray well-sorted sand a few
shells, but not significant. Very similar to the sand north ofthe
inlet. This sample is really 5C90 and is in the cloth bag. It was
photographed as 4C90.
DESCRIPTION OF THE VIBRACORES
VC1A90 length is 96.5 cm. Lt. brown to brown, homogeneous
fine-grained sand. Shell zone at 81.3 cm which extends downward,
becoming a dark brown, silty sand to the base of the core.
Unit 1 81.3 cm of recent deposition.
Unit 2 older unit, beginning with shelly layer.
VC2A90 Length is 5.9 cm. Lt. brown to yellow brown, fine to
medium sand to 20.3 cm. Dark brown silty unit containing shells
extends to base, becoming very shelly near base.
Unit 1 20.3 cm of recent deposition.
Unit 2 Silty sand with shell concentrations [shell are
a broken-up hash no in-place material seen].
VC3A90 Length is 80 cm. Lt. brown, fine to medium grained
sand. Reduced zone of blackened sand occurs between 12.7 to
Unit 1 At least 80 cm of recent deposition.
VC4A90 Length 60.9 cm. Lt. brown, fine to medium grained
sand down to 43.2 cm. Color change to dark brown, texture change
to silty sand, no shells seen.
Unit 1 43.2 cm of recent deposition.
Unit 2 older unit of dark brown, silty sand, no
VC5A90 Length is 73.7 cm. Sea grass at surface. Thin layer
of dark brown silt (5mm). Lt. brown, fine to medium sand to 48.3
cm. Dark brown silty sand containing several reduced patches,
extends to 63.5 cm where fine fragmental shelly layer begins. Layer
appears discontinuous, patchy. Shell hash composed of small wheat-
grain sized fragments. Next unit to base of core is dark brown
Unit 1 48.3 cm of recent deposition.
Unit 2 15.24 cm of dark brown silty sand with
Unit 3 6.35 cm shelly zone.
Unit 4 repeat of Unit 2 (without reduction patches).
Table 1. Grain Size Parameters
SO Sk Sand Silt Clay
AREA A SAMPLE DATA (includes estuary west of the railroad
1 2.4 0.195 1.36 0.96 100 Fine sand
2 4.1 0.058 5.12 0.16 48 28 24 SaSiCl
3 3.1 0.116 4.12 0.13 61 19 20 Clayey sand
4 3.3 0.110 1.52 0.60 73 17 10 Silty sand
5 2.8 0.140 1.19 1.04 100 Fine sand
6 2.8 0.145 1.21 1.17 100 Fine sand
7 Not analyzed (lost?)
8 1.9 0.260 1.08 0.78 100 Med. sand
9 3.1 0.120 1.36 0.96 100 VF sand
10 2.6 0.017 5.60 0.24 17 50 33 Clayey silt
11 5.3 0.026 5.70 0.53 35 39 26 SaSiCl
12 4.5 0.045 4.70 0.24 44 32 24 SaSiCl
13 2.6 0.170 1.28 0.98 100 Fine sand
14 5.3 0.026 3.74 0.58 31 48 21 SaSiCl
15 5.6 0.021 4.47 0.41 25 49 26 SaSiCl
16 3.3 0.100 1.90 0.47 68 18 14 Silty sand
17 3.7 0.078 4.80 0.12 54 24 22 SaSiCl
18 3.3 0.108 1.59 0.66 74 15 11 Silty sand
19 3.3 0.110 1.31 0.45 82 11 7 VF sand
20 1.9 0.260 1.22 1.07 100 Med. sand
21 2.0 0.251 1.26 1.16 100 Med. sand
22 3.0 0.122 1.38 1.04 100 VF sand
23 3.0 0.127 1.34 1.12 100 VF sand
24 3.3 0.105 1.15 1.18 100 VF sand
25 3.1 0.118 1.28 1.18 100 VF sand
26 2.1 0.240 1.41 0.89 100 Fine sand
27 1.5 0.360 1.38 0.92 100 Med. sand
28 3.2 0.110 1.07 1.18 100 VF sand
Not analyzed (lost?)
3.2 0.112 1.17 1.15
3.0 0.128 0.94 1.13
3.0 0.127 1.21 1.09
2.9 0.132 1.18 1.05
2.9 0.130 1.21 1.04
3.3 0.108 2.21 0.30
5.2 0.027 4.33 0.41
6.2 0.013 4.06 0.28
3.3 0.102 2.22 0.37
4.2 0.056 4.47 0.20
2.8 0.146 1.31 1.10
# PHI D50
Table 1. Grain Size Parameters (continued)
# PHI D50
So Sk Sand Silt Clay
41 Not analyzed (lost?)
42 3.1 0.120 1.26 1.07
43 3.2 0.111 1.16 1.09
44 3.2 0.110 1.10 1.01
45 2.8 0.146 1.01 1.20
46 3.2 0.110 1.21 1.10
47 3.1 0.120 1.20 1.03
48 3.1 0.123 1.20 1.08
49 3.0 0.130 1.23 1.09
50 3.0 0.128 1.21 1.07
51 2.7 0.140 1.23 1.15
AREA B SAMPLE DATA (Area east of
C SAMPLE DATA (includes
2.9 0.140 1.20 1.15
2.7 0.148 1.17 0.95
0.7 0.610 2.10 1.37
0.0 1.040 1.44 1.62
3.1 0.118 1.13 1.01
railroad bridge to inlet
Explanation of symbols:
# = sample number, e.g., 9A90, 3B90. etc.
PHI = median diameter in phi units
D50 = median diameter in millimeters
So = sorting coefficient of Trask
Sk = skewness coefficient of Trask
Sand = % of particles >0,062 mm (4 phi)
Silt = % of particles between 0.0625 and 0.0039 mm (4 8 phi)
Clay = % of particles smaller than 0.0039 mm (8 phi)
Classification textural classes based upon the nomenclature
developed by Shepard (1954) see Figure 1
APPENDIX III Table 2. Particle Size Conversion Chart
WENTWORTH SIZE CLASS
WENTWORTH SIZE CLASS
s aa ,
Udden-Wentworth grain-size scale and //mm conversion chart.
Table 3. Organic Matter Content (%)
is expressed as % of dry bulk sample weight.