• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Acknowledgement
 Table of Contents
 List of Figures
 List of Tables
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Summary and conclusions
 Appendix A. Wave data plots
 Appendix B. Sedimentation data
 Reference






Group Title: UFLCOEL-95003
Title: Impact of Longboat Key beach nourishment on hard bottom sedimentation rates
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00085016/00001
 Material Information
Title: Impact of Longboat Key beach nourishment on hard bottom sedimentation rates
Series Title: UFLCOEL-95003
Physical Description: x, 148 p. : ill. ; 28 cm.
Language: English
Creator: Stubbs, Darwin C
University of Florida -- Coastal and Oceanographic Engineering Dept
Publisher: Coastal & Oceanographic Engineering Dept., University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1995
 Subjects
Subject: Beach nourishment -- Mathematical models -- Florida -- Longboat Key   ( lcsh )
Sedimentation and deposition -- Mathematical models -- Florida -- Longboat Key   ( lcsh )
Dissertations, Academic -- Coastal and Oceanographic Engineering -- UF   ( lcsh )
Coastal and Oceanographic Engineering thesis, M.E   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Darwin C. Stubbs.
Thesis: Thesis (M.E. in Engineering)--University of Florida, 1995.
Bibliography: Includes bibliographical references (p. 146-147).
 Record Information
Bibliographic ID: UF00085016
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 33143322

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page i
    Acknowledgement
        Page ii
        Page iii
    Table of Contents
        Page iv
        Page v
    List of Figures
        Page vi
    List of Tables
        Page vii
        Page viii
    Abstract
        Page ix
        Page x
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
    Methods
        Page 11
        Page 12
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        Page 29
        Page 30
    Results
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
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        Page 53
        Page 54
        Page 55
    Discussion
        Page 56
        Page 57
        Page 58
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        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
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        Page 67
        Page 68
    Summary and conclusions
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
    Appendix A. Wave data plots
        Page 76
        Page 77
        Page 78
        Page 79
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    Appendix B. Sedimentation data
        Page 111
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    Reference
        Page 146
        Page 147
Full Text



UFL/COEL-95/003


IMPACT OF LONGBOAT KEY BEACH NOURISHMENT
ON HARD BOTTOM SEDIMENTATION RATES






by



Darwin C. Stubbs





Thesis


1995
















IMPACT OF LONGBOAT KEY BEACH NOURISHMENT ON HARD BOTTOM
SEDIMENTATION RATES










By

DARWIN C. STUBBS


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING

UNIVERSITY OF FLORIDA


1995















ACKNOWLEDGMENTS


I would like to express my gratitude to my advisor and supervisory committee

chairman, Dr. Daniel M. Hanes, and the members of my supervisory committee, Dr.

Robert G. Dean and Dr. J. Ashish Mehta.

I must also thank the indispensable staff of the Coastal Engineering Laboratory

for meeting and exceeding the many demands of my research work. Thanks go to

Vernon Sparkman and Daniel Brown for the construction of my sediment traps.

Thanks also go to Viktor Adams, Don Mueller and Mark Sutherland for their tireless

effort and humor in the field.

I am also very appreciative of the assistance I received in the analysis of my

data. Thanks go to Konstantin Marusin for developing the wave analysis software

and Ani Akarjalian for analyzing my sediment samples.

My parents deserve special thanks for their constant support and

encouragement.

I owe a large debt of gratitude to my friends, especially Tim, Thermo, Choad,

Tweety, Slick, Robcindyandbud, Mr. and Mrs. Man and Dave. They deserve thanks

for listening to me, pretending to listen to me, laughing with me, laughing at me,

surfing with me and surfing on me.








Miscellaneous thanks go to Negra, Avellanas, Little Hawaii, Grande, Langosta,

Roca Bruja, Dominical, Poof, Reggie, Scooter, Slugwood, barley, malt, hops, MSP,

Orifice, P-a-B Lounge, Chim Chim, Cindy Loftgreen, Holly Golightly, Brett Ashley

and Jake Barnes for keeping it all in perspective.











TABLE OF CONTENTS

page

A CK N O W LED G M EN TS .................................................................................... ii

LIST OF FIGURES ............................................................. vi

LIST O F TA BLES ............................................................ ........................... vii

A B ST R A C T ...................................................................................................... ix

CHAPTERS

1 INTRODUCTION

1.1 Introduction to Sedimentation
1.1.1 D definition ..................................................... ........................... 1
1.1.2 Environmental Impact .............................. .............. ............... 2
1.1.3 Study Objectives ............................................ ................................... 3
1.2 The Longboat Key Nourishment Project
1.2.1 Project Location ............................ .. ..................... 5
1.2.2 Project Specifications .......................................... 5
1.2.3 Project Schedule ............................................ 7
1.2.4 Monitoring Station Sites .................... ................... 8

2 METHODS

2.1 Introduction ........................................................................................ 11
2.2 Wave and Turbidity Packages
2.2.1 Peripheral Sensors .................... .... ................. 12
2.2.2 Sam pling Schem e ............................................... ....................... 14
2.2.3 Field C configuration ............................................. ........................ 15
2.3 Sediment Traps
2.3.1 Sedim ent Trap D esign Criterion ................................................... ... 17
2.3.2 O original Trap D esign ........................................ ........................ 19
2.3.3 Second Trap Design ..................... .......................................... 21
2.3.4 Final Trap Design ............................................. 24
2.3.5 Sediment Sample Analysis Procedure ............................................ 29







3 RESULTS

3.1 Introduction ........................................................................................... 31
3.2 Manual Turbidity Monitoring
3.2.1 Method ................... .. ............................ 31
3.2.2 M annual Turbidity Data ....................................... ....................... 32
3.3 Sensor Data
3.3.1 Sensor Deployment Schedule ..................................... ........... .. 36
3.3.2 O B S D ata ....................................................... ............................ 40
3.3.3 W ave D ata ...................................................... ............................ 42
3.4 Sedimentation Data
3.4.1 Sediment Trap Sampling Schedule ................................................. 47
3.4.2 Sedim entation Data ................................................................... 47

4 DISCUSSION

4.1 Introduction ........................ ......... .. ............................................ 56
4.2 Trendline and R-Squared Value Equations ............................................. 58
4.3 Significant Wave Height
4.3.1 Significant Wave Height Data ........................... ....... ............ 59
4.3.2 Significant Wave Height Sedimentation Relationship ................ 60
4.4 Maximum Horizontal Velocity
4.4.1 Maximum Horizontal Velocity Calculations ................................. 62
4.4.2 Maximum Horizontal Velocity Sedimentation Relationship .......... 64
4 .5 Sum m ary .................................................... ............... ................................ 68

5 SUMMARY AND CONCLUSIONS

5.1 Introduction ...................................................... .............................. 69
5.2 Summary
5.2.1 Monitoring Methods ......................... ................... 70
5.2.2 Monitoring Results ........................................... 70
5.2.3 Wave Force and Sedimentation Analysis ....................................... 72
5.3 Sediment Monitoring Requirements Recommendations ........................ 72
5.3.1 Standardized Sedimentation Monitoring ........................................ 73
5.3.2 Am ended Sam pling Schedule .................................... .... ....... .... 73
5.4 Suggestions for Further Investigation ............................ ........... 74

APPENDIX A: W AVE DATA PLOTS ......................................................... ... 76

APPENDIX B: SEDIMENTATION DATA ..................................... .... 111

R E F E R E N C E S ........................................ ............ ........................................ 146

BIOGRAPHICAL SKETCH ....................................................... 148













LIST OF FIGURES

Figure page


1.1 Nourishment location map ................... ........................................... 6

1.2 Time line of nourishment and monitoring activities ...................................... 8

1.3 M monitoring project location map ............................................... ............ 10

2.1 System I package field configuration ...................................... . ............ .. 16

2.2 System II package field configuration ...................... ................. .. 16

2.3 Original sediment station configuration .......................... .............. ........... 21

2.4 Sedim ent trap stand ............................................................. .................... 22

2.5 Second sediment station configuration .......................... ........ ........... .. 23

2.6 Final sedim ent trap design ................................. .... ........................ 25

2.7 Final sediment stand design ......................... ........ ................ 26

2.8 Final sediment station configuration .................... ................... .. 27

3.1 Time line of wave data coverage ....................................... .... 39

3.2 Average sand sedimentation rates, hard bottom vs. control ........................ 52

3.3 Average fines sedimentation rates, hard bottom vs. control ........................ 54

4.1 Sand sedimentation rate versus significant wave height ............................. 61

4.2 Fines sedimentation rate versus significant wave height ............................. 62

4.3 Sand sedimentation rate versus maximum horizontal velocity ................... 65

4.4 Fines sedimentation rate versus maximum horizontal velocity ................... 66











LIST OF TABLES


Tables p


1.1 Sedim ent characteristics ............................................................................ 7

1.2 M monitoring locations ...................................................... .......................... 9

2.1 Performance of sediment trap designs ............................................. ........... .. 29

3.1 Manual turbidity readings, during nourishment ............................................ 32

3.2a Manual turbidity readings, after nourishment ............................................ 33

3.2b Manual turbidity readings, after nourishment ............................................... 34

3.3 Average manual turbidity readings, during and after nourishment ................. 35

3.4 Summary of deployment activities .......................................... ... 37

3.5 W ave data availability summary ................................. ..... .... ....... ..... 38

3.6 Average wave data characteristics ........................................ .... 44

3.7 Average wave data characteristics .................................... .... 45

3.8 Maximum height and period for five storm events ...................................... 46

3.9 Sediment sampling deployment/retrieval schedule ...................................... 49

3.10 Average sand sedimentation rates ........................................................ 49

3.11 Average fines sedimentation rates .................................. ...... .............. 50

3.12 Average sand sedimentation rates, hard bottom vs. control ....................... 51

3.13 Average fines sedimentation rates, hard bottom vs. control ....................... 53

3.14 Average sedimentation rates before, during and after nourishment ............. 54

4.1 Significant wave height and sedimentation rates ...................................... 60








4.2 Maximum horizontal velocity and sedimentation rates ............................... 64

4.3 Trendline and r-squared values for sand sedimentation data ....................... 67

4.4 Trendline and r-squared values for fines sedimentation data ...................... 68














Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering

IMPACT OF LONGBOAT KEY NOURISHMENT ON HARD BOTTOM
SEDIMENTATION RATES

By

Darwin C. Stubbs

May 1995

Chairman: Daniel M. Hanes
Major Department: Coastal and Oceanographic Engineering


A sedimentation, wave climate and turbidity monitoring project was conducted

before, during, and after construction of the nourishment of Longboat Key, Florida.

This study attempts to evaluate the effects of the Longboat Key beach nourishment

on hard bottom sedimentation rates. The second objective of this study is to analyze

and evaluate the sedimentation monitoring methods employed at Longboat Key and

to propose a standard sedimentation monitoring procedure. This study describes the

monitoring methods, monitoring results, and analyzes the interaction between wave

activity and sedimentation.

Three sediment trap designs were employed and evaluated during the course of

this study. The final trap design and field configuration proved very effective. The

sturdy construction allowed for a 99% sediment sample retrieval rate. In addition, a








low relative standard deviation between the field replicates at each site indicates

representative sampling.

The results of the monitoring data shows two important facts. First of all, the

hard bottom sites of Longboat Key experienced larger wave conditions than the

control sites. Secondly, the hard bottom sites showed significantly larger sand

sedimentation rates than the control sites.

The analysis of the relationship between the wave parameters of significant

wave height and maximum horizontal water particle velocity and sedimentation rates

as measured by the sediment traps point out several interesting facts. Apparently, the

relationship between fines sedimentation and wave activity is fairly linear. However,

sand sedimentation seems to related to a power of wave activity. This analysis also

indicates that the wave parameter of maximum horizontal water particle velocity

offers the best correlation to both fines and sand sedimentation.

Finally, this study offers four recommendations. First of all, it is proposed that

the final sediment trap design and configuration employed in this study be adopted as

the standard wherever feasible. Secondly, it is recommended that in conjunction

with sedimentation, relative bed level measurements be obtained with the use of a

ruled post jetted at each monitoring site. Thirdly, the sedimentation monitoring

schedule should be amended so that sedimentation and wave climate monitoring

begins at least six months prior to nourishment and monthly sediment sampling

periods be maintained throughout the study. Finally, it is recommended that flow

studies be conducted on the existing trap configuration as well as a trap configuration

featuring staggered replicate heights.












CHAPTER 1

INTRODUCTION



1.1 Introduction to Sedimentation



1.1.1 Definition

Sedimentation can be defined as the precipitation of sediment in the water

column. The significant portion of the sediment in suspension is locally eroded from

the sea bed. As the sea bed is agitated by the hydraulic forces of waves and currents,

the sediment is entrained into the water column where it may be transported by these

same forces. Deposition occurs when these mobilized particles settle out of the

water column and back into the sea bed. The sedimentation rate as measured by a

sediment trap is the quantity of sediment per unit area that precipitates into a trap

over time. It may be important to point out that, in the context of this study, the

sedimentation rate is not a measure of accretion or net sediment accumulation but of

sediment flux. It accounts only for the sediment that settles onto an area, not the

subsequent transport of sediment away from an area.

One important byproduct of sedimentation is increased turbidity or the reduced

clarity of water due to the scattering and absorption of light by the suspended

particles. This is especially true of sediment with a high concentration of fine

material (Dompe, 1993).







1.1.2 Environmental Impact

Sedimentation directly affects the growth and survival of marine communities,

particularly the benthic organisms associated with reefs, such as the stony corals

prevalent in Florida. First of all, the activity of sediment removal greatly taxes

energies that are usually reserved for growth and reproduction. In extreme cases,

excessive sedimentation can smother and ultimately destroy the coral tissue.

Secondly, sedimentation increases turbidity which can greatly reduce the amount of

light that penetrates to the photosynthetic coral community. This light is vital to the

zooxanthellae plant cells that reside within the living tissue of the coral. These plant

cells provide the coral colony with nutrients and assist in the removal of waste. This

symbiotic relationship promotes rapid growth and the accretion the limestone

skeleton that support the coral polyps and serve as the foundation of the reef

environment (Dodge, 1987).

The rate of sedimentation is a result of both natural and human activities. The

most common natural events that may increase sedimentation are storms. The

intensified wave action associated with storms tends to suspend sediment into the

water column where it can be transported. Coral communities can contend with

these relatively short-lived, natural events. However, the long-term increase in

sedimentation associated with beach nourishment dredging projects may be far more

detrimental.

Beach nourishment activities involves dredging sand from a borrow site,

transporting and discharging the material to the nourishment site. Sediment

suspension and subsequent increases in turbidity are induced at the borrow site





3

where the sand is dredged by excavation and suction, and at the nourishment site

where the slurry is discharged. In some cases, there is substantial leakage of the

dredge pipeline that contributes to sedimentation as well. Studies have shown

reduced growth rates and mortality of coral communities as a result of beach

nourishment activities (Dodge 1987; Goldberg, 1988). In addition, there can be a

long term increase in sedimentation associated with beach nourishment projects.

Elevated levels of sediment activity are experienced until the nourished beach

eventually achieves an equilibrium profile.



1.1.3 Study Objective

In order to evaluate the environmental effects of beach nourishment projects,

the former Florida Department of Environmental Regulation (now the Department of

Environmental Protection) has established wave, turbidity and sedimentation

monitoring requirements. The results presented in this study represent a component

of the monitoring program for Longboat Key Florida. This program includes the

measurement of sedimentation of four offshore study sites along the nourishment

project and at three adjacent control sites. In addition, wave and turbidity

measurements have been monitored at two of the study sites and two of the control

sites. In accordance with the Department of Environmental Regulation nourishment

permit, sedimentation monitoring was conducted before, during and after

nourishment. Construction began in March, 1993 and concluded in August, 1993

and the monitoring program began in November, 1992 and concluded in August,

1994.





4

The environmental impacts of sedimentation associated with beach

nourishments is a relatively new consideration and monitoring has taken place only

since the past decade (Goldberg, 1988). Thus, the monitoring process is still in an

evolutionary state; as new knowledge of environmental impact becomes available,

monitoring requirements are amended or broadened. Currently, this requirement is a

very general provision.

The sedimentation monitoring schedule, collection methodology, analysis

methodology, and results presentation is outlined in the second section of the

monitoring requirement of the Longboat Key nourishment permit. This section lists

four stipulations. First of all, sedimentation in milligrams (dry weight) per square

centimeter per day are to be measured every 30 days for a 90 day period prior to

construction and every 30 days during construction and every 60 days for one year

after construction. Secondly, these dry weight measurements are to be stratified

according to the fines portion and the sand portion. Thirdly, three replicates shall be

sampled at each site. Finally, "the methods used to collect and analyze the

sedimentation rates can be any scientifically viable procedure" (Department of

Environmental Regulation, 1992, p. 12) subject to approval from the Bureau of

Wetland Resource Management prior to monitoring. It is apparent that the required

method of sediment collection and analysis lacks specific instruction.

The focus of this study is to analyze the sedimentation monitoring of the

Longboat Key nourishment project and to evaluate the existing Department of

Environmental Regulation monitoring guidelines. This will include an examination

of the performance of the of the sediment trap design, the sediment analysis





5

procedure, and the resulting data analysis methodology incorporated in the Longboat

Key monitoring project. These findings will be utilized to judge the feasibility of the

requirements of the Department of Environmental Regulation. Finally,

sedimentation monitoring recommendations will be presented. This evaluation may

lead to a standardized method to obtain and analyze sedimentation rates.



1.2 The Longboat Key Nourishment Project



1.2.1 Project Location

The DER issued permit number 41 & 581938039 June 18, 1992, to nourish the

coastline of Longboat Key, Florida. The nourishment construction contract was

granted to Applied Technology and Management, Inc. The entire length of the Gulf

Coast town of Longboat Key, Florida, was nourished in the Spring and Summer of

1993. Longboat Key is a barrier island on the Gulf of Mexico that stretches

approximately ten miles along the west coast of Florida. It is located south of St.

Petersburg and Tampa Bay as shown on the following page in figure 1.1.



1.2.2 Project Specifications

The nourishment permit was issued on June 18, 1992, construction began on

February 28, 1993, and construction ended on August 12, 1993. One million, one

hundred and sixty thousand cubic yards of material from the New Pass ebb-tidal

shoal at the south end of Longboat Key nourished the south beach, from DNR

monument R-13 south to R-29B, near the terminal groin at the southern tip of the





6

island. One million, six hundred and fiflty thousand cubic yards of material from the

Longboat Pass ebb-tidal shoal at the northern end of Longboat Key was

hydraulically excavated for the nourishment of the north beach, from monument R-

47 south to R-13. These DNR monuments are marked on figure 1.1. This represents

9.28 miles of beach front nourishment (ATM, 1994).


Longboat Pass


R-47


Longboat


R-12


R-29B -6-
New Pass


Figure 1.1: Nourishment location map





7

The New Pass borrow site consisted of material with a mean grain size of .22

mm which was placed on the south beach with a native mean grain size of .19 mm.

The Longboat Pass borrow site consisted of material with a mean grain size of .19

mm which was placed on the north beach with a native mean grain size of .21 mm.

This is summarized in table 1.1 (ATM, 1994).



Table 1.1: Sediment characteristics

Location Mean Sorting,
Diameter (mm) )
Longboat Pass Borrow Site 0.19 0.78
Native North Beach 0.21 0.57
New Pass Borrow Site 0.22 1.52
Native South Beach 0.19 1.20


1.2.3 Project Schedule

The nourishment project was completed in two stages. The first stage

consisted of the nourishment of the southern portion of the island from DNR

monument R-29B, beginning on February 28, moving north and ending at monument

R-12 on May 2, 1993. The second stage consisted of the nourishment of the northern

portion from DNR monument R-47, beginning on May 3, moving south and ending

at monument R-12 on July 12, 1993. This was followed by spot refills which ended

on August 12, 1993.

In accordance with the nourishment permit, a sedimentation and turbidity

monitoring project was implemented at the end of October of 1992, coinciding with

the subsequent nourishment of Longboat Key in March of 1993. Sedimentation and







manual turbidity monitoring began 90 days prior to nourishment and continued for

one year after the completion of nourishment. Turbidity and wave climate

monitoring began after the completion of nourishment and continued for one year

thereafter. Figure 1.2 is a time line of these activities.



10/25/92 2/28/93 8/12/93 1/1/94 8/12/94

Nourishment
Sedimentation Monitoring
Manual Turbidict Monitoring
Wave and Turbidity Monitoring

4/7/93 8/25/93


Figure 1.2: Time line of nourishment and monitoring activities



1.2.4 Monitoring Station Sites

The monitoring locations include four stations at hard bottom sites along

Longboat Key and control stations on adjacent Siesta Key, Anna Maria Island and

Long Key. Presented below in Table 1.2 are the names, locations and mean lower

low water depths of each site.

Sedimentation is monitored at all seven of these locations through the use of

sediment traps mounted to the ocean bottom. Turbidity and wave climate are

monitored at the Long Key and Siesta Key control sites and the Longboat Key #34

and Longboat Key #2 hard bottom sites. This is accomplished through the use of

electronic instrument packages mounted to the ocean bottom. Figure 1.3, on the





9

following page, is a map of the monitoring sites and the equipment deployed at the

respective sites.


Table 1.2: Monitoring locations


Site NAD System Latitude Longitude Depth
Siesta Key SK 1064582 N, 476646 E 27"15'40" N 82033'09" W 4.6 m
Longboat Key #6, LBK6 1111215 N, 446697 E 27023'21" N 82o38'43" W 4.5 m
Longboat Key #2, LBK2 1112927 N, 445498 E 27023'38" N 82038'57" W 5.6 m
Longboat Key #43, LBK43 1123050 N, 436808 E 27025'28" N 82040'34" W 4.6 m
Longboat Key #34, LBK34 1123256 N, 436055 E 27025'19" N 82040'42" W 5.3 m
Anna Maria Island, AM 1156367 N, 420896 E 27030'47" N 82043'33" W 4.6 m
Long Key, LK 1227089 N, 415328 E 27042'27" N 82044'39" W 4.5 m









NORTH Long Key
NORTH Lo
LK O0





Tampa Bay

6?


Anna Maria


Figure 1.3: Monitoring project location map


* Sediment Station
0 Instrument Package















CHAPTER 2

METHODS



2.1 Introduction



This chapter will focus on the measurement methodologies incorporated in

obtaining the wave climate, turbidity and the sedimentation data. The wave climate

and turbidity measurements were collected through the use of self-contained, in-situ

electronic packages. These packages were equipped with a nephelometer, a pressure

transducer, and in some cases, a current meter. Sediment traps were employed to

obtain the sedimentation measurements.

A description of the wave and turbidity packages and the sediment traps will

be presented in this chapter. The wave and turbidity package will be examined first.

This examination will include an explanation of the package sensors, sampling

scheme and field configuration. This will be followed by a detailed description of

the sediment trap design, field configuration and sediment sample analysis. As

previously stated, sedimentation monitoring is a relatively new nourishment permit

requirement and there are no standardized collection or analysis procedures. Thus,

the sediment trap utilized in this project was a new design and will be emphasized.








2.2 Wave and Turbidity Packages

The wave and turbidity packages are based on a previous design that has been

successfully utilized in past projects, specifically the 1991 Hollywood renourishment

(Dompe, 1993). The instrument package consists of a watertight PVC body and the

peripheral sensors. The body houses the battery pack, sensor circuitry, and the data

logger, which controls the sampling scheme and data storage. Two instrument

package designs were employed in the turbidity and wave climate monitoring, the

system I and system II. The peripheral sensors of the system I consist of two

nephelometers, a pressure transducer, and a current meter. The peripherals of the

system II package consists of one nephelometer and a pressure transducer. These

peripherals, as well as the package sampling scheme and field configuration will be

described in this section.



2.2.1 Peripheral Sensors

The peripheral sensors will be described in this section. This will include only

a brief explanation of the physical measurement principles of the instruments and

calibration methods. The analog voltage signals of these instruments are converted

to a digital bit signal and saved on an Onset Computer Corporation Tattletale data

logger.

The two system I nephelometers used to measure turbidity are OBS-1 Optical

Backscatterance Sensors manufactured by Downing and Associates. The system II

nephelometer is the OBS-3 Optical Backscatterance Sensors manufactured by








Downing and Associates as well. The OBS-1 and OBS-3 models operate under the

same principles which will be briefly discussed. These instruments will be

collectively referred to as OBS. OBS is an optical sensor that measures turbidity by

detecting infrared radiation scattered from suspended matter in the water column (D

& A Instrument Company, 1991). A diode in the center of the OBS face emits

infrared light and photo diodes, which comprise the remaining portion of the OBS

face, and detect the infrared light that is reflected or backscattered from the particles

in the water. The use of infrared light prevents significant signal degradation due to

the interference of sunlight (Dompe, 1993).

Calibration of the OBS is performed by relating the signal outputs of a sensor

in formazin solution samples to the known turbidity levels of the samples. The

turbidities of the formazin solution samples, measured in nephelometric transmission

units (NTU), are determined through the use of a portable nephelometer

manufactured by H-F Scientific, model DRT-15C. The relationship between the

OBS signal and the NTU turbidity level is linear and easily derived.

Wave climate is measured through the use of a Transmetrics P-21 pressure

transducer. The transducer measures total pressure through the varying resistance of

a strain gauge. Incorporating linear wave theory, this pressure data yields wave

amplitude, wave period, and tidal oscillations. Calibrations are performed by

comparing the transducer signal to known values of pressure by using a compressed

air source and by immersing the packages in a cylinder of water at varying depths.

This is a simple linear relationship as well.







Currents are measured using a Marsh McBimey electromagnetic current meter

which operates on the Faraday principle of electromagnetic induction. The

movement of seawater, a conductor, in the magnetic field induced by the current

meter produces a voltage which is proportional to the velocity of the sea water.

Calibration of the current meter is performed periodically by Marsh McBirney.



2.2.2 Sampling Scheme

The system I package was programmed to sample at one hertz for 1024

seconds every two hours. Data files generated by the four sensors are downloaded to

the data logger every twenty-four hours. These packages are equipped with the

Onset Computer Corporation model TT6 data logger with a 20 megabyte hard drive.

With this sampling scheme, the TT6 data logger is capable of storing one hundred

days of data. However, the 12V power source which drives the system I must be

renewed approximately every six weeks.

The system II package sampled at one hertz for 512 seconds every two hours.

These packages utilized the model TT4 data logger which is equipped with over one

megabyte of RAM. This represents a storage capacity of almost 60 days. The

system II was also powered by a 12 V battery pack but only required to be renewed

approximately every three months.

Field visits to download the data and change batteries, if necessary, were

scheduled every four to six weeks.








2.2.3 Field Configuration

As stated earlier, the wave and turbidity packages were deployed at four of the

seven monitoring sites. System II packages were employed at the Long Key and

Siesta Key control sites and at the Longboat Key #34 study site. A system I package

was primarily used at the Longboat Key #2 study site. In cases when the system I

was not available, due to maintenance requirements or field damage, a system II was

deployed at Longboat Key #2. The packages at these four monitoring sites were

supplied from a pool of four system II packages and two system I packages. This

allowed for a spare system II and a spare system I package.

These packages are mounted to steel frames which are secured to the sea bed.

This frame consists of two pipes which are jetted vertically, approximately eight feet,

into the sea bed and connected by a horizontal cross bar at the surface of the bed.

Mounting collars secure the package to the cross bar. The sensors are attached to the

jetted pipe that extends approximately five feet out of the sea bed.

In the system I configuration, the two OBS face opposite each other,

approximately five feet from the sea floor. The pressure transducer and current

meter is mounted approximately three feet and five feet from the sea floor,

respectively. Figure 2.1 illustrates the system I configuration.

In the system II configuration the OBS is mounted approximately five feet

from the sea floor and the pressure transducer is mounted to the lid of the package

body, approximately 2 feet from the sea floor. The exact heights are recorded during

each deployment. Figure 2.2 illustrates the system II configuration.






















PVC body


current meter




OBS -






pressure transducer


support frame


Figure 2.1: System I package field configuration



OBS






pressure
transducer


support frame


PVC body


Figure 2.2: System II package field configuration








2.3 Sediment Traps

Sediment traps were used to collect suspended sediments at a fixed point in

space over a period of time. The use of sediment traps as a permit requirement is a

relatively new development. Thus standardized sample collection or analysis

methods have yet been formulated. However, sediment traps have been used in the

natural science fields since the turn of the century and, in limited cases, in

engineering applications. In the case of the natural sciences, these time integrated

samplers, also referred to as settling chambers, are employed primarily to sample

settling or suspended particulate matter (SPM) which includes bioseston as well as

sediment (Rosa et al., 1991). In the limited cases of engineering applications,

sediment traps have been utilized in sediment transport studies, predominantly in

streams and reservoirs. Due to their prevalence, many studies have been conducted

to test the performance of sediment trap design (Rosa et al., 1991). The design of our

sediment traps are based on the results of these studies. The design process and

various sediment trap designs as well as the sediment sample analysis method will be

presented in the following sections.



2.3.1 Sediment Trap Design Criterion

The objective of a sediment trap is to obtain a representative sample of

downward settling sediment. The downward sediment flux can be calculated from

this sample. Two conditions are required to accurately measure settling flux using a

sediment trap. First of all, the sediment concentration at the mouth of the trap must








be identical to that outside of the trap mouth. In other words, the trap design should

not induce flow dynamics that would alter the sediment concentration at the mouth

of the trap. This can lead to a increased or decreased probability that sediment will

be trapped. Secondly, sediment that has collected in the trap must not be

resuspended by turbulent flow conditions at the mouth and expelled. Simply stated,

sediment that accumulates in the trap must be retained.

Extensive testing has indicated that traps which meet these two requirements

most effectively are cylindrical traps with an appropriate aspect ratio

(length:diameter). In flowing, turbulent waters the aspect ratio must be at least 5:1

(Bale, 1993). Another important criteria is a trap diameter of at least five

centimeters. Traps with a smaller diameter may undertrap small dense particles and

overtrap large, less dense particles (Rosa, 1991). Finally, in the case of replicate

traps, the field configuration must not cause significant flow interference between the

traps at a given site. This interference can cause the sediment concentration at the

mouth of one or more of the replicates to differ from local sedimentation conditions.

We imposed two other design requirements to meet the demands of the field

conditions encountered in beach nourishment projects. The first requirement is a

design that facilitates efficient and timely installation and removal as divers are often

subject to adverse weather conditions and low visibility. The second requirement is

a design of sturdy construction to withstand storm-induced wave forces in shallow

waters.








In summary, four important sediment trap design criteria must be met to

facilitate representative replicate sampling: 1) the trap tube must be cylindrical, 2)

the aspect ratio of the trap tube must be at least 5:1, 3) the trap mouth must have a

diameter greater or equal to 5 cm, and 4) the field configuration of the replicates

must not cause concentration interference between the traps. In addition, the field

configuration of the sediment traps should comply with two general requirements:

1) the field configuration must allow for easy trap retrieval and replacement and 2)

be of sturdy construction. An evaluation of the two interim trap designs and the final

trap design, based on the criteria outlined above, will be presented in the following

sections.



2.3.2 Original Trap Design

The original sediment traps, designed by Applied Technology and

Management, Inc., were deployed in the end of October of 1992. This design

consists of a 1.5 inch (3.81 cm) inner diameter, schedule 40 PVC trap tube attached

to a 1000 ml nalgene sample bottle. The length of the trap tube is approximately

30.5 cm and is fastened to the mouth of the sample bottle with a rubber coupling

equipped with stainless steel hose clamps. Three of these traps rest on a flat,

triangular PVC stand which is secured to a 2 inch ( 5.08 cm) inner diameter

aluminum post. The aluminum mounting post is hydraulically jetted approximately

eight feet into the sea bed. The traps sit on the PVC stand and are fastened to the

post with tie-wraps around each of the sample bottles. The mouth of the trap tube is








between three and four feet from the sea bed. Figure 2.3 illustrates the configuration

of this sediment station.

A sediment trap is replaced in the following manner: 1) the tie-wraps around

the sample bottle are cut, 2) the hose clamp on the rubber coupling which fit over the

mouth of the sample bottle is loosened, 3) the sample bottle is carefully detached

from the trap tube and rubber coupling and the sample bottle is immediately capped,

4) the trap tube and rubber coupling is fitted over the mouth of a new sample bottle

and the hose clamp is tightened, and 5) the new trap is resecured to the mounting

post with tie-wraps.

This design and field configuration presents four problems. First of all, the

trap tube diameter violates the minimum diameter criteria. Secondly, the close

proximity of the replicate traps to each other and the mounting post is sure to

significantly disrupt the flow pattern. Thus, this configuration may cause

interference between the samples. Thirdly, the sample retrieval and replacement

process is far to complicated. Field reports show that it requires two divers up to

twenty minutes to perform the replacement. Finally, this configuration is far too

unstable. Often sediment traps would be lost in the field and, in fact, the entire

samples for one sampling period were lost. This design experienced a sediment

sample retrieval rate of only 59% over three deployments. The remaining samples

were lost in the field. At the start of the fourth sampling period, March 6, 1993, a

new design was implemented.






















nalgene
sample bottle



PVC stand


E- PVC trap tube






rubber coupling
tie-wrap







. mounting post


_____ I I


Figure 2.3: Original sediment station configuration



2.3.3 Second Trap Design

The second trap design features two new changes to the original. The trap

tubes are 2 inch (5.08 cm ) outer diameter copper tubing and the traps rest on an

aluminum stand which is fastened to the mounting post. This stand design is

illustrated in figure 2.4.








The sediment trap stand consists of a flat circular platform welded to one end

of a section of 2.5 inch (6.35 cm) inner diameter pipe which acts as a shaft. A flat

circular plate with three 2.5 inch (6.35 cm) diameter circles cut out acts as the trap

tube guides and is welded to the other end of the shaft.


trap guide


platform


set bolt '

Figure 2.4: Sediment trap stand


The samples bottles sit on the platform and are secured to the shaft with tie-

wraps. The trap tubes extend through the guide holes on the top plate. The shaft fits

over the mounting post and is secured by two set bolts on each end of the sediment

trap stand. This configuration is illustrated in figure 2.5.








This configuration offers two improvements to the original design. The trap

tube diameter is larger and the traps are far more secure. This design was utilized for

only one sampling period, from March 6 to April 7, 1993, during which time Florida

experienced a hundred year storm. Despite these harsh conditions, fifteen of the

twenty-one samples were retrieved. This represents a 71% retrieval rate.


set bolt
=---


nalgene
sample bottle


trap stand


copper tube


Rubber coupling




- -- tie-wrap


- -1 mI -


- mounting post


Figure 2.5: Second sediment station configuration








However, despite the improvements, two original shortcomings remain. The

trap tubes are still in close proximity to each other, potentially interfering with the

sampling within a sediment station. In fact, the presence of the sediment stand may

contribute to this as well. In addition, the sediment trap retrieval and replacement

steps are identical to the original configuration. Thus, this process still requires

substantial diver down time. By the fifth deployment beginning April 7, 1993, the

final sediment station was designed and implemented.



2.3.4 Final Trap Design

The final sediment trap and configuration is drastically different from the

previous two designs. The sediment trap is composed entirely of two inch (5.08

cm)inner diameter, schedule 40 PVC. The trap consists of two parts, the tube and the

canister as illustrated in figure 2.6. The suspended sediment travels down the tube

and settles in the canister. The trap tube is 46 cm in length and equipped with a

female adapter on one end. This connects to the male adapter on top of the trap

canister. The canister is 15 cm in length and is sealed with and end cap at the

bottom.

In the field, the canister is attached to the trap tube. During replacement the

entire trap is removed and a new trap is installed. The canister is unscrewed from the

tube at the lab when the sediment sample is to be analyzed.










trap tube



46 cm





!-- female adapter

-- male adapter

canister 15c
15 cm

S -- end cap



Figure 2.6: Final sediment trap design



The final sediment trap stand consists of four, six inch sections of 2.5 inch

inner diameter, aluminum pipes arranged in a tripod configuration. This design is

illustrated in figure 2.7.

The center pipe section acts as the shaft which fits over the mounting post and

is secured by two set bolts. Three aluminum plates extend the remaining pipe

sections 11.4 centimeters from the shaft. These sections act as trap holders. The

sediment trap slides into the holder and is secured with two set bolts. This final field

configuration is illustrated in figure 2.8.









K trap holder

11.4 cm


O 6.35 cm

Asset bolt

top view





20.3 cm 15.2 cm


side view



Figure 2.7: Final sediment stand design



Two trap replacement procedures were considered for this new design. The

first alternative was to replace the canisters in the field. This would entail

unscrewing the canisters from the trap tube and screwing on a new canister. The

second alternative was to simply replace the entire trap, the tube and canister, as one

piece. The latter procedure was adopted for two reasons. First of all, the biofouling

in the study area was much more severe than anticipated. Thus, to prevent growth on

the traps, particularly the inside of the tubes, the traps were painted with anti-fouling

paint after each sampling period. If the trap tubes were to remain in the field for

extended periods the fouling would significantly decrease the effective diameter.








Secondly, the act of unscrewing the canisters would resuspend the sediment sample

and increase the chances of sediment loss during the replacement. Therefore, sample

replacement was performed in the following steps: 1) the set bolts on the holder are

loosened and the entire trap is pulled out and immediately capped with a PVC end

cap and 2) the new trap is inserted into the holder and the set bolts are tightened.


aluminum
stand


set bolt


PVC tube











--- PVC canister






mounting post


Figure 2.8: Final sediment station configuration








It is evident that this final configuration meets all four design criteria. The

inner diameter of the trap tube is two inches or 5.04 centimeters and the aspect ratio

is 9:1. The potential of sample interference is reduced due to the greater distance

between the replicate traps. In addition, the two field requirements are met.

Replacement of the sediment traps in this new configuration is much simpler than the

former designs. It can be executed by two divers in almost five minutes. This

configuration also proved far more sturdy than the previous designs. A 99% retrieval

rate was accomplished with this new design.

Table 2.1 summarizes the performance of the three sediment trap designs. For

each design the average relative standard deviation between replicates and sample

retrieval rates are given as well as the number of sampling periods in which these

statistics were calculated.

The relative standard deviation is calculated by taking the standard deviations

of the replicates at a site and dividing by the average rate of sedimentation. This can

be seen as a measurement of the flow interference between replicates. For instance,

large values of standard deviations suggest that the flow induced by the sediment trap

configuration may be interfering with the sediment concentration at the mouth of

adjacent replicates.

It is evident from table 2.1 that the final trap design and configuration

performed the best.








Table 2.1: Performance of sediment trap designs

Relative Standard Deviation Retrieval Sampling
Design Sand Fines Rate Periods
Original 0.28 0.27 59% 2
Second 0.13 0.15 71% 1
Final 0.13 0.15 99% 14


2.3.5 Sediment Sample Analysis Procedure

Once the samples are retrieved they are sterilized with mercurium (HgC12) to

prevent biological growth during transport to the lab. The sample is analyzed in a

lab to determine dry weight of the sand portion, dry weight of the fines portion, and

organic weight. This method follows accepted sediment testing guidelines (Mudroch

et al., 1991) and is outlined below:

1) The cap is removed from the trap tube and the water above the canister is

carefully removed using a vacuum pump. The trap tube is unscrewed from

the canister.

2) All of the contents of the canister is washed onto a 63 micron sieve for wet

sieving. The sieve is seated onto the lid of a receptacle so that the water and

fines that pass is retained.

3) The sample in the sieve is gently brushed until the mixture of fines and

water passes through the sieve.

4) The remaining sand contents of the sieve is carefully washed into a labeled

and tared drying tin.

5) The sand sample is dried in an oven at 110' C.








6) The weight of the dried sand sample is recorded. This represents the dry

weight of the sand sediment and organic of the sand portion of the sample.

7) The remaining portion of fines and water that passed through the sieve is

washed into a labeled container and allowed to settle for 24 hours.

8) Once the fines have settled, the excess water in the container is removed

using a vacuum pump.


9) The fines portion is carefully washed into a labeled and tared drying tin and

dried in an oven at 1100 C.


10) The weight of the dried fines sample is recorded. This represents the

dry weight of the fines sediment and organic of the fines portion of the

sample.


11) The dried sand sample is ashed in and oven at 5000 C for two hours.


12) The ashed weight of the sand sample is recorded. This represents the

dry weight of the sand sediment portion of the sample.


13) The dried fines sample is ashed in an oven at 5000 C for two hours.


14) The ashed weight of the fines sample is recorded. This represents the

dry weight of the fines sediment portion of the sample.













CHAPTER 3

RESULTS



3.1 Introduction

The results of the manual turbidity measurements, electronic sensor

instrumentation, and sediment trap data will be presented in this chapter. The

manual turbidity readings will be presented first. This will be followed by a

discussion of the sensor data. This will include the package deployment schedule,

data processing methods, and a presentation of the processed data. A similar

treatment of the sediment data will follow. This examination will include the

sediment sampling schedule and the presentation of the sediment data.

This chapter serves to present all of the data collected from the Longboat Key

monitoring project. These results will be evaluated to determine the effects of the

nourishment on hard bottom sedimentation rates.



3.2 Manual Turbidity Monitoring



3.2.1 Method

Manual measurements of turbidity were obtained during each field trip. Divers

obtained a water sample near the surface, mid-depth, and near the bottom of the








water column. The surface and bottom samples were obtained approximately two

feet from the surface or bottom. The water samples were then sub-sampled on board

the boat and inserted into an H-F Scientific Model DRT-15C portable turbidometer

for measurement.



3.2.2 Manual Turbidity Data

Table 3.1 provides the results of the manual turbidity readings obtained during

nourishment. These turbidity values are all well within the critical 29 NTU criterion.

These values seem reasonably low for the nourishment activity that was ongoing

during this period. It should be noted however, that this table represents only three

separate sampling dates.



Table 3.1: Manual turbidity readings (NTU), during nourishment

DATE level SK LBK6 LBK2 LBK43 LBK34 AM LK AVG
4/7/93 bot. 8 3.2 10.5 10.5 6.8 3.6 7.5 7.2
5/1/93 surf. 5.0 4.9 2.5 3.0 2.1 3.5
..m .......... . . ..................4 .................. .. ................. .... ................. .......... ....................... ....................... ..... .. ...
mid 4.9 4 2.9 1.6 1.3 2.9
bot. 3.6 3.4 1.9 2.2 1.9 2.6
7/14/93 surf. 1.9 5.2 9.1 4.7 5.4 2.5 2.8 4.5
.............. ....................... ....................... ....................... ....................... ....................... ........................ ....................... ........... ....
mid 3.4 9.7 15.3 5.4 5.8 2.4 5.6 6.8
bot. 6.5 9.3 16 5.5 9.3 2.3 7.2 8.0
surf. 3.5 5.0 5.8 3.9 3.8 2.5 2.8 4.0
Mean mid 4.2 6.9 9.1 3.5 3.6 2.4 5.6 5.0
bot.. ... 5. ......5 6.1 6.0 3.0 7...............2. ......... ........
______bo. 60 .3 .5 6.1 &6. 30 7.4 6.2








Tables 3.2a and 3.2b show the manual turbidity readings after completion of

the nourishment. In most cases, these turbidity samplings were obtained over the

course of several days so the dates given in Tables 3.1, 3.2a and 3.2b are the first day

of each of the samplings. Table 3.2a presents the manual turbidity readings after

completion of the nourishment from 9/29/93 to 3/22/94.



Table 3.2a: Manual turbidity readings (NTU), after nourishment
(9/29/93 3/22/94)

DATE level SK LBK6 LBK2 LBK43 LBK34 AM LK AVG
9/29/93 surf. 4.9 1.8 4.1 5.1 3.8 4.0
mid 4.8 2.4 1.6 5.7 5.8 4.0
bot. 4.8 2.5 2.7 13.3 8.5 6.4
10/23/93 surf. 2.8 1.8 8.7 4.5
...... ... ........... ......... ................................. ....... ............................... .... .......... ......... .... .................... ....................... ....... ................
mid 3.2 3.3 8.8 5.1
___bot. 3.1 3.0 .. 8.1 .......4.7
11/10/93 surf. 14.1 3.3 3.7 3.9 4.0 9.2 8.9 6.7
mid 15.3 4.2 4.1 5.9 22.2 19.0 15.6 12.3
___ bot. 24.9 5.7 8.3 6.3 5.5 33.8 23.1 15.4
11/30/93 surf. 5.3 2.0 2.7 12.0 5.5
mid 5.9 2.0 2.3 13.0 5.8
bot. 6.0 3.2 2.8 15.5 6.9
12/22/93 surf. 22.9 5.5 16.3 14.9
... .......... .............................................................................................................. ....... ........ .................................... ....... .... .. .. ...
mid 23.2 5.8 27.9 19.0
___ bot. 30.9 17.2 60.3 36.1
12/29/93 surf. 2.1 3.4 3.8 3.0 3.5 3.2
mid 2.2 3.0 2.7 2.9 4.3 3.0
bot. 2.6 3.1 4.7 3.8 5.2 3.9
1/11/94 surf. 5.3 2.4 3.9
mid 4.3 4.3 4.3
... ....................... ....................... .......I.4. 5.......... ....................... ....................... ....................... ........I. 4. .. ....... ...... ............
bot. 14.5 __ 14.5 14.5
2/16/94 surf. 2.7 2.1 1.6 1.2 2.0 4.1 2.8 2.4
mid 3.5 2.1 3.0 2.1 1.4 4.2 7.2 3.4
..b .. ........ ... ................ ............. 9" ........ ........ ...... .... ........... ........ 5.......... ......... .... ........ ...
bot. """10.4 3.1 9.6 2.5 29.6 5.1 10.8 10.2
3/22/94 surf 1.1 4.2 0.7 1.8 1.7 3.0 3.1 2.2
mid 1.9 3.2 1.9 2.5 1.0 4.5 2.0 2.4
bot. 3.4 3.5 7.5 3.2 1.3 1.9 13 4.8








The remainder of the post nourishment turbidity measurements are presented in

table 3.2b, the manual turbidity readings from 4/16/94 to 8/13/94. The last row in

table 3.2b represents the averages of the entire set of post nourishment turbidity

readings from 9/29/93 to 8/13/94.



Table 3.2b: Manual turbidity readings (NTU), after nourishment
(4/16/94- 8/13/94)

DATE level SK LBK6 LBK2 LBK43 LBK34 AM LK AVG
4/16/94 surf. 1.9 2.5 1.1 1.6 1.2 3.7 2.5 2.1
mid 1.5 2.2 1.4 2.5 1.9 5.8 3.1 2.6
bot. 2.6 2.9 4.9 2.7 2.1 8.0 3.7 3.8
4/30/94 surf. 1.5 1.2 1.4
mid 3.1 1.8 1.3 1.9 1.5 1.2 2.2 1.9
bot. 3.4 2.1 1.3 6.3 1.8 4.1 9.8 4.1
5/14/94 surf. 1.2 0.7 0.9 0.8 0.7 8.7 2.5 2.2
........ ........ .... .......... ......... .... ......... ............. .......... ............. .......... ........ ..... .................... ....... .. ............................ ......
mid 3.5 0.8 0.9 0.9 1.3 1.2 3.3 1.7
bot. 6.2 1.1 1.2 1.8 1.1 1.1 4.7 2.5
6/11/94 surf. 11.2 3.1 7.5 3.5 4.2 5.0 3.7 5.5
mid 12.0 4.2 9.2 4.9 3.9 5.1 3.7 6.1
bot. 12.0 7.3 1.4 5.3 7.0 6.5 4.6 6.3
6/29/94 surf. 5.4 0.9 1.2 1.4 1.6 2.1 3.1 2.2
............. ....................... ....... .... ....................... ........ .... ........... ........ .... ........... ....................... ............... ..... .. .....
mid 6.5 1.0 1.6 1.5 1.7 2.3 3.1 2.5
bot. 7.1 1.9 1.6 1.5 2.6 4.1 9.8 4.0
7/16/94 surf. 1.3 1.8 2.2 1.4 1.1 2.5 3.1 1.9
mid 1.2 1.7 2.2 1.5 1.5 2.7 3.6 2.1
__ bot. 1.8 2.1 2.7 1.7 1.9 3.4 4.6 2.6
8/4/94 surf. 1.2 0.8 1.6 1.3 1.4 1.4 3.7 1.6
mid 1.1 0.7 1.2 1.8 1.7 2.3 4.1 1.8
bot. 1.5 1.4 1.5 2.0 1.9 2.6 8.5 2.8
8/13/94 surf. 1.7 1.2 1.3 1.7 1.5 4.4 1.5 1.9
... ........... .... ................. ... ...............3^ ................. ... .... .............. ..... ..-.. ........ 8... ... .............. .... ... .......... .. ......
mid 1.8 1.2 1.5 1.2 1.2 8.1 1.5 2.4
bot. 1... 9 ....... ..... 4 1... 5 ....... ... 3 .....4 ...... 8.3 2.0 ............. ...
surf. 3.4 1.4 2.2 1.3 3.6 3.3 4.2 3.9
AVG mid 4.0 1.5 2.5 1.7 4.7 4.0 5.9 4.7
bot. 5.4 2.1 4.1 2.3 6.2 6.4 11.4 7.7








The data in tables 3.2a and 3.2b indicate that, on the whole, the manual

turbidity readings are relatively low compared to the 29 NTU standard. It must be

noted here that these turbidity values represent discrete measurements and that this

sampling cannot be considered random. These manual turbidity samples were taken

only when weather permitted. Obviously weather is a very significant forcing

mechanism for turbidity. Thus, in all likelihood, these values underestimate actual

time-average turbidity levels.

Table 3.3 shows the average manual turbidity readings for hard bottom and

control sites and presents the ratio of hard bottom to control turbidities (HB/Con) for

the nourishment and post nourishment periods.



Table 3.3: Manual turbidity readings (NTU), during and after nourishment

level Hard Bottom Control HB/Con
During surf. 4.6 2.9 1.6
Nourishment mid 5.8 4.0 1.5
bot. 7.5 5.5 1.4
After surf. 2.8 4.4 .64
Nourishment mid 3.2 5.5 .58
bot. 4.4 9.2 .48


Table 3.3 clearly illustrates three facts. First, the turbidity at the hard bottom

sites was larger than at the control sites during nourishment. Secondly, the turbidity

at the hard bottom sites decreased significantly after nourishment. Finally, the








turbidity of the hard bottom sites was significantly less than the control sites after the

nourishment. These average values are based on seventeen sampling dates.



3.3 Sensor Data



3.3.1 Sensor Deployment Schedule

The field servicing schedule for the instrument packages is dependent

primarily on their battery and data storage capacities. In the case of the system I

packages, servicing entails removing the original package for data offloading, battery

replacement, recalibration, general cleaning, and installing the spare system I

package. Due to the battery limitations of the system I, this rotation must be

performed every four to six weeks. However, the batteries of the system II package

require renewal only every three months. The limiting factor of the system II is the

memory capacity, which is filled approximately every six weeks. Data offload can

be performed in the field via a communications cable. Thus, in the case of the

system II packages, servicing would include general cleaning and data offloading in

the field approximately each month. Removal for battery replacement and

recalibration was required every third month.

The initial instrument package deployment began August 25, 1993. The

preliminary plan was to schedule field servicing every month thereafter. However,

due to severe biofouling and unforeseen package damage, the deployments were

interspersed as conditions demanded. This is illustrated in Table 3.4, a summary of








the instrument package deployments. The biofouling on the face of the OBS was

especially troublesome. It served to block out the OBS signal in a matter of days in

some cases. This problem will be discussed in greater detail in section 3.3.2.



Table 3.4: Summary of deployment activities

DATE SK LBK2 LBK34 LK
8/25/93 installed installed installed installed
9/29/93 offloaded replaced offloaded offloaded
10/23/93 offloaded replaced offloaded replaced
11/10/93 removed replaced removed removed
11/30/93 installed replaced installed installed
12/22/93 cleaned cleaned cleaned cleaned
1/11/94 replaced removed removed removed
2/16/94 replaced installed installed installed
3/22/94 removed replaced replaced replaced
4/15/94 cleaned cleaned cleaned cleaned
4/30/94 replaced replaced offloaded offloaded
5/14/94 cleaned replaced cleaned cleaned
6/11/94 offloaded replaced offloaded replaced
6/29/94 cleaned cleaned cleaned cleaned
7/16/94 replaced offloaded offloaded removed
8/4/94 cleaned cleaned cleaned
8/13/94 removed removed removed


Fortunately, the performance of the pressure transducers was very consistent.

The wave climate characteristics of average depth, significant wave height and peak

period are calculated from the pressure data. Thus, the wave climate coverage was

relatively complete. The dates of valid pressure data coverage for each deployment


are given in Table 3.5.








Table 3.5: Wave data availability summary

DEP# DATE SK LBK2 LBK34 LK
1 from 8/25/93 8/25/93 8/26/93 8/26/93
to 9/30/93 9/30/93 9/30/93 9/29/93
2 from 9/30/93 9/30/93 9/30/93 9/29/93
to 10/23/93 10/23/93 10/23/93 10/23/93
3 from 10/23/93 10/23/93 10/24/93
to 11/11/93 11/1/93 11/1/93
4 from 11/11/93
.......................... ................................. ................................. ........................... .................................
to 11/20/93
5,6 from 12/1/93 12/1/93 12/1/94 11/30/94
to 1/11/94 1/11/94 1/11/94 1/12/94
7 from 1/11/94
.......................... ................................. ................................ ................................. .................................
to 1/15/94
8 from 2/16/94 2/17/94 2/16/94
. .. .. . . .. . .. .. .. .. . ... 7 ..... ... ..... .... .. ......... ......
to 3/22/94 3/22/94 3/24/94
9 from 3/23/94 3/23/94 3/22/94
to 4/30/94 4/30/94 4/25/94
10,11 from 5/1/94 5/1/94 5/1/94 4/30/94
to 6/12/94 5/14/94 6/11/94 6/11/94
12 from 6/12/94 6/12/94 6/12/94 6/11/94
___to 7/16/94 7/16/94 7/16/94 7/12/94
13 from 7/16/94 7/17/94 7/17/94
____to 8/25/94 8/25/94 8/24/94 ....


A graphical representation of table 3.5 is given in figure 3.1, a time line of the

wave data coverage for the monitoring project. Lapses in coverage were largely due

to equipment damage and maintenance. These interruptions occurred from 11/1/93

to 12/1/93 and from 1/11/94 to 2/16/94. The first incident was due to the unexpected

severity of the biofouling of the OBS sensors. The packages were taken back to the

coastal lab for maintenance, data offload and recalibration.









9/1/93 11/1/93 1/1/94 3/1/94 5/1/94 7/1/94 9/1/94
I I II I I I I I !
SK
LBK2
LBK34
LK |
10/1/94 12/1/94 2/1/94 4/1/94 6/1/94 8/1/94

Figure 3.1: Time line of wave data coverage



The second interruption was due to extensive field damage incurred during the

sampling period beginning on 12/1/93. In this case, crab traps and their buoy lines

collected around the system I instrument package at LBK #2. Damage was inflicted

as the crab fishermen attempted to retrieve the traps and lines which were tangled

around the package. The package was damaged beyond repair. Each of the sensors

on the package was sheared off. Remarkably, the package housing was intact and we

were able to access the data for the sampling period. The second system I was not

installed at this time due to damage to the support frame. In addition, the package

sampling program for the system II packages malfunctioned and prevented data

offload. Therefore, all packages were removed from the field.

Once again, during the 2/16 to 3/22/94 sampling period, the second system I

package suffered significant damage due to crab traps. The current meter and both

OBS were damaged and the communications port was cracked. Unfortunately, the

data was lost for the deployment. The repairs required almost two months of work

and consequently the spare system II package was utilized at the Longboat Key #2

site. Furthermore, even after the repairs to the system I package, the current meter








was no longer functioning and much of the OBS signal was unsatisfactory for the

remainder of the monitoring.



3.3.2 OBS Data

As mentioned previously, the performance of the OBS sensors was dismal and

painstaking efforts to correct the problem were generally ineffective. Biofouling was

anticipated before the initial package deployment and the OBS face was painted with

tributal, an optical grade anti-biofoulant. The OBS were subsequently painted

whenever the packages were removed from the field.

It was evident that the severity of the fouling was grossly underestimated. As a

result, caustic hoods, manufactured by Oceanographic Industries, were attached to

the OBS sensors. Although this decreased the amount of fouling, the effect of the

hoods did not improve the OBS signal. The next plan of attack was to simply

remove the packages from the field more frequently to repaint and recalibrate the

OBS on location. The system II packages were eventually removed monthly for this

purpose. Unfortunately, this provided disappointing results as well. Eventually, in

addition to the monthly tributal paintings, the OBS face were subjected to

underwater field cleaning biweekly. Despite these efforts, the OBS collected valid

turbidity data for less than seven days after the OBS faces were painted with anti-

biofoulant and less than three days after cleaning with a nonscouring pad in the field.

By the eighth deployment, an 'OBS wipe' instrument was designed and

implemented. It was mounted to the OBS and mechanically cleaned the face of the








OBS every hour. Once again, this proved ineffective. The final decision was to

continue with monthly removal to repaint the OBS of the system II packages and

biweekly field cleaning and to concentrate efforts on manual turbidity readings and

maintaining our wave data coverage.

For obvious reasons, the OBS sensor data was subjected to a quality check to

assess the validity of the readings. Quality factors of one, two or three were assigned

to each burst. A quality factor of one is assigned to invalid data, two is assigned to

data of reduced accuracy and three is assigned to valid data. These assignments are

determined based on inspection of the burst turbidity mean, standard deviation,

minimum and maximum values. Invalid data is very easily determined. This data is

predominantly either a saturated or a noise signal. Thus, quality assignment of

invalid data is very objective. However, the assignment of reduced accuracy or valid

data is far more subjective and therefore prone to error. These two categories are

judged primarily by the standard deviation and secondarily by the mean value. The

nature of biofouling is such that it inflates the mean background turbidity with time

but, to some extent, relative values are not effected. Thus, before the biofouling

reaches the signal-saturation level the OBS signal may still exhibit valid standard

deviation characteristics although the mean value is actually inflated. Based on this

reasoning we believe that the data that is considered valid and reduced accuracy may

actually be inflated values.

As a result of the severe biofouling and lack of confidence in the validity of the

OBS signal, this turbidity data is deemed inconclusive. It is not appropriate to use








this data for assessment of turbidity variations in the field and will not be included in

this study.



3.3.3 Wave Data Results

The wave characteristics of average depth, significant wave height and peak

period are calculated using linear wave theory and are based solely on the pressure

signal. The pressure signal is calibrated at pounds per square inch and converted to

meters of sea water. At this point, average depth is calculated for each burst. A

spectral analysis of the pressure time series produces a wave energy spectrum which

yields significant wave height and the corresponding peak period. The influence of

high frequency surface chop and low frequency infragravity waves are eliminated by

filtering out frequencies of three seconds or less and twenty seconds or more.

A quality check of the wave data was also performed. Due to the consistent

performance of the pressure transducer, the wave data is nearly one hundred percent

valid when deployed in the field. Unfortunately, the same cannot be said for the

performance of the current meter. The reason for this is two fold. First of all the

calibration of the current meter could not be performed at our facilities. Thus, all

calibrations were done by the vendor. In addition, the field configuration of the

current meter and the field conditions encountered served to expose the sensor to

harm. When the current meter was not operating properly we were faced with the

time consuming prospect of vendor repair and recalibration. More often than not, we

opted to redeploy the package with the malfunctioning current meter rather than to








suspend wave data coverage to wait for repairs. Secondly, the current meters

suffered severe damage due to the crap traps during deployments five and eight. The

damage incurred to the system I package during deployment five was irreparable.

All sensors were sheared from the package lid and not recovered, including the

current meter. The damage inflicted during deployment eight left the remaining

current meter beyond repair. These current meter problems are reflected by the poor

coverage in the directional current data.

The plots of the wave characteristics of the complete set of valid wave data

statistics of each data burst is given in Appendix A. Each page represents the data

collected for one deployment at a given site. The characteristics plotted in each page

include average depth, significant wave height and peak period. In the calculation of

significant wave height, any value below 5 cm is considered to be zero.

The average values of the wave characteristics of average depth (Dav),

significant wave height (Hmo) and peak period (Tp), as well as, days of wave data

coverage within the period are summarized in table 3.6.

For purposes of comparison, the values in table 3.6 were calculated to

correspond to the sedimentation data periods. These values represent the averages of

the available wave data within these periods. The average values in the last row and

column are weighted to reflect the varying days of coverage within periods and

monitoring sites.








Table 3.6: Average wave data characteristics


Date Site Weighted
Start End LK LBK34 LBK2 SK Average
8/25/93 9/29/93 Dav, m 4.27 5.55 5.60 4.59 5.00
Hmo, m 0.16 0.26 0.26 0.21 0.22
Tp, s 5.65 4.97 5.02 5.27 5.23
Days 35 34 36 36 35
9/29/93 11/10/93 Dav, m 4.53 5.38 5.52 4.65 5.08
Hmo, m 0.21 0.30 0.30 0.19 0.26
Tp, s 5.02 5.47 5.59 5.44 5.39
........................ .............................................. ................................................ ................ .........
Days 32 32 40 23 32
11/10/93 12/22/93 Dav, m 4.51 5.29 5.89 5.00 5.23
Hmo, m 0.26 0.35 0.32 0.29 0.31
Tp,s 5.13 5.92 6.02 5.83 5.75
Days 22 21 30 21 24
12/22/93 2/16/94 Dav, m 4.38 5.02 5.84 4.87 5.02
Hmo, m 0.32 0.40 0.49 0.34 0.39
Tp, s 6.47 6.55 6.33 6.74 6.53
Days 21 20 20 24 21
2/16/94 3/22/94 Day, m 4.67 5.64 4.47 4.92
Hmo, m 0.26 0.32 0.26 0.28
Tp, s 5.46 5.73 6.10 5.76
....... s ...... ... .... ....... ......... 3....... ........ ....................... ........3....... ........ ........3....... ........
Days 36 33 34 34
3/22/94 4/30/94 Dav, m 5.16 5.75 4.59 5.19
Hmo, m 0.24 0.25 0.21 0.23
...... p................. ....................... .... 2 o............. .... .. .... .............. ...... ............ .... ......... ..........
Tp,s 5.20 5.02 5.11 5.11
Days 38 38 34 37
4/30/94 6/12/94 Dav, m 4.41 5.17 5.35 4.67 4.80
Hmo, m 0.15 0.18 0.15 0.16 0.16
Tp, s 3.84 4.50 3.03 4.32 4.11
Days 42 41 13 42 35
6/12/94 7/18/94 Dav, m 4.85 5.23 5.44 4.80 5.09
Hmo, m 0.21 0.27 0.28 0.25 0.25
....................... ....................... ......................................................................... ........................
Tp, s 4.70 4.34 4.18 4.03 4.30
Days 31 34 34 34 33
7/18/94 8/25/94 Dav, m 5.36 5.54 4.28 5.05
........ . . *....... ..... .... ... ... ............. ... ...... ....... ......... ........
Hmo, m 0.30 0.33 0.23 0.29

Days 38 39 40 39


Weighted
Average


Day, m


4.52


5.32


5.62


4.63


Hmo, m .21 .28 .30 .23
..... .T p..:. ............. :0 ...... ......... f ^..... .. ....... .. ........ ......
Tp,s 5.07 5.19 5.14 5.27
Days 33 34 34 34


__ __ _ __ _I __ _ L J








This time averaged data clearly shows that the hard bottom sites experience

larger significant wave heights. This trend of disproportionate wave conditions

between hard bottom and control sites is highlighted in table 3.7. Table 3.7 is a

comparison of the wave characteristics between the hard bottom (H.B.) and control

(Con) sites.



Table 3.7: Average wave data characteristics

Characteristic H.B. Con H.B./Con
Average Depth, Dav 5.47 m 4.58 m 1.19
Significant Wave Height., Hmo .29 m .22 m 1.32
Peak Period, Tp 5.17 s 5.17 s 1.0


It is evident from this table that the hard bottom sites have experienced larger

waves than the control sites while the peak period remained constant. This 32%

difference in average wave height is significant in two respects. First of all, the

average significant wave height at the hard bottom sites is larger despite the fact that

the average depth is 19% deeper than the control site. Secondly, this difference in

average significant wave heights translates to dramatic disparity when calculating

wave energy. These two ramifications will be further examined in the following

chapter.

An inspection of discrete storm events confirms the results of the time average

data. The five largest storm events recorded by our packages were examined and

these results are presented in table 3.8.







Table 3.8: Maximum wave height and period for five storm events

Event Date SK LBK2 LBK34 LK
10/29/93 to Hmo(max) 1.78 m 1.99 m 1.42 m
11/1/93 Tp(max) 10.7 s 10.7 s 10.7 s
12/14/93 to Hmo(max) 1.28 m 1.40 m 1.43 m 1.11 m
12/17/93 Tp(max) 9.1 s 9.8 s 9.1 s 9.1 s
1/03/94 to Hmo(max) 1.84 m 2.23 m 2.15 m 1.62 m
1/05/94 Tp(,ax) 10.7 s 11.6 s 12.8 s 10.7 s
3/1/94 to Hmo(max) 1.43 m 1.63 m 1.61 m
3/5/94 Tp(max) 10.7 s 10.7 s 10.7 s
8/13/94 to Hmo(max) 1.26 m 1.51 m 1.72 m
8/18/94 Tp(max) 8.0 s 7.5 s 8.0 s
Average Hmo(max) 1.45 m 1.73 m 1.77 m 1.44 m
Tp(max) 9.6 s 9.9 s 10.3 s 10.3 s


The maximum significant wave height (Hmo(max)) and maximum peak period

(Tp(max) ) for the storm events are given for each of the sites. The largest waves of the

monitoring project was recorded at LBK2 and LBK34 from 1/3/94 to 1/5/94. The

most recent storm event beginning on 8/13/94 and subsiding on 8/18/94 was tropical

storm Beryl.

Table 3.8 clearly illustrates that once again, the hard bottom sites experience

larger maximum significant wave heights in discrete storm events. This data shows

that in every case, larger maximum significant wave heights were recorded at the

hard bottom sites. In addition, the average peak period were longer at the control

sites during the storms.







3.4 Sedimentation Data



3.4.1 Sediment Trap Sampling Schedule

The sediment trap retrieval/deployment schedule is summarized in Table 3.9.

After the initial deployment in October, 1992, field trips to retrieve the samples were

scheduled for the first week of January, 1993, and approximately every four weeks

thereafter during nourishment. After the completion of nourishment, field trips were

scheduled at a maximum of every six weeks, well within the eight week retrieval

interval specified in the permit.



3.4.2 Sedimentation Data

Presented in Table 3.10 are the average sand sedimentation rates for each

sampling period. Sedimentation rates, given in milligrams per centimeters squared

per day, were calculated by dividing mass by the area of trap entrance and Julian

days in the sampling period.









Table 3.9: Deployment/Retrieval schedule


DATE SK LBK6 LBK2 LBK43 LBK34 AM LK
10/26/92 15:00 14:00 13:00 12:00
10/27/92 12:00 10:00 11:00
1/2/93 15:00 14:00
1/3/93 09:30 10:30 11:00 11:30 12:00
2/6/93 11:00 11:45 12:15 13:30 14:00 15:00 16:10
February 28, 93 Start of Nourishment
3/6/93 09:30 10:11 10:50 11:15 12:30 13:30 15:00
4/7/93 10:00
4/8/93 10:00 12:35 11:30 13:15 14:15 15:40
5/1/93 09:56 11:24 11:45 12:10 12:35 13:07 14:15
5/29/93 10:02 10:58 11:22 11:55 12:24 13:05 14:11
6/26/93 10:00 10:45 12:15 13:15 13:55 14:30 15:25
7/14/93 12:15
7/15/93 9:51
7/16/93 13:15 14:55 15:25
7/21/93 10:45 9:45 11:51
August 12, 1993 End of Nourishment
8/25/93 13:35 18:45 18:00
8/26/93 9:15 8:10 10:00 13:30
9/29/93 13:15
9/30/93 8:30 14:30 13:00 15:05 15:30 15:55
11/10/93 17:00
11/11/93 8:30 13:25 12:20 14:15 13:52 10:50
12/22/93 16:30 15:00
12/23/93
12/29/93 11:15 10:30 9:50 9:20 8:50
2/16/94 15:31 11:40
2/17/94 9:00 9:57 11:24 11:40 12:55
3/22/94 10:30 13:20 14:52 16:12 16:30
3/23/94 11:03
3/24/94 11:20
4/30/94 12:00 13:30 14:05 14:40 15:30 8:45 10:55
6/11/94 14:00 13:05 12:00 11:15 9:34
6/12/94 12:55 12:20
7/16/94 13:14 11:48 14:32 11:08 9:42
7/17/94 9:56 10:36
8/13/94 9:11
8/24/94 16:49 16:18 14:26
8/25/94 9:03 10:03 10:21 __








Table 3.10: Average sand sedimentation rates (mg/cm2/day)


Sample Period Site
Start End LBK6 LBK2 LBK43 LBK34 SK AM LK
10/26/92 1/2/93 4.64 2.87 4.28 3.26 1.53 1.23 2.65
1/2/93 2/6/93 1.49 0.36 1.10 2.11 0.09 0.97 1.89
2/6/93 3/6/93
3/6/93 4/7/93 814.37 456.51 184.63 241.15 165.85 38.31
4/7/93 5/1/93 7.89 5.18 14.67 6.44 9.44 7.65 1.59
5/1/93 5/29/93 3.29 0.72 0.47 0.71 0.79 1.00 0.92
5/29/93 6/26/93 0.91 0.41 23.12 0.87 1.43 1.04 1.09
6/26/93 7/14/93 1.01 1.07 24.97 1.01 1.84 1.75 2.96
7/14/93 8/25/93 1.08 0.98 1.39 2.75 2.48 2.55 4.02
8/25/93 9/29/93 3.34 1.28 0.90 1.34 1.12 2.17 1.95
9/29/93 11/10/93 45.00 20.55 133.40 69.56 32.41 100.36 8.29
11/10/93 12/22/93 11.69 8.34 50.10 6.44 24.93 12.58 3.70
12/22/93 2/16/94 158.04 192.22 44.01 126.27 35.16 14.02
2/16/94 3/22/94 201.40 275.02 92.22 112.86 30.85 7.54
3/22/94 4/30/94 3.94 6.33 9.94 7.94 1.06 3.07 3.14
4/30/94 6/12/94 0.98 1.25 0.75 0.98 0.65 0.98 2.83
6/12/94 7/18/94 0.89 1.35 6.35 5.54 2.78 3.86 1.79
7/18/94 8/25/94 12.08 12.95 78.42 50.57 7.47 1.96 4.67


The data presented in table 3.10 is punctuated by high sedimentation rates for

the sampling periods with ending dates of 4/7/93, 11/10/93, 12/22/93, 2/16/94,

3/22/94 and 8/25/94. This coincides to corresponding periods of high seas, presented

in the wave data results.

Presented in Table 3.11 are the average fines sedimentation rate for each


deployment/retrieval.








Table 3.11: Average fines sedimentation rates (mg/cm2/day)


Sample Period Site
Start End LBK6 LBK2 LBK43 LBK34 SK AM LK
10/26/92 1/2/93 18.19 16.30 15.03 14.71 12.44 20.08 22.44
1/2/93 2/6/93 22.90 11.50 31.20 27.02 3.58 81.26 20.43
2/6/93 3/6/93
3/6/93 4/7/93 80.72 65.35 53.65 43.72 62.20 70.74
4/7/93 5/1/93 24.06 24.00 30.63 30.40 27.66 29.99 24.21
5/1/93 5/29/93 20.47 18.86 19.10 15.92 10.13 10.79 11.04
5/29/93 6/26/93 10.20 6.81 11.19 5.90 5.04 6.80 5.26
6/26/93 7/14/93 12.17 13.42 14.19 8.44 7.21 6.39 14.72
7/14/93 8/25/93 8.09 10.04 12.20 7.45 7.12 5.86 10.78
8/25/93 9/29/93 8.58 10.22 7.93 6.57 5.44 8.08 9.42
9/29/93 11/10/94 26.02 29.91 36.49 30.73 24.33 18.87 25.11
11/10/94 12/22/93 29.70 30.09 41.58 35.20 26.02 36.75 32.22
12/22/93 2/16/94 41.41 42.95 39.34 39.02 28.75 27.61
2/16/94 3/22/94 50.41 43.50 36.58 30.08 24.78 36.68
3/22/94 4/30/94 15.06 18.87 17.35 16.02 10.42 11.32 27.35
4/30/94 6/12/94 6.64 7.50 6.87 6.35 9.02 7.41 20.92
6/12/94 7/18/94 1.52 9.52 10.54 10.04 8.81 11.85 13.60
7/18/94 8/25/94 10.74 12.35 20.58 15.44 8.82 7.64 18.66


It is evident from table 3.11 that high sedimentation values were recorded for

the sampling retrieval dates of 4/7/93, 11/10/93, 12/22/93, 2/16/94, 3/22/94 and

4/30/94. However, the values are not as dramatic as those for sand sedimentation.

This may indicate that fines sedimentation is not as sensitive to wave climate as sand


sedimentation.








Table 3.12 shows the average sand sedimentation rates of the four hard bottom

sites of Longboat Key and the average rates of the three control sites for each

deployment.


Table 3.12: Average sand sedimentation rates (mg/cm2/day)
hard bottom sites vs. control sites

Sample Period SITE
Start End H.B. Control
10/26/92 1/2/93 3.76 1.81
1/2/93 2/6/93 1.27 .99
3/6/93 4/7/93 485.17 148.44
4/7/93 5/1/93 8.55 6.23
5/1/93 5/29/93 1.30 0.91
5/29/93 6/26/93 6.33 1.19
6/26/93 7/14/93 7.02 2.19
7/14/93 8/25/93 1.55 3.02
8/25/93 9/29/93 1.71 1.75
9/29/93 11/10/94 67.13 47.02
11/10/94 12/22/93 19.14 13.74
12/22/93 2/16/94 131.42 58.48
2/16/94 3/22/94 189.55 50.41
3/22/94 4/30/94 7.04 2.42
4/30/94 6/12/94 0.99 1.49
6/12/94 7/18/94 3.53 2.81
7/18/94 8/25/94 38.50 4.7
AVERAGE 57.29 20.45


There is a very significant difference in sand sedimentation between the hard

bottom and the control sites. It seems evident that the sedimentation rate is much









higher for the sites at Longboat Key. This is illustrated in figure 3.2, a plot of this

data. It is important to note that the y-axis is this plot is in log scale.







Average Sand Sedimentation Rates


485 I Hard Bottom
190 0 Control
148 131
S47 58 50








l C7 N ON O C, 1 ON OC7S Cl Cm CR Ce Cv 00 (t
, t- l - - Cl- -l -
S T 0edm ON CR l N ca 'C N 00 W

Sediment Retrieval Date


Figure 3.2: Average sand sedimentation rates, hard bottom vs. control




In contrast, the difference in fines sedimentation rates between hard bottom

and control sites is not very pronounced. This can be seen in table 3.13. the average

fines sedimentation rates of the hard bottom and control sites for each sampling

period.


1000.00



100.00



10.00


1.00


0.10








Table 3.13: Average fines sedimentation rates (mg/cm2/day)
hard bottom sites vs. control sites


DATE SITE
Start End H.B. Control
10/26/92 1/2/93 16.06 18.32
1/2/93 2/6/93 23.15 35.09
3/6/93 4/7/93 66.57 58.89
4/7/93 5/1/93 27.27 27.29
5/1/93 5/29/93 18.59 10.65
5/29/93 6/26/93 8.53 5.70
6/26/93 7/14/93 12.06 9.44
7/14/93 8/25/93 9.44 7.92
8/25/93 9/29/93 8.32 7.65
9/29/93 11/10/94 30.79 22.77
11/10/94 12/22/93 34.14 31.66
12/22/93 2/16/94 41.24 31.80
2/16/94 3/22/94 43.50 30.51
3/22/94 4/30/94 16.82 16.36
4/30/94 6/12/94 6.84 12.45
6/12/94 7/18/94 7.91 11.42
7/18/94 8/25/94 14.78 11.71
AVERAGE 22.71 20.57


A graphical representation of table 3.13 is given in Figure 3.3. It is evident

that the temporal fluctuations in fines sedimentation are not as extreme as that for

sand and there is a less dramatic difference between the hard bottom and control


sites.









Average Fines Sedimentation Rates


70.00
60.00
50.00
< 40.00
E
S30.00
E
' 20.00
10.00
0.00


[ Hard Bottom
n Control


~No ON ^o N N ON 0 c"N N. CN- o Cl 00 ti
O' .0 1- C\ o\ C C- 00 N Cl Cl C 0----
Sediment Retrieval Date


Figure 3.3: Average fines sedimentation rates, hard bottom vs. control




Given in table 3.14 is the average sand and fines sedimentation rates of hard

bottom (HB) and control sites before, during and after nourishment. These values


are given in mg/cm2/day. The ratio of sedimentation rates of the hard bottom to

control sites (HB/Con) is also given.




Table 3.14: Average sedimentation rates before, during and after nourishment


Sand Sedimentation Rates Fines Sedimentation Rates


Control HB/Con HB


Control HB/Con


Before 2.51 1.40 1.80 19.61 26.71 0.73
During 84.94 26.99 3.15 23.74 19.98 1.19
After 51.00 20.31 2.51 22.70 19.59 1.16










The cursory analysis presented here seems to suggest three important facts.

First of all, the study period was characterized by moderate sedimentation through

the first nine months with the notable exception of the hundred year storm in March

of 1993. In contrast, sedimentation in the Fall/Winter of 1993/1994 and again in

Summer of 1994 were marked by significant activity, especially at the hard bottom

sites. Secondly, the data shows that fines sedimentation is less volatile than sand

sedimentation. Finally, there is notably greater sand sedimentation at the hard

bottom sites. However, this does not necessarily indicate that the higher rate of hard

bottom sand sedimentation is due to the nourishment. The analysis of the wave data

revealed greater wave activity for the hard bottom sites. Thus, until the relationship

between wave activity and sedimentation is understood, it is very difficult to make

any conclusions. In summary, a more thorough analysis of the sedimentation data in

conjunction with the wave data is necessary to obtain a true picture of the sediment

dynamics in Longboat Key and the adjacent control sites. This is performed in the

next chapter.

The complete set of sedimentation data is presented in Appendix B. This data

includes the dry weight of sand and the organic component of sand, the dry weight of

fines and the organic component of fines, sand and fines sedimentation rates, and the

related statistics of each site.












CHAPTER 4

DISCUSSION



4.1 Introduction

This chapter serves to determine if a general relationship exists between wave

activity and sedimentation rate as measured by the sediment traps. Specifically, this

analysis will propose a general model between sedimentation rate and wave activity.

In addition, two wave parameters will be analyzed to determine which offers the

strongest correlation to sedimentation rates.

The two wave parameters that will be examined in this analysis are significant

wave height and maximum water particle velocities. Significant wave heights have

been calculated and presented in the previous chapter. The maximum horizontal

water velocity calculations will be based on the significant wave height, as well as

the average depth and the peak period data presented in the third chapter. These

parameters will be formulated using linear wave theory and are limited to it's

assumptions. In each case, the equations used to determine the wave parameter will

be presented. This will be followed by a comparison of the wave parameter and the

sand and fines sedimentation rate for the corresponding sampling period. Finally, a

summary of the results will be presented.








A preliminary review of the wave and sedimentation data shows increasing

sedimentation with increasing wave conditions. A more detailed examination of the

monitoring data reveals two facts. First of all, the sand sedimentation, which

experience extreme temporal fluctuations, are related to a power of the wave activity.

In contrast, the fines sedimentation, which exhibit moderate temporal fluctuations are

related to wave activity linearly.


It is evident from the significant wave height and sand sedimentation data, that

sand sedimentation is related to significant wave height exponentially. Two

exponential relationships were tested. The first, the exponential power model, relates

sand sedimentation to an exponential power of the significant wave height as

follows:


bx
y = ce


where y is the sand sedimentation rate, x is the significant wave height and b and c

are constants. The second, the power model, relates sand sedimentation to a power

of significant wave height as follows:


b
y = cx

where y is the sand sedimentation rate, x is the significant wave height and b and c

are constants. The sand sedimentation rate data was plotted against the significant

wave height. The exponential power and power model trendline was formulated

and corresponding R-squared values were calculated for this data. The power








trendline showed better agreement, based on higher R-squared values. In fact, in the

case of sand sedimentation, the power trendline showed better agreement for

maximum horizontal velocity as well. Additionally, the fines sedimentation data

consistently showed the best agreement with a linear trendline for all three wave

parameters. Thus, a power relationship has been adopted for the sand sedimentation

data and a linear relationship has been adopted for the fines sedimentation data for

the significant wave height and maximum horizontal velocity analysis.

The following sections will determine which wave parameter shows the

strongest correlation to sedimentation. This chapter will evaluate the wave

parameter that exhibits the strongest correlation to sedimentation rates measured by

the sediment traps and formulate a general expression for this relationship.



4.2 Trendline and R-Squared Value Equations

The power trendline is calculated by the least squares fit of the data points

using the equation:

b
y = cx


where c and b are constants. The linear trendline is calculated by the least squares fit

of the data points using the equation:

y = mx + b

where m is the slope and b is the intercept. The R-squared value is calculated using

the equation:









R2 SSE
SST



where the error sum of squares,

2
SSE = (y, y,')


and total sum of squares,




SST= Y Yi
=l n

where y, is the wave data and yi' is the expected value of the wave data (Hines,

Montgomery, 1980).



4.3 Significant Wave Height

4.3.1 Significant Wave Height Data

The hard bottom (H.B.) and control (Con) site significant wave heights (Hmo),

sand and fines sedimentation rates for each sampling period are presented in table

4.1. In addition, the hard bottom to control site ratios (HB/Con) are presented. It is

apparent from this table that the sand increases nonlinearly with significant wave

height while the fines sedimentation exhibits a far more linear relationship.








Table 4.1: Significant wave heights and sedimentation rates

Date Hmo (m) Sand Fines
(mg/cm2/day) (mg/cm2/day)
Start End H.B. Control H.B. Control H.B. Control
8/25/93 9/29/93 .26 .19 1.71 1.75 8.32 7.65
9/29/93 11/10/93 .30 .20 67.13 47.02 30.79 22.77
11/10/93 12/22/93 .34 .28 19.14 13.74 34.14 31.66
12/22/93 2/16/94 .45 .33 131.42 58.48 41.24 31.80
2/16/94 3/22/94 .32 .26 189.55 50.41 43.50 30.51
3/22/94 4/30/94 .25 .21 7.04 2.42 16.82 16.36
4/30/94 6/12/94 .17 .16 0.99 1.49 6.84 12.45
6/12/94 7/18/94 .28 .23 3.53 2.81 7.91 11.42
7/18/94 8/25/94 .32 .23 38.50 4.70 14.78 11.71
Averages .30 .23 50.00 20.31 22.70 19.59
Ratios HB/Con 1.30 HB/Con 2.46 HB/Con 1.16


4.3.2 Significant Wave Height Sedimentation Relationship

The data from table 4.1 is presented in figure 4.1, a plot of the significant wave

height and sand sedimentation for hard bottom and control sites. The power

trendlines, equations of the trendlines, and corresponding R-squared values are

included in the plot.

This plot illustrates two interesting facts. First of all, the relatively high R-

squared values indicate agreement with the power model of sand sedimentation and

wave climate. Secondly, the trendline of the control site data lies higher than the

hard bottom sites. This is in apparent contrast with the sand sedimentation data that

showed much larger sedimentation rates at the hard bottom sites as indicated by the









hard bottom to control site ratio. This is explained partially by the fact that the wave

heights were generally larger at the hard bottom sites relative to the control sites.




Sand Sedimentation vs Significant Wave Height


0 Hard Bottom
A Control
-- Hard Bottom
- - Control


0 y= 19000x57
R2 = 0.65 A


A
A A -
y = 8900x4.7
R2 = 0.48 C


200.00
180.00 4
160.00
140.00 -
120.00
100.00
80.00 +
60.00.
40.00
20.00
0.00
0.00


0.30 0.35 0.40 0.45


Figure 4.1: Sand sedimentation rate versus significant wave height




Figure 4.2 is a plot of fines sedimentation versus significant wave heights.

Included in this figure are the linear trend lines, equations of the trendlines and

corresponding R-squared values. Figure 4.2 illustrates good agreement of the linear

relationship of significant wave height to fines sedimentation. Once again, based on

the trend lines, the control sites are predicted to experience larger rates of fines

sedimentation for a given wave size. However, the ratio of hard bottom to control

data of fines sedimentation shows slightly higher sedimentation at the hard bottom

sites due to the relatively larger waves.


0.05 0.10 0.15 0.20 0.25
Hmo (m)









Fines Sedimentation vs Significant Wave Height


45.00 Hard Bottom i
40.00 A Control /
S-- Hard Bottom
S35.00
E i - Control
S30.00 y= 140x-13 A 0 /
SR2 059 y= 150x 21
S25.00 R2 = 0.57
20.00 + /
15.00 1 o
S10.00
9i '=- -21
00 5.00 = 0
0
0.00 _-

0.00 0.10 0.20 0.30 0.40 0.50
Hmo (m)

Figure 4.2: Fines sedimentation rate versus significant wave height




4.4 Maximum Horizontal Velocity

4.4.1 Maximum Horizontal Velocity Calculations

The final wave parameter to be analyzed is maximum horizontal velocity. It

should be noted here that this represents the maximum horizontal component of

water particle velocity under a progressive wave at the depth of the mouth of the

sediment trap. Due to the sparse coverage of the current meters, this analysis does

not take into account current velocities.

The wave data were converted to horizontal velocity, u, using the following

equation:








H,,,, cosh k(h + z) c
u = "( cos(kx oat)
2 sinh kh

(Dean, Dalrymple, 1991). Thus the maximum horizontal velocity, Umax, is given

simply as:

H,,, coshk(h + z)
ma 2 sinh kh

2FI 21I
where frequency, a = -, is based on and peak period, T,; wave number, k = -,
T L

is calculated using the dispersion relation; depth, h, is equivalent to average depth,

Da,; and the height to the mouth of the sediment trap, z, is approximately 1.07 m (z is

a negative value).

The results of this conversion are given in table 4.2. The maximum horizontal

velocity and sand and fines sedimentation are given for the hard bottom and control

sites.








Table 4.2: Maximum horizontal velocity and sedimentation rates

Date Max. U-Velocity Sand Fines
(m/s) (mg/cm^2/day) (mg/cm^2/day)
Start End H.B. Control H.B Control H.B Control
8/25/93 9/29/93 .123 .111 1.71 1.75 8.32 7.65
9/29/93 11/10/93 .155 .116 67.13 47.02 30.79 22.77
11/10/93 12/22/93 .177 .158 19.14 13.74 34.14 31.66
12/22/93 2/16/94 .248 .209 131.42 58.48 41.24 31.80
2/16/94 3/22/94 .164 .158 189.55 50.41 43.50 30.51
3/22/94 4/30/94 .120 .120 7.04 2.42 16.82 16.36
4/30/94 6/12/94 .058 .075 0.99 1.49 6.84 12.45
6/12/94 7/18/94 .117 .110 3.53 2.81 7.91 11.42
7/18/94 8/25/94 .155 .144 38.50 4.70 14.78 11.71
Averages .146 .133 50.00 20.31 22.70 19.59
Ratios HB/Con 1.10 HB/Con 2.46 HB/Con 1.16


4.4.2 Maximum Horizontal Sedimentation Velocity Relationship

Presented in figure 4.3 is the plot of the sand sedimentation data and the

maximum horizontal velocity. This plot illustrates two important facts. First of all,

of the three wave parameters analyzed, the maximum horizontal velocity gives the

best correlation to sand sedimentation rate. The high R-squared values attest to this

point. Although the R-squared value for the hard bottom data shows only modest

improvement, the control data shows significant improvement. Perhaps more

importantly, however, is the fact that the hard bottom trendline predicts larger rates

of sand sedimentation than the control trendline. This supports the conclusions of

the sand sedimentation data. In addition, the values of the exponents of the hard

bottom and control trendline are much closer.









The threshold velocity for the initiation of sand grain motion, assuming a .2

millimeter diameter sand grain, and a density of 2.65 g/cm3, is approximately .15 m/s

(Bagnold, 1946). This compares favorably with the maximum horizontal velocity

values in figure 4.3. Although we find sand sedimentation occurring below .15 m/s,

it must be noted that these are average velocities over a sampling period.




Sand Sedimentation vs Maximun U-Velocity


200.00
180.00
160.00
140.00 _
120.00
100.00
80.00
60.00 -
40.00 _
20.00
0.00
0.000


o Hard Bottom
A Control
- Hard Bottom
- - Control


0.050


y= 38000x39
R2 = 0.68 /


0.100 0.1
Maximum Velocity (


A
A -
'y 19000x38
0A " R2 = 0.52


50 0.200

m/s)


0.250


Figure 4.3: Sand sedimentation rate versus maximum horizontal velocity



Figure 4.4 is a plot of the fines sedimentation data versus the maximum

horizontal velocity. In contrast, the fines data illustrates a marked improvement in

the hard bottom R-squared value and a slight drop in control R-squared values.

However, the maximum horizontal velocity data shows the greatest similarity

between the hard bottom and the control trendlines. This corresponds to the









sedimentation data that shows very little difference between hard bottom and control

fines sedimentation rates.


Fines Sedimentation vs Maximum


0 Hard Bottom
A Control
Hard Bottom
- - Control


U-Velocity

y =230x- 11
R2 = 0.65


y= 190x-6
R2 = 0.57


AO
A'O


50.00
45.00

40.00

35.00

30.00

25.00

20.00
15.00 .

10.00

5.00

0.00
0.000


0.100 0.150

Maximum Velocity (m/s)


0.200


Figure 4.4: Fines sedimentation rate versus maximum horizontal velocity




4.5 Summary

This analysis established two important facts concerning the relationship

between the two wave parameters of significant wave height and maximum

horizontal velocity and sedimentation as measured by the sediment traps. First of all,

the data indicates that a power model and a linear model best describes the

relationship between wave climate and sand sedimentation and wave climate and

fines sedimentation, respectively. Secondly, the maximum horizontal water particle


0.050


0.250








velocity at the mouth of the trap seems to offer the best correlation to sedimentation

rate.

Table 4.3 is a summary of the results of the wave parameter analysis for the

sand sedimentation data. The trendline equation and corresponding R-squared value

are given for both hard bottom and control data. This table shows that the maximum

horizontal velocity (max u-vel) parameter offers the highest R-squared value for both

hard bottom and control sites. In addition, the maximum horizontal velocity

trendline is the only one that predicts higher sedimentation rates at the hard bottom

sites for the range of data collected. This coincides with the results of the sand

sedimentation data conclusions.



Table 4.3: Trendline and R-squared Values for Sand Sedimentation Data

Parameter Site Equation R

Hmo H.B. y= 19000x57 0.65
(m) Con y = 8900x47 0.48
Max U-Vel H.B. y = 38000x3.9 0.68
(m/s) Con y = 19000x38 0.52


Table 4.4 presents the same information for fines sedimentation data. This

table shows that the maximum horizontal velocity wave parameter offers a

significantly higher R-squared value for the hard bottom trendline and an average R-

squared value for the control trendline.








Table 4.4: Trendline and R-squared values for fines sedimentation data

Parameter Site Equation R
Hmo H.B. y = 150x -21 0.57
............ .............. ... .- ............. .. .. ... .................................. .0....... ...................
(m) Con y = 140x 13 0.59
Max U-Vel H.B. y = 230x 11 0.65
(m s) Con y 1 90x 6 0..................... ...........
(ms)- Co-n y 19 0x -6 0.57


Two important facts concerning this analysis must be noted. First of all, the

relationships suggested in this analysis are simply data curve fits. These empirical

equations are not developed from sedimentation theory. Perhaps more important

than the actual equations is the fact that the trendlines are similar for both control and

hard bottom data, as would be expected. Secondly, this analysis is based on

sedimentation rates measured by the sediment traps. The equation developed in this

analysis simply relates wave forces to sedimentation rates obtained by the sediment

traps. A more sophisticated analysis must be performed to relate wave climate to

true sedimentation rates.













CHAPTER 5

SUMMARY AND CONCLUSIONS



5.1 Introduction

The focus of this study is to analyze the sedimentation monitoring of the

Longboat Key nourishment project and to evaluate the existing monitoring

guidelines. In conjunction with sedimentation, wave climate and turbidity

monitoring was conducted. This study presents the methods of monitoring with

emphasis on the new sediment trap configuration implemented for this study and the

design process. This is followed by a presentation of the results of the

sedimentation, wave climate and turbidity monitoring. Finally, an evaluation of the

relationship between wave climate and sedimentation is conducted.

A brief summary of each chapter of this study will be presented in the

following section. This will be followed by recommendations concerning the

sedimentation monitoring requirement. Finally, suggestions for further investigation

will be presented.








5.2 Summary



5.2.1 Monitoring Methods

The wave climate and turbidity monitoring was performed through the use of

in-situ instrument packages. These packages are equipped with pressure transducers,

current meters and optical backscatter sensors. The turbidity measurements were

augmented by manual turbidity readings, using a portable nephelometer. Sediment

traps were employed to obtain the sedimentation measurements.

Sedimentation monitoring is a relatively new requirement and there are no

standardized collection or analysis procedures. Thus, the design of the sediment

traps is stressed in this study. The final sediment trap configuration design consists

of two inch PVC sediment traps secured in an aluminum sediment stand which is

mounted to an aluminum post jetted into the sea bed. It has been shown that this

configuration facilitates accurate sediment sampling and reduces replicate

interference. In addition, this design proves to be sturdy and allows for effortless

trap replacement.



5.2.2 Monitoring Results

Maintaining the instrument packages proved to be a challenging task. Severe

biofouling served to undermine the integrity of all of the package turbidity data. In

addition, the packages incurred substantial damage due to crab traps, rendering the

current meters defective. However, frequent manual turbidity readings were taken in








the course of the many field trips to maintain the packages. Additionally, the

packages managed to collect consistent pressure data. Thus, a comprehensive record

of average depth, significant wave height and peak period was obtained. In contrast,

the sediment traps performed very well. In particular, the final sediment trap

configuration allowed for remarkable sedimentation coverage.

The manual turbidity readings were relatively low compared to the 29 NTU

standard. The turbidity measurements at the hard bottom sites proved to be higher

than the control sites during nourishment but were lower afterwards. On the whole,

the manual turbidity measurements seem to suggest that the nourishment did not

affect the turbidity level at Longboat Key. It is important to note that these are

discrete measurements and cannot be considered random. In reality, these values

probably underestimate actual turbidity conditions.

The results of the wave climate monitoring demonstrate that the hard bottom

sites experienced average significant wave heights 32% larger than the control sites.

An investigation of discrete storm events confirm this trend. In addition, the hard

bottom sites experienced waves with longer peak periods for these storm events.

Two important facts are evident in the results of sedimentation data. Fist of all,

the data shows that sand sedimentation experience extreme temporal fluctuations

while fines sedimentation is characterized by moderate temporal fluctuations.

Secondly, there is a significantly larger rate of sand sedimentation for the hard

bottom sites in comparison to the control sites.








5.2.3 Wave Force and Sedimentation Analysis

An analysis of the manner in which wave forces determine sedimentation as

sampled by the sediment trap is conducted in the fourth chapter of this study. This

analysis seems to establish two important facts. First of all, the data suggests that

sand sedimentation is related to a power of wave activity. In contrast, the fines

sedimentation seems to be linearly related to wave activity. Secondly, the wave

parameter of maximum horizontal water particle velocity seems to offer the best

correlation to sedimentation rate.



5.3 Sediment Monitoring Requirement Recommendations

Due to the novelty of sedimentation monitoring, present permit requirements

allows for much flexibility in sediment sample collection and analysis. In fact, the

monitoring requirement portion of the Longboat Key nourishment permit states that

"any scientifically viable procedure" can be used in the collection and analysis

methods to determine sedimentation rate (State of Florida Department of

Environmental Regulation, 1992). However, the information gained from this

monitoring project suggests that specific methods to obtain sedimentation rates can

now be defined.

Two primary recommendations are proposed here. The first recommendation

is to establish a standardized sediment trap design and field configuration. The

second recommendation is to amend the sediment sampling schedule.








5.3.1 Standardized Sedimentation Monitoring

There are two primary reasons a standardized sediment sampling method must

be specified. A tested, standardized method of sediment sampling eliminates the

start up time associated with designing, implementing and evaluating a new design.

The data collected during this start up period or before a viable method is established

may be invalid. In addition, measured sedimentation rates are dependent to some

extent on the sampling method employed. Thus, cross nourishment sedimentation

comparisons cannot be made unless a standardized method is utilized.

It is proposed that the final sediment trap configuration designed in this study

be adopted as the standard design. It performed very well over the course of the

monitoring project and has been tested and analyzed in this study. In conjunction

with this, it is recommended that the monitoring requirements be expanded to

include measurements of relative bed level at the sampling sites. This measurement

is to be taken during each sediment trap replacement using a ruled post that is jetted

into the sea floor. This not only allows for an accretional or erosional

characterization of the sedimentation rate obtained by the traps but it also would

provide valuable information on net sedimentation. Furthermore, the cost and effort

to obtain this useful data is minimal.



5.3.2 Amended Sampling Schedule

The second recommendation proposed in this study involves a minor change to

the sediment sampling schedule. Sedimentation sampling should begin at least six








months prior to nourishment and continue for a year after construction. Wave

climate monitoring should coincide with this sediment sampling schedule. In

addition, samples should be replaced monthly throughout the entire duration of the

monitoring.

The reason for this extended monitoring period before construction is to

establish a statistically significant wave climate and sedimentation baseline prior to

nourishment. An analysis of the relationship between wave forces and

sedimentation, similar to the analysis performed in chapter five of this study, can be

established for the period before and after nourishment. Thus, sedimentation rates

for a given wave condition before and after nourishment can be compared. This

would allow for a more accurate and comprehensive assessment of the nourishment

impact on sedimentation.

The increased frequency in sample replacement offers two benefits. First of

all, it will increase data points which will serve to increase statistical significance.

Secondly, the shorter sampling period will allow for a more thorough analysis of the

relationship between wave forces and sedimentation.



5.4 Suggestions for Further Investigation

The two suggestion for further investigation involves lab tests on sediment trap

designs. Important information may be gained from a comprehensive investigation

of the flow dynamics around the proposed standard sediment trap design. These

experiments may determine if the trap design facilitates representative sampling. For








example, it may determine if there is significant flow interference between the

replicates. This information can lead to improved trap designs if necessary. In

addition, a relationship between true sedimentation rates and measured sedimentation

rates may be established. This ultimately may lead to valuable insights into the

complicated dynamics of sedimentation.

Lab tests on a variation of the proposed sediment trap configuration also merits

investigation. Although current monitoring requirements specifies replicate

sampling at one height, the alternative of staggering the three replicates at different

heights from the sea floor should be analyzed. This would provide much more useful

sedimentation data. Perhaps a sedimentation profile can be interpolated from the

three sampling heights of this configuration. The replicates in this current

configuration show very little standard deviation, thus replicate sampling at one

height seems redundant. An examination of the flow dynamics around this

alternative sediment trap design may determine if representative sampling is possible

for this staggered configuration.
































APPENDIX A
WAVE DATA PLOTS









LONG KEY WAVE DATA SUMMARY DEPLOYMENT #1

Sampling Period:
8/26/93@15:40:6 9/29/93@11:40:6 {bursts:12 418}

Deployment Averages:
Depth = 4.27m Significant Wave Height = 0.16m Peak Period = 5.65s





Average Depth


240.82 244.99 249.15 253.32 257.49 261.65 265.82 269.99


Significant Wave Height


240.82 244.99 249.15 253.32 257.49 261.65 265.82 269.99


Peak Period


240.82 244.99 249.15 253.32 257.49 261.65 265.82 269.99
Julian Day


-0.3
o 0.2
E
" 0.1









LONGBOAT KEY 34 WAVE DATA SUMMARY DEPLOYMENT #1

Sampling Period:
8/26/93 @ 10:43:54 9/30/93@ 12:43:54 {bursts:11 432}

Deployment Averages:
Depth = 5.55m Significant Wave Height = 0.26m Peak Period = 4.97s





Average Depth


240.70 244.86 249.03 253.20 257.36 261.53 265.70 269.86


Significant Wave Height


240.70 244.86 249.03 253.20 257.36 261.53 265.70 269.86


Peak Period


240.70 244.86


249.03 253.20 257.36
Julian Day


261.53


265.70 269.86


-5.8
S5.6
5.4
5.2


0.6

S0.4
E
0.2









LONGBOAT KEY 2 WAVE DATA SUMMARY DEPLOYMENT #1

Sampling Period:
8/25/93@18:0:15 9/30/93@12:0:15 {bursts:2 431}

Deployment Averages:
Depth = 5.47m Significant Wave Height = 0.25m Peak Period = 5.06s





Average Depth


240.75 244.92 249.08 253.25 257.42 261.58 265.75 269.92


Significant Wave Height


240.75 244.92 249.08 253.25 257.42 261.58 265.75 269.92


Peak Period


240.75 244:92 249.08 253.25 257.42 261.58 265.75 269.92
Julian Day


0.5
0.4
E0.3
0.2









SIESTA KEY WAVE DATA SUMMARY DEPLOYMENT #1

Sampling Period:
8/25/93@14:41:51 9/30/93@6:41:51 {bursts:1 429}

Deployment Averages:
Depth = 4.59m Significant Wave Height = 0.21m Peak Period = 5.27s





Average Depth


-4.8
> 4.6
4.4


240.70 244.86 249.03 253.20 257.36 261.53 265.70 269.86


Significant Wave Height


240.70 244.86 249.03 253.20 257.36 261.53 265.70 269.86


Peak Period


240.70 244.86 249.03 253.20 257.36 261.53 265.70 269.86
Julian Day


0.5
-0.4
o 0.3
E
10.2
0.1







10

g 8
S6










LONG KEY WAVE DATA SUMMARY DEPLOYMENT #2

Sampling Period:
9/29/93@16:44:45 10/23/93@14:44:45 (bursts:1 288}

Deployment Averages:
Depth = 4.5m Significant Wave Height = 0.15m Peak Period = 4.73s





Average Depth


275.78 279.95 284.11 288.28 292.45


Significant Wave Height


275.78 279.95 284.11 288.28 292.45


Peak Period


6-

4
2


275.78


279.95


284.11
Julian Day


288.28


292.45


-0.4
E
o
E 0.2
-1










LONGBOAT KEY 34 WAVE DATA SUMMARY DEPLOYMENT #2

Sampling Period:

9/30/93@ 18:0:39 10/23/93@6:0:39 {bursts:1 271}

Deployment Averages:

Depth = 5.38m Significant Wave Height = 0.23m Peak Period = 5.11s






Average Depth


276.83 281.00 285.17 289.33 293.50


Significant Wave Height


276.83


281.00


285.17


289.33


293.50


Peak Period


276.83 281.00 285.17 289.33 293.50
Julian Day


5.8
--5.6
E
d5.4
o 5.2


- 1
E
o
E 0.5
"1


n









LONGBOAT KEY 2 WAVE DATA SUMMARY DEPLOYMENT #2

Sampling Period:

9/30/93@18:0:15 10/23/93@8:0:15 {bursts:1 252}

Deployment Averages:
Depth = 5.86m Significant Wave Height = 0.24m Peak Period = 4.89s





Average Depth


622!
6
E 5.8
5.6


276.83 281.92 286.83 291.00 295.17


Significant Wave Height

1-


E 0.5 Hmo

I.


276.83


281.92


286.83


291.00


295.17


Peak Period


276.83 281.92 286.83 291.00 295.17
Julian Day










SIESTA KEY WAVE DATA SUMMARY DEPLOYMENT #2

Sampling Period:
9/30/93@10:58:59 10/23/93@8:58:59 {bursts:1 276}

Deployment Averages:
Depth = 4.65m Significant Wave Height = 0.19m Peak Period = 5.44s






Average Depth


276.54 280.71 284.87 289.04 293.21


Significant Wave Height


276.54 280.71 284.87 289.04 293.21


Peak Period


-4.8
>4.6
M


E
o0.5
E
"1


276.54 280.71 284.87 289.04 293.21
Julian Day









LONG KEY WAVE DATA SUMMARY DEPLOYMENT #3

Sampling Period:
10/24/93@10:0:55 11/1/93@18:0:55 {bursts:1 101)

Deployment Averages:
Depth = 4.62m Significant Wave Height = 0.38m Peak Period = 5.85s





Average Depth


297.17 298.00 298.83 299.67 300.50 301.33 302.17 303.00 303.83 304.67


Significant Wave Height







297.17 298.00 298.83 299.67 300.50 301.33 302.17 303.00 303.83 304.67


Peak Period




~. t n / / \


297.17 298.00 298.83 299.67 300.50 301.33 302.17 303.00
Julian Day


303.83 304.67


E 4.
>4.
O 4.


1.4
1.2

0 0.8
E 0.6
0.4
0.2





86



LONGBOAT KEY 34 WAVE DATA SUMMARY DEPLOYMENT #3

Sampling Period:
10/23/93@10:1:2- 11/1/93@18:1:2 {bursts:1 113}

Deployment Averages:
Depth = 5.39m Significant Wave Height = 0.48m Peak Period = 6.34s





Average Depth


296.17 297.00 297.83 298.67 299.50 300.33 301.17 302.00 302.83 303.67 304.50


Significant Wave Height






- ------T- -- ------


296.17 297.00 297.83 298.67 299.50 300.33 301.17 302.00 302.83 303.67 304.50


Peak Period


296.17 297.00 297.83 298.67 299.50 300.33 301.17 302.00 302.83 303.67 304.50
Julian Day


-1.5
E
o 1
E
1 0.5


u









LONGBOAT KEY 2 WAVE DATA SUMMARY DEPLOYMENT #3

Sampling Period:
10/23/93@ 12:0:15 11/11/93@ 12:0:15 {bursts:1 229}

Deployment Averages:
Depth = 5.01m Significant Wave Height = 0.35m Peak Period = 6.4s





Average Depth


297.08 298.75 300.42 302.08 303.75 305.42 307.08 308.75 310.42 312.08 313.75


Significant Wave Height


297.08 298.75 300.42 302.08 303.75 305.42 307.08 308.75 310.42 312.08 313.75


Peak Period


297.08 298.75 300.42 302.08 303.75 305.42 307.08 308.75 310.42 312.08 313.75
Julian Day









LONGBOAT KEY 2 WAVE DATA SUMMARY DEPLOYMENT #4

Sampling Period:
11/11/93@14:0:48 11/20/93@20:0:48 (bursts:2 113}

Deployment Averages:
Depth = 5.71m Significant Wave Height = 0.2m Peak Period = 7.07s


Average Depth
I -II



-


315.25 316.08 316.92 317.75 318.58 319.42 320.25 321.08


321.92 322.75 323.58


Significant Wave Height


315.25 316.08 316.92 317.75 318.58 319.42 320.25 321.08 321.92 322.75 323.58


Peak Period


315.25 316.08 316.92 317.75 318.58 319.42 320.25 321.08 321.92 322.75 323.58
Julian Day


6.2
6
E
S5.8
S5.6
5.4
5.2


8

C'3
46
4-
4










LONG KEY WAVE DATA SUMMARY DEPLOYMENT #5

Sampling Period:
11/30/93@ 16:0:52 1/12/94@4:0:52 {bursts:1 -511)

Deployment Averages:
Depth = 4.45m Significant Wave Height = 0.29m Peak Period = 5.78s





Average Depth


E4.5

0 .


337.75 341.92 346.08 350.25 354.42 358.58 362.75 1.92 6.08 10.25


Significant Wave Height

5-


15
g:-----------------------r -----


337.75 341.92 346.08 350.25 354.42 358.58 362.75 1.92
337.75 341.92 346.08 350.25 354.42 358.58 362.75 1.92


6.08 10.25


Peak Period

10


5


0
337.75 341.92 346.08 350.25 354.42 358.58 362.75 1.92 6.08 10.25
Julian Day




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