Citation
Impact of Longboat Key beach nourishment on hard bottom sedimentation rates

Material Information

Title:
Impact of Longboat Key beach nourishment on hard bottom sedimentation rates
Series Title:
UFLCOEL-95003
Creator:
Stubbs, Darwin C
University of Florida -- Coastal and Oceanographic Engineering Dept
Place of Publication:
Gainesville, Fla.
Publisher:
Coastal & Oceanographic Engineering Dept., University of Florida
Publication Date:
Language:
English
Physical Description:
x, 148 p. : ill. ; 28 cm.

Subjects

Subjects / Keywords:
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

Thesis:
Thesis (M.E. in Engineering)--University of Florida, 1995.
Bibliography:
Includes bibliographical references (p. 146-147).
Statement of Responsibility:
by Darwin C. Stubbs.

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University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
33143322 ( oclc )

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 CKN OW LEDGM EN TS ....................................................................................... ii
LIST OF FIGURES ................................................................................................. vi
LIST OF TABLES ................................................................................................... vii
ABSTRA CT ............................................................................................................ ix
CHAPTERS
I INTRODUCTION
1. 1 Introduction to Sedimentation
1.1.1 Definition ............................................................................................ 1
1.1.2 Environm ental Im pact ....................................................................... 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 M onitoring 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 Configuration ............................................................................ 15
2.3 Sediment Traps
2.3.1 Sedim ent Trap Design Criterion ........................................................ 17
2.3.2 Original Trap Design ......................................................................... 19
2.1.3 Second Trap Design ........................................................................... 21
2.3.4 Final Trap Design .............................................................................. 24
2.3.5 Sedim ent Sam ple Analysis Procedure ............................................... 29
iv




3 RESULTS
3.1 Introduction ................................................................................................. 31
3.2 Manual Turbidity Monitoring
3.2.1 M ethod ............................................................................................... 31
3.2.2 M anual Turbidity Data ...................................................................... 32
3.3 Sensor Data
3.3.1 Sensor Deploym ent Schedule ............................................................ 36
3.3.2 OBS Data ........................................................................................... 40
3.3.3 W ave Data .......................................................................................... 42
3.4 Sedimentation Data
3.4.1 Sedim ent Trap Sam pling 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 W ave Height Data ........................................................... 59
4.3.2 Significant Wave Height Sedimentation Relationship .................... 60
4.4 Maximum Horizontal Velocity
4.4.1 M axim um 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 M onitoring M ethods .......................................................................... 70
5.2.2 M onitoring Results ............................................................................ 70
5.2.3 W ave Force and Sedim entation Analysis .......................................... 72
5.3 Sediment Monitoring Requirements Recommendations ............................ 72
5.3.1 Standardized Sedim entation M onitoring ............................................ 73
5.3.2 Am ended Sam pling Schedule ............................................................ 7 3
5.4 Suggestions for Further Investigation ......................................................... 74
APPEN DIX A : W AVE DATA PLOTS .................................................................. 76
APPEN DIX B: SEDIM EN TATION DATA ........................................................... III
REFEREN CES ........................................................................................................ 146
BIOGRAPHICAL SKETCH ................................................................................... 148




LIST OF FIGURES
Figure p1ge
1. 1 Nourishment location map ............................................................................... 6
1.2 Time line of nourishment and monitoring activities ........................................ 8
1.3 M onitoring project location map ..................................................................... 10
2.1 System I package field configuration .............................................................. 16
2.2 System Il package field configuration ............................................................. 16
2.3 Original sediment station configuration .......................................................... 21
2.4 Sediment trap stand .......................................................................................... 22
2.5 Second sediment station configuration ............................................................ 23
2.6 Final sediment 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. ) Sand sedimentation rate versus maximum horizontal velocity ....................... 65
4.4 Fines sedimentation rate versus maximum horizontal velocity ....................... 66




LIST OF TABLES

Tables pjgje
1. 1 Sedim ent characteristics .................................................................................. 7
1.2 M onitoring 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 Wave 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
33.11 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
31.14 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 I
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 nourishm-ent 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
nourishment 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 Pro-ject 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 199' 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, 199' 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-2913, near the terminal groin at the southern tip of the




6
island. One million, six hundred and fifty 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 R47 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 Ke
R-12

R-29B Pas
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) q
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-29B3, 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.Mo.nitoring
Manual, Turbidity Monitoring
W....ave~a ad Turbidity Monitorin
4/7/93 8/593
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 27015'40" N 82O33'09' W 4.6 n
Longboat Key #6, LBK6 1111215 N, 446697 E 27023'21' "N 82-38'43" 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 n Long Key, LK 1227089 N, 415328 E 27042'27" N 82044'39? W 4.5 m




NORTH

Long Key
LKO00
L 4r Tampa Bay

Anna Maria

Figure 1.3: Monitoring project location map

n Sediment Station o 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-1 5C. 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 MeBimney 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 McBimey.
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 11 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 11 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 11 packages were employed at the Long Key and Siesta Key control sites and at the Longboat Key 434 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 Il was deployed at Longboat Key #2. The packages at these four monitoring sites were supplied from a pool of four system 11 packages and two system I packages. This allowed for a spare system 11 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 11 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 11 configuration.




current meter
OBS
pressure transducer

PVC body

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

---PVC trap tube rubber coupling
tie-wrap mounting post

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 tiewraps. 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

copper tube

-rubber coupling

nalgene sample bottle

trap stand

Lie-wrap

. mounting post

-~ ~ ~ i v WO

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 Deaign
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 15 c
L4- 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.




trap holder
11.4 cm
6.35 cm
s t 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.
--PVC tube
aluminum
stand
s e t b o l tP V C c a n i s t e r

mounting post

Figure 2.8: Final sediment station configuration

r-_




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
O rig in al..... ... ............... .................... 0.................... 5 9%... 2 ............... ...............
Second 0.13 0.15 71% 1
SFinal 0.13 0.15 1 99% 1 14

2.3.5 Sediment Sample Analysis Procedure
Once the samples are retrieved they are sterilized with mercurium (HgCl2) 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 100 C.




6) The weight of the dried sand sample is recorded. This represents the dry
weight of the sand sediment and organics 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 100 C.
10) The weight of the dried fines sample is recorded. This represents the
dry weight of the fines sediment and organics 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-l 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 ILK 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
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
surf. 3.5 5.0 5.8 3.9 3.8 2.5 2.8 4.0
t__ bot .... 6.0 5...... 3' 9... ..I..... 5 ..........6.1 ..... 6 .0 .........3.0 .........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
S b o t ... ....... 3 .......... ......................1 3........ ............................... 1 .. ....................................................... 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................. ........... ............... .............................. ..................... ........................
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
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
... ... ... . .............. . ...... .....'... ......... 0... *..... .... ..... 2...... .......... ............ ........ ... . .. . . 7 .. . . ..... ..... . . .
mid 3.5 2.1 3.0 2.1 1.4 4.2 7.2 3.4
............. ....................... ........................ ................ ....... ................ . ... . . . . ....................... .......................i ..... . . .
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
...................................2. ..................................... .......... .......... ........ 2.. .......... .......... .......... .......... ......... ...... 8........
____ 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
............................. ........7.. ............. ..... I............... ........ 5.. .......... ................... ........ 6.. .......... .......... ... ............ ............
__ 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
................ ..I........... ........ .. .......... ........ .. .......... ........ .... ........... ....... ........... ........4. I......... .......... ................................
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
m.i ............. ......... .......... 6 ............ ..... i ........... ..... ...................... ...................... ... .... ............ ................ ... .....
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
..m.i... ............;........... ...........................g............. -. -................--- ........ ......... i ........ ......... 1".'"5 ... *..... ..... 2 4 ......
mid 1.8 1.2 1.51.12 8115 24
. ... .. ........ .................. . . ................. . ................. .... ................ .. ............... ................ ............. .....
bot. 1.9 1.4 1.5 1.3 1.4 8.3 2.0 2.5
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
b o.......... 5 .......... 1 .............. 4 ........ ......... 6 .................. ................ .................. ....... I .7.....
bot. 5.4 2.1l 4.1 2.3 6.2 ,4 11.4 L 77




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 (UB/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
After surf. 2.8 4.4 .64
Nourishment mid 3.2 5.5 .58
bot. 9.2 4 8

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 1, this rotation must be performed every four to six weeks. However, the batteries of the system 11 package require renewal only every three months. The limiting factor of the system 11 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 11 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
.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ............... .. ... .. ........ .. ... i ....... ....... .. . . .
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
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
..................t .o ........... ....... ....... ....... /4....... ................. 7 T................. 6 / .9 ............ ....... . .9 4........
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
SK LBK4C
L K. .......... ...
collcte around.... the system IisrmnpakgatLK. Dmae.asinlite
as~ ~~.... th.rbfsemnatmte. ortiv.h rp ndlnswihwr age
aroundFiur the pakae Thee pakane am ae beyon roear.achogtesesr
onThe acge wasnseredtioff Radeky thenie pakel housige ainntactd aurnd whe
wereliableetoaccessnthegdata1for/the samplingperiod.aThersecond sytemr Iuo waso installed atrthis tme dusem to damaguet sportag fame n 2adtinte anced
amplngh pogm frThe stIIpackage malfunciond nrevenEahfte dataor
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 11 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 antibiofoulant 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 11 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 harmi-. 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
...... .... .... ... ..... ... i .... ...6 3 .......0 ...... ..... ." i .... .. .
lmo, m 0.2 6 0.3 5 0.3 2 0 .2 9 0.3 1
......... ............. ....................... ................................................ ........................ .........................
Tp, s 5.13 5.92 6.02 5.83 5.75
Days 22 21 30 21 24
12/22/93 2/16/94 Day, 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
.. ... m.... ....... m..... ........... ....... ............... ....... .. . . . .. . . . . .. . . . . ... ... . .
limo, m 0.26 0.32 0.26 0.28
..... ........................... ............ 1 ... ................ ........ ....................... .......... ............. ... .... -.........
Tp, s 5.46 5.73 6.10 5.76
......6 y. ...... ......... ......... ......... ........... ................................... ................ .... ......... .
____Days 36 33 _____ 34 34.
3/22/94 4/30/94 Dav, m 5.16 5.75 4.59 5.19
. . . . . . . . . . . . .. . . . . ............................................ .. .... .. .. . . .
lmo, m 0.24 0.25 0.21 0.23
....................... ....................... ................. .............................. ........................ .........................
Tp, s 5.20 5.02 5.11 5.11
.............. . ............... ...................... . .............. ... 2 ........ ...... ................. :.... ..........
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
...... D .p.y s ...... .........4 ......... ........ 4 ..I ........ ....... I3..03 ......... ..... 4 ..2 ......... .... 5.. .........
_ _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
. . . . . . . . . . . . .. . . . . ............................................... .. ... .. .. . . .
lmo, m 0.30 0.33 0.23 0.29
Tp,.s 5.07 5.13 5.51 5.24
ays ......... ....38 39 40 39.

Weighted Average

Dav, m

4.52

5.32

5.62

4.63

lmo, m .21 .28 .30 .23
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, Day 5.47 m 4.58 m 1.19
................................ ....v e a .e ....h .. ........................... ...... ................... .......8... m....................... !.:... 9.......................
Significant Wave Height., Hmo .29 m .22 m 1.32
Peak Period, Tp 5.17s 5.17s 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) 1.28mi 1.40mi 1.43mi 1.11 mn
.1..1 4...9..to..... . ............. 2 ... m.................. ... ................... !... 3...... ................... ..-. ... ...................
12/17/93 Tp(max) 9.1 s 9.8s 9.1 s 9.1 s
1/03/94 to Hmo(max) 1.84.m 2.23.m 2.15m 1.62m .
1/05/94 Tp(max) 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
......................... ...................................t .................................. t.................................. ...................................
3/5/94 Tp(max) 10.7s 10.7s 10.7s
8/13/94 to HMO(Max) 1.26mi 1.51mi 1.72mi
8 / 3 9 o .. o. ..m.... .....ax ................... .......................... ,.. ... ................... .... .......... ...................................
8/18/94 Tp(max) 8.0s 7.5 s 8.Os
Average lln(max) 1.45mi 1.73mi 1.77mi 1.44mi
. ....................... .. 5.. ................ .. .......... ........ .... ......... ............ .. .........
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 11:00 111:45 112:15 113:30 114:00 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 10:58 111:22 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 13:15 114:55 15:25 1
7/21/93 1110:45 ,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 1___ 1____ 1___




Table 3. 10: Average sand sedimentation rates (mg/cm 2/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 15/29/93 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 12.17 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 11.79 7/18/94 8/25/94 112.08 112.95 78.42 150.57 17.47 1.96 14.67

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/cm 2/day)

Sample Period Site
Start End LBK6 LBK2 LBK43 LBK34 SK IAM 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 j24.00 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 12.35 120.58 115.44 18.82 7.64 118.66

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: Average sand sedimentation rates (mg/cm 2 /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/l/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 8,125/93 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. 5 3 2.81
1 7/18/94 8/25/94 38.50 1 4.7 1
1 AVERAGE 57.29 1 20.45 1

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.

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

1000.00

* Hard Bottom

148 131 190 control
100.00 67
10.00 5
1.00 LLLJII
ON CN c, C, C, CN O7N ON ON ON ON ON ON ON ON ON ON W) -, C' NN 11C) 0 V
- Q I ,, ( N N 7N N 7 :
0.10 0C ooei N entRetr l00
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.

I




Table 3.13: Average fines sedimentation rates (mg/cm 2 /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 1 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
30.00 Ei
20.00
10.00 ]
0.00

0 Hard Bottom [] Control

ON C0 r- ON ON C, C, 01 ON 0 Cl 0 01 C71 00 0*
-~ ~ -~ 'r l C -l -l -l -l
V) t 0 ON C l ~ '0 N 00 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

Control I HB/Con HB

Fines Sedimentation Rates

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 perfon-ned 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 Ws 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:




R'= 1 SSE
SST
where the error sum of squares,
2
SSE =y -(~ y')
i=1
and total sum of squares,
SST __i=1
n
where yj 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/cm 2/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 Rsquared 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 200.00 [o Hard Bottom
0 Y =1I9000X1 I
"- 180.00 A Control Ry 065
- 160.00 Hard Bottom
140.00 - Control
E 120.00
100.00
= 80.00
60.00 1 A
A A
40.00 -y 900X4.
20.00 R2 = 0
0.00 -..
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 Hmo (m)
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.




Fines Sedimentation vs Significant Wave Height
45.00 3 Hard Bottom.
' 40.00 A Control 0
--35 0 Hard Bottom:
2 - Control I
30.00 1 y=140x-13 A 0A
R2 -059 y= 150x 21
25.00 R 0 R20.57
20.00 A /
. 15.00 __ 13
-r-A
10.00
"0 5.00 t
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:




u = H (, cosh k(h + z) cos(kx t)
2 sinh kh
(Dean, Dalrymple, 1991). Thus the maximum horizontal velocity, Umax, is given simply as:
H,,, cosh k(h + z)
2max 2 sinh kh
2H 2-I
where frequency, a = Tr, is based on and peak period, Tp; wave number, k = L Tp
is calculated using the dispersion relation; depth, h, is equivalent to average depth, Day; 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/cmA2/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 j 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 10
0 00
"0 Y = 19000x38
.0', 0 c 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

o Hard Bottom
A Control
- Hard Bottom
- - Control

U-Velocity
y =230x- 11
R2 = 0.65

1 0y=-190x -6
R' 0.57

A
AOO

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)

I
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 R2
Hmo H.B. y = 19000x57 0.65
(in) Con y 8900x4.7 0.48
Max U-Vel H.B. y -380OO3.9 0.68
........ ........... ........................... ... .. 6. ....................
(m/s) ,Con ,y = 19000x 3.8 0.52 1

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 Rsquared value for the control trendline.




Table 4.4: Trendline and R-squared values for fines sedimentation data
Parameter Site Equation RHmo H.B ..... ] 50x 2] 0.57
............. m. o. ............... .....-B................. ... .. ... ............... .... ...................... .-.........................
(in) Con y = 140x 13 0.59
Max U-Vel H.B. y =.230x 1] 0.65
(m/s) Con y = 190x-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 Analy1is
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} Dep!cymernt 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} Deoloyment 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
I11I I I j

240.70 244.86

249.03 253.20 257.36
Julian Day

261.53

265.70 269.86

-5.8
E 5.6 5.4 5.2

0.6
E 0.4
0
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} Depioyment 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 24492 249.08 253.25 257.42 261.58 265.75 269.92 Julian Day

0.5
0.4 E 0.3 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 = 0.21 m Peak Period = 5.27s
Average Depth

E 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
o-0.3
E
0.2 0.1

10




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
-
2-

275.78

279.95

284.11 Julian Day

288.28

292.45

0
E 0.2




LONGBOAT KEY 34 WAVE DATA SUMMARY DEPLOYMENT #2
Sampling Period:
9/30193@18:C:39 10/23/93@6:0:39 (bursts:1 2711 Deployment Averages: Depth = 5.38m Significant Wave Height = 0.23m Peak Period = 5.11 s
Average Depth

276.83 281.00 285.17 289.33 293.50

Significant Wave Height

0.5

276.83

281.00

285.17

289.33

293.50

Peak Period

276.83 281.00 285.17 289.33 293.50
Julian Day

U,




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

E 5.
5.

276.83 281.92 286.83 291.00 295.17

Significant Wave Height E 0.5 nHmo
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

E4.8
> 4.6
MA

E5
0 0.5
E

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/l/93@18:0:55 {bursts:1 -101) Deployment Averages: Depth = 4.62m Significant Wave Height = 0.38m Peak Period = 5.85s
Average Depth

E 4. >4.
0 4.,

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

297.17 298.00 298.83 299.67 300.50 301.33 302.17 303.00
Julian Day

303.83 304.67

1.4
__1.2
o00.8 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
I- I

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 w

-1.5
E
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 2291 Deployment Averages: Depth = 5.01 m 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[I/

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
E6
05.6
5.4 5.2

8 C.6
I-




LONG KEY WAVE DATA SUMMARY DEPLOYMENT #5 Sampling Period:
11 /10/93 @16:0:52 1/12/94 @4:0:52 f{bursts: 1 511) Deployment Averages: Depth = 4.45m Significant Wave Height = 0.29m Peak Period = 5.78s
Average Depth

337.75 341.92 346.08 350.25 354.42 358.58 362.75 1.92 6.08 10.25

Significant Wave Height 5
5

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

E 4.5
0.