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Physical modeling of nearshore response to offshore borrow pits

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Title:
Physical modeling of nearshore response to offshore borrow pits
Series Title:
Physical modeling of nearshore response to offshore borrow pits
Creator:
Williams, Brian P.
Place of Publication:
Gainesville, Fla.
Publisher:
Coastal & Oceanographic Engineering Dept. of Civil & Coastal Engineering, University of Florida
Language:
English

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University of Florida
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University of Florida
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UFL/COEL-2002/005

PHYSICAL MODELING OF NEARSHORE RESPONSE TO OFFSHORE BORROW PITS
by
Brian P. Williams

THESIS

2002




PHYSICAL MODELING OF NEARSHORE RESPONSE TO
OFFSHORE BORROW PITS
By
BRIAN P. WILLIAMS

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

2002

wppw-




Copyright 2002 by
Brian P. Williams




ACKNOWLEDGMENTS
This work is the result of many dedicated individuals in the Department of Civil and Coastal Engineering at the University of Florida. Dr. Robert G. Dean, my advisor and committee chair, deserves special thanks for his guidance and assistance during the past two years. I would also like to thank the other members of my committee, Dr. Robert J. Thieke, and Dr. Ashish J. Mehta. In addition, Becky Hudson deserves special recognition for keeping me on track and informed during my graduate studies. Finally, this thesis would not have been possible without the efforts of the staff at the Coastal Engineering Laboratory. James Joiner, Vernon Sparkman, Vic Adams, and Sidney Schofield were always around to lend a helping hand during my laboratory experiments.
The project under which this study was conducted was sponsored by the Bureau of Beaches and Coastal Systems of the Florida Department of Environmental Protection; this support is appreciated greatly.




TABLE OF CONTENTS
pg&e
A CKN OW LED GM EN TS ................................................................................................. iii
LIST OF TAB LES ............................................................................................................. vi
LIST OF FIGURES .......................................................................................................... vii
ABSTRACT ....................................................................................................................... xi
CHAPTERS
I INTRODU CTION ............................................................................................................ I
Problem Statem ent .......................................................................................................... I
Objectives ....................................................................................................................... 2
2 BA CK GROUN D .............................................................................................................. 3
Grand Isle, LA ................................................................................................................ 3
Previous Investigations ................................................................................................... 5
H orikaw a et al. (1977) ............................................................................................. 5
M otyka and W illis (1974) ........................................................................................ 7
K ojim a et al. (1986) ................................................................................................. 8
Price et al. (1978) ................................................................................................... 10
3 PRELIM IN ARY EXPERIM EN TS ................................................................................. 12
Sm all Basin Experim ents .............................................................................................. 12
Experim ent Setup and Equipm ent .......................................................................... 12
Borrow Pit M odels ................................................................................................. 14
Results of Sm all Basin Experim ents ............................................................................. 16
Prelim inary Large Basin Experim ents .......................................................................... 18
Experim ent Setup and Equipm ent .......................................................................... 18
Profile M easurem ents ............................................................................................ 20
Shoreline M easurem ents ........................................................................................ 21
Results of Large Basin Experim ents ............................................................................. 21
4 FINAL LARGE BA SIN EXPERIM EN TS .................... ................................................ 24
A ccuracy of Laser Level ............................................................................................... 24




Experim ent Setup and Equipm ent ................................................................................ 25
Profile M easurem ents ............................................................................................ 28
Bathym etric M easurem ents .................................................................................... 30
Shoreline M easurem ents ........................................................................................ 31
Measurement Procedure and Sequencing of Experiments ............................................ 31
5 RESULTS AN D DISCU SSION ..................................................................................... 33
Shoreline Change Trends .............................................................................................. 33
V olum e Change Trends ................................................................................................ 36
Partial Explanation for V olum e Change ....................................................................... 45
Even-O dd Analysis ....................................................................................................... 45
V olum e Change ............................................................................................................ 51
Effective Vertical D im ension of A ctive Profile ............................................................ 52
N earshore Bathym etric Trends ..................................................................................... 53
Com parison of Current Results to Previous Investigations .......................................... 57
6 SUM M ARY AN D CON CLU SION S ............................................................................. 60
APPENDICES
A COM PLETE BEACH PROFILES ................................................................................. 64
First Final Large Basin Experim ent .............................................................................. 64
Second Final Large Basin Experim ent ......................................................................... 69
Third Final Large Basin Experim ent ............................................................................ 73
B OV ERHEAD D IGITAL PH OTOGRAPH S ................................................................... 78
First Final Large Basin Experim ent .............................................................................. 78
Second Final Large Basin Experim ent ......................................................................... 85
C EV EN/ODD COM PARISON S ...................................................................................... 92
First Final Large Basin Experim ent .............................................................................. 93
Second Final Large Basin Experim ent ......................................................................... 94
Third Final Large Basin Experim ent ............................................................................ 95
LIST OF REFEREN CES ................................................................................................... 96
BIO GRAPH ICAL SKETCH ............................................................................................. 97




LIST OF TABLES

Table page
4. 1: Results of repeated measurements........................................................... 25
4.2: Physical characteristics of final large basin experiments.................................. 27
5. 1: Comparison of relative influence of odd components of shoreline and volume
change to shifted even components of shoreline and volume change ................ 51
5.2: Comparison of current results to Irorikawa et al. (1977) and Motyka and Willis
(1974) ..................................................................................... 58




LIST OF FIGURES
Figure pae
2. 1: Aerial photo of salients and erosional hot spots at Grand Isle, LA. in December,
1986 ............................................................................................................................ 5
3. 1: Small basin setup for preliminary experiments ............................................................ 13
3.2: Cross-sectional view of plastic cylinder setup ............................................................. 15
3.3: Results of preliminary small basin experiment using trimmed plastic cylinder .......... 17
3.4: Results of preliminary small basin experiment using rectangular wooden box ........... 17
3.5: Plan view of large basin setup ...................................................................................... 19
3.6: Cross-section view of large basin setup ......................................................................... 19
3.7: Summary of shoreline changes for the preliminary large basin experiments .............. 22
3.8: Center profile of the first experiment of the second large basin setup ......................... 23
4.1: Plan view of laboratory setup for final large basin experiments .................................. 26
4.2: Cross-sectional view of laboratory setup for final large basin experiments ................ 27
4.3: Locations of survey stations ......................................................................................... 29
4.4: Example of measured beach profiles for one survey station ........................................ 30
4.5: Experiment progression timeline ................................................................................... 32
5.1: Shoreline change for the first final large basin experiment ........................................... 34
5.2: Shoreline change for the second final large basin experiment ..................................... 35
5.3: Shoreline change for the third final large basin experiment .......................................... 35
5.4: Measurement setup for an example profile .................................................................. 37
5.5: Volume change for first final large basin experiment .................................................. 38




5.6: Volume change for second final large basin experiment ............................................. 39
5.7: Volume change for third final large basin experiment ................................................. 39
5.8: Cumulative volume change per unit length for first final large basin experiment ........ 41 5.9: Cumulative volume change per unit length for second final large basin experiment. A2 5. 10: Cumulative volume change per unit length for third final large basin experiment.....43 5.11: Total volume change estimates for all final large basin experiments ........................ 44
5.12: Shifted even component of shoreline change for the first final large basin
experim ent ................................................................................................................ 47
5.13: Shifted even component of shoreline change for the second final large basin
experim ent ................................................................................................................ 47
5.14: Shifted even component of shoreline change for the third final large basin
experim ent ................................................................................................................ 48
5.15: Shifted even component of volume change per unit length for the first final large
basin experim ent ....................................................................................................... 49
5.16: Shifted even component of volume change per unit length for the second final large
basin experim ent ....................................................................................................... 49
5.17: Shifted even component of volume change per unit length for the third final large
basin experim ent ....................................................................................................... 50
5.18: Determination of the effective vertical dimension of the active profile for the final
large basin experim ents ............................................................................................ 53
5.19: Initial contours of the first large basin experiment ...................................................... 54
5.20: Contours of the first large basin experiment after six hours with the pit covered ....... 55
5.21: Contours of the first final large basin experiment after six hours with the pit
uncovered ................................................................................................................... 55
5.22: Initial contours of the second final large basin experiment ......................................... 56
5.23: Contours of the second final large basin experiment after six hours with the pit
covered ....................................................................................................................... 56
5.24: Contours of the second final large basin experiment after six hours with the pit
uncovered ................................................................................................................... 56
A. 1: Profiles for 120 cm survey station of first final large basin experiment ................... 64




A.2: Profiles for -80 cm survey station of first final large basin experiment ..................... 65
A.3: Profiles for -40 cm survey station of first final large basin experiment ..................... 65
AA Profiles for -20 cm survey station of first final large basin experiment ..................... 66
A.5: Profiles for 0 cm survey station of first final large basin experiment ......................... 66
A.6: Profiles for +20 cm. survey station of first final large basin experiment ..................... 67
A.7: Profiles for +40 cm survey station of first final large basin experiment ..................... 67
A.8: Profiles for +80 cm survey station of first final large basin experiment ..................... 68
A.9: Profiles for + 120 cm survey station of first final large basin experiment ................... 68
A.10: Profiles for -120 cm survey station of second final large basin experiment .............. 69
A. 11: Profiles for -80 cm survey station of second final large basin experiment ................ 69
A. 12: Profiles for -40 cm survey station of second final large basin experiment ................ 70
A. 13: Profiles for -20 cm survey station of second final large basin experiment ................ 70
A. 14: Profiles for 0 cm survey station of second final large basin experiment .................... 71
A. 15: Profiles for +20 cm survey station of second final large basin experiment .............. 71
A. 16: Profiles for +40 cm survey station of second final large basin experiment .............. 72
A. 17: Profiles for +80 cm survey station of second final large basin experiment .............. 72
A. 18: Profiles for +120 cm survey station of second final large basin experiment ............ 73
A. 19: Profiles for -120 cm survey station of third final large basin experiment ................ 73
A.20: Profiles for -80 cm survey station of third final large basin experiment .................. 74
A.2 1: Profiles for -40 cm survey station of third final large basin experiment .................. 74
A.22: Profiles for -20 cm. survey station of third final large basin experiment .................. 75
A.23: Profiles for 0 cm survey station of third final large basin experiment ...................... 75
A.24: Profiles for +20 cm survey station of third final large basin experiment .................. 76
A.25: Profiles for +40 cm survey station of third final large basin experiment .................. 76
A.26: Profiles for +80 cm survey station of third final large basin experiment .................. 77




A.27: Profiles for +120 cm survey station of third final large basin experiment ................ 77
B. 1: Photo of first final large basin experiment at 0.0 hr time step ...................................... 78
B.2: Photo of first final large basin experiment at 1.5 hr time step ...................................... 79
B.3: Photo of first final large basin experiment at 3.0 hr time step ...................................... 80
BA Photo of first final large basin experiment at 6.0 hr time step ...................................... 81
B.5: Photo of first final large basin experiment at 7.5 hr time step ...................................... 82
B.6: Photo of first final large basin experiment at 9.0 hr time step ...................................... 83
B.7: Photo of first final large basin experiment at 12.0 hr time step .................................... 84
B.8: Photo of second final large basin experiment at 0.0 hr time step ................................ 85
B.9: Photo of second final large basin experiment at 1.5 hr time step ................................ 86
B. 10: Photo of second final large basin experiment at 3.0 hr time step .............................. 87
B. 11: Photo of second final large basin experiment at 6.0 hr time step .............................. 88
B. 12: Photo of second final large basin experiment at 7.5 hr time step .............................. 89
B. 13: Photo of second final large basin experiment at 9.0 hr time step .............................. 90
B. 14: Photo of second final large basin experiment at 12.0 time step .................................. 91
C. 1: Odd and shifted even components of shoreline change for first final large basin
experim ent ................................................................................................................ 93
C.2: Odd and shifted even components of volume change for first final large basin
experim ent ................................................................................................................ 93
C.3: Odd and shifted even components of shoreline change for second final large basin
experim ent ................................................................................................................ 94
CA: Odd and shifted even components of volume change for second final large basin
experim ent ................................................................................................................ 94
C.5: Odd and shifted even components of shoreline change for third final large basin
experim ent ................................................................................................................ 95
C.6: Odd and shifted even components of volume change for third final large basin
experim ent ................................................................ 4 ............................................... 95




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 Science
PHYSICAL MODELING OF NEARSHORE RESPONSE TO OFFSHORE BORROW PITS
By
Brian P. Williams
August 2002
Chair: Dr. Robert G. Dean
Cochair: Dr. Robert J. Thieke
Department: Civil and Coastal Engineering
Beach nourishment has become the shore protection method of choice for many communities and states in recent years. Despite all that is currently known about the planning and scheduling of a successful beach nourishment project, questions remain concerning some of the possible impacts of dredging and placing sand. Dredging compatible, "beach quality" sand from offshore sources is the most widely implemented procedure for obtaining the large volumes of sediment required. The dredging process leaves depressions in the seabed called offshore borrow pits. These offshore borrow pits can alter the waves approaching the shoreline and thus alter the shoreline itself. While the complete relationship between dredged offshore borrow pits and the adjacent shoreline is not currently understood, it is recognized that the position, dimensions, and configuration of the pit, along with the site specific wave characteristics, are important




factors in determining whether the pit will cause adverse effects or not and, if so, the magnitude of the effect.
To investigate the nearshore response to borrow pits, a physical model study of a
beach and borrow pit system was conducted in the Coastal Engineering Laboratory at the University of Florida in Gainesville, Florida. A wavemaker produced shore-normal waves and the model beach was subjected to waves both with and without the presence of an offshore borrow pit. Numerous experiments were carried out from June 2001 to March 2002, but only three contained information specific and complete enough to be included in the final data set. Measurements of the shoreline location relative to a preestablished, fixed baseline, nine beach profiles, and digital photographs of nearshore contours were collected during the experiments. Upon completion of the experiments, data analysis focused on the shoreline changes due to the presence of the borrow pit and volume changes as determined by beach profiles. Reviewing the results of the shoreline changes revealed shoreline advance due to the presence of the borrow pit on the leeward shore. Volume gains, from the profile data, were generally experienced in the same areas as shoreline advance.
It is clear from the data collected that under the conditions of the experiments, the
existence of the borrow pit was responsible for both shoreline advance and volume gains on the beach in the lee of the pit. These results agree with previous experiments using physical models but are contrary to previous results based on numerical modeling.




CHAPTER I
INTRODUCTION
Problem Statement
Since the 1970s, beach nourishment has been a popular alternative to hardened
structures such as seawalls, breakwaters, and groins for communities seeking to maintain the natural character of their beaches. As more Americans continue to relocate to coastal communities or choose beaches as vacation destinations, the popularity of beach nourishment will continue to grow. Millions of dollars are spent on beach nourishment projects each year in the United States. The State of Florida alone spends roughly $30 million each year. That total increases to approximately $ 100 million considering that most of the projects within Florida receive matching funds from both the federal and local governments. In view of the vast amount of resources spent on beach nourishment, there continues to be a need to better understand the results of nourishment projects.
The majority of beach nourishment projects are dependent on the availability of large offshore deposits of "beach quality" sand. The performance of a beach nourishment project can be correlated directly to the compatibility of the fill with the native sediment. When deposits meeting compatibility requirements are located, dredging equipment is required to relocate the sediment to the beach where it can be placed to increase the beach width and volume. The complete effects of the offshore borrow pit, created during dredging, on the landward wave climate and surrounding beach are still unknown. However, it is clear that the pit size, configuration, and location offshore will influence




the magnitude of its effects. Some researchers suggest that borrow pits are responsible for erosion of the leeward beach in question, while others contend that accretion results.
Objectives
This study employs physical models to examine the relationship between offshore borrow pits and the adjacent nearshore environment. Through the course of experimentation it became clear that, in the laboratory environment, shoreline response alone was not sufficient to understand the complex nature of the interaction between the offshore borrow pit and the nearshore environment. Therefore measurements of beach profiles and nearshore bathymetry were undertaken in addition to shoreline observations. Beach profiles, taken at specific intervals during experimentation, will allow calculations of volume per unit length changes at specific locations along the model beach. The volume changes and shoreline changes will then be used to better understand the results a borrow pit can have on adjacent nearshore environments. Wave field measurements were not obtained during these experiments due to the fact that a previous student, Christopher Bender (200 1, p. 105) (in his MS Thesis), had already undertaken a wave field investigation within the same laboratory set-up. Mr. Bender noted the following:
The data (wave height) obtained were very erratic and inconsistent. While the general trends of wave height reduction inside and behind the pit were
seen, other areas showed trends that were conflicting and unexpected.
Also, consistent and repeatable wave height values for the case of no pit
were elusive for most incident waves trials.
The inability to quantify the effects of the test pit on the wave field is believed to be due to the somewhat irregularity of the wave field and the small changes induced in the wave field. Thus, the experiments reported here did not include any investigation of the wave fields in the vicinity of the pit.




CHAPTER 2
BACKGROUND
The effects on the adjacent shoreline of borrow pits created for beach nourishment remain a subject of considerable debate. At this time, it is unclear whether borrow pits are responsible for shoreline advance or retreat or a combination of both. It is possible that offshore borrow pits can have either effect depending on the dimensions and shape of the pit, its location relative to the shoreline, and the dominant wave climate at the site. The analysis is further complicated due to the four different wave transformation processes an offshore borrow pit can cause: wave refraction, wave diffraction, wave reflection, and wave dissipation (Bender, 2001). The combination of these processes could result in sheltering of the shoreline leeward of the pit and sediment transport towards the centerline of the borrow pit (Dean and Dalrymple, 2001). Wave refraction can also be used to support theories of shoreline retreat leeward of offshore borrow pits. As waves encounter the borrow pit, the wave celerity increases due to the deeper water and a convex shoreward wave front forms. The resulting refraction pattern would cause the waves to break at larger angles at the shore and create sediment transport divergent from the centerline of the pit (Komar, 1998).
Grand Isle, LA
Grand Isle, Louisiana is the site of one of the most well known examples o f documented interaction between a borrow pit and the surrounding beach. The development of the salient features at Grand Isle was one of the motivating factors behind




the research presented in this thesis. A nourishment project completed in the summer of 1984 resulted in a complex borrow pit shaped much like a dumbbell. The borrow area was located approximately 914 m offshore and measured nearly 2,740 m in the longshore direction by 460 m in the cross-shore direction (Combe and Soileau, 1987). The "bells" were excavated to approximately 6 m below the seabed and the middle portion was excavated to 3 m below the seabed (Combe and Soileau, 1987). The centroids of the two bell shaped pits were located about 1,370 m apart (Combe and Soileau, 1987). By August of 1985, the beach experienced growth of two salients and three erosional hot spots. It appears that the borrow pits are responsible for the development of both the salients and erosional hot spots. Figure 2.1 below provides an aerial view, taken in December of 1986, of the nourishment area and the aforementioned features.




Figure 2.1: Aerial photo of sahents and erosional hot spots at Urana Isle, LA. in December, 1986.
Previous Investigations
Borrow pit influence on adjacent nearshore environments has been investigated
previously. This section summarizes the experiments undertaken by three earlier groups of researchers.
Horikawa et al. (1977)
Horikawa et al. (1977) investigated, through the use of mathematical and laboratory models, the effects on shoreline shape due to removal of submarine deposits of sediment. The mathematical model was designed to simulate the shoreline changes of a beach subjected to an altered topography and wave climate resulting from offshore dredging. Dredged borrow pits have the ability to change the pattern and magnitude of the waves




approaching the shoreline. The changes in the waves can be manifested by alterations in the wave height and direction. The assumptions of the mathematical model were as follows:
" The initial shoreline is infinitely long and straight.
" The beach is composed of the same profile everywhere before dredging
(straight, parallel contours).
* Only longshore sediment transport is* taken into account.
" Erosion or accretion has no effect on the beach profile shape in the nearshore
region.
" Only wave refraction due to the pit was considered.
The mathematical "one-line" model first calculated breaking wave conditions by refracting given offshore wave conditions over the altered offshore topography. It then calculated rates of longshore sediment transport on the beach and determined changes in shoreline shape. The model was used to predict shoreline changes for six different cases of dredge pit location. The cross-shore position and length of the pit were varied, as was the duration of testing.
The mathematical model results showed accretion behind the dredge pit and slight
erosion on either side of the pit. The prediction of accretion is somewhat puzzling since no wave diffraction, reflection, or dissipation were taken into consideration. The model simulations revealed the following trends:
" The effects on a shoreline are reduced, as the pit is located farther seaward.
* As the cross-shore length of the pit increases, the amount of accretion increases,
but the increase in erosion is only minor.
" The erosive areas display rapid changes for approximately half a year and then
undergo slower changes. The area of accretion experiences large increases in
magnitude for about one year and shows little change thereafter.




The laboratory studies were conducted in a 6 m long, 1.2 m wide, and 0.15 m deep wave basin. The model beach was constructed with a 1/10 slope from mesalite (specific gravity 2.4 and median diameter 0.66 mm) and the rectangular borrow pit was 40 cm long, 30 cm wide, and 1.25 cm deep. The pit was located approximately 100 cm from the stillwater line of the beach. Waves with a period of 0.41 sec and constant offshore wave height of 1.3 cm were generated over a filled pit for 5.5 hours, to approximate an equilibrium condition. Then the pit was opened and the model was subjected to waves with the same characteristics for a period of 3 hours. The shape of the shoreline and the distribution of wave height were measured after periods of 1, 2, and 3 hours.
The results of the laboratory experiment showed accretion behind the pit and erosion on either side. Thus qualitative agreement between the mathematical and laboratory models existed. However, the magnitude of accretion during the laboratory model was much greater than that predicted by the mathematical model with otherwise identical characteristics. Both the magnitudes of accretion and erosion were greater in the laboratory model than predicted by the mathematical model. Motyka and Willis (1974)
Motyka and Willis (1974) also employed a mathematical model to investigate the
effects of borrow pits on adjacent coastlines. The mathematical model consisted of two parts:
1. A wave refraction model to calculate the paths of wave orthogonals over the
nearshore topography.
2. A beach plan shape model that calculated time dependent changes in beach shape
produced by longshore sediment transport.
The model first calculated breaking wave conditions using the refraction model and then calculated the rates of longshore sediment transport due to the breaking waves and




determined changes in the beach plan shape. An 880 mn long and 305 mn wide rectangular pit was selected for the mathematical model. The pit's depth and its cross-shore position on the model beach were varied during the model testing. The model beach configuration was selected from a composition of numerous profiles on Great Britain's Great Yarmouth coast. The wave climate was also selected from typical conditions on the North Sea and English Channel coasts of Britain.
Preliminary tests of the mathematical model were analyzed for a period equivalent to 10 years. However, it became clear that the results were reasonably stable after a period equivalent to 2 years. The results of the mathematical model showed erosion behind the borrow pit and accretion on either side. These results are contrary to those presented by Horikawa et al. (1977). The mathematical model also revealed the following trends:
" Erosion magnitude increased with increasing pit depth.
" Erosion magnitude also increased as the pit's location was moved closer to the
shoreline and into shallower water depths.
The reasons behind the diametrically opposed results of these two previous
investigations are not clear. Both mathematical models used a range of wave heights, periods, and durations. The magnitude of the wave heights and periods were also very similar. Hopefully, the results from the physical models being presented in this thesis will serve to reduce some of the confusion surrounding the conflicting findings presented above.
Kojima et al. (1986)
Since the early 1970s, sediment has been removed from offshore locations along the coast of the Genkai Sea in the northern part of Kyushu, Japan, for use as aggregate in concrete. This study was undertaken due to public concern that dredging of sand and




gravel from the sea bed was causing erosion of beaches previously considered stable. The goals of this study were as follows:
1. Identify historical shoreline changes and their characteristics;
2. Investigate causes of significant beach erosion and accretion through
considering wave and climatic characteristics of the area as well as human
activities like offshore dredging and coastal structures;
3. Evaluate the relationship between beach erosion and offshore dredging;
4. Propose guidelines on how offshore mining should be conducted.
In order to complete the defined objectives, the following studies were undertaken from 1981 to 1985.
1. Meteorological surveys including assemblage of wind data since 1896 and
the number of typhoon attacks.
2. Assemblage of offshore wave data from 1975 to 1984.
3. Assemblage of permitted volume of sand removed from the sea bed
between 1972 and 1983.
4. Analysis of aerial photographs taken from 1947 to 1982 to determine
historical shoreline change.
5. Hydrographic surveys to obtain profile changes in beach and dredged
holes during the study period.
6. Fluorescent tracer studies and sea bed level measurements to obtain data
on sediment movement.
This study found the major cause of severe beach erosion within the study area to be the results of an abnormally high frequency of destructive wave attacks, which were inferred from the storm-wind data. However, the offshore dredging areas seemed to be responsible for some degree of shoreline recession. This assertion was aided by the fact that dredged holes in water shallower than 30 meters were found to be refilled with sand. The main source of sand filling the holes originated from the onshore environment.




Therefore, the dredged holes were trapping sand that naturally moves in either crossshore or longshore directions. Despite the inability of this study to establish a cause-andeffect relationship between offshore dredging and beach instability, it recommended that dredging be discouraged within the water depth where drastic beach profiles changes occur. This depth is commonly referred to as the critical or closure depth. Price et al. (1978)
In the United Kingdom in 1976, roughly 11% of the total sand and gravel production was provided by offshore dredging. Therefore, the Hydraulics Research Station sought answers to the following questions before licensing a dredging application.
1. Is the area of dredging far enough offshore to prevent beach drawdown into the
deepened area?
2. Is the dredging going to take place in deep enough water so as not to affect
onshore movement of shingle?
3. Does the dredging area include features like bars and banks that might provide
protection from wave attack?
4. Is the area to be dredged far enough offshore and in deep enough water that
refraction of waves will not cause significant changes to the pattern of sediment
transport?
The Hydraulic Research Station referenced previous studies in California and instituted the criteria that dredging must occur at a minimum depth of 10 meters and a minimum offshore distance of 600 meters. The results of field tracer studies lead to the criterion that shingle not be removed in depths shallower than 18 meters. They also established that offshore banks should not be modified by dredging unless special circumstances are met and the quantity of dredged material is limited. Finally, a mathematical model using wave refraction and sediment transport yielded that, in general, the effects of wave




11
refraction due to dredging that takes place in water depths greater than 14 meters are insignificant.




CHAPTER 3
PRELIMINARY EXPERIMENTS
All physical modeling during this investigation was conducted in the Coastal Engineering Laboratory on the campus of the University of Florida in Gainesville Florida. Two different wave basins were used during this investigation. Every effort was taken during experimentation to document all findings accurately and to maintain consistency in measurement procedures.
Small Basin Experiments
These initial experiments were intended to provide insight into the processes due to borrow pit interaction with the nearshore environment. It was necessary to become familiar with and develop testing procedures and alternative methods of quantifying nearshore response. Thus, these experiments were undertaken as training exercises before the main experiments began.
Experiment Setup and Equipment
Initial investigations began in a relatively small wave basin measuring 5 0 feet (15.24 mn) by 50 feet (15.24 in). The model measured 11I feet (3.35 mn) in the longshore direction, 18 feet (5.49 mn) in the cross-shore direction, and was bordered by rows of concrete blocks as wave-guides. The offshore portion of the model consisted of small rocks, varying in size, and was separated from the sandy beach by a wooden partition that ran the width of the model. Figure 3.1 shows a plan view of the basin setup.




Figure 3. 1: Small basin setup for preliminary experiments. This setup was established by a previous student and since these experiments were meant to be initial investigations, no effort was made to replace the rocks with sand.
Several methods were implemented to simulate the existence of a borrow pit. A
hollow plastic cylinder, cinder block, and rectangular wooden box were all used to model the borrow pit. Each model was tested at different cross-shore positions and wave characteristics. The only constants during each experiment were the water depth and the angle of approach of the waves. Realistically, the water depth was not truly constant since leaks in the basin and evaporation during the summer months were responsible for lowering the water level slightly. However, the water depth was established at the proper level prior to each new phase of experimentation.




Waves were generated by a paddle-type wavemaker, hinged at the floor, with both an adjustable stroke and period. Other equipment consisted of a stopwatch, a meter stick, and a shovel.
Each experiment consisted of a control phase and a test phase. The control phase
began by smoothing the beach to provide straight and parallel contours and was followed by an interval of waves to establish an equilibrium condition. The test phase consisted of introducing the borrow pit model which was subjected to waves of the same height, period, and duration as the equilibrium condition. The results of each phase were recorded in the form of shoreline response. The shoreline response was determined by recording the distance from a stationary baseline to the stillwater line at six-inch (15.25 cm) intervals along the width of the project beach. The longshore locations of these measurement intervals remained constant throughout testing in this basin to allow shoreline changes to be calculated.
Borrow Pit Models
Each physical model of the borrow pit underwent different testing conditions. The wave period, wavemnaker stroke, and position of the physical model relative to the baseline were all varied during these preliminary small basin experiments. Initially, a 12.75 inch (32.4 cm) diameter, hollow cylinder, extending through the entire water column was used to test the nearshore response to an obstruction. This condition simulates a detached breakwater rather than an offshore borrow pit, but the results could be helpful in determining whether a borrow pit behaves similar to a breakwater. Figure
3.2 below provides a cross-sectional view of the setup.




Figure 3.2: Cross-sectional view of plastic cylinder setup.
For the next set of experiments, the plastic cylinder was trimmed to a height of 4.5 inches (11.43 cm) so that it could be buried with its top rim level with the surrounding sand. During control phases, the cylinder was filled with rocks and the rocks were excavated prior to test phases. Later, the plastic cylinder was replaced by a concrete block measuring 4 inches (10. 16 cm) wide, 16 inches (40.64 cm) long, and 7.5 inches (19.05 cm) high. Like the full height plastic cylinder, the concrete block modeled a breakwater rather than a borrow pit. Next, a rectangular box was nailed to the partition, such that the inside of the box was buried in the sand. The inside dimensions of the box were 35 inches (88.90 cm) in the longshore direction and 9.5 inches (24.13 cm) in the cross-shore direction. During control phases, rocks filled the interior of the box and were then removed for test phases. Two additional experiments used the rectangular box in a




partially filled condition. Rocks were piled against each short side during test phases, reducing the area and introducing tapered sides to the borrow pit.
Next, the model beach was reshaped in order to more closely approximate the
conditions at Grand Isle. The wave period, wavemaker stroke, and water level were adjusted in order to scale the model as closely as possible to the natural conditions at Grand Isle. The rectangular box was also relocated closer to the baseline to achieve a better representation of Grand Isle conditions.
After reviewing the results of the previous experiments and after having made
numerous visual observations during the experiments, sediment mobility emerged as a concern. Efforts to increase sediment mobility included inserting a "soaker hose" underneath the sand portion of the model and replacing the existing sediment with much smaller diameter sediment. After several attempts with the soaker hose and the smaller sediment, it became clear that the limitations of this wave basin were such that adequate shoreline response could not be obtained apparently due to the small forces available for sediment movement.
Results of Small Basin Experiments
Experiments using the full height plastic cylinder and concrete block exhibited an overall trend towards shoreline advancement in the lee of the cylinder. However, since these were not tests of borrow pit interaction with the nearshore environment, they were conducted for general purposes only. In contrast, experiments with the trimmed cylinder and rectangular wooden box failed to exhibit clear trends towards either shoreline advance or retreat. Introduction of the soaker hose failed to produce any definitive results, as did replacing the larger sand with finer sediments. Figures 3.3 and 3.4 present




17
representative results of experiments with the trimmed cylinder and rectangular box respectively.
Plastic Cylinder Pit

0 20 40 60 80
Longshore Position (in.)

Control Phase.....--TestPhs

Figure 3.3: Results of preliminary small basin experiment using trimmed plastic cylinder.

Period =0,53 sec Pha=-tI
Stroke =4.0 In -Test Phase
Figure 3.4: Results of preliminary small basin experiment using rectangular wooden box.
Unfortunately, the results from these preliminary experiments were inconclusive as to whether any relationship between the borrow pit models and shoreline existed. Because of this, the experiments were relocated to a larger scale wave basin where it was believed




a better and more energetic wave field could be obtained and thus more sediment transport and a greater possibility for measurable results.
Preliminary Large Basin Experiments
A model similar to that used by Horikawa et al. (1977) was constructed in the large
wave basin of the Coastal Engineering Laboratory at the University of Florida by Bender (2001) for a previous experiment. The experiments discussed in this section were all carried out in this model.
Experiment Setup and Equipment
The dimensions of the model were 15 m in the cross-shore direction and 3 m in the longshore direction. The offshore portions of the model consisted of a constant depth section of concrete floor leading to a sloped concrete section. The nearshore portion of the model consisted of another constant depth section of concrete floor. The rectangular offshore borrow pit was located in the center of the nearshore portion and had a depth of 12 cm relative to the adjacent bathymetry. Control phases (no pit) of these experiments were performed by inserting a weighted, wooden cover into the borrow pit. The model beach was placed "landward" of the rectangular pit using sand sized sediment. Figure 3.5 shows a plan view and Figure 3.6 shows a cross-section view of the model.




The equipment used during the experiments consisted of a snake-type wavemaker, Lasermark@ Rotary Laser Level, microcassette recorder, meter stick, metric measuring tape, tripod, and a small survey rod. The wavemaker had individually controlled paddles with adjustable phase and stroke. Each paddle was set to the same phase and the stroke was constant throughout the experiments. The period could also be regulated and was kept constant throughout. The first two experiments utilized a baseline 270 cm from the landward edge of the borrow pit. Following the second experiment, the setup was changed in order to advance the beach closer to the borrow pit by adding sand such that the stillwater line was advanced seaward by approximately 60 cm. In addition, the baseline was relocated 90 cm towards the borrow pit. Profile Measurements
Beach profiles were measured using the laser level, measuring tape, and survey rod. A metal beam was placed with a shore-parallel orientation across the concrete blocks directly above the landward edge of the borrow pit. The measuring tape was fixed to a sliding sleeve on the metal beam. The other end of the measuring tape rested on a chair beyond the baseline. This allowed the tape to stretch the entire length of the survey area and be relocated between the various survey stations. The first experiment in this series used three survey stations across the width of the beach, while the next three experiments used five survey stations. During the first experiment, one survey station was located above the centerline of the borrow pit, while the two remaining stations were spaced relative to the center as follows, -56 cm and +64 cm. The convention used places negative values to the left of the pit and positive values to the right as an observer looks from the beach toward the wavemaker. The next three experiments had survey stations at




o cm, -28 cm, -59 cm, +31.5 cm, and +59.5 cm relative to the centerline of the borrow pit. Recordings of the elevations along the beach profile were taken at 5 cm intervals beginning at the baseline and ending at the last position of sand on the model floor. During the surveys, which were conducted by one person, the coordinates of each survey point were read aloud and recorded via a microcassette recorder. The coordinates were later entered into a spreadsheet for analysis. After draining the model, the measurements were made by standing on the model beach with the survey rod. Shoreline Measurements
Shoreline or stillwater line positions were obtained for all experiments except for the first. These measurements were obtained by measuring the distance from the baseline to the stillwater crossing for the entire longshore distance of the model at 10 cm intervals. The cross-shore distances were obtained with a meter stick and can be used only as approximations.
Results of Large Basin Experiments
This model allowed greater water depths and thus larger wave heights. The possible wave periods were still limited; however, overall it was believed this setup could provide the necessary sediment mobility to produce better results. It was apparent both by visual inspection and from the results, that this new setup in the large basin provided increased sediment mobility.
Shoreline analysis of the second experiment using the first baseline showed accretion in the lee of the borrow pit and erosion on both sides. The first and second experiments of the second baseline did not demonstrate agreement between their locations of shoreline retreat and advance. The first experiment showed erosion of the shoreline in the lee of the borrow pit and trends toward accretion on both sides, while the second experiment




showed the opposite. The figure below depicts the shoreline change between the control phase (no pit) and the test phase (pit open) for the second experiment (#2) of the initial setup (first baseline) and both the first (#3) and second (#4) experiments of the second setup (second baseline).
Shoreline Change (Preliminary Large Basin)
/
C -10 -3 11 9/ -03 0 1 3,
6.0
-3 \10 90 -7 -0 -0 N 4. 0 /t 50 7 1 /1
8.0
40.
longshor Poeltion (cm)
I E~peinert #2 Expeimrt #3.-----Epernmert #4 Figure 3.7: Summary of shoreline changes for the preliminary large basin experiments.
After examining the beach profiles in concert with the shoreline responses, it became clear that the results did not always agree with the assumption that shoreline retreat would correspond to volume loss or that shoreline advance would correspond to volume being gained. This is illustrated in Figure 3.8 below, where sediment has been redistributed to advance the shoreline, but the profile has experienced an overall loss in volume.




Center Profile (First Experiment, Second Setup)
4.0 2.0
E
- 0.0
2: 1 40 60 80 100 11
-2.0
4, -4.0 -6.0
*
C -8.0
ao
-10.0
LU -12.0
-14.0
Cross-shore Distance (cm)
- Cotro Phe.-- Phas-Figure 3.8: Center profile of the first experiment of the second large basin setup.
Again, preliminary experiments in the large basin focused on establishing whether a
relationship exists between the borrow pit and the adjacent shoreline. When these experiments failed to yield repeatable results, it was concluded that a more complete data set was needed. Therefore, the number of profile survey stations was increased to nine
and nearshore bathymetry measurements were included in the survey procedure. These changes were instituted during the final two preliminary large basin experiments and carried on through all three final large basin experiments. These experiments are presented in detail in the following chapter.




CHAPTER 4
FINAL LARGE BASIN EXPERIMENTS
The experiments presented in this chapter are similar to those large basin experiments presented in the previous chapter, except that these experiments included the addition of bathymetric observations in addition to shoreline measurements, thus allowing volume changes to be calculated. Each experiment included measurements of the shoreline and profiles and digital photographs of nearshore bathymetric contours. In addition, the data analysis for these experiments was more extensive than those presented previously. Shoreline changes and volume per unit length changes were determined for each survey station and were subjected to even-odd analysis. The results of the even-odd analysis were used in the determination of the value of effective vertical dimension of active profile, (h. + B), for the model studies.
Before collecting what would become the final three data sets, two preliminary large basin experiments were carried out in order to test both the accuracy of the data and the validity of the procedures more completely. The results of these experiments were not used as data sets for the final results.
Accuracy of Laser Level
The instruction manual for the Lasermark Rotary Laser Level states that the device is accurate to 5 mm at 30 m distance and 3 mm at 15 m distance. Despite the manual's assurance of accuracy, the accuracy of the measurements being taken was evaluated. The farthest distance surveyed was approximately 5 m from the laser level. Therefore, during




the preliminary large basin experiments immediately prior to the three final large basin experiments, some of the profile measurements were repeated. During the two preliminary experiments a total of 11 profiles were duplicated. A total of 324 measurements were taken along the I I profiles. The following table summarizes the analysis of the repeated measurements.
Table 4. 1: Results f repeated measurements.
Difference (cm) Number of Occurrences Percentage Cumulative
(+/-) Percentage
0.0 34.26 34.3
0.1 133 41.05 75.3
0.2 67 20.68 96.0
0.3 10 3.09 99.1
0.4 3 0.92 100.00
By examining the table above, it is clear that the measurement techniques used for the laser profiles were accurate and repeatable. Ninety-nine percent of the repeated measurements fall within the 3 mm published accuracy of the laser for a distance of 15 meters and 75.3 percent are within 0. 1 cm, which is the scaled accuracy for the 5 meter distance encompassing the measurements.
Experiment Setup and Equipment
The experiments discussed in this section were all carried out with a model similar to that used by Horikawa and presented in the previous chapter. A model beach was




constructed with a 1/9 slope from quartz sand (specific gravity 2.65 and median diameter
0.24 mm) and the rectangular borrow pit was 80 cm long, 60 cm wide, and 12 cm deep. The first two final large basin experiments had a baseline 175 cm from the landward edge of the borrow pit and an average distance from the borrow pit to the shoreline of 160 cm. The third experiment had a baseline 245 cm from the landward edge of the borrow pit and an average distance from the borrow pit to the shoreline of 200 cm. The data collection procedure was identical for all three experiments. Figure 4.1 shows a plan view and Figure 4.2 shows a cross-sectional view of the model.
Basellne For
Baseline for
fir two experimenis

Figure 4. 1: Plan view of laboratory setup for final large basin experiments.




Base(Ine for

Figure 4.2: Cross-sectional view of laboratory setup for final large basin experiments.
Table 4.2 provides some of the physical characteristics of the three final large basin experiments.

Table 4.2: Physical characteristics of final large basin experiments.
Characteristic First and Second Final Third Final
Wave Period (sec) 1.35 1.35
Approx. Wave 6.0 6.0
Height (cm)
Beach Slope 0.112 0.122
Distance to borrow 160 200
pit (cm)
Water depth
immediately 15 15
landward of pit (cm)

y I Pnl~p




The equipment used during the experiments consisted of a snake-type wavemaker, laser level, microcassette recorder, meter stick, metric measuring tape, digital camera, and a small survey rod. Both the stroke and period of the wavemaker remained constant throughout all experiments. The water depth was also held constant. Assuming the stroke, period, and water depth remained constant, the approaching waves should, under ideal circumstances, have had identical characteristics. Profile Measurements
Profiles of the beach were measured using the laser level, measuring tape, and survey rod. The same setup and procedure were used during these final three experiments as was used during the initial large basin experiments presented in the previous chapter. The only difference was that the number of survey stations across the width of the beach was increased from five to nine. One survey station was located along the centerline of the borrow pit, while the remaining eight stations were spaced relative to the centerline as follows, -120 cm, -80 cm, -40 cm, -20 cm, 0 cm, +20 cm, +40 cm, +80 cm, and +120 cm. As for the previous experiments, positive and negative values indicate positions to the right and left of the borrow pit, respectively as an observer looks from the beach toward the wavemaker. Figure 4.3 presents the survey station locations.




rvqy

Figure 4.3: Locations of survey stations.
Recordings of the vertical position of the beach profile were taken at 5 cm intervals beginning at the baseline and ending at the cross-shore position of the landward edge of the borrow pit. To ensure that the sand bed was not disturbed during the measurements, the investigator conducted these measurements while standing on a wooden plank, supported on the concrete block wave guides, above the sand bed and oriented in the cross-shore direction. Figure 4.4 provides an example of the beach profile recordings for one of the survey stations.




0 10Oc
Profile at -120 cm
Crn
Previous Open (0,0 hr)
_-,_-, ,: 1 i Covered (3.0 hr) Covered (6,0 hr)
Open (75 hr) Open (9,0 hr) .... Open (12,0 hr)
Figure 4.4: Example of measured beach profiles for one survey station. Bathymetric Measurements
Nearshore contours were quantified as follows. Upon completion of each control and test phase, the water surface was allowed to become calm. A length of yarn was then laid at the stillwater location on the beach face. A release valve was then opened to allow water to escape from the basin. This process of laying lengths of yarn at the stillwater crossing was then repeated for every 0.5 cm change in the water level. This was done until the bathymetry became too complex for a single length of yarn. Usually five contour lines could be laid before the bathymetry became too complex. Following the completion of establishing the contours, an overhead digital picture was taken of the model. Using the baseline and sidewalls as reference points, the individual digital photos could then be scaled and compared. These photos were used for qualitative comparisons only.




Shoreline Measurements
Shoreline measurements were taken at the same time as the profiles. Instead of recording shoreline data at 10 cm intervals as during the preliminary large basin procedure, the cross-shore distance to the stillwater line was recorded only for each profile survey station. This reduced the number of data points for the shoreline comparisons, but was not a concern due to the amount of data being collected on the profiles.
Measurement Procedure and Sequencing of Experiments
Preliminary experiments began from a smoothed beach with straight and parallel
contours. During the final experiments, however, there were no modifications made to the beach before another experiment began. The first experiment of this final group began after the completion of the test phase (with the pit uncovered) of the last preliminary large basin experiment. This process allowed the investigation to monitor whether the model reverted back to original conditions after experiencing control phases and test phases. All the profiles and volume calculations were based on relative measures to the test phase of the previous experiment, hereafter referred to as the 0.0 hour observation. The second experiment began after the test phase of the first experiment. Each phase consisted of three different time steps. The duration of the time steps were as follows: 1.5 hours, 1.5 hours, and 3.0 hours. Each time step was followed by bathymetric, profile, and shoreline measurements. Thus, the total testing time for each phase was 6 hours and each total experiment time was 12 hours. Figure 4.5 provides a timeline representation of the experiment sequence.




Complete Experiment
Current Control Next Control
6.0 7.5 9.0 0,0 1.5 3.0 6.0 7,5 9.0 12.0 1.5 3.0 6.0
(12.0) (0.0)
Time Step (Hours)
Figure 4.5: Experiment progression timeline. Hereafter, each phase will be referred to by its completion time after the 0.0 hour observation (example: The final control phase was the 6.0 hour time step and the final test phase was the 12.0 hour time step).
The third experiment involved reshaping the model and shifting both the baseline and stillwater line landward. In order to maintain the procedure of the previous final large basin experiments, the initial straight and parallel contours were subjected to 6 hours of waves in the presence of the borrow pit prior to initiation of the control phase. The full battery of measurements then commenced and the control and test phases followed.




CHAPTER 5
RESULTS AND DISCUSSION
Shoreline Change Trends
In order to obtain shoreline change magnitudes, the difference between the cross-shore position at the time step in question and the cross-shore position at the 0.0 hour time step was obtained. The following equation illustrates the process.
Ay(x) = y(x,t)- y(x,) (5.1)
where: Ay(x) is the shoreline change at survey station "x" between times "t"
and t = 0.
y(x,t) is the cross-shore distance to the stillwater line at time step "t"
y(x,0) is the cross-shore distance to the stillwater line at time step 0.0
hours
* "x" denotes the longshore survey station position (-120, -80, -40,
-20, 0, 20, 40, 80, 120 cm)
and
* "t" indicates the time step (1.5, 3.0, 6.0, 7.5, 9.0, 12.0 hr)
Figures 5.1 through 5.3 below present the shoreline changes for the first, second, and third final laboratory experiments respectively. The line labeled "0 to 6 Hours" denotes the shoreline change between the end of the last preliminary large basin experiment (0.0 hour) and the end of the control phase of the first final large basin experiment (6.0 hours). Note that retreat of the shoreline during this phase amounts to re-




equilibration of the shoreline when the borrow pit was not present. Similarly, the line labeled "6 to 12 Hours" denotes the shoreline change between the end of the control phase of the first final large basin experiment (6.0 hours) and the end of the test phase of the first final large basin experiment (12.0 hours). Figure 4.5 in the previous chapter presents a timeline representation of the experiment progression and may assist in better understanding the relationship between the control and test phases.
Shoreline Change (First Final Large Basin) 25
e2
.. 1 120 J 20 20 40 60 80 -f 120O
20
Longs hare Position (cm)
------ -00 to 46 Hour -0 6"100ur

Figure 5.1: Shoreline change for the first final large basin experiment.




Shoreline Change (Second Final Large Basin)

Longshore Position (cm)
....... 0 to 6 Hours 6to12Hours

Figure 5.2: Shoreline change for the second final large basin experiment.
Shoreline Change (Third Final Large Basin)
20
40
20
16
0
6,6
_ -IO 1 "10 -8 60 ",40 -20 20 40 6 ,6 0 ..100_ 120 1
.................................................
og
Longshore Position (cm)
-...... Oto6 Hours 6to2Hours Figure 5.3: Shoreline change for the third final large basin experiment.
During the control phase, in the absence of the borrow pit, all of the final large basin experiments exhibited shoreline retreat in the lee of the borrow pit. In each case, the magnitude of retreat was greatest at the centerline of the borrow pit, survey station 0.0 cm. Each experiment also experienced shoreline retreat adjacent to the boundaries of the




borrow pit. The third large basin experiment was the only one not to experience shoreline advance at the edges of the survey area (-120 cm and +120 cm).
Each of the final large basin experiments also demonstrated shoreline advance in the lee of the borrow pit during the test phases (when the borrow pit was uncovered). Only the first experiment did not show the maximum advance located at the centerline of the borrow pit. Almost every survey station that experienced shoreline retreat during control phases experienced advance during test phases. In each experiment, the magnitude of largest retreat was closely matched by the magnitude of largest advance. With this evidence, one can conclude that under the conditions being tested, the presence of the borrow pit resulted in shoreline advance for the area of the model beach landward of the borrow pit. The positive effect of the borrow pit may also extend to the adjacent areas, however the results do not provide enough conclusive evidence to establish definite limits.
Volume Change Trends
Volume change between consecutive time steps was obtained after the recorded measurements were converted to coordinates relative to the initial, 0.0 hr time step. Because the ends of the measuring tape were fixed at each survey station and the baseline position was constant, the cross-shore position (y coordinate) of each survey point remained constant along each profile. In order to track changes in the cross-shore position of the stillwater point at each survey station in a time-dependent manner, all cross-shore measurements were adjusted to be relative to the stillwater point of the initial,
0.0 hr time step. This results in survey points landward of the stillwater point having negative cross-shore positions and survey points seaward of the stillwater point having positive cross-shore positions.




The vertical positions of each survey point were read from the intersection of the laser with the survey rod. In order to make the plotting of the profiles easier, the measured vertical positions (z coordinate) of each survey point were adjusted to be relative to the vertical position of the stillwater point of the initial, 0.0 hr time step. Figure 5.4 provides the measurement setup for an example profile. This resulted in positive vertical positions for survey points landward of the stillwater point and negative positions for those points seaward of the stillwater point.
z
Figure 5.4: Measurement setup for an example profile.
After obtaining relative coordinates for all the survey points along each survey station, the coordinates were plotted using AutoCAD. The volume change per unit length for each time step at each survey station was determined from the plotted profiles using the built-in area determination function of AutoCAD to evaluate the differences in area of consecutive profiles at the same survey station. The area difference corresponds to the




volume change per unit length. Next, the volume change per unit length was plotted for each time step across the width of the model, one volume change for each survey station. Again, AutoCAD was used to determine the area under this plot, giving an estimate of total volume change for each time step. Figures 5.5 through 5.7 provide the volume change per unit length versus longshore position plots for all three final large basin experiments.
Volume Change (First Final Large Basin)

-J
E
_0
E
0

S 158
.120 o .- a .60 .*4 -20 20 40 60 80 -1; 120 14
Longshore Position (cm) to6Fours 6to12Hours

Figure 5.5: Volume change for first final large basin experiment.




Volume Change (Second Final Large Basin)

L40 12 -60 -40 -20 20 40 60 80 120 it
.................................. .
Longshore Position (cm) ....... 0 to 6 Hours 6to12Hours

Figure 5.6: Volume change for second final large basin experiment.
Volume Change (Third Final Large Basin)

200,
10 -1 100 -80 -60 40 zo 20 40 60 80 10 120
S %. 60
- 100' -,
g0
Longshore Position (cm) .. ........to6 Hours 6 to 12 Hours

Figure 5.7: Volume change for third final large basin experiment.
With the exception of a few survey station locations, the entire model beach lost volume after 6 hours of wave interaction with the borrow pit covered. Most of the locations that experienced a gain in volume were located at the edges of the survey area.

0 U
J '-S
C.L E
E .5

0B
'E
E
-2
Cn
E 0)
_u-
o.




Losses for all of the experiments were of the same order of magnitude, with the second and third experiments exhibiting the largest losses.
After six hours of testing with the borrow pit present, most of the survey stations that previously experienced losses regained some or all of the volume lost. The second final large basin experiment was the only experiment that did not recover approximately the same magnitude of volume that was lost. For this experiment, the average magnitude regained was less than the magnitude lost by approximately 50 cm 3/cm. The second experiment also continued to lose volume at the -120 cm survey station while the borrow pit was present. This was the only experiment to exhibit this behavior. In addition, most of the survey stations that gained volume in the absence of the borrow pit lost volume in the presence of the pit. Although accurate conclusions cannot be drawn as to where the volume gained originated, it is evident that the presence of the borrow pit has a positive volumetric relationship with the adjacent beach.
By integrating curves of cumulative volume change per unit length versus longshore position for each testing period, it was possible to determine an estimate for the total volume change as a function of time for the survey area. Figures 5.8 through 5. 10 provide plots of the cumulative volume change per unit length versus longshore position of each testing period for the final large basin experiments.




0
N 40
U 30 .
eoI
-- 0-120 -80 0 O 40 80 120
C -40.
U -0. /-60. .
S -100.
-I ./
-110. V
1. Hou = 3,0 Hours 6.0 Hours 9,0 Hours 12.0 Hours
Figure 5.8: Cumulative volume change per unit length for first final large basin experiment.




Figure 5.9: Cumulative volume change per unit length for second final large basin experiment.




a'
Figure 5. 10: Cumulative volume change per unit length for third final large basin experiment.
By examining the cumulative volume change plots, it is evident that volume is lost at the survey stations within and immediately adjacent to the boundaries of the borrow pit during phases when the borrow pit was covered. Recall that these volume changes are relative to the volumes present at the beginning of each experiment. Since each experiment begins at the conclusion of a test phase, the greatest changes would be expected at the 6.0 hour and 12.0 hour time steps. Ideally, one would expect that the cumulative volume change would return to zero at the 12.0 hour test phase.
The cumulative volume change curves were integrated for each experiment and the results were plotted versus time in order to produce the results in Figure 5.11 below.




Total Volume Change vs. Time
00
E 0. C3.0 4.5 6.0 7.5 9.0 11 .0
-5000
"3 /
.... .. .. .. .. ..-....
Z -5000
-20000
Time (Hours)
- Frt Expenmet ....... Second Experment - Third Experment
Figure 5.11: Total volume change estimates for all final large basin experiments.
The results presented in Figure 5.11 should be considered as estimates as there were only nine survey stations across a 3.0 m wide beach. These were the most complete results that could be calculated with the data available from these experiments. This figure reinforces the fact that volume was recovered due to the presence of the borrow pit. Note the increases in total volume change immediately after the 6.0 hour period in each experiment.
The volume losses can be attributed to several factors, consolidation of sediment,
infilling of the borrow pit, and cross-shore transport of sediment outside the survey area. In addition, volume changes were calculated at the survey stations alone and no data exist for the model in between these locations. The cumulative volume change curves in Figures 5.8 through 5.10 were produced by linearly connecting the values at the survey stations. The assumption of linear interpolation between survey stations is believed to introduce only secondary errors in the results.




Partial Explanation for Volume Change
During the course of experimentation, significant amounts of sediment were observed to deposit in the borrow pit. By visual inspection, it was evident that approximately three times the amount of sediment was deposited in the borrow pit during the second final large basin experiment as during the first. The amount of sediment removed from the borrow pit during the second experiment was estimated to be between 2500 and 3000 cm 3. This may explain the difference in the total volume change estimates between the first and second experiments. Since the water depth, wavemaker stroke, and wave period were constant throughout these experiments, a change in test conditions cannot be responsible for the increased infilling of the borrow pit. The amount of sediment deposited in the borrow pit during the third final large basin experiment was far less than the previous two experiments. This is most likely due to the fact that the model beach was located farther away from the borrow pit during the third experiment. During each of the three final large basin experiments, sediment deposited inside the borrow pit was removed after each testing phase and was permanently removed from the system. In hindsight, the volume of sediment removed from the pit should have been quantified for each experiment. This volume could have then been compared to the estimates for total volume change.
Even-Odd Analysis
In an effort to isolate the changes (shoreline or volumetric) due to the presence of the borrow pit from other background processes, an even-odd analysis was performed on both the shoreline and volumetric change observations. The process decomposes longshore distributions of shoreline or volumetric changes into an even and an odd function about the origin of a longshore coordinate system where the origin is located at




the feature being considered (Dean and Dalrymple, 2001). Normally, an even-odd analysis is used in situations where inlets or coastal structures are present, but in this case, an even-odd analysis was used to examine shoreline and volume changes associated with the borrow pit. The total volume or shoreline change (AVr) can be written as the sum of the even and odd components of change.
AV~ =AVe (x)+ A V.(x) (5.2)
When using this technique for a groin, the even function can be interpreted as the ongoing changes in the absence of the feature and the odd function interpreted as changes due to the feature alone. However, since the waves in the laboratory model approach the shoreline nearly shore-normal and the borrow pit is a symmetric feature, the even function represents the shoreline and volumetric signals due to the borrow pit. Reflection of the waves due to the sidewalls of the model can affect the signal. However, for purposes of this investigation, these effects were assumed to be negligible. The even and odd components are determined through Equations 5.3 and 5.4 respectively.
AVe(X)= (AV (x) + AV,(x)) (5.3)
2
2V AV x ) 54
The even function is symmetric about the axis and the odd function is anti-symmetric. The even function should result in equal positive and negative areas. This was not the case for the laboratory results. Therefore, the results were adjusted so that the areas were equal. This was accomplished by integrating the even function curve, thus obtaining an area, and dividing the area by the longshore distance (240 cm.). This result was then subtracted from the original even function values to produce new values resulting in an




47
integral equal to zero. The shifted/offset curves of the even components of shoreline change are presented in Figures 5.12 through 5.14 below.
Shifted Even Component of Shoreline Change (First Final Large Basin)

4
0
E
o8
uJ

20
15
10
120 .100 .60 .20 20 4.u E0 "o 100 120 1
5i
13 >," ""
.I4

Longshore Position (cm) S 0 to 6 Hours - - 6 to 12 Hours Figure 5.12: Shifted even component of shoreline change for the first final large basin experiment.
Shifted Even Component of Shoreline Change (Second Final Large Basin)
__ 15
0
00
0 .
EC
> W 120 100 0 40 20 ) 20 .40- -60 80 100 120 140
I
Longshore Position (cm)
------- Oto6Hours ----6to 12 Hours
Figure 5.13: Shifted even component of shoreline change for the second final large basin experiment.




Shifted Even Component of Shoreline Change (Third Final Large Basin)
Re
0
0.
O .............. ....... " .o .. . . ...- --. .........
4 ) 4)
> 140 .10 0 40 1010210
M. 65
0
Longs hore Position (cm)
....... Oto6 Hours --- -6to 12 Hours
Figure 5.14: Shifted even component of shoreline change for the third final large basin experiment.
For each experiment, the shifted even component of shoreline change for the period from 6 hours to 12 hours is positive for the longshore position ranging from approximately -40 cm to +40 cm and negative outside this range. For the period from 0.0 Hours to 6 Hours, the shifted even component of shoreline change is approximately opposite (a mirror image). These results reinforce the interpretation that the borrow pit was responsible for shoreline advancement on the leeward shore.
Figures 5.15 through 5.17 present the shifted/offset even component of volume change per unit length for each final large basin experiment.




49
Shifted Even Components of Volume Change (First Final Large Basin)

130 125
100 750
50
r 1 so '0o .20 1 2 \ 0
75
Longshore Position (cm)

S --- 0 to 6 Hours ---- 6 to 12 Hours

Figure 5.15: Shifted even component of volume change per unit length for the first final large basin experiment.
Shifted Even Component of Volume Change (Second Final Large Basin)

o E
E-u
o 4) >c.
E
uJ 0)
U)

150
125
I 100
4 120 100 20 25 1 120
o
I.I
Longshore Position (cm)

- --....... 0 to 6 Hours - - 6 to 12 Hours
Figure 5.16: Shifted even component of volume change per unit length for the second final large basin experiment.




Shifted Even Component of Volume Change (Third Final Large Basin)

E
.2
oE
'-2
r (n
5
CL

10
'7 / Ii

Longshore Position (cm)
.........to 6Hours --to2 ur
Figure 5.17: Shifted even component of volume change per unit length for the third final large basin experiment.
For the period from 6 hours to 12 hours, each experiment exhibits positive values for the shifted even component of volume change in the lee of the borrow pit and negative values to the sides of the pit. The magnitudes and the ranges for which they are positive varied from one experiment to the next. Conversely, the shifted even component of volume change is negative in the lee of the pit and positive to the sides for the period from 0.0 hours to 6 hours. Again, these results support the earlier findings that the borrow pit was responsible for volume gains of the leeward beach.
The odd components of shoreline and volume change are not presented within this
chapter because the even components provide the shoreline and volumetric signals due to the borrow pit. However, since it was still possible that the odd components contributed significantly to the total shoreline or volume change, they were compared to the shifted even components of shoreline and volume change. Comparisons were made both graphically and numerically. Graphical comparisons of the shifted even and odd




components of shoreline and volume change for each experiment in the final data set appear in Appendix C. Numerical comparisons were made by taking the mean value of the shifted even and odd components squared for each experiment. Only the shifted even and odd components of shoreline and volume change due to the presence of the borrow pit were used for this analysis. The relative influence of the odd components can be quantified by calculating the ratio defined in Equation 5.5. Ratio Ay 2 (5.5)
A e2

Table 5.1: Comparison of relative influence of odd components of shoreline and volume change to shifted even components of shoreline and volume change.
Shoreline Changes
First Experiment Second Experiment Third Experiment
Shifted Shifted Shifted
Even Odd Ratio Even Odd Ratio Even Odd Ratio
(cm) (cm) (cm) (cm) (cm2) (cm2)
32.27 7.28 0.23 55.35 25.17 0.45 25.00 6.06 0.24
Volume Change
First Experiment Second Experiment Third Experiment
Shifted Shifted Shifted
Even Odd Ratio Even Odd Ratio Even Odd Ratio
(cm4) (cm4) (cm4) (cm4) (cm4) (cm4)
525.3 543.6 1.03 1756 227.4 0.13 1931 1008 0.52
The ratios from the table above indicate that only the contribution of the odd component of volume change for the first experiment equaled or exceeded the contribution from the




shifted even component. All of the other ratios indicate ratios of odd to even component mean square values ranging from approximately one-eighth to one-half.
Effective Vertical Dimension of Active Profile The sum of the depth of the active profile, h., and the berm height, B, is an extremely useful quantity for coastal engineers. Application of the Bruun Rule is perhaps the most common use for this quantity. The Bruun Rule is the earliest relationship between increased water level and profile response (Dean and Dalrymple, 2001). The form of the Rule being applied here is to relate the volume change to a horizontal profile change. The volume is the product of the horizontal profile recession or shoreline change and the vertical dimension of the profile out to the width of the active profile. The resulting formula is presented below.
AV = Ay(h. + B) (5.6)
The vertical dimension of the profile out to the width of the active profile was
determined for the first two final experiments and the third final experiment. Using the values of the shifted/offset even components of shoreline change and volume change per unit length, a plot was generated with shoreline change on the x-axis and volume change per unit length on the y-axis. A linear regression line was then plotted through the data points. The slope of the regression line corresponds to the (h. + B) value for the model beach in question. Figure 5.18 presents the data points and the regression line used to determine the (h. + B) value of all the final large basin experiments.




E Volume Change vs. Shoreline Change
150
E Linear Regression
. First 0 to 6
S] First 6 to 12
2 100 J A Second0to6
,-E Second 6 to 12
, Third 0 to 6
. Third 6 to 12
G)
c- 50
0
o 1
A+
CX
o
E -50, m = 4.7811
o b = 0.4270
E 0
-o
"E -100 m... 7 1
. -15 -10 -5 0 5 10 15 20
) Shifted Even Component of Shoreline Change (cm)
Figure 5.18: Determination of the effective vertical dimension of the active profile for the final large basin experiments.
The slope, (h. + B), of the linear regression line is 4.78 cm. In order to conform to the Bruun Rule, the line should pass through the origin. Therefore, the slope (effective vertical dimension of the active profile) was determined using a least squares technique and found to be about 5.6 cm. This value seems too small, especially considering that with an approximate wave height of 6.0 cm, the depth of the active profile (h.) would be approximately 7.7 cm alone. The addition of a berm height between 2 and 3 cm would increase the effective vertical dimension of the active profile to about 10 cm, almost twice the amount determined from the data shown above.
Nearshore Bathymetric Trends Overhead digital photographs taken of the contour lines were used to qualitatively compare successive phases of each experiment. Photographs were taken after each




control and test phase of the first two final large basin experiments. Originally, the photographs were planned for use to quantitatively determine volume changes in the nearshore, but the lack of an effective method for digitizing the contours resulted in a qualitative analysis. For this reason, the digital photos were discontinued during the third final large basin experiment. After converting all the photos to the same scale, analysis could begin. Figures 5.19 through 5.21 provide the contours for the 0.0, 6.0, and 12.0 hour time steps of the first large basin experiment. For each figure in this section, the first contour is the stillwater line and the elevation of each subsequent contour is 0.5 cm lower. If Figure 5.19 is used as an example, the first contour is the stillwater line (0.0 cm), the elevation of the second contour is -0.5 cm, the third is -1.0 cm, and the fourth is
-1.5 cm. The intermediate photos are not presented here, but are available in Appendix B.

Figure 5.19: Initial contours of the first large basin experiment.




00
[fig,
Figure 5.21: Contours of the first final large basin experiment after six hours with the pit uncovered.
These overhead photos reinforce the previous shoreline change observations in that they show the 0.0 contour moving towards the baseline after six hours of waves without the pit present. In addition, Figure 5.21 shows the shoreline approaching the initial configuration. Figures 5.22 through 5.24 provide the contours for the 0.0, 6.0, and 12.0 hour time steps of the second large basin experiment.

Figure 5.20: Contours of the first large basin experiment after six hours with the pit covered.




Figure 5.22: initial contours of the second final large basin experiment.

Figure 5.23: Contours of the second final large basin experiment after six hours %N pit covered.

Figure 5.24: Contours of the second final large basin experiment after six hours with the pit uncovered.
Figure 5.21 and 5.22 are the same since the second final large basin experiment began directly following the end of the first experiment with no modifications to the model beach. Comparing Figures 5.22 and 5.23 further reinforces shoreline retreat in the lee of




57
the pit and Figure 5.24 clearly illustrates the shoreline approaching a configuration similar to the initial.
Comparison of Current Results to Previous Investigations
The results of the current laboratory models show that the leeward beach generally experiences shoreline advancement and volume increases, which agrees with the results presented by Horikawa et al. (1977), but conflicts with the results of Motyka and Willis (1974). Table 5.2 below summarizes the significant elements of each model.




Table 5.2: Comparison of current results to Horikawa et al. (1977) and Motyka and Willis (1974).
Horikawa et al. Horikawa et al. Motyka and Willis Physical Current (Physical (Mathematical (Mathematical
Property Experiments Model) Model) Model)
Wave Period Variable Variable
(sec.) (6-13) (5-8)
Beach Slope 0.11 / 0.12 0.10 Natural Natural
Wave Height 6.00 1.30 Variable Variable
(cm) (25 -270) (40-200)
Pit Distance
from shoreline 160 / 200 100 Variable Variable
(cm)
Pit Length 80 40 Variable 880 m
(cm) (2 4 km)
Pit Width (cm) 60 30 2.0 km 305 m
Pit Depth (cm) 12 1.25 300 Variable
Water Depth
adjacent to pit 15 4.1 Variable 18 m
(cm)
Sediment Qat
Median Quartz Mesalite
dia 0.24 mm 0.66 mm Unknown NA
Diameter ( .5 24
(Sp. Gravity) (2.65) (2.4)
Max Shoreline +13/+19/
Response in +13 +6 cm +2.7 m -30 m
Lee of Pit (cm)
The physical model presented in this thesis used longer period and larger waves, a
deeper borrow pit with twice the plan area, a larger water depth, and a greater density
sediment with a smaller median grain size than the physical model used by Horikawa et
al. (1977). Despite these differences, the models produced similar results. That the two
physical models resulted in similar positive shoreline responses is encouraging.
However, that encouragement is tempered by the results presented by the mathematical




59
model of Motyka and Willis (1974). The differences between the two mathematical models represented above is interesting and perplexing considering that both models relied on wave refraction as their only wave transformation process.




CHAPTER 6
SUMMARY AND CONCLUSIONS
Following preliminary experiments to establish methodology, three sets of final laboratory experiments were conducted on a physical model of a beach and offshore borrow pit system. The results of the nearshore response to the borrow pit for these three experiments form the basis for this thesis. Each of the final experiments exhibited shoreline advancement and volume increases on the leeward beach due to the presence of the borrow pit. This agrees with the results of physical and mathematical models presented by Horikawa et al. (1977), but conflicts with the results of mathematical models by Motyka and Willis (1974).
Overall, shoreline response trends for each of the three final large basin experiments were consistent. The leeward shoreline advanced after 6 hours under the influence of the borrow pit. The longshore limits of shoreline advance varied for each experiment, with +80 cm and -80 cm in the longshore direction as average limits of advance compared to the pit width of 60 cm. There was no conclusive evidence to suggest that altering the distance between the pit and the beach, from 160 cm to 200 cm, had any effect on the magnitude or width of the area of shoreline advance. With the exception of four survey stations, two in each of the first and third experiments, all of the survey stations that experienced shoreline advance also experienced an increase in volume due to the presence of the borrow pit. The exceptions exhibited shoreline retreat, but actually




gained volume. That the majority of locations exhibiting shoreline advance also gained volume demonstrates an overall agreement with the Bruun Rule.
The even/odd analysis revealed similar signals for all three experiments. The even function displayed strong signals towards shoreline advance in the lee of the pit and shoreline retreat at both edges due to the presence of the pit. Again, relocating the beach farther from the borrow pit did not affect the magnitude of change or its longshore limits. The even component of volume change also displayed volume increases leeward of the borrow pit for each experiment. The even components of shoreline and volume change for the first and third experiment behaved in a similar fashion to the total shoreline and volume change results, in that the limits of shoreline advance in the longshore direction were greater than the limits of increased volume.
It was relevant to determine whether or not the odd components, of both shoreline and volume change, constituted a large percentage of the overall change. The graphical comparisons between the shifted even and odd components of both shoreline and volume changes for each experiment are presented in Appendix C of this thesis. It was determined that the ratios of odd to shifted even mean squared values ranged from approximately one-eighth to one-half. Inspection of the results in Appendix C suggests that the "true" center of the model was not the physical or geometric center; rather it was offset due possibly to an angle of wave approach other than normal.
Of particular interest is the difference between the magnitude of the estimated total
volume change for the second final large basin experiment (-11,900 cm 3) when compared to the estimates for the first (+2,200 cm 3) and the third (-2,900 cm 3) experiments. This can be partially explained due to the fact that more sediment was deposited in the borrow




pit during the second experiment than during the other two experiments. However, attributing the entire volume loss during the second experiment to borrow pit infilling would require a uniform infilling depth of approximately 2.5 cm. Although measurements of the depth were not taken during experimentation, it is not believed that this amount of infilling occurred. Therefore, the remaining discrepancy in total volume change could be explained in part by sediment transported outside of the survey area. It was noticed that the amount of sediment seaward of the borrow pit appeared to increase from the beginning of the first final large basin experiment to the end of the second final large basin experiment.
The physical experiments undertaken during this investigation were all performed with constant wave conditions; i.e. period, wave height, and direction were not varied during the course of the experiments and thus, the results cannot be interpreted as being applicable for all situations. It is unknown what differences may have occurred by changing the period or wave height for the same borrow pit configuration.
Future model studies should include different wave periods and heights for the same borrow pit configuration; size, distance to shoreline, relative depth, and beach slope. Perhaps then, a more complete understanding of the relationship between the borrow pit and the leeward nearshore environment can be provided. In addition, with more advanced survey equipment and techniques, additional profiles could be obtained in a shorter time, allowing for a more complete data set across the model beach. This would help to provide more complete definitions of the measured shoreline and volume changes. Although Bender (2001) noted that the spatial variations in wave height in this model were so small that they were inconsistent and not repeatable, future efforts should




63
attempt to modify the model in such a way as to allow consistent measurements of the effects of the wave guides and the wave field adjacent to the borrow pit.




APPENDIX A
COMPLETE BEACH PROFILES
First Final Large Basin Experiment

Pro4lRe at -120 cm

0 10 cm K-H

5I
Previous Open (0,0 hr)
,. inr', __ Covered (3,0 hr) Covered (6,0 hr)
Open (7,5 hr) O Open (9,0 hr) Opera, (12.0 hr)
Figure A. 1: Profiles for- 120 cm survey station of first final large basin experiment.




Pro'ike at -80 cm

0 10 cm

51 cm
Previous Open (0,0 hr)
i ,j 1 l __ Covered (3,0 hr) Covered (6.0 hr)
Open (7,5 hr> O Open (9.0 hr) ....Open (12,0 hr)
Figure A.2: Profiles for -80 cm survey station of first final large basin experiment.

Profile at -40 cm

0 10 cm

0
51
cr1
Previous Open (0.0 hr)
- I _- Covered (3,0 hr) Covered (6,0 hr)
Open (7,5 hr) Open (9,0 hr) Open '12.0 hr)

Figure A.3: Profiles for -40 cm survey station of first final large basin experiment.




Profile at -20 cm

0 0 cm

0
51 cm
Previous Open (0,0 hr)
C, e- 5 I _t- Covered (3,0 hr) Covered (6,0 hr)
Open (7,5 hr) Open (9.0 hr) Open (12.0 hr)
Figure A.4: Profiles for -20 cm survey station of first final large basin experiment.

Pro'file at 0 cm

0 10 cm

a
Previous Open (0.0 hr)
Ci: -E E: I i Covered (3.0 hr) Covered (6.0 hr)
Open (7,5 hr) Open (9.0 hr) Open (12,0 hr)
Figure A.5: Profiles for 0 cm survey station of first final large basin experiment.




Profile at +20 cm

0 10 cm

51
Previous Open (0,0 hr)
C o -Ie, I hr-__ Covered (3.0 hr) Covered (6.0 hr)
Open (7.5 hr) Open (9.0 hr) _. Open (12.0 hr)
Figure A.6: Profiles for +20 cm survey station of first final large basin experiment.

Profile at +40 cm

0 10 cm

0
51 cm
Previous Open (0,0 hr)
[--, h, __ Covered (3.0 hr) Covered (6.0 hr)
Open (7,5 hr) Open (9.0 hr) Open (12,0 hr)
Figure A.7: Profiles for +40 cm survey station of first final large basin experiment.




Profile at +80 cm

0 10 cm K-A

I I I 1 1 1 1 1 1 1 1 1 I
0
51
cm
Previous Open (0,0 hr)
C c ;..r__ Covered (3.0 hr) Covered (6.0 hr)
Open (7,5 hr) Open (9,0 hr) O.. Open (12,0 hr)
Figure A.8: Profiles for +80 cm survey station of first final large basin experiment.

Profile at +120 cm 0 10 cm

0
CMq
Previous Open (0,0)
i- 5 I __ Covered (3.0 hr) Covered (6.0 hr)
Open (7,5 hr) Open (9,0 hr) Open (12,0 hr)
Figure A.9: Profiles for +120 cm survey station of first final large basin experiment.




69
Second Final Large Basin Experiment

ProFile at -120 cm

0 10 cm

cm
Previous Open (0.0 hr)
-_ hr__ Covered (3.0 hr) Covered (6.0 hr) Open (7.5 hr) Open (9.0 hr) Open (12.0 hr)
Figure A. 10: Profiles for -120 cm survey station of second final large basin experiment.

Profile at -80 cm

0
IT

0 10 cm

Previous Open (0.0 hr)
-. I-, Covered (3.0 hr) Covered (6,0 hr) Open (7.5 hr) Open (9.0 hr) Open (12.0 hr)

Figure A. 11: Profiles for -80 cm survey station of second final large basin experiment.




0 10 cm

Profile at -40 cm

51
cm
Previous Open (0.0 hr)
-- I H i1 Covered (3.0 hr) Covered (6,0 hr)
Open (75 hr) Open (9.0 hr) Open (12.0 hr)
Figure A. 12: Profiles for -40 cm survey station of second final large basin experiment.

ProPiLe at -20 cm

0 10 cm

Previous Open (0.0 hr)
, : hr __ Covered (3.0 hr) Covered (6.0 hr)
Open (7,5 hr) Open (9,0 hr) Open (12.0 hr)

Figure A. 13: Profiles for -20 cm survey station of second final large basin experiment.




Profite at 0 cm

0 10 cm

,I I II . I
C P
Previous Open (0,0 hr)
- .ere-d 1.'5 hr_ Covered (3.0 hr) Covered (6.0 hr)
Open (7.5 hr) Open (9,0 hr) Open (12,0 hr)
Figure A. 14: Profiles for 0 cm survey station of second final large basin experiment.

ProFile at +20 cm

0 10 cm

0
51
CM
Previous Open (0.0 hr)
I ,er 1 -, ,-I t, -- Covered (3.0 hr) Covered (6,0 hr)
Open (7,5 hr) -o- Open (9,0 hr) .. Open (12,0 hr)

Figure A. 15: Profiles for +20 cm survey station of second final large basin experiment.




Prof'ite ot 4-40 cm

0 I I I I I
51
cm
Previous Open (0,0 hr)
i. V K _I Covered (30 hr) Covered (6,0 hr)
Open (7,5 hr) O Open (9,0 hr) Open (12.0 hr)
Figure A. 16: Profiles for +40 cm survey station of second final large basin experiment.

Profile at +80 cm

0 10 cm H--H

Previous Open (0.0 hr)
A IS-__ Covered (3.0 hr) Covered (6.0 hr)
Open (7,5 hr) Open (9,0 hr) -... Open (12.0 hr)

Figure A. 17: Profiles for +80 cm survey station of second final large basin experiment.

a 10 CM




0 10 cm

Profile at +120 cm

0
51 CM
cm
Previous Open (0.0)
CLClred (1.5 h-, Covered (3.0 hr) Covered (6.0 hr)
Open (7.5 hr) -, Open (9.0 hr) Open (12.0 hr)
Figure A. 18: Profiles for + 120 cm survey station of second final large basin experiment.

Third Final Large Basin Experiment
ProPLe ot -120 cm 0 10 cm
F--

.. Previous Open (0.0 hr)
-,.E- I hr __ Covered (3.0 hr) Covered (6,0 hr) Open (7.5 hr) Open (9.0 hr) Open (12.0 hr)

Figure A.19: Profiles for -120 cm survey station of third final large basin experiment.




Prol'le at -80 cm 0 10 cm
-]

Previous Open (0.0 hr) Cover-ed 1,- h __ Covered (3,0 hr) Covered (6,0 hr) Open (7.5 hr) Open (9.0 hr) ....Open (12,0 hr)
Figure A.20: Profiles for -80 cm survey station of third final large basin experiment.
0 10 cm
ProFie at -40 cm

Previous Open (0.0 hr)
C ..,-1 .5 hr __ Covered (3.0 hr) Covered (6.0 hr)
Open (7.5 hr) Open (9,0 hr) O ripen (12,0 hr)

Figure A.2 1: Profiles for -40 cm survey station of third final large basin experiment.




ProFile at -20 cm

0 [0 cm

. Previous Open (00 hr)
Co ,erci ,1.5 hr Covered (3.0 hr) Covered (6.0 hr) Open (7.5 hr) Open (9.0 hr) .- Open (12.0 hr)
Figure A.22: Profiles for -20 cm survey station of third final large basin experiment.

Profile at 0 cm

0 10 cm
H-H

.. PrevIous Open (0.0 hr)
F,0, er d, I t hi Covered (3.0 hr) Covered (6.0 hr)
Open (7.5 hr> Open (9.0 hr) pen 12.0 hr>

Figure A.23: Profiles for 0 cm survey station of third final large basin experiment.




ProPle at 4-20 cm 0 to cm

Previous Open (0.0 hr)
Covered '1,5 hr Covered (3.0 hr) Covered (6.0 hr)
SOpen (7.5 hr) Open <9.0 hr) Open (12.0 hr)
Figure A.24: Profiles for +20 cm survey station of third final large basin experiment.

Prof'e at +40 cm

0 i0 cN

.. Previous Open (0.0 hr)
Co- 1 .1.5 h,-__ Covered (3.0 hr)
Open (7.5 hr) Open (9.0 hr)

CovQred (6.0 hr) S Open (12.0 hr)

Figure A.25: Profiles for +40 cm survey station of third final large basin experiment.




ProfILe at +'80 cm

0 10 cm P-A-

.. Previous Open (0.0 hr)
CorEd L5 h__ Covered (3.0 hr) Covered (6.0 hr) Open (7.5 hr) Open (9.0 hr) Open (12.0 hr)
Figure A.26: Profiles for +80 cm survey station of third final large basin experiment.

Profile at I120 cm

0 10 cm
I I

.. Previous Open (0.0)
I re 1, hr Covered (3.0 hr) Covered (6.0 hr)
Open (7,5 hr) Open (9,0 hr) -. Open (12.0 hr)

Figure A.27: Profiles for +120 cm survey station of third final large basin experiment.




APPENDIX B
OVERHEAD DIGITAL PHOTOGRAPHS
First Final Large Basin Experiment

Figure B. 1: Photo of first final large basin experiment at 0.0 hr time step.




Figure B.2: Photo of first final large basin experiment at 1.5 hr time step.




Figure B.3: Photo of first final large basin experiment at 3.0 hr time step.




Figure BA Photo of first final large basin experiment at 6.0 hr time step.




Figure B.5: Photo of first final large basin experiment at 7.5 hr time step.




Figure B.6: Photo of first final large basin experiment at 9.0 hr time step.




Figure B.7: Photo of first final large basin experiment at 12.0 hr time step.




Second Final Large Basin Experiment

Figure B.8: Photo of second final large basin experiment at 0.0 hr time step.




Figure B.9: Photo of second final large basin experiment at 1.5 hr time step.




Figure B. 10: Photo of second final large basin experiment at 3.0 hr time step.

ABEHERM--




Figure B. 11: Photo of second final large basin experiment at 6.0 hr time step.