• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Abstract
 Disclaimer
 SI (modern metric) conversion...
 Table of Contents
 List of Figures
 List of Symbols
 Introduction
 Storm surge hydrograph study
 Field measurement program
 Reference
 Figures 1-53
 Appendix A. Sensitivity of bridge...
 Appendix B. Field performance of...














Group Title: UFLCOEL
Title: Coastal hydrology and hydraulics
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00091082/00001
 Material Information
Title: Coastal hydrology and hydraulics
Series Title: UFLCOEL
Physical Description: 89 p. (various pagings) : ill., maps ; 28 cm.
Language: English
Creator: Sheppard, D. M ( Donald Max ), 1937-
University of Florida -- Coastal and Oceanographic Engineering Dept
Publisher: University of Florida, Coastal & Oceanographic Engineering Dept.
Place of Publication: Gainesville Fla
Publication Date: 1997
 Subjects
Subject: Scour at bridges   ( lcsh )
Scour (Hydraulic engineering)   ( lcsh )
Coastal engineering   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 14).
Statement of Responsibility: principal researcher D. Max Sheppard.
General Note: Final report.
 Record Information
Bibliographic ID: UF00091082
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 39059227

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Title Page 1
        Title Page 2
    Abstract
        Abstract 1
        Abstract 2
    Disclaimer
        Page a-1
        Page a-2
    SI (modern metric) conversion factors
        Page a-3
        Page a-4
    Table of Contents
        Page i
    List of Figures
        Page ii
        Page iii
        Page iv
        Page v
    List of Symbols
        Page vi
    Introduction
        Page 1
        Page 2
    Storm surge hydrograph study
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
    Field measurement program
        Page 11
        Page 12
        Page 13
    Reference
        Page 14
    Figures 1-53
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
    Appendix A. Sensitivity of bridge scour producing currents to storm surge parameters
        Appendix A
        Appendix A-1
        Appendix A-2
        Appendix A-3
        Appendix A-4
        Appendix A-5
        Appendix A-6
    Appendix B. Field performance of an acoustic scour-depth monitoring system
        Appendix B
        Appendix B-1
        Appendix B-2
        Appendix B-3
        Appendix B-4
        Appendix B-5
Full Text




UFL/COEL-97/018


COASTAL HYDROLOGY AND HYDRAULICS
FINAL REPORT










by

D. Max Sheppard




1997


Sponsor:

Florida Department of Transportation
Tallahassee, Florida












FINAL REPORT





COASTAL HYDROLOGY AND HYDRAULICS












PRINCIPAL RESEARCHER

D. MAX SHEPPARD
COASTAL AND OCEANOGRAPHIC ENGINEERING DEPARTMENT
UNIVERSITY OF FLORIDA
GAINESVILLE, FLORIDA


December 1997













FINAL REPORT


COASTAL HYDROLOGY AND HYDRAULICS


HPR STUDY No.
WPI No.
STATE JOB No.
CONTRACT No.
UPN No.
ACCOUNT No.
CONTRACT PERIOD


0679
0510679
99700-3524-119
B-8357
93030119
451127712
08/20/93 10/31/97


PRINCIPAL RESEARCHER

D. MAX SHEPPARD
COASTAL AND OCEANOGRAPHIC ENGINEERING DEPARTMENT
UNIVERSITY OF FLORIDA
GAINESVILLE, FLORIDA


December 1997





Technical Report Documentation Page
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
WPI 0510679

4. Title and Subtitle 5. Report Date
Coastal Hydrology and Hydraulics 12/97
6. Performing Organization Code
4910451127712
8. Performing Organization Report No.
7. Author(s) UFL/COEL-97/006
D.M. Sheppard
9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)
Coastal and Oceanographic Engineering Department 99700-3524-119
University of Florida 11. Contract or Grant No.
336 Weil Hall B8357
Gainesville FL 32611-6590 13. Type of Report and Period Covered
12. Sponsoring Agency Name and Address Final Report
Florida Department of Transportation 8/20/93 10/31/97
605 Suwannee Street
Tallahassee FL 32399-0450 14. Sponsoring Agency Code


15. Supplementary Notes
Prepared in cooperation with the U.S. Department of Transportation and the Federal Highway Administration


16. Abstract

This report covers two related but separate topics. The first reports on a sensitivity study regarding hurricane storm
surge generated hydraulics in tidal waters. That is, the hydraulics in tidally influenced coastal water bodies such as
bays, estuaries, rivers, coastal waterways etc. More specifically, the study examines the sensitivity of flow velocity
and water elevation at various points in a tidal system to variations in an open coast storm surge hydrograph. A depth
averaged, finite element flow model is used to perform numerical experiments where certain hydrograph parameters
(rate of water rise, duration of peak water elevation, and rate of water elevation) are varied and the hydraulics
monitored at points within the system. The results are presented in a variety of plots of non-dimensional quantities.
Some general conclusions are made that should be of interest to those modeling hurricane induced flows in tidal
waters.

The second part of the report describes an unsuccessful attempt to measure currents and waves at a site near the
Bonner Bridge over Oregon Inlet, North Carolina. Sediment scour at the ends of eight bridge piers on the Bonner
Bridge were being monitored by the North Carolina Department of Transportation (NCDOT) and the U.S. Geological
Survey (USGS) for operational purposes. The objective of this project was to measure current velocities and waves
near two of the piers so that local scour prediction equations could be tested for larger structures. Problems were
encountered due to the extreme dynamic nature of the sediment transport in the vicinity of the inlet. This resulted in
the deposition of large quantities of sand at the location of the instruments which buried one of the instruments and
severely damaged the other two.


17. KeyWords 18. Distribution Statement
Bridge scour, Pier scour, Maximum scour No restrictions. This document is available to the public
through the National Technical Information Service,
Springfield, VA, 22161


19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price
Unclassified Unclassified 89

Form DOT F 1700.7 (8-72)
Reproduction of completed page authorized










DISCLAIMER

"The opinions, findings and conclusions expressed in this
publication are those of the authors and not necessarily those of the
Florida Department of Transportation or the U.S. Department of
Transportation."

"Prepared in cooperation with the State of Florida Department
of Transportation and the U.S. Department of Transportation."









SI* (MODERN METRIC) CONVERSION FACTORS
APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol |ISymbol When You Know Multiply By To Find Symbol


LENGTH
in inches 25.4 millimeter
ft feet 0.305 meters
yd yards 0.914 meters
mi miles 1.61 kilometen
AREA
in2 square inches 6452 square mi
ft2 square feet 0.093 square m
yd2 square yards 0.836 square m
ac acres 0.405 hectares
mF square miles 2.59 square ki
VOLUME
fl oz fluid ounces 29.57 miiliters
gal gallons 3.785 iters
ft3 cubic feet 0.028 cubic met
yd3 cubic yards 0.765 cubic met
NOTE: Volumes greater than 10001 shall be shown in m3.


oz ounces
bR pounds
T short tons (2000


*F Fahrenheit
temperature


fc foot-candles
fl foot-Lamberts


s
8




ilimeters
eters
eters

ometres



ers
ers


MASS
28.35 grams
0.454 kilograms
b) 0.907 megagrams


Temperature (exact)
5(F-32)/9 Celcius
or (F-32)/1.8 temperature


ILLUMINATION


lux
candela/m2


FORCE and PRESSURE or STRESS
Ibf poundforce 4.45 newtons
psi poundforce per 6.89 kilopascals
square inch


mm
m
m
km


mm2
m2
m2
ha
km2


ml
I
m3
m3




g
kg
Mg


*C



Ix
b(
cd/m2


N
kPa


InI


LENGTH


mm millimeters
m meters
m meters
km kilometers


0.039
328
1.09
0.621


inches
feet
yards
miles


AREA
mm2 square millimeters 0.0016 square inches
m2 square meters 10.764 square feet
m2 square meters 1.195 square yards
ha hectares 2.47 acres
km2 square kilometers 0.386 square miles


ml milliiters
I iter
m3 cubic meters
m3 cubic meters




g grams
kg kilograms
Mg megagrams


C Ceicius
temperature


x klux
cd/m2 candela/m2

FOR(
N newtons
kPa kilopascals


VOLUME
0.034 fluid ounces
0.264 gallons
35.71 cubic feet
1.307 cubic yards


MASS
0.035 ounces
2.202 pounds
1.103 short tons (2000 Ib)

Temperature (exact)
1.8C +32 Fahrenheit
temperature

ILLUMINATION
0.0929 foot-candles
0.2919 foot-Lamberts

CE and PRESSURE or STRESS
0.225 poundforce
0.145 poundforce per
square inch


in2?
ft2
yd2
ac
mF


floz
gal
ft"
yd2



oz
b
T


(Revised August 1992)


* SI is the symbol for the International System of Units. Appropriate
rounding should be made to comply with Section 4 of ASTM E380.


10.76
3.426










Table of Contents


L ist of Figures ................................................................................................... ii
List of Sym bols................................................................................................ vi
1. Introduction .................................................................................................. 1
2. Storm Surge Hydrograph Study.................................................................3
2.1 Procedures ....................................................................................... 3
2.2 Model Test Results..........................................................................5
2.2.1 St. Lucie study area............................................................6
2.2.2 St. Johns River study area.................................... ............ 8
2.3 Conclusions ........................................ ................. ............................ 9
3. Field Measurement Program.................................................................... 11
3.1 B background ........................................ ................ ........................... 11
3.2 Scour-Depth Monitoring System...................................................... 11
3.3 Conclusions ........................................ ................ ........................... 12


4. R eferences.................................................................................................. 14
Appendix A Sensitivity of Bridge Scour Producing Currents to
Storm Surge Parameters
Appendix B Field Performance of an Acoustic Scour-Depth
Monitoring System










List of Figures

Figure 1. General location of study areas..............................................................15

Figure 2. St. Lucie Estuary study area .................................................................16

Figure 3. St. Johns River study area......................................................................17

Figure 4. St. Lucie Estuary finite element mesh..............................................18

Figure 5. St. Johns River finite element mesh .................................................19

Figure 6. St. Lucie & St. Johns River storm surge variation .................................20

Figure 7. St. Lucie study area locations ........................................... ................ 21

Figure 8. St. Johns River study area locations .................................................22

Figure 9. Maximum elevation comparisons Indian River Lagoon......................23

Figure 10. Maximum water elevation and elevation at maximum
velocity magnitude comparisons- Indian River Lagoon........................24

Figure 11. Maximum velocity magnitude comparisons Indian
River Lagoon ........................................ ................. ........................... 25

Figure 12. Maximum velocity magnitude vs. distance Indian River
L agoon ................................................................................................26

Figure 13. Velocity magnitude vs. time at Gage 2 rate of rise
variation Indian River Lagoon...........................................................27

Figure 14. Velocity magnitude vs. time at Gage 2 rate of fall
variation Indian River Lagoon............................................................28

Figure 15. Velocity magnitude vs. time at Gage 2 duration of peak
variation Indian River Lagoon............................................................29

Figure 16. Velocity magnitude vs. time at Gage 1 rate of rise
variation Indian River Lagoon............................................................30

Figure 17. Velocity magnitude vs. time at Gage 1 rate of fall
variation Indian River Lagoon...........................................................31

Figure 18. Velocity magnitude vs. time at Gage 1 duration of peak
variation Indian River Lagoon...........................................................32










Figure 19. Maximum elevation comparisons Intracoastal
W aterw ay........................................... ................. .............................. 33

Figure 20. Maximum water elevation and elevation at maximum
velocity magnitude comparisons Intracoastal Waterway ....................34

Figure 21. Maximum velocity magnitude comparisons Intracoastal
W aterw ay......................................... ................... .............................. 35

Figure 22. Maximum velocity magnitude vs. distance Intracoastal
W aterw ay......................................... ................... ..............................36

Figure 23. Velocity magnitude vs. time at Gage 3 rate of rise
variation Intracoastal Waterway ....................................................37

Figure 24. Velocity magnitude vs. time at Gage 3 rate of fall
variation Intracoastal Waterway ....................................................38

Figure 25. Velocity magnitude vs. time at Gage 3 duration of peak
variation Intracoastal Waterway ....................................................39

Figure 26. Velocity magnitude vs. time at Gage 4 rate of rise
variation Intracoastal Waterway ....................................................40

Figure 27. Velocity magnitude vs. time at Gage 4 rate of fall
variation Intracoastal Waterway....................................................41

Figure 28. Velocity magnitude vs. time at Gage 4 duration of peak
variation Intracoastal Waterway....................................................42

Figure 29. Maximum elevation comparisons St. Lucie Estuary ...........................43

Figure 30. Maximum water elevation and elevation at maximum
velocity magnitude comparisons St. Lucie Estuary.............................44

Figure 31. Maximum velocity magnitude comparisons St. Lucie
E stuary ..........................................................................................4.....45

Figure 32. Maximum velocity magnitude vs. distance St. Lucie
E stu ary ............................................................................................. ....46

Figure 33. Velocity magnitude vs. time at Gage 5 rate of rise
variation St. Lucie Estuary ................................................................47

Figure 34. Velocity magnitude vs. time at Gage 5 rate of fall
variation St. Lucie Estuary ................................................................48










Figure 35. Velocity magnitude vs. time at Gage 5 duration of peak
variation St. Lucie Estuary ................................................................49

Figure 36. Velocity magnitude vs. time at Gage 6 rate of rise
variation St. Lucie Estuary ................................................................50

Figure 37. Velocity magnitude vs. time at Gage 6 rate of fall
variation St. Lucie Estuary ................................................................51

Figure 38. Velocity magnitude vs. time at Gage 6 duration of peak
variation St. Lucie Estuary ................................................................52

Figure 39. Maximum elevation comparisons St. Johns River ..............................53

Figure 40. Maximum water elevation and elevation at maximum
velocity magnitude comparisons St. Johns River................................54

Figure 41. Maximum velocity magnitude comparisons St. Johns
R iver ................................................................................................. . 55

Figure 42. Maximum velocity magnitude vs. distance St. Johns
R iv er ................................................................................................. . 56

Figure 43. Velocity magnitude vs. time at Gage 1 rate of rise
variation St. Johns River............................. .......................................57

Figure 44. Velocity magnitude vs. time at Gage 1 rate of fall
variation St. Johns River............................. .......................................58

Figure 45. Velocity magnitude vs. time at Gage 1 duration of peak
variation St. Johns River............................. .......................................59

Figure 46. Velocity magnitude vs. time at Gage 2 rate of rise
variation St. Johns River.............................. .......................................60

Figure 47. Velocity magnitude vs. time at Gage 2 rate of fall
variation St. Johns River............................. .......................................61

Figure 48. Velocity magnitude vs. time at Gage 2 duration of peak
variation St. Johns River............................. .......................................62

Figure 49. Velocity magnitude and baseline elevation vs. time St.
Johns River ......................................... ................. .............................63

Figure 50. Vicinity map for Oregon Inlet ..............................................................64

Figure 51. Drawing of Herbert C. Bonner Bridge over Oregon Inlet......................65










Figure 52. Tethered current meter installation...................................................66

Figure 53. Electromagnetic current meter, pressure transducer, data
acquisition (puv) installation................................................................67










List of Symbols


Hi = peak water elevation at a given point,
Hb = peak baseline water elevation at the same point,
Vi = maximum velocity at a given point,
Vb = maximum baseline velocity at the same point,
Hv = peak water elevation at maximum velocity magnitude,
Him = peak water elevation at inlet or entrance.












Coastal Hydrology and Hydraulics


1. INTRODUCTION

Two important parameters needed in the design of structures that will be subjected
to forces from flowing water are water depth and flow velocity. If the bed material where
the structure is to be located is erodible, (i.e. if for the range of bed shear stresses
anticipated exceed that needed to move the sediment) then these two parameters are also
needed to estimate the sediment scour depths near the structure. In tidal inlets, bays and
coastal waterways in Florida as well as many other coastal states in the United States on
the Gulf of Mexico and Atlantic Ocean the event that produces the most extreme flow
conditions is hurricane generated meteorological tide or storm surge. One-in-one-
hundred and one-in-five-hundred year return interval storm surges are used in the design
of bridges over waterways in the United States. The open coast hydrographs (water
elevation versus time plots) for these design surges are usually obtained with the use of
computer models that solve for the flow induced by the wind and pressure in the
hurricane. Numerous (hypothetical or real) hurricanes must be hindcast in order to
generate the database for the extremal analysis needed to produce the one in one and five
hundred year surges. Comparisons of predicted and measured storm surges on the open
coast indicate that the predicted peak water elevation is often close to measured values,
but other features of the hydrograph such as rate of rise or fall can differ greatly.

The propagation of storm surges through tidal inlets and/or river mouths into bay-
estuary-river systems is a complex process due to the highly irregular boundaries and in
some cases the flooding of barrier islands and other subaerial lands. It is therefore not
usually obvious how the difference in predicted and actual open coast hydrographs affect
the currents and water elevations at various locations in the bay-estuary-river system.
Variations in design currents and water elevation can have a major impact on design
scour depth predictions and therefore it is important to know how sensitive these
quantities are to variations in the storm surge parameters. To address these issues, a
study was conducted to examine the sensitivity of design scour producing currents in a
tidal system to certain variations in the open coast storm surge parameters.

The research conducted under this contract is divided into two related but separate
categories. The objective of the first category (Storm Surge Hydrograph Study) was to
examine the sensitivity of bridge scour producing currents in a tidal environment to
variations in certain parameters associated with open coast storm surges. The objective
of the second category (Field Measurement Program) was to measure the scour producing
water currents and waves near the Bonner Bridge over Oregon Inlet, North Carolina,
where bridge pier scour was already being monitored. The two projects are related in that
they both are directed at obtaining a better understanding of the processes that cause
sediment scour near bridges.









The specific objectives of the Storm Surge Hydrograph Study were to:


1. Pick two locations on the Florida coast to be representative of the types of conditions
found in Florida for the purposes of the sensitivity study,
2. Configure a two-dimensional, depth averaged circulation model for the two locations,
3. Calibrate the models using data,
4. Conduct numerical experiments where certain storm surge parameters are varied and
the current velocities and water elevations at different locations throughout the inlet,
bay, estuary, and river system are monitored,
5. Establish a means of quantifying the sensitivity of the currents and water elevations to
variations in the storm surge parameters, and
6. Using the methodology developed in Item 5 above, quantify the sensitivity of currents
to storm surge parameters.

A description of the procedures used in this study, a discussion of the hydrograph
parameters examined and ranges tested, the model test results, and the conclusions from
the study are presented in Section 2 of this report. Two technical papers on the results of
this study have been presented, one at the Florida Department of Transportation (FDOT)
Design Conference on August 10, 1994 [Sheppard et al. (1994)] and one at the ASCE
Water Resources Engineering Conference in San Antonio Texas from August 14-18,
1995 [Sheppard et al. (1995)]. A copy of the ASCE paper is included as Appendix A.

The objective of the Field Measurement Program was to work with the North
Carolina Department of Transportation (NCDOT) and the U.S. Geologic Survey (USGS)
to obtain environmental data in Oregon Inlet near the area where bridge pier scour was
being monitored. The environmental data to be measured/obtained was wave magnitude,
direction and frequency, water temperature, current magnitude and direction, and surface
sediment samples.

A summary of the Field Measurement Program is presented in Section 3 of this
report. Two technical papers were presented on the results of this work. The first paper
was presented at the FDOT Design Conference in Orlando, Florida in August 1994 and
the second at the ASCE Hydraulics Engineering Conference in Buffalo, New York in
August 1994 [Robert R. Mason, Jr. and D. Max Sheppard]. A copy of the ASCE paper is
included in this report as Appendix B.









2. STORM SURGE HYDROGRAPH STUDY


Included in this section are 1) the procedures used in the Storm Surge Hydrograph
Study, 2) the rationale for selecting the two coastal system scenarios, 3) the hydrograph
parameters and ranges tested, and 4) the model test results and conclusions of this part of
the study.


2.1 Procedures

The first step was to select two locations in Florida's coastal waters that would be
representative of the types of coastal conditions found in Florida. The two sites selected
were:

* The St. Lucie Estuary and portions of Indian River Lagoon (more specifically, the
area between Ft. Pierce and Jupiter Inlets) and
* The lower St. Johns River (from the mouth of the river at Mayport to Palatka, over 50
miles up river).

The St. Lucie Estuary was selected for two reasons. First, it is somewhat
representative of the inlet/bay/estuary systems found in Florida. Secondly, data suitable
for calibration of the hydrodynamic model was available from previous field monitoring
programs. The lower St. Johns River was selected as a representative riverine coastal
system in Florida and, in addition, the St. Johns River is an area of immediate interest for
bridge construction by the FDOT. A general location map for the two sites is presented
in Figure 1. A more detailed map of the St. Lucie Estuary study area is given in Figure 2
and one for the St. Johns River study area in Figure 3.

There were a number of two-dimensional, depth averaged flow models available
for use in this study, but the one selected was RMA2 (Norton and McAnally, 1973,
Thomas and McAnally, 1991) with the BOSS International pre and post processor. When
the project was initiated, the BOSS software was called "FASTTABS". Later,
(improved) versions of this software are called "SMS". RMA2 is a depth-averaged two-
dimensional model employing a finite element solution procedure to solve the shallow
water wave equations. The pre and post processors provide a graphical interface for
efficient mesh generation, boundary condition specification and presentation of the
results. Additionally, pre-processing software developed by Reed and Sheppard to
expedite mesh generation was also used in this study.

As stated above, there were several hydrodynamic models available that could
have been used in this study. RMA2 was selected as it was specifically developed for
coastal hydraulics and has been used extensively by the U.S. Army Corps of Engineers
and the consulting engineering community for coastal hydraulics problems.
Meshes for the two study areas were generated for RMA2. The St. Lucie Estuary
mesh is shown in Figure 4 and the St. Johns River mesh in Figure 5.









Since only the changes in the flow parameters (and not their specific values) were
of interest in this study, it was not necessary to have a precise calibration of the models.
It was, however, necessary for the model parameters (mean water depths, bottom
roughness, turbulence exchange coefficients) to be approximately correct; thus
calibrations were performed using (primarily) existing data. The St. Lucie Estuary study
area model was calibrated using data from a number of previous modeling studies
(Williams, 1985; Morris, 1987; Sheng, et al., 1990; Smith, 1990) as well as information
from the NOAA Tide Tables. There was less existing data for the St. Johns River
suitable for calibration purposes. This model was calibrated using stage and discharge
data obtained as part of another FDOT District 2 sponsored study. The ranges of
Manning's n and turbulence exchange coefficients used in the analysis were 0.018-0.028
lbs/ft2 and 141-1450 lbs/ft2, respectively.

On completion of the calibrations, numerical experiments were performed using
first a "baseline" hydrograph as an input followed by hydrographs where specific
parameters (rate of rise, rate of fall and duration of the peak) were varied. The baseline
hydrograph was similar to those computed by NOAA (National Oceanic and
Atmospheric Administration) for the east coast of Florida.

For each storm surge hydrograph variation considered, water elevations and depth
averaged velocities were monitored at various points along the river or within the
bay/estuary system. The flow parameters that are important to bridge scour prediction
include: water depth and elevation, local depth average velocity, channel average
velocity, and the duration of these quantities. The bay, river, estuary, or tributary system
was divided into regions according to how the above quantities were anticipated to
respond to a storm surge at the inlet or mouth. The response was believed to depend
primarily on the:

1. distance from the inlet or mouth (or in some cases from the open bay),
2. width or depth of the channel connecting the point of interest to the inlet or mouth,
and
3. channel bottom roughness.

The relative importance of these factors was examined as part of the sensitivity
analysis. Two different approaches were taken to the sensitivity analysis. The first
approach was that of constant storm surge energy. In this approach, the storm surge
hydrographs were varied (rate of rise, rate of fall, and duration of peak) from the baseline
hydrograph while holding the energy in the hydrograph approximately constant. Using
this approach, a sensitivity analysis was performed on the St. Lucie study area. The
results of this analysis were presented at the FDOT Design Conference in August 1994
and at ASCE Water Resources Engineering Conference in San Antonio, Texas in August
1995 [Sheppard et al. (1995)]. As stated previously, a copy of this paper is included as
Appendix A in this report.









The second approach taken was that of a constant storm surge peak height. The
surge parameter variations were made while holding the maximum height of the
hydrograph constant. Even though the constant energy approach is thought to be more
scientifically correct, the constant maximum height method is perhaps more useful for
this particular problem. Users of the results of this study will most likely have accurate
(1 in 100 and 1 in 500 year) storm surge maximum elevation predictions and less accurate
storm surge hydrograph shapes. As with the constant energy method, the surge
parameters such as rate of rise, rate of fall and duration of peak were varied and the flow
monitored at points throughout the tidal system. To vary the rate of rise, the maximum
slope of the rise was decreased from the baseline. To vary the rate of fall, the maximum
slope of the fall was decreased from the baseline. Both of these variations increased the
area under the hydrograph by approximately 20%. Therefore, for uniformity, the duration
of peak was extended so as to produce a 20% increase in the area under hydrograph. It is
important to note that while the area under the hydrographs were increased from that of
the baseline hydrograph, the amount of increase was the same in all three cases. Figure 6
shows the storm surge hydrograph variations used for both study areas. The model test
results and conclusions for the constant peak height hydrograph approach are presented in
Sections 2.2 and 2.3 of this report, respectively.


2.2 Model Test Results

The points monitored in the St. Lucie study area are within three distinct areas -
the Indian River Lagoon, the Intracoastal Waterway, and St. Lucie Estuary. These areas
are shown in Figure 7. The monitoring areas for the St. Johns River study are shown in
Figure 8.

For each location monitored the model output was analyzed and the results
presented in a series of graphs. Some of the quantities in the graphs were
nondimensionized so as to extend their range of application. A discussion of the
quantities used in the graphs are given below:

Maximum Water Elevation and Water Elevation at the time of Maximum Velocity

For some situations there are major differences between the maximum water
elevation at a point and the water elevation at the time of maximum velocity at that point.
Since both quantities are of interest to the design engineer, both are examined in this
study. The maximum (or peak) water elevation at a given point in the coastal system
during a storm surge event is denoted by Hi. The peak water elevation at that point due to
the baseline storm surge is denoted by Hb. The ratio of the difference between the peak
water elevation, Hi, (for a particular hydrograph variation) and the baseline peak water
elevation, Hb, to the peak baseline water elevation, [i.e. (Hi-Hb)/Hb] is used to illustrate the
sensitivity of the water elevation at a point to the variation in the hydrograph.

Note that the maximum water elevation may occur at a different time during the
surge for the baseline hydrograph than the hydrograph with the modified parameter.









To illustrate the difference in the range of values for the maximum water
elevation and the water elevation at the time of maximum velocity magnitude (for the
hydrograph variations in this study) comparisons between the two quantities are made in
Figures 10, 20, 30 and 40. The maximum (or peak) elevation at the time of maximum
velocity magnitude is denoted by HI,. The peak water elevation at the inlet or entrance is
denoted by Him. The ratio of the difference between peak water elevation, Hi, and the
peak elevation at the time of maximum velocity magnitude, H,, to the peak water
elevation at the inlet, [i.e. (Hi-HpHi,)] is used to illustrate the difference in the
elevations.

Maximum Velocity

The maximum depth averaged velocity that occurs at a point during the course of
a storm surge event is denoted by Vi. The maximum velocity that occurs at that point
during the baseline storm surge is denoted by Vb. The ratio of the difference between the
maximum depth averaged velocity, Vi, for a particular hydrograph variation and the
baseline maximum velocity, Vb, at the same point to the maximum baseline velocity [i.e.
(Vi-Vb)/Vb] is used to show the sensitivity of the maximum velocity to the hydrograph
variation. The dependence of maximum velocity on the distance from the inlet or river
mouth is illustrated in plots of dimensional velocity versus distance. Time variation of
depth averaged velocities are presented for selected locations. The locations of the points
(denoted as gages) for the St. Lucie study are shown in Figure 7 and those for the St.
Johns River study in Figure 8.


2.2.1 St. Lucie study area

The St. Lucie study area was evaluated in three areas: Indian River Lagoon,
Intracoastal Waterway, and St. Lucie Estuary. The model results are described below.

Indian River Lagoon

Figure 9 presents the Maximum Elevation Comparisons for the Indian River
Lagoon area. As shown in the graph, the largest percentage differences occur within the
lagoon, not near St. Lucie and Fort Piece Inlets. The peak height was most sensitive to
variations in the duration of peak and least sensitive to rate of rate of fall.

Figure 10 shows a comparison between the maximum water elevation and the
water elevation at the maximum velocity magnitude within the Indian River Lagoon area.
As seen in the graph, the elevation differs by less than 15%.

Figure 11 presents the Maximum Velocity Magnitude Comparisons. As with the
peak height comparisons, the largest differences occur within the lagoon, not at the inlets.
Variations in the rate of rise and rate of fall have maximum depth averaged velocity
magnitudes less than the baseline within the center of the lagoon. The variation in the
duration of peak produces a greater maximum depth averaged velocity magnitude
throughout the lagoon. It is important to note that the largest velocity magnitude









differences occur near the two causeways within the lagoon. This implies that the
sensitivity of the velocity magnitude is dependent on the geometry and the constriction of
the flow at these locations. Figure 12 presents the magnitudes of the velocities
throughout the lagoon. While Figure 11 shows large variations within the lagoon, the
magnitude of these velocities are small at these locations (less than 1 foot per second).
Therefore, a small increase or decrease in velocity at these points will cause a significant
percentage difference.

The velocity magnitude time series at two points within Indian River Lagoon
(Gages 1 and 2) for the storm surge variations are presented in Figures 13 through 18.
The locations of the two gages are shown in Figure 7. These graphs show where the
maximum velocity magnitude occurs in relation to the baseline velocity magnitude at the
same location. Note that these graphs only show magnitude of the flow, not direction.
These figures show the effect of the variation of the hydrograph parameters on velocity at
two distinct points within the system.

Intracoastal Waterway

The comparisons of maximum water elevations within the Intracoastal Waterway
are shown of Figure 19. Similar to the Indian River Lagoon, the largest percentage
differences occur within the Intracoastal Waterway, and the percentage difference
decreases toward the St. Lucie and Jupiter Inlets. It also appears that the peak elevation is
most sensitive to variations in the duration of peak and least sensitive to rate of fall.

As shown in Figure 20, the largest differences between the maximum water
elevation and the water elevation at maximum velocity magnitude is 20% for the
variation in the duration of peak parameter near the inlet. The remaining parameters have
differences within 10- 15%.

There does not seem to be a consistent trend regarding the sensitivity of the
maximum velocity to the hydrograph parameters (Figure 21). In a manner similar to that
for the Indian River Lagoon, the percentage differences are small near the inlets (less than
15%) and greatest within the Intracoastal Waterway. The rationale as to the variation
may be explained as it relates to the geometry of the waterway. However, as shown in
Figure 22, the magnitudes of the velocities are small (less than 1 foot per second) within
part of the Intracoastal Waterway, which may explain the variation of the maximum
velocities.

Figures 23 through 28 show the effect of the hydrograph parameter variations in
velocity at two locations within the Intracoastal Waterway. The locations are shown in
Figure 7.

St. Lucie Estuary

The Maximum Elevation Comparisons are shown in Figure 29 for the St. Lucie
Estuary. As with the Indian River Lagoon, the percentage differences are relatively small









(less than 10%) near the inlet, but reach an approximately constant value as one moves in
the upstream direction of the estuary. Again the peak height appears to be more sensitive
to variations in the duration of peak and least sensitive to the rate of fall.

As shown in Figure 30, the largest differences between maximum water elevation
and the water elevation at maximum velocity magnitudes is less than 15%.

The maximum velocity does not appear to be very sensitive to any of the
variations in the storm surge hydrograph in the St. Lucie Estuary. The maximum
variation was about 10% and only had a 5% change with the duration of peak and rate of
fall changes. Figure 31 shows the Maximum Velocity Comparisons and Figure 32 shows
the magnitude of the velocities in St. Lucie Estuary.

Figures 33 through 38 show the effect of the hydrograph parameter variations on
velocity at two locations within the estuary. The locations of these gages are shown in
Figure 7.


2.2.2. St. Johns River study area

Due to the St. Johns River's large drainage basin, the net discharge is quite large.
The value used in this study was 35,000 m3/sec. A discharge was not included in the
hydrodynamic model of the St. Lucie Estuary. Thus, the discharges used are close to
those that occur under average conditions.

As shown in Figure 39, the nondimensional peak water elevation difference
increased with distance from the mouth of the river, but the values did not exceed 15%.
The peak water elevation appears to be most sensitive to variations in the duration of
peak and least sensitive to variations in the rate of fall.

The difference between the peak water elevation and the water elevation at
maximum velocity magnitude was less than 12%. There does not appear to be a
correlation between distance from the river mouth and these differences.

As shown in Figure 41, it appears that variations to the duration of peak and rate
of fall have virtually no effect near the mouth of the river, but do have a slight effect (less
than 10%) upstream. However, variations to the rate of rise are most influential at the
mouth and decrease upstream. The maximum velocity magnitudes were found during the
flood stage. The magnitudes of these velocities are shown in Figure 42.

Figures 43 through 48 show the effect of the hydrograph parameter variations on
velocity at two locations within the estuary. The locations of these gages are shown in
Figure 8.

Figure 49 is a graph of the velocity and water elevation for the baseline
hydrograph at the gages in the St. Johns River. This shows the time lag between the peak
water elevation and peak velocity at Gages 1 and 2 for the baseline hydrograph.









2.3 CONCLUSIONS


In drawing conclusions from the results of this study the assumptions made and the
limitations of the procedures and computer models used in the analysis must be kept in
mind. For example, all real flows are three dimensional in nature and thus are only
approximated with a two dimensional flow model. Even if water density stratification
(due to, for example, temperature and/or salinity differences) does not exist, the
secondary flows that occur in the sharp bends of rivers and streams cannot be accounted
for with a two dimensional model. In spite of these shortcomings many of the important
processes can be simulated with the procedures and models used in this study. Thus, a
number of important conclusions can be derived from the results of such an analysis.
Some of the conclusions are summarized below:

* The peak water elevation at a point in the coastal system appears to be most sensitive
to the duration of the peak and least sensitive to the rate of fall of the open coast storm
surge hydrograph. This is most likely due to the flow at the point having a longer
time to respond to the surge (i.e.. the "effective frequency" at the peak of the surge is
lower resulting in a greater response). Varying the rate of fall of the open coast storm
surge increases the duration of the flow at lower water elevations, but not at the peak
elevation, thus the lesser sensitivity to this parameter. Therefore for design high
water elevation calculations the open coast hydrograph with the longest duration peak
anticipated should be used for the analysis.

* The peak height is not as sensitive to variations in the hydrograph parameters near the
inlet locations as it is away from the inlets in the bodies of water such as estuaries,
rivers, or lagoons.

* There does not appear to be a correlation between maximum elevation and peak
elevation at maximum velocity magnitude, and distance from the inlets or river
mouth. There is considerable variatin of values along the study areas. For design
variation purposes, the peak elevation (rather than the elevation at maximum velocity
magnitude) could be used for sediment scour and structure loading calculations.
While this is conservative, the differences between peak elevation and elevation at
maximum velocity are relatively small (usually less than 15%).

* In general, increases in the duration of the storm surge peak results in higher
velocities than those produced by the baseline surge. An increase in peak duration
that produces a 20% increase in area under the hydrograph results in maximum
velocity increases up to 20%. The variation with distance from the inlet/river mouth
can be seen in Figures 11, 21, 31, and 41. As would be expected, the maximum
velocity magnitude and their sensitivities are functions of the geometry of the water
body being evaluated. It is believed that the variations in maximum velocity and
sensivity to the hydrograph parameters in Indian River Lagoon can be attributed in
part to the presence of causeways in that body of water. Flow separation and eddy
formation on the down flow side of the causeway were observed in the model output.
Again, as anticipated, the large flow discharge in St. Johns River impacted the









maximum values of the velocity in the river. It should be noted that the maximum
velocity magnitude occurred during the flood stage of the surge propagation in the St.
Johns River.

*It is important to remember that for most numerical models, such as that used in this
study, the results are less accurate near the boundaries. This is particularly true for
the water boundaries such as those at the north and south boundaries of the St. Lucie
Model. The model imposes an artificial vertical wall at these points and, thus, both
the absolute flow values and the sensitivities will be inaccurate in the immediate
neighborhood of these boundaries and should not be used.









3. FIELD MEASUREMENT PROGRAM


This section presents a brief summary of the Field Measurement Program, the
scour-depth monitoring system, and conclusions. Details of this work can be found in the
paper titled "Field Performance of an Acoustic Scour-Depth Monitoring System" by
Robert R. Mason, Jr. and D. Max Sheppard. This paper was presented at the FDOT
Design Conference in Orlando, Florida from August 12-14, 1994. A copy of this paper is
included with this report as Appendix B.


3.1 Background

Since completion of the Bonner Bridge in 1962, the North Carolina Department of
Transportation (NCDOT) has made periodic soundings of Oregon Inlet to monitor
channel migration, deposition, and local scour. The vicinity map for Oregon Inlet is
shown in Figure 50 and the study area is shown in Figure 51. These data indicate that
some sections of Oregon Inlet have scoured and filled through an 11 m range. In 1978,
NCDOT discovered that, as a result of scour, several pilings were penetrating only 2.1 m
into the channel bottom. In response to this history of channel instability, the USGS and
NCDOT joined in a cooperative effort to develop and install a data-collection system to
permit continuous remote monitoring of scour depth at 16 bridge pilings. The system
was installed in September 1992.

A second data-collection program began in November 1993 and ended in January
1994. This effort consisted of deployment and operation of three instrument packages
that measure and record current magnitude and direction, wave frequency and direction,
water-surface elevation, and water temperature near Bonner Bridge. This program was a
cooperative effort between the FDOT, the University of Florida Coastal and
Oceanographic Engineering Department (UFCOE), the NCDOT and USGS.

The objective of this study was to obtain information about the flow that was
producing the scour and deposition at the piers on Bonner Bridge. Scour depths were
already being measured at both ends of the nine consecutive piers by the NCDOT and
USGS.


3.2 Scour-Depth Monitoring System

Instrumentation to measure flow and wave parameters were installed
approximately 30 meters seaward of two of the piers being monitored for scour.

The main component of the Bonner Bridge scour-depth monitoring system is a
Datasonics PSA 902 digitally-recording, acoustic fathometer operating 16 transducers,
each generating a 200-kHz acoustic beam with a conical 10-degree spread. At the time of
deployment in 1992, each transducer was mounted at least 1.5 m above the channel
bottom and between 1.8 m and 4 m below the water surface.










The fathometer is configured as two separate channels, each controlling eight
transducers. A time-varying gain circuit, one for each channel, can be adjusted to
calibrate the transducers on that channel to an overall (group) optimal setting.

On November 4, 1993, three additional hydrographic instruments were installed
near the Bonner Bridge. Two of these instruments were Endeco current meters (type
174SSM) that measure and record water temperature as well as current magnitude and
direction. The third instrument was a Seadata wave-tide recorder that measures and
records current magnitude and direction, wave frequency and direction, and water-surface
elevation. The current meter and puv installations are shown in Figures 52 and 53,
respectively.

The water depth at the instrumentation at the time of deployment was
approximately 5 m. The insitu recording instrumentation was deployed for
approximately 3 months. Even though there were no major storms during the
deployment of the flow and wave instruments, there was a significant deposition of
sediment in the study area. This completely buried one of the flow meters and the wave
instrumentation and damaged the other two flow meters. The damaged flow meters
contained approximately one months flow velocity data.


3.3 Conclusions

Approximately one and one-half months of current data were recovered from the two
current gauges that survived. This data was reduced analyzed and attempts were made to
correlate the measured scour depths with the flow velocities from the current meters. The
measured scour depths are a combination of aggradation and degradation, contraction
scour and local scour. The component that would correlate with the flow velocity
immediately upstream from the pier is local scour. The primary objective of this
measurement program was to obtain more information about local scour for larger scale
structures. The problem with any field experiment is, of course, the lack of control of the
quantities influencing the phenomena being studied and this is a text book example of the
problems that can be encountered. The global movement of sediment in this tidal inlet
was such that it completely overshadowed the local scour. Thus, the "noise" was much
greater than the "signal" and little or no correlation between scour depth and flow
velocity was observed. This illustrates the importance and need for controlled laboratory
experiments when trying to isolate a single component of a complex process, such as
local bridge pier scour. Since the ultimate goal this and similar research is to understand
and predict bridge scour under field conditions, field data are equally important but the
measurements must be sufficient to allow the prediction of all of the primary processes
affecting the phenomena. Lessons learned from this experience can be summarized as
follows:

*If the objective of a study is to isolate a single component of a complex process in a
field measurement program then a site where the other components are negligible or
at least small should be located. In this case, by far the most expensive part of the









measurement program (the scour measurement instrumentation) was already in place
for operational monitoring purposes. Therefore, for a small investment there was
potentially much to be gained.

* The global movement of sediment in this inlet under "normal" ambient conditions
was under estimated. Perhaps a closer examination of historical surveys and more
discussions with local workers in the area would have revealed the extreme dynamic
nature of the study site.

* When deploying instrumentation at a location somewhat unfamiliar to the researcher,
more frequent site visits should be planned, budgeted and conducted. Had this been
done the instrument fixed to the bottom would not have been lost.

* Controlled laboratory experiments for investigating a single component of a complex
process with many input parameters are the most cost effective way to obtain high
quality data.









4. REFERENCES


Sheppard, D.M., C.W. Reed, and S. Harr, (1994) "Sensitivity of Bridge Scour Producing
Currents to Storm Surge Parameters Progress Report," FDOT Design Conference,
Orlando, Florida, August 10, 1994.

Mason, R.R., Jr. and D.M. Sheppard, (1994) "Field Performance of an Acoustic Scour-
Depth Monitoring System," FDOT Design Conference, Orlando, Florida, August,
12-14, 1994.

Morris, F.W. (1987) "Modeling of Hydrodynamics and Salinity in the St. Lucie Estuary,"
SFWMD Technical Publication 87-1, January.

Norton, W.A. and W.H. McAnally, (1973) "A Finite Element Model for Lower Granite
Reservoir," Water Resources Engineers, Inc., Walnut Creek California.

Thomas and McAnally, (1991) "User's Manual for the Generalized Computer Program
System: Open-Channel Flow and Sedimentation, TABS-2', U.S. Army Engineer
Waterways Experiment Station, Vicksburg, Mississippi.

Fasstabs User's Manual, (1992) Boss Corporation and Brigham Young University.

Sheng, Y.P., S. Peene and Y.M. Liu, (1990) "Numerical Modeling of Tidal
Hydrodynamics and Salinity Transport in the Indian River Lagoon," Florida
Scientist, vol.53, No.3, p.147.

Smith, N.P., (1990) "Longitudinal Transport in a Coastal Lagoon," Estuarine, Coastal and
Shelf Science, Vol.31, 835-849.

SMS User's Manual, (1995) Boss Corporation and Brigham Young University.

Williams, J.L., (1985) "Computer Simulation of the Hydrodynamics of the Indian River
Lagoon," MS Thesis, Florida Institute of Technology, Melbourne.











STUDY AREA


GULp



+

0


FLOOR DA


Figure 1. General location of study areas.


STUDY
AREA






0
0
iv
^.












St. Lucie


Fort Pierce Inlet


OQ FORT
0


St Lucie Inlet


Rood '


C Study Area
' -------lrr sI


Figure 2. St. Lucie Estuary study area.


00'c
0 r~j
o Q~~
0


Jupiter Inlet





















































County boundary
Hydrologic unit boundary

Waterbodies


BUNNELL


DAYTONA
BEACH


5 0 5
Miles


Figure 3. St. Johns River study area.


- -30 25' 25"


-30 01' 54"














--29 38' 23













+


Sebastian Inlet





Ft. Pierce Inlet
St. Lucie
Estuary

St. Lucie Inlet


Jupiter Inlet

Figure 4. St. Lucie Estuary finite element mesh.























































Figure 5. St. Johns River finite element mesh.

































4 8 12 16 20


Time (hr)
Figure 6. St. Lucie & St. Johns River storm surge variation.


- Baseline
Rate of Rise
- - Rate of Fall
Duration of Peak


'i

t


















Gage 6


St. Lucie
Estuary


Gage 5


Gage 3


Gage 4


- Gage 1

Indian
River
Lagoon


SGage 2




Intracoastal
Waterway


Figure 7. St. Lucie study area locations.


+


























Gage 1


Gage 2


Figure 8. St. Johns River study area locations.










Indian River Lagoon


Rate of Rise
-- Rate of Fall
- Duration of Peak


- I I I I I I I I
0 5 10 15 20 2

Distance from St. Lucie Inlet (mi)

Figure 9. Maximum elevation comparisons Indian River Lagoon.


30 -


- - 0- -


0
0





-D


- 0-


20









10


- 4









Indian River Lagoon


16 -





12 -


/% / ,



I /

I
/,


\,


~I~i I



I


0 I I1 I II

0 4 8 12 16 20 24
Distance from St. Lucie Inlet (mi)

Figure 10. Maximum water elevation and elevation at maximum velocity magnitude comparisons Indian River Lagoon.


7


0
0

*


Baseline
S- Rate of Rise
- Rate of Fall
Duration of Peak


8 -


4-










Indian River Lagoon


-0- Rate of Rise
-@- Rate of Fall


20 Duration of Peak








-10
/
















-20




-30 I I I

0 5 10 15 20 25

Distance from St. Lucie Inlet (mi)

Figure 11. Maximum velocity magnitude comparisons Indian River Lagoon.









4 -


3






2-






1-


Indian River Lagoon


I II I I I I
0 5 10 15 20 2

Distance from St. Lucie Inlet (mi)

Figure 12. Maximum velocity magnitude vs. distance Indian River Lagoon.


' --- j J


,' "


J








2.0 Indian River Lagoon
Gage 2 Baseline
S- - Rate of]
I
I
I
1.5-
4",

AI


1.0-- I
I





0.5- /
/





0.0 -I I


0 4 8 12 16

Time (hrs)

Figure 13. Velocity magnitude vs. time at Gage 2 rate of rise variation Indian River Lagoon.


2








2.0 Indian River Lagoon
Gage 2 B aseline
\ - Rate of Fall


1.5

W1



S1.0-





0.5-





0.0 -

0 4 8 12 16 20
Time (hrs)

Figure 14. Velocity magnitude vs. time at Gage 2 rate of fall variation Indian River Lagoon.







3 -- Indian River Lagoon
Gage 2 Baseline
Duration of Peak






bLI







0
s / \ I

3 \ \

,




0 4 8 12 16
Time (hrs)
Figure 15. Velocity magnitude vs. time at Gage 2 duration of peak variation Indian River Lagoon.


20


1









1.6 Indian River Lagoon
Gage 1 Baseline
S- - Rate of Rise
I
I

1.2 I
I/

.) I

I
I 0.8 -
I

o /

a.) /
0.4-






0.0 I

0 4 8 12 16

Time (hrs)

Figure 16. Velocity magnitude vs. time at Gage 1 rate of rise variation Indian River Lagoon.


20








1.6 Indian River Lagoon
Gage 1 Baseline
\ - Rate of Fall
I

1.2 V
. I I




0.8-





0.4 -
I




0.0 -

0 4 8 12 16 20
Time (hrs)

Figure 17. Velocity magnitude vs. time at Gage 1 rate of fall variation Indian River Lagoon.








1.6 Indian River Lagoon -
Gage 1 '\ Baseline
Gage I
- Duration of Pi


1.2-





0.8-





0.4





0.0 -

0 4 8 12 16
Time (hrs)

Figure 18. Velocity magnitude vs. time at Gage 1 duration of peak variation Indian River Lagoon.











Intracoastal Waterway



? -a


SRate of Rise
SRate ofFall
Duration of Peak


U- -


4 8 12


Distance from St. Lucie Inlet (mi)

Figure 19. Maximum elevation comparisons Intracoastal Waterway.


30 -


0
0


20









10


I.









Intracoastal Waterway


15 Rate of Fall /

C Duration of Peak



10 1

I \,


/
0- \/


I I I




0 4 8 12 16 20
Distance from St. Lucie Inlet (mi)

Figure 20. Maximum water elevation and elevation at maximum velocity magnitude comparisons Intracoastal Waterway.









Intracoastal Waterway


SRate of Rise
- Rate of Fall
k Tt I. n. I_


20 LJI UmDlOn OI of eaK


o '\ /
-10 -


0 0



> -10





-20



-30 I I
0 4 8 12 16

Distance from St. Lucie Inlet (mi)

Figure 21. Maximum velocity magnitude comparisons Intracoastal Waterway.








6 -


2-


Intracoastal Waterway


I I I I I
0 4 8 12 16 2
Distance from St. Lucie Inlet (mi)

Figure 22. Maximum velocity magnitude vs. distance Intracoastal Waterway.


P2






C3
ID


I m,,


Baseline
- Duration of Peak
- *Rate of Fall
- Rate of Rise







4 Intracoastal Waterway
Gage 3 Baseline
Rate of Rise


3
3 -- A r \







0 0
S- / i

I II
I -
II

0- I / I 1 1


0 4 8 12 16
Time (hrs)

Figure 23. Velocity magnitude vs. time at Gage 3 rate of rise variation Intracoastal Waterway.


20


1








3 Intracoastal Waterway
Gage 3


-- Baseline
Rate of Fall


C2
I I I I\







o I
- 2 / I'
' 0 \ tt






I \I




0 4 8 12 16 20
Time (hrs)

Figure 24. Velocity magnitude vs. time at Gage 3 rate of fall variation Intracoastal Waterway.








4 Intracoastal Waterway
Gage 3 Baseline
- Duration of Peak


3 /
I \




o \ \II




SI I
2 / \










0-

0 4 8 12 16 20
Time (hrs)

Figure 25. Velocity magnitude vs. time at Gage 3 duration of peak variation Intracoastal Waterway.







3 Intracoastal Waterway
Gage 4 Baseline
- Rate of Rise




I
S2 -

S -- I




0 I
.U I



I i I



0 4 8 12 16
Time (hrs)

Figure 26. Velocity magnitude vs. time at Gage 4 rate of rise variation Intracoastal Waterway.


20


1


E


1








3 Intracoastal Waterway Be
Gage 4 Baseline
4- - Rate of Fall



S/ \\
4 2- -






1
SI I





0 -,I' -| ------- \ ---- I --- \ ----------


0 4 8 12 16 20
Time (hrs)

Figure 27. Velocity magnitude vs. time at Gage 4 rate of fall variation Intracoastal Waterway.


_ ___






3 Intracoastal Waterway
Gage 4 Baseline
Duration of Peak

/ \






S1 I -




0 I

0 4 8 12 16
Time (hrs)
Figure 28. Velocity magnitude vs. time at Gage 4 duration of peak variation Intracoastal Waterway.


20


1











St. Lucie Estuary


0 -


- a


SRate of Rise
-- Rate of Fall
- Duration of Peak


I I I I I

0 2 4 6 8 1

Distance from St. Lucie Inlet (mi)

Figure 29. Maximum elevation comparisons St. Lucie Estuary.


30 -


O
O

X
9
X


~de
I
~cl
v


20 -


10 -









20 -


--, /

/
s 7i
"\ .'/

/<7 /


1 I I I I I I I I


Distance from St. Lucie Inlet (mi)

Figure 30. Maximum water elevation and elevation at maximum velocity magnitude comparisons St. Lucie Estuary.


St. Lucie Estuary



Baseline
S- Rate of Rise
Rate of Fall
Duration of Peak


15 -


0
0
*


10 -


5-


0











St. Lucie Estuary


- --


--- Rate of Rise

-- Rate of Fall

- Duration of Peak


W &


I ~~~-_--


I I I

2 4 6

Distance from St. Lucie Inlet (mi)


Figure 31. Maximum velocity magnitude comparisons St. Lucie Estuary.


30





20


0
0


>





S*,
>^


10





0





-10


-20 -


320


- I

0


I


I


-


-








6 -


41






2-


St. Lucie Estuary


II I I I I
0 2 4 6
Distance from St. Lucie Inlet (mi)

Figure 32. Maximum velocity magnitude vs. distance St. Lucie Estuary.








6 St. Lucie Estuary
Gage 5 Baseline
- Rate of Rise





4 ;
I
_ I



I
/ /

S2
1 ,



0 /\ I I



0 4 8 12 16
Time (hrs)

Figure 33. Velocity magnitude vs. time at Gage 5 rate of rise variation St. Lucie Estuary.


20


1






6 St. Lucie Estuary
Gage 5 -Baseline
Rate of Fall








-2-
o




0 I' I' II I
0 4 8 12 16
Time (hrs)
Figure 34. Velocity magnitude vs. time at Gage 5 rate of fall variation St. Lucie Estuary.


20


1









St. Lucie Estuary
Gage 5


1 I I

0
*\
0 / I









0 4 8 12 16 20

Time (hrs)

Figure 35. Velocity magnitude vs. time at Gage 5 duration of peak variation St. Lucie Estuary.








1.6 St. Lucie Estuary -
Gage 6 Baseline
_- - Rate of Rise


1.2- I
rf I




S0.88-
I
I


/ I
0.4 I





0.0 -

0 4 8 12 16
Time (hrs)

Figure 36. Velocity magnitude vs. time at Gage 6 rate of rise variation St. Lucie Estuary.


20


1\








1.6 St. Lucie Estuary
Gage 6 Baseline
e - Rate of Fall


1.2


r7i

S0.8--




0.4-
I -



0.0-
0.0 ..----- ---------------i ----


0 4 8 12 16
Time (hrs)

Figure 37. Velocity magnitude vs. time at Gage 6 rate of fall variation St. Lucie Estuary.


20


1







1.6 St. Lucie Estuary
Gage 6 Baseline
- Duration of Peak


1.2 -




0.8 -




o I
0.4




0.0 -
0 4 8 12 16
Time (hrs)
Figure 38. Velocity magnitude vs. time at Gage 6 duration of peak variation St. Lucie Estuary.


1


20








20- St. Johns River eof ise

Rate ofFall
Duration of Peak


15




10 -






5







0 5 10 15 20 25 30
Distance from River Mouth (mi)

Figure 39. Maximum elevation comparisons St. Johns River.










St. Johns River


- J \ I

i /



/ '/


/
/ -
I ~


\ \ -


0 5 10 15 20 25

Distance from River Mouth (mi)

Figure 40. Maximum water elevation and elevation at maximum velocity magnitude comparisons St. Johns River.


0
*


Baseline
- Rate of Rise

-- Rate of Fall

-- Duration of Peak









30 St. Johns River Rate ofRise
*C Rate of Rise
Rate of Fall
20 - Duration of Peak




C 10 -. .




0
S -10








-20




-30 I I I

0 5 10 15 20 25 30

Distance from River Mouth (mi)

Figure 41. Maximum velocity magnitude comparisons St. Johns River.









St. Johns River


5 10 15 20

Distance from River Mouth (mi)

Figure 42. Maximum velocity magnitude vs. distance St. Johns River.


8





v- 6



Cd








2





0


Baseline

- Rate of Rise

-Rate of Fall

Duration of Peak

^ ______









8 St. Johns River
Gage 1 Baseline
Rate of Rise



6


4- I





1~ 1 I
I
I 4-





/



0 I I I
2




0-

0 4 8 12 16

Time (hrs)

Figure 43. Velocity magnitude vs. time at Gage 1 rate of rise variation St. Johns River.


20








8 St. Johns River
Gage 1 Baseline
- Rate of Fall









g 4-
S- \



-\ /
2-







0
0 I I IIII '



0 4 8 12 16 20
Time (hrs)

Figure 44. Velocity magnitude vs. time at Gage 1 rate of fall variation St. Johns River.








8 St. Johns River B e
Gage Baseline
- Duration of Peak



6 /

oiI \ I



4
I


SI \ \I
2 --








0 4 8 12 16 20
Time (hrs)

Figure 45. Velocity magnitude vs. time at Gage 1 duration of peak variation St. Johns River.







3 St. Johns River I
Gage 2 Beline
- Rate of Rise



/

/ 1 /
I
SII

9 b



0
/\ /
0 I '




0 4 8 12 16
Time (hrs)
Figure 46. Velocity magnitude vs. time at Gage 2 rate of rise variation St. Johns River.

60


2


20


f









3 St. Johns River
Gage 2 Baseline
- Rate of





\











0 4 8 12 16
Figure 47. Velocity magnitude vs. time at Gage 2 rate of fall variation St. Johns River.\'





\ !/
I

I





0 4 8 12 16

Time (hrs)

Figure 47. Velocity magnitude vs. time at Gage 2 rate of fall variation St. Johns River.


Fall


20


... ---


f









3 St. Johns River
Gage 2 Baseline
- Duration of Peak




S/ \









S/ \


I
2-














I

0 I I I I I

0 4 8 12 16 20
Time (hrs)

Figure 48. Velocity magnitude vs. time at Gage 2 duration of peak variation St. Johns River.








12 St. Johns River I
Gage 1 Elevation from MWL
- Gage 1 Velocity Magnitude
Gage 2 Elevation from MWL
Gage 2 Velocity Magnitude










0 4









0 4 8 12 16 20


Time (hrs)

Figure 49. Velocity magnitude and baseline elevation vs. time St. Johns River.
I


0 I/ \\ 4













0 4 8 12 16 20
Time (hrs)

Figure 49. Velocity magnitude and baseline elevation vs. time St. Johns River.





























FACILITY


WAVE GAGE

INLET


HATTERAS
TOWER


VICINITY MAP
10 5 0 20
SCALE IN MILES


Figure 50. Vicinity map for Oregon Inlet.


FIELD
(FRF)


















D *, a

a, .
a, c
a; *


a,


aY
a
a'


a
* a
af V


Figure 51. Drawing of Herbert C. Bonner Bridge over Oregon Inlet.











Surface Marker Buoy


Current Meter


Inlet Bottom


17 ft.


Support Pipes
Jetted into

Note:
Figure Not to Scale




Figure 52. Tethered current meter installation.


6 ft.


-r











-Surface Marker
Buoy


-6f.





~6 ft. F-


Electromagnetic
Current Meter with
Pressure Transducer
and Data Acquisition System


T
Inlet Bottom
3 ft. I


- 17 ft.


-I-


Support Pipes
Jetted into Bottom


Note:
Figure Not to Scale


-I


Figure 53. Electromagnetic current meter, pressure transducer, data acquisition (puv)
installation.


















Appendix A












ASCE Conference on
Water Resources Engineering
San Antonio TX, August 14-18, 1995



Sensitivity of Bridge Scour Producing Currents to Storm Surge Parameters

Christopher W. Reed', Susan Harr2 and D. Max Sheppard3, M. ASCE


Abstract
A study has been conducted to determine the sensitivity of storm surge
induced currents in a tidal system to variations in the storm surge parameters.
Numerous storm surge hydrographs have been developed which are representative of
surges predicted for the southeast coast of Florida. A depth averaged, finite-element
hydrodynamic model (RMA2) has been used to calculate the velocities within a
shallow water estuary system for systematic variations in the surge hydrograph.
Results indicate significant sensitivity to surge parameters such as the peak surge
elevation, duration, and rate-of-rise for the tidal system studied.

Introduction
Design scour computations in tidal inlets, bays, estuaries and rivers use one in
one-hundred and one in five-hundred year return interval storm conditions. Storm
surge hydrographs, predicted at the coastline for each storm, are used as the basis for
calculating the associated surge velocities in the inlets and adjacent tidal waters.
Comparisons of predicted and measured storm surges on the open coast indicate that
the predicted peak water elevations are relatively close to the measured value, but
other features of the hydrograph, such as the rate of rise or fall, can differ greatly. The
propagation of meteorological tides (storm surges) through a tidal inlet or river
mouth into a bay-estuary-river system can be extremely complex. The complexity is
enhanced when there is flooding of barrier islands and other low lying subaerial lands.
It is by no means obvious how the "errors" in the predicted coastal hydrograph
influence the currents and water elevations at various locations in the
bay-estuary-river system. Variations in design currents and water elevation can have
a major impact on design scour depth predictions and therefore it is important to

S Post Doctoral Fellow in the Coastal and Oceanographic Engineering
Department, University of Florida, Gainesville, FL 32611.
2 Graduate Assistant in the Coastal and Oceanographic Engineering Department,
University of Florida, Gainesville FL 32611.
3 Professor of Coastal and Oceanographic Engineering, University of Florida,
Gainesville FL 32611.










know how sensitive these quantities are to variations in the storm surge parameters.
In order to address these issues, a study has been conducted to determine the
sensitivity of design scour producing currents in a tidal system to variations in the
storm surge parameters. A calibrated depth averaged, two-dimensional, finite-
element hydrodynamic model has been used to provide the velocity predictions for
each variation in the surge hydrographs.
It should be noted that surge models, such as SLOSH (Jarvinen and Gebert,
1987), were developed primarily for obtaining peak elevations for use in flood
evacuation planning for severe storms events. To this end the models have been
relatively successful. For instance, a comparison of SLOSH predicted surge
elevations with measured water elevation data for Hurricane Gloria's landfall over
Long Island (Jarvinen and Gebert, 1987) and for Hurricane Hugo's landfall near
Charleston, South Carolina (Garcia et al., 1990) show generally good agreement. In
these cases, the variations between the predicted and measured hydrographs may be
insignificant since the peak water elevations are usually well predicted. However, for
the purposes of design scour calculations, it is necessary to accurately predict the
storm driven currents as well as water elevations. The effects of hydrograph
variations on storm currents is not well documented. Furthermore, many of the other
hydrograph features, such as rate of rise and fall, duration of the peak, etc., are not
well predicted. Since hydrographs are typically used in design storm velocity
predictions, it is important to quantify the sensitivity of the predictions to velocity
uncertainties in the hydrographs.

Sensitivity Analysis
The approach for determining the sensitivities is based on the application of a
two-dimensional, depth averaged hydrodynamic model to a southern Florida tidal
system, namely the St. Lucie Estuary and portions of the Indian River Lagoon. The
hydrodynamic model used is RMA2 (Norton and McAnally, 1973; Thomas and
McAnally, 1991) with the FASTTABS pre and post processor (Fasttabs, 1992).


st LucIe Estuary (SLE)




Intra-Coastal 1 Station B
Waterway South (ICW) Indian River Lagoon (IRL)

Station A I *
St. Lucie Inlet


Figure 1. Contour and Station Map of Estuary System










RMA2 is a depth averaged two-dimensional model employing finite-element solution
methods to solve the shallow water wave equations. The tidal system is characterized
by relatively shallow water, generally 2 to 6 ft deep at MLW, throughout most of the
system with maximum depths of 10 ft in narrow maintained channels. A portion of
the modeled area is shown in Figure 1 which shows bathymetric contours on 2.5 ft
intervals. The Intracoastal Waterway extends southward to Jupiter Inlet. A section of
the Indian River Lagoon is represented, including Fort Pierce Inlet and portions of the
lagoon to the north.
Calibration of the model to normal tidal conditions was completed prior to
beginning the sensitivity analysis. A number of modeling studies have been conducted
for portions of the estuary system, (Williams, 1985; Morris, 1987; Sheng et al., 1990;
Smith, 1990) and were used to investigate estuary hydrodynamics, salinity transport
and water quality. Data obtained for these studies as well as information from the
NOAA Tide Tables was used for calibration of the St. Lucie Estuary model.
The sensitivity analysis was conducted for the tidal system by driving the
flows at the inlets with a typical surge hydrograph superimposed on a normal tide.
The surge parameters such as amplitude, duration and shape were varied and then the
calculated flows for each surge within the tidal system were compared. In each case
the surge parameter variations were scaled such that each of the surges had the same
energy. This was necessary to eliminate effects of the surge size on the results, and
focus only on the effects due to "shape" parameters. The energy associated with each
surge was calculated by considering the surge as a solitary wave propagating with
speed gh where g is gravity and h is the water depth. This definition allows one to
transform the surge hydrograph (i.e. time series) into a wave profile, from which the
total kinetic and potential energy could be calculated. Typical perturbations used are


8 Baseline -
Station A
82
e- Peak Duration (s0) 4 -
Pea Durat io
g Skewnass (S3)
Duratilon (82)

4 \\
/ g Basn. Station B
2 4/ 82

0 -- 0--
-0 -10 0 10 20 40 50 so 70 80 0
Time (hrs) Time (hrs)

Figure 2. Surge Variations Figure 3. Computed Hydrographs










shown in Figure 2, representing changes in height and duration, rate-of-rise, skewness
and peak duration. The variations in height and duration of these surges averaged
about 15% of the baseline surge values.

Results
The water elevation time series plots shown in Figure 3 (corresponding to
points A and B in Figure 1), are representative of results from the hydrodynamic
model. Note that the tidal influence associated with the astronomical tide has been
removed from the curves. Comparison of the three curves representing perturbations
to the baseline indicate that the variations in the surge height and width are of similar
magnitude (averaging 15%) to those of the input hydrographs. The discharge time
series corresponding to the water elevation plots in Figure 3 are shown in Figure 4.
The differences in the maximum discharge (and subsequently the maximum velocity)
at these stations vary greatly with the type of surge perturbation and can exceed 50%.
Using changes in maximum discharge as an indicator of sensitivity, plots of the
sensitivity for points along the St. Lucie Estuary, Intracoastal Waterway (South) and
the Indian River Lagoon can be developed. These plots are shown in Figure 5. The
results indicate that the highest sensitivity and largest range of sensitivities are in the
Intracoastal Waterway (South), and the least occur in the Indian River Lagoon. Note
that the Intracoastal Waterway and the Indian River Lagoon represent the smallest
and largest water volume respectively within the system.

20000 Baseine i

SStationConclusions A








reached depend on, among other quantities, the local depth average velocity. JustCW8
h ns0 Ir des
0 -
100000- -I - ---- ---- I-W|2)


0- ( 2 SL1
0 tIRLI682)





Figure 4. Computed Discharges Figure 5. Sensitivities of Discharge

Conclusions
Equilibrium sediment scour depths and the rates at which these depths are
reached depend on, among other quantities, the local depth average velocity. Just
how dependent scour is on velocity again depends on several quantities, including the
magnitude of the velocity, but under certain circumstances it can be sensitive to
changes in velocity. Thus, the relatively large dependence of velocity on the storm
4










surge parameters found in this study can translate into an even greater dependence of
scour on these parameters. The results of this study provide some guidelines for
determining the locations within a tidal system and the conditions under which the
currents are most sensitive to variations in storm surge parameters. Improvements in
storm surge predictions are needed. Meanwhile, for points of interest within the tidal
system that are in sensitive areas, a range of the critical design storm surge
hydrograph parameters (around the predicted values) should be investigated.

Acknowledgments
The authors would like to thank the Florida Department of Transportation for
supporting this research. The authors also acknowledge the valuable technical
contributions to this work made by Shawn McLemore and Luis Maldonado of FDOT
in Tallahassee.

References
Fasttabs User's Manual (1992) Boss Corporation and Brigham Young University.
Garcia, A.W., B.R. Jarvinen and R.E. Schuck-Kolben (1990) "Storm Surge
Observations and Model Hindcast Comparison for Hurricane Hugo," in Shore
and Beach, October, Vol.58-59, p.15.
Jarvinen, B.R. and J. Gebert (1987) "Observed Versus SLOSH Model Storm Surge
for Connecticut, New York and Upper New Jersey in Hurricane Gloria,
September 1985," NOAA Technical Memorandum, NWS NHC 36, August.
Morris, F.W. (1987) "Modeling of Hydrodynamics and Salinity in the St. Lucie
Estuary," SFWMD Technical Publication 87-1, January.
NOAA Tide Tables, Department of Commerce.
Norton, W.A. and W.H. McAnally (1973) "A Finite Element Model for Lower
Granite Reservoir," Water Resources Engineers, Inc., Walnut Creek
California.
Sheng, Y.P., S. Peene and Y.M. Liu (1990) "Numerical Modeling of Tidal
Hydrodynamics and Salinity Transport in the Indian River Lagoon," Florida
Scientist, Vol.53, No.3, p.147.
Smith, N.P. (1990) "Longitudnal Transport in a Coastal Lagoon," Estuarine, Coastal
and Shelf Science, Vol.31, pp.835-849.
Thomas, W.A. and W.H. McAnally (1991) "User's Manual for the Generalized
Computer Program System: Open-Channel Flow and Sedimentation,
TABS-2," US Army Engineer Waterways Experiment Station, Vicksburg,
Mississippi.
Williams, J.L. (1985) "Computer Simulation of the Hydrodynamics of the Indian
River Lagoon," M.S. Thesis, Florida Institute of Technology, Melbourne.

















Appendix B







FIELD PERFORMANCE 367


results from the monitoring system are presented. Although the scour-depth
monitoring system was installed in September 1992, most of the discussion is limited
to data collected in November 1993, the period for which there are concurrent scour-
depth and other hydrographic data.


75* 35'


FIELD PERFORMANCE OF AN ACOUSTIC
SCOUR-DEPTH MONITORING SYSTEM

By Robert R. Mason, Jr.1, Member ASCE, and D. Max Sheppard2


75 30'


35' 5r


Abstract
The Herbert C. Bonner Bridge over Oregon Inlet serves as the only land link
between Bodie and Hatteras Islands, part of the Outer Banks of North Carolina.
Periodic soundings over the past 30 years have documented channel migration, local
scour, and deposition at several pilings that support the bridge. In September 1992, a
data-collection system was installed to permit the off-site monitoring of scour at 16
bridge pilings. The system records channel-bed elevations at 15-minute intervals and
transmits the data to a satellite receiver. A cellular phone connection also permits
downloading and reviewing of the data as they are being collected. A digitally
recording, acoustic fathometer is the main component of the system. In November
1993, current velocity, water-surface elevation, wave characteristics, and water
temperature measuring instruments were also deployed at the site. Several
performance problems relating to the equipment and to the harsh marine environment
have not been resolved, but the system has collected and transmitted reliable scour-
depth and water-level data.
Introduction
Scour processes at bridges are very difficult to predict as they are dependent
on the physical properties of the bridge and many environmental factors, such as
sediment transport rates. Some bridges are known to be scour-critical and may need to
be continuously monitored pending remedial repair or replacement (Johnson and
Jones, 1993). A variety of scour-depth monitoring systems have been proposed for this
task ranging from simple mechanical devices to elaborate bottom-penetrating sonar
and radar systems (Jarrett and Boyle, 1986; Skinner, 1986; Gorin and Haeni, 1989;
Butch, 1991). The most efficient and cost-effective way to monitor scour depends on
the type and location of the structure, hydraulic and environmental conditions, and
sediment characteristics and concentrations (Fenner, 1993).
This paper describes the acoustic scour-depth monitoring system used at the
Herbert C. Bonner Bridge, Oregon Inlet, North Carolina, including its design, its
performance, and the conditions under which the system has operated. Instruments
used to collect ancillary hydrographic data also are described, and some preliminary

Hydrologist. U.S. Geological Survey, 3916 Sunset Ridge Road, Raleigh, NC 27607.
2 Professor. Coastal and Oceanographic Engineering Department, University of Florida,
Gainesville. FL 32611.


35* 45'


Figure 1. Location of Herbert C. Bonner Bridge and Oregon Inlet, North Carolina.

Background
Oregon Inlet is a narrow, shallow, and dynamic waterway connecting
Albemarle and Pamlico Sounds to the Atlantic Ocean and separating Bodie and
Hatteras Islands, two in a chain of barrier islands commonly referred to as North
Carolina's Outer Banks (fig. 1). Since its formation by a severe Atlantic storm in 1846,







368 HYDRAULIC MEASUREMENTS AND EXPERIMENTATION

the inlet has frequently shifted in depth, width, and location as a result of persistent
southward migration of Bodie and Hatteras Islands; local scour produced by tide and
wind-driven currents and waves; deposition due to long-shore sediment transport; and
transport of sand from shoals in the sound during periods of strong easterly currents
(Dolan and Lins, 1986). The rate of southward migration of the inlet varies greatly but
has averaged 21 meters (m) per year from 1846 to 1993 (U.S. Department of
Transportation, 1993). Currently (January 1994), the inlet is approximately 1.6
kilometers (km) wide and ranges from 2 to 3 m deep, except for the navigation
channel, which is maintained at about 12 m deep. The channel bed is composed of
thick deposits of coarse sand with little to no vegetative cover.
Oregon Inlet is spanned by the Herbert C. Bonner Bridge. Built in 1962 and
located 1,200 m inland of the Atlantic Ocean and partly within the surf zone, the bridge
is 4 km long, I m wide, and crests 20 m over the mean low-water level of Oregon
Inlet. The Bonner Bridge is supported by 240 pile bents each capping clusters of 8-12
driven piles, which penetrate 15-27 m into the channel sediments. The bridge is the
main component of the only land link from the mainland to Hatteras Island and carries
an average daily traffic load of 6,900 vehicles during the summer months.
Since completion of Bonner Bridge in 1962, the North Carolina Department of
Transportation (NC-DOT) has made periodic soundings of Oregon Inlet to monitor
channel migration, deposition, and local scour. These data indicate that some sections
of Oregon Inlet have scoured and filled through an 11-m range (fig. 2). In 1978, NC-
DOT discovered that, as a result of scour, several pilings were penetrating only 2.1 m




CHANNEL BOOM



jU %A
9
JANUARY 1994 dof of \ 1
2 CHANNEL BOTM


S15 LOCATION OF
NAVIGATION CHANNEL MINIMUM ELEVATION

18 - * i , , *
0 1,000 2,000
DISTANCE ALONG BONNER BRIDGE FROM NORTH END OF BRIDGE, IN METERS

Figure 2. Cross section of Oregon Inlet at Bonner Bridge showing maximum and
minimum channel-bottom elevations and January 1994 channel-bottom elevation.


FIELD PERFORMANCE 369


into the channel bottom. From that year to 1992, scour-preventive and remedial
actions to protect the bridge have cost over $9 million. In response to this history of
channel instability, the U.S. Geological Survey (USGS) and the NC-DOT joined in a
cooperative effort to develop and install a data-collection system to permit continuous
remote monitoring of scour depth at 16 bridge pilings. The system was installed in
September 1992.
A second data-collection program began in November 1993 and ended in
January 1994. This effort consisted of deployment and operation of three instruments
that measure and record current magnitude and direction, wave frequency and
direction, water-surface elevation, and water temperature near the Bonner Bridge.
This program was a cooperative effort between the Florida Department of
Transportation (F-DOT), the University of Florida, Coastal and Oceanographic
Engineering Department (UFCOE), the NC-DOT, and the USGS. In conjunction with
the scour-depth data, the resulting hydrographic data can enable evaluation of
theoretical scour-depth predictive equations.
Scour-Depth Monitoring System
The main component of the Bonner Bridge scour-depth monitoring system is
a Datasonics PSA 902a digitally-recording, acoustic fathometer operating 16
transducers, each generating a 200-kHz acoustic beam with a conical 10-degree
spread. At the time of deployment in 1992, each transducer was mounted at least 1.5
m above the channel bottom and between 1.8 and 4 m below the water surface. These
depths were chosen to minimize interference from entrained air, surface turbulence
(waves), suspended sediment, and debris. Transducers are secured to the inside of 7-
degree battered pilings on both ends of eight consecutive pile bents (fig. 3).
The fathometer is configured as two separate channels, each controlling eight
transducers. A time-varying gain circuit, one for each channel, can be adjusted to
calibrate the transducers on that channel to an overall (group) optimal setting.
However, the transducers cannot be calibrated individually.
The distances between the transducers and the channel bottom (scour depths)
are recorded at 15-minute intervals and are output through a standard RS-232 port to
a Vitel VX1004 programmable electronic datalogger and then transmitted to a
Geostationary Earth Orbiting Satellite (GOES) receiver. The data logger is also
equipped with a Mitsubishi CDL 100 cellular phone and computer modem for
downloading of data and for changing software attributes remotely.
On November 4, 1993, three additional hydrographic instruments were
installed near the Bonner Bridge in the project area (fig. 1). Two of these instruments
were Endeco current meters (type 174SSM) that measure and record water
temperature as well as current magnitude and direction. The third instrument was a
Seadata wave-tide recorder that measures and records current magnitude and
direction, wave frequency and direction, and water-surface elevation. The current-
meter instruments were located in line with three consecutive piers and approximately
30 m east (ocean side) of the bridge.

aAny use of trade, product, or firm names is for descriptive purposes only and does not imply
endorsement by the U.S. Government.







370 HYDRAULIC MEASUREMENTS AND EXPERIMENTATION


increased to 2.6 m due to erosion from currents associated with Hurricane Emily
(August 31 to September 1, 1993). Following the passage of the hurricane through
September 12, there was a net deposition of approximately 0.5 m of sediment as
indicated by a sustained reduction in scour depth. From October 12 to November 14,
there was a net erosion of approximately 1 m of sediment. Periods of significant fill
occurred on September 18 (0.4 m), November 15 (0.9 m), and November 27 (0.2 m),
1993. In addition to scour associated with Hurricane Emily, scour also occurred on
October 12 and November 28. On November 30, the channel bed was 2.0 m below the
transducer, having traversed a minimum to maximum change in depth of 1.2 m.


(NOTTO SCALE) --


Figure 3. Transducer mounting on Bonner Bridge.

Monitoring System Performance
The performance of an acoustic scour-depth monitoring system is influenced
by its design, its mounting, and by the environment in which it operates. Mounting
considerations include the rigidity of the mounting and the location of the transducer
relative to the piling, the channel bottom, and the water surface. Environmental
factors, which can influence system performance, include suspended debris,
suspended sediment, entrained air, biological growth, varying bed-slopes and bed-
forms, and possibly, electronic interference from radios, radars, power lines, and other
sources.
Four calibration checks were made during the period from November 17,
1992, to May 25, 1993. In each case the distances from the transducers to the channel
bottom (scour depths) were physically measured by NC-DOT scuba divers. Some
transducers were mounted closer to the channel bottom than were others. This
difference and likely differences in bed-form and local bed-slope beneath each
transducer probably resulted in slightly different acoustic-signal properties and rates
of attenuation. Thus, the resulting operational settings were not necessarily optimum
for each individual transducer. Some transducers, therefore, could be expected to
perform more reliably than others. Overall, however, the correlation between the
physically measured and acoustically sensed data is very good. The results of the
calibration checks for transducer 10 are typical of the overall correlations (fig. 4).
Fathometer records for transducer 13 typify the variability of scour and fill
during the data-collection period from August to November 1993 (fig. 5). On August
30, the channel bed beneath transducer 13 was 2 m below the transducer. This depth


3 4 5
PHYSICALLY MEASURED DEPTH, IN METERS
Figure 4. A typical result of transducer-calibration checks.

For the purposes of this paper, the reliability of the Bonner Bridge scour-depth
monitoring system during November 1993 was evaluated using two performance
characteristics: (1) the percentage of transmitted acoustic signals that were not
recorded by the datalogger (failed signal return) and (2) the consistency of computed
distances from one reading to the next (table 1). For the 16 transducers, the percentage
of failed signals during November ranged from about 6 percent for transducers 13 and
14 to nearly 100 percent for transducer 7 (table 1). Failed signals are shown in the
record for transducer 13 as lines extending to the top of the graphs (fig. 5).
The cause of the failed signals is unknown. Attempts to correlate signal
dropouts or no returns with hydraulic phenomena such as tidal current magnitude and
direction have been unsuccessful. However, strong daily cycles are evident in the
frequency of failure of transducers 1 and 8. In both instances the highest frequency of
failure occurs from 700 hours to 1700 hours, when the solar panel battery-chargers are
in operation. Intermittent current surges resulting from battery recharging operations
during daylight could be the source of the problem with these transducers.
Modifications to the system to remedy this problem are planned. Failures of the


FIELD PERFORMANCE 371








372 HYDRAULIC MEASUREMENTS AND EXPERIMENTATION


29 1 5 10 15 20 25 30
AUGUST SEPTEMBER 1993


I )




2

O
U 3






2



3


8|


a. 0

0

-1


1 5 10 15 20 25 30
OCTOBER 1993


5 10 15 20 25 30
NOVEMBER 1993


1 5 10 15 20 25 30
NOVEMBER 1993


Figure 5. Scour depth at transducer 13 for September-November 1993
and tidal current velocity for November 1993.


remaining transducers appear to be random in a temporal sense, but are highly
correlated to one another. When a failure occurs on a normally reliable transducer,
transducer 2 for instance, the remaining transducers usually also fail. This correlation
is probably the result of communication anomalies between system components.


Table 1.--Percentage offailed signal returns and consecutive readings differing
by selected ranges for each transducer, November 1993
[m, meter]

Trans- Failed signal Percent of consecutive readings differing by Mean distance
ducer returns indicated ranges to channel
no. (percent) 0.25-0.49 (m) 0.50-0.99 (m) 1.0-1.5 (m) bottom (n)
1 81.9 14.5 37.3 28.6 0.80
2 8.8 4.2 17.6 10.0 3.67
3 8.8 4.1 8.8 4.4 .45
4 8.8 7.0 25.1 13.6 2.13
5 8.8 2.9 12.9 8.4 2.36
6 8.8 8.8 3.9 1.5 1.38
7 99.6 0 81.8 81.8 5.10
8 32.1 19.2 27.6 27.6 2.26
9 55.7 1.8 1.0 .1 2.15
10 14.4 2.4 4.6 6.3 2.90
11 12.8 2.1 6.3 2.0 1.68
12 9.1 1.3 7.7 4.8 3.12
13 6.4 .10 .30 .20 2.24
14 6.4 .20 .30 .50 2.07
15 68.6 0 .1 3.7 2.10
16 66.0 .2 .6 3.9 2.72

Movement of sediment after episodes of scour or fill is detected by the
fathometer as a change in scour depth. Although changes are expected, they are
usually small (<0.25 m) for consecutive 15-minute readings. To evaluate measurement
consistency, the differences between consecutive scour-depth measurements were
computed, and the percentage of these differences exceeding selected thresholds (0.25
m, 0.5 m, 1.0 m, and 1.5 m) were summarized for each transducer (table 1). The
magnitude and frequency of differences between consecutive readings were examined
for correlations with current magnitude and direction and temporal patterns, but none
were detected.
Large differences between consecutive readings also can be caused by multiple
echoes of the same transducer signal. Multiple echoes occur when a transducer return
signal is emitted from the transducer, bounces off the channel bottom, then off the
transducer, and back off the channel bottom for a second time before it is detected by


FIELD PERFORMANCE 373







374 HYDRAULIC MEASUREMENTS AND EXPERIMENTATION


the fathometer. Multiple echoes result in computed depths that are twice the actual
depth to the channel bottom (fig. 6).


ACTUAL DEPTH
c.n s (APPROXIMATELY
/ 1.7 METERS)



FAILED SIGNAL
3 RETURN (SHOWN OFF
3 SCALE)
0

4
0
a" MULTIPLE ECHOES INDICATE
TRAVEL TIME OF TWICE ACTUAL
DEPTH (APPROXIMATELY 3.4 METERS)
2400 0400 0800 1200 1600 2000 2400
NOVEMBER 7. 1993

6. Depth to channel bottom for transducer 3 showing effects
of multiple echoes.

Large differences in depth readings also can be the result of suspended debris.
An object could enter the signal path and cause abnormal readings. A similar condition
could also result from high concentrations of suspended sediment as during live-bed
conditions. Such conditions were not noted during the period when the current meters
were deployed (November 1993); however, a live-bed condition could have developed
during the passage of Hurricane Emily (fig. 5). As the hurricane currents abated, some
of the suspended sediment was transported, leaving the channel bed approximately 0.6
m below its previous elevation.
The performance of the other hydrographic instruments was likely hampered
by the movement of suspended and bed-load sediment Prior to deployment of the
current meters and wave-tide recorder on November 3, 1993, a bathymetric survey of
an area approximately 300 m by 300 m on either side of the bridge was conducted. On
January 25, 1994, 83 days after the instruments were deployed, an attempt was made
to retrieve the instruments and download the data. While making a second bathymetric
survey of the same area, it became evident that a significant quantity (2 to 3 m) of sand
had been deposited in the study area since November. The dive to recover the
instruments verified this fact The Seadata meter was completely buried, and the two
Endeco meters were just above the channel bottom. Tethers on the Endeco meters
allowed them to move up and remain above the deposited sediment The meters did,
however, suffer some damage. The impellers on both instruments were missing. The
top of the Seadata meter that was originally 2 m above the channel bottom is believed
to be buried under 0.5 m of sediment and is yet to be recovered. Current velocity data


FIELD PERFORMANCE


for November, downloaded from one of the Endeco meters, are shown in figure 5.
There is little, if any, apparent correlation between these velocities and changes in
scour depths for the same period.
Conclusions
Remote collection of acoustically sensed scour-depth data in a dynamic tidal
environment such as Oregon Inlet is possible. Even though there is considerable
unexplained variation within the Bonner Bridge scour-depth data, they do demonstrate
the overall trends of scour and deposition. However, the Bonner Bridge data-
collection system deployed is susceptible to errors arising from failed signal returns,
multiple echoes, live-bed conditions, and suspended objects. Modifications of the
data-collection system hardware and software are underway to improve the reliability
and accuracy of the data. In addition, deployment of current meters and other
hydrographic sensors are expected to yield more information about the effect of the
Oregon Inlet environment on system performance. Assuming the Seadata velocity
meter can be recovered and that it functioned properly during November 1993, the
complete data set will include scour depth, wave frequency and direction, water-
surface elevation, and water temperature.
References
Butch, G.K., 1991, Measurement of bridge scour at selected sites in New York,
excluding Long Island: U.S. Geological Survey Water-Resources Investigations
Report 91-4083, 17 p.
Dolan, Robert, and Lins, Harry, 1986, The Outer Banks of North Carolina: U.S.
Geological Survey Professional Paper 1177-B, 46 p.
Fenner, T.J, 1993, Scoping out scour: Civil Engineering, v. 63, no. 3, p. 75-77.
Gorin, S.R., and Haeni, F.P., 1989, Use of surface-geophysical methods to assess
riverbed scour at bridge piers: U.S. Geological Survey Water-Resources
Investigations Report 88-4212, 33 p.
Jarrett, R.D., and Boyle, J.M., 1986, Pilot study for collection of bridge-scour data:
U.S. Geological Survey Water-Resources Investigations Report 86-4030, 89 p.
Johnson, P.A., and Jones, J.S., 1993, Merging laboratory and field data in bridge
scour: Journal of Hydraulic Engineering, v. 119, no. 10, p. 1176-1181.
Skinner, J.V., 1986, Measurement of scour-depth near bridge piers: U.S. Geological
Survey Water Resources Investigations Report 85-4106, 33 p.
U.S. Department of Transportation, Federal Highway Administration, and North
Carolina Department of Transportation, 1993, Administrative action, draft
environmental impact statement and draft section 4(F) evaluation: Federal
Highway Administration FHWA-NC-EIS-93-01-D, p. 3.1, 3.30-3.38.




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