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Title: Independent analysis of porous groun installations at Eglin Air Force Base, Florida
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Title: Independent analysis of porous groun installations at Eglin Air Force Base, Florida
Series Title: Independent analysis of porous groun installations at Eglin Air Force Base, Florida
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Language: English
Creator: Dean, Robert G.
Publisher: Coastal & Oceanographic Engineering Dept. of Civil & Coastal Engineering, University of Florida
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Table of Contents
    Front Cover
        Front Cover
    Half Title
        Half Title
    Title Page
        Title Page
    Table of Contents
        Page i
        Page ii
        Page iii
    Executive summary
        Page 1
        Page 2
    Main
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Conclusion
        Page 14
    Appendix
        Page 15
        Page A-1
        Page A-2
        Page A-3
        Page A-4
        Page A-5
        Page A-6
Full Text




UFL/COEL-2001/013


INDEPENDENT ANALYSIS OF POROUS GROIN INSTALLATIONS
AT EGLIN AIR FORCE BASE, FLORIDA
(INTERIM REPORT)


by


Robert G. Dean
and
Subarna Malakar



November 12, 2001

(Revised to Include August Data For Site 2
and to Provide Even/Odd Analysis Results)


Prepared for:

Benedict Engineering Company, Inc.
3600 Hartsfield Road
Tallahassee, FL 32399


Coastal & Oceanographic Engineering Program ."
Department of Civil & Coastal Engineering "-- -- -- "
433 Weil Hall *P.O. Box 116590 Gainesville, Florida 32611-6590

UNIVERSITY OF
FLORIDA








UFL/COEL-2001/013


INDEPENDENT ANALYSIS OF POROUS GROIN INSTALLATIONS
AT EGLIN AIR FORCE BASE, FLORIDA
(INTERIM REPORT)








by


Robert G. Dean
and
Subarna Malakar


November 12, 2001

(Revised to Include August Data For Site 2
and to Provide Even/Odd Analysis Results)


Prepared for:

Benedict Engineering Company, Inc.
3600 Hartsfield Road
Tallahassee, FL 32399










INDEPENDENT ANALYSIS OF POROUS GROIN
INSTALLATIONS
AT EGLIN AIR FORCE BASE, FLORIDA
(INTERIM REPORT)




November 12, 2001
(Revised to Include August Data For Site 2
and to Provide Even/Odd Analysis Results)






Prepared For:

Benedict Engineering Company, Inc.
3600 Hartsfield Road
Tallahassee, FL 32399








Prepared By:

Robert G. Dean and Subarna Malakar
Department of Civil and Coastal Engineering
University of Florida
Gainesville, FL 32611









TABLE OF CONTENTS

Page Number

EXECUTIVE SUMMARY ..................................................... 1

1.0 INTRODUCTION .......................................................... 3

2.0 GENERAL DISCUSSION OF NATURAL PROCESSES ON BEACH SYSTEMS ....... 3
2.1 Natural Changes .................................................... 3
2.1.1 Longshore Variability ......................................... 3
2.1.2 Seasonal Variations ................. ..........................3
2.1.3 Storm Induced Changes ..................................... ..4
2.2 Human Related Changes ................................................4

3.0 MONITORING AND ANALYSIS PROGRAMS ...............................4
3.1 Monitoring Program .................................................. 4
3.2 Analysis Programs ................................................... 5

4.0 RESULTS AND DISCUSSION .............................................. 5
4.1 Shoreline Changes .................................................. 6
4.2 Volume Changes .................................................... 9

5.0 CONCLUSION ........................................................... 13


APPENDIX A


A.1 INTRODUCTION ..................................................... A 1

A.2 RESULTS ........................................................... A 1

A.2.1 Site 1 Shoreline Changes ........................................ A- 1

A.2.2 Site 1 Volume Changes .......................................... A 1

A.2.3 Site 2 Shoreline Changes ......................................... A 4

A.2.4 Site 2 Volume Changes .......................................... A 4

A.3 SUMMARY OF EVEN/ODD ANALYSIS ................................ A -6










LIST OF FIGURES


Figure Number Page Number

1 Site Location Map .......................................................... 5
2 Longshore Distribution of Shoreline Changes. Site 1 ................................ 7
3 Longshore Distribution of Shoreline Changes. Site 2 ................................. 7
4 Distributions of Volume per Unit Length Change Within Net Width. Site 1. .............. 9
5 Distributions of Volume per Unit Length Change Within Net Width. Site 2. .............. 9
6 Distributions of Volume per Unit Length Change Within 150 feet Gulfward of Nets. Site 1.
................ .......... ....... . . .... ..... .. .......10
7 Distributions of Volume per Unit Length Change Within 150 feet Gulfward of Nets. Site 2.
............... ......................... . .. 11


APPENDIX A


A. 1 Even Components of Shoreline Change. Site 1 ............................... A 2
A.2 Odd Components of Shoreline Change. Site 1 ............................... A- 2
A.3 Even Components of Volume Density Change Within Groin Width. Site 1.......... A- 3
A.4 Odd Components of Volume Density Change Within Groin Width. Site 1. .......... A 3
A.5 Even Components of Shoreline Change. Site 2 ............................... A- 5
A.6 Odd Components of Shoreline Change. Site 2 ................................ A- 5
A.7 Even Components of Volume Density Change Within Groin Width. Site 2 ......... A 6
A.8 Odd Components of Volume Density Change Within Groin Width. Site 2. ......... A 6









LIST OF TABLES


Table Number Page Number

1 Longshore Locations of Survey Lines
(Notes: The Centerline of the Installation is at 1,800 feet and the Stationing
Increases From East to West) .............................................. 6
2 Shoreline Change Characteristics (ft) in Various Longshore Zones. Site 1
(Shaded Cells Denote Zones Occupied by Groins) ............................. 8
3 Shoreline Change Characteristics (ft) in Various Longshore Zones. Site 2
(Shaded Cells Denote Zones Occupied by Groins) .............................. 8
4 Volumetric Change Characteristics in Various Zones. Site 1
(Shaded Cells Denote Extent of Groins) ............... ................... 12
5 Volumetric Change Characteristics in Various Zones. Site 2
(Shaded Cells Denote Extent of Groins) ............... ................... 13









EXECUTIVE SUMMARY


This report presents the results of an independent analysis of survey data in the vicinity of the
installations of two experimental porous groins on Eglin Air Force property, Florida. Sites 1
and 2 are centered approximately 0.75 mile and 2.75 miles west, respectively from the west
jetty of Destin Pass. The available survey data included a pre-installation survey and four post-
installation surveys at Site 1 and a pre-installation survey and five post-installation surveys at
Site 2. The total shoreline length monitored at each installation was 3,600 feet centered about
the 1,500 feet groin system. The analysis consisted of determination of shoreline and volume
changes relative to the pre-installation survey. The volume change information was
summarized for the nominal 150 foot cross-shore dimension of the groin installations and the
150 foot zone seaward of the installations. The analysis results are presented in graphs and
tables. The interpretation of the analysis results are complicated somewhat due to the well
known tendency of the shoreline systems in the Panhandle area of Florida to exhibit natural
undulations in the longshore direction.

The average shoreline and volume changes within the groin field were calculated and tabulated
relative to the average shoreline changes in the project adjacent areas. In addition, the
shoreline and volume changes were subjected to an even/odd analysis procedure which has the
capability to identify some of the characteristics of the interaction between the nearshore
system and the porous groin installation. These results are presented in Appendix A. At Site 1,
as of the latest (July 2001) survey available, the shoreline had advanced by an average of
approximately 10 feet relative to the adjacent shorelines monitored (Table 2). For the three
previous surveys (after the pre-nourishment survey), the shoreline differences within the groin
field ranged from a relative recession of approximately 9 feet (January survey) to a relative
advancement of approximately 21 feet (February survey). At Site 2, as of the latest survey
(August 2001), the average shoreline within the groin limits had advanceded by an average of
approximately 1 foot relative to the adjacent shorelines monitored (Table 3). For the four
previous surveys (after the pre-nourishment survey), the shoreline differences within the groin
field ranged from a relative recession of approximately 13 feet (July survey) to a relative
advancement of approximately 21 feet (January survey).

The volume changes were analyzed and presented in a manner similar to those discussed
above for the shorelines. For Site 1, as of the latest survey available (July 2001), the average
volume per unit length within the groin limits had increased by approximately 4 cubic yards
per foot of beach relative to the adjacent shorelines monitored (Table 4). For the three previous
surveys (after the pre-nourishment survey), the volume per unit length differences within the
groin field ranged from no relative change (January survey) to a relative gain of approximately
6 cubic yards per foot of beach (February survey).


(Executive Summary Continued on Next Page)











EXECUTIVE SUMMARY
(Continued)

At Site 2, as of the latest survey (August 2001), the average relative volume per unit length
within the groin limits had decreased by approximately 6 cubic yards per foot (Table 5). For
the four previous surveys (after the pre-nourishment survey), the average volume per unit
length differences within the groin limits ranged from a loss of approximately 8 cubic yards
per foot of beach (July survey) to a gain of approximately 2 cubic yard per foot of beach
(January survey).

In interpreting the analyzed results, it is interesting to note that they differ substantially with
the installation at Site 1 performing much better than that at Site 2. The relative (to the
adjacent areas) shoreline changes first increased and then later decreased at both sites with the
last shoreline change results at both sites being positive at Site 1 and negative at Site 2 relative
to the adjacent shorelines. The volume per unit shoreline length changes were similar but to a
lesser degree. As of the latest survey, neither of the two installations had achieved the
"pass/fail" criterion of accumulating 13,000 cubic yards at the 75% level relative to the
adjacent areas. Averaging the results at the two installations, the total change relative to the
adjacent areas as of the latest surveys is negative, that is the areas within the groin installations
had lost volume relative to the adjacent beaches. As evident from Table 5, this is due
predominantly to the volumetric losses at Site 2.

In addition to the survey data which were the subject of the analysis here, Benedict
Engineering provided aerial photographs which showed a considerably greater length of
shoreline than that surveyed. These photographs, taken in March 2001, showed that Site 2 was
located at the "trough" erosionall portion) of one the natural shoreline undulations discussed
previously. Thus, one could argue that the relatively poor performance at Site 2 should be
discounted. However, even at Site 1, as of the latest survey available (July 2001), the average
shoreline advancement was approximately 10 feet with a relative volume gain of
approximately 4 cubic yards per foot compared with somewhat typical beach nourishment
projects which place on the order of 60 to 100 cubic yards per foot and result in shoreline
advancements of 60 to 100 feet.

Iis my understanding that additional surveys are planned at both sites. Analysis of these data
will allow a more complete understanding of the performance of these systems.









INDEPENDENT ANALYSIS OF POROUS GROIN
INSTALLATIONS
AT EGLIN AIR FORCE BASE, FLORIDA


1.0 INTRODUCTION

This report presents the results of an independent "third-party-review" of the survey and other
data from the two "porous groins" installations on Eglin Air Force property in Okaloosa County,
Florida. The data available at the time of writing this report include a pre-installation survey at
each site and four post-installation surveys for Site 1 and five post-installation surveys for Site 2.
The sole purpose of this third-party-review is related to interpretation of the physical response of
the beaches to the installed systems.

2.0 GENERAL DISCUSSION OF NATURAL PROCESSES ON BEACH SYSTEMS

In order to better understand the effects of the porous groin installations, it is useful to describe in
general terms, the natural changes that occur in the absence of the installation.

2.1 Natural Changes

2.1.1 Longshore Variability

As will be discussed later in this report, it is well-documented that the beach system in general
and the shorelines in particular along the Panhandle area of Florida tend to be quite variable in
the longshore direction. This variability can appear in the form of undulations in the shoreline
with shoreline positions that vary by tens of feet in the cross-shore direction with shoreline
advancements at some portions of the undulation and shoreline recession (erosion) at other
portions. The relevance of this variability in this case is that it makes interpretation of the survey
data more difficult and uncertain.

2.1.2 Seasonal Variations

Beaches change both in the short- and long-term in response to natural and human related causes.
The natural changes include seasonal changes in which sand is usually eroded from the dry beach
during the Fall and Winter seasons. This is in response to the more vigorous wave conditions and
possible elevated water levels which occur during these periods. This sand that is transported
seaward is stored in an offshore bar. During the Spring and Summer seasons, the sand stored in
the offshore bar is returned to and widens the beach. Although there have not been any definitive
studies of the magnitudes of these natural seasonal shoreline fluctuations in the area of interest
and they certainly vary from year to year and from location to location, my estimates are that, on
average, they are on the order of 30 feet.









2.1.3 Storm Induced Changes


Beaches also exhibit an erosional response to major storms such as hurricanes which can cause
beach and dune recession on the order of 100 feet.

2.2 Human Related Changes

Human related beach and dune changes usually occur due to modifications of the longshore
sediment transport. In Florida, the single most impactive human related change is due to those
inlets which were either constructed or modified for navigational purposes and which interrupt
the natural longshore sediment transport patterns and deprive the downdrift shorelines of sand.
With the average annual net westward sediment transport in the area of interest, East Pass into
Choctawhatchee Bay (also referred to as Destin Pass) generally interferes with this net transport
and causes downdrift erosion which is undoubtedly the cause of the erosion along the shoreline
of interest. It is relevant to note that in most locations along the Florida shoreline and certainly in
the area of interest, there may be sustained periods of transport reversal, in this case, transport to
the east.

Structures such as groins and/or detached breakwaters also induce shoreline response. A well
documented effect is the trapping of sediment from the longshore sediment transport. In areas
where the net longshore transport is weak, these structures tend to trap sand in a more symmetric
pattern whereas in areas of strong net longshore transport, the trapping patterns in the vicinity of
such structures tend to include deposition on the updrift side and erosion on the downdrift side.
The monitoring and analysis programs described in the next section have been designed to aid in
the interpretation of the shoreline changes.

3.0 MONITORING AND ANALYSIS PROGRAMS

3.1 Monitoring Program

The two installations are located west of Destin Pass as shown in Figure 1. Sites 1 and 2 are
centered approximately 0.75 mile and 2.75 miles west of the west Destin Pass jetty, respectively.
The monitoring program consisted of 33 lines encompassing a length of 3,600 feet at each
installation and centered around the porous groin installations each of which consisted of 16
porous groins spaced at 100 feet. Although more than 33 profile lines were surveyed during some
of the various surveys, only the 33 lines listed in Table 1 were surveyed consistently and form
the basis for the analysis presented here. The rationale for the profile line layout was to identify
any patterns of change for interpretation in accordance with the general discussion in the
preceding paragraphs. A condition of the permit was that each installation accumulate 13,000
cubic yards at a 75% level relative to the adjacent shoreline segments and that the accumulated
material be brought from offshore rather than trapped from the longshore transport discussed
earlier. To date, the survey data have been provided through the July survey for both sites and
through August for Site 2. Although the surveys at the two sites occurred at somewhat different








times, the surveys are referred to herein as the "December (pre-installation) Survey", "the January
Survey," "the February Survey", "the April Survey", "the July Survey" and the "August Survey".

For presentation of the results, the survey area at each site is represented in terms of various
zones. The longshore zones are numbered from Longshore Zone (LZ) 1 to LZ4 with LZ1 being
to the east and LZ4 to the west. The longshore lengths of longshore zones LZ1 and LZ4 which
are outside the groin limits, are each 1,050 feet and the longshore lengths of the two zones (LZ2
and LZ3) within the groin limits are each 750 feet. Two cross-shore zones are defined. Cross-
shore Zone (CZ) 1 is that within the net confines and CZ2 is the zone extending 150 feet
Gulfward of the nets.


1


Choctawhatchee Bay

0 5,000
Scale (ft)


Destin


Site 2


Site 1


Figure 1. Site Location Map




3.2 Analysis Programs

Programs were developed to analyze the survey data provided by Morgan and Eklund, Inc. a
professional surveying company responsible for documenting the geometric changes in the area.

4.0 RESULTS AND DISCUSSION

The results are presented as distributions of shoreline and volume per unit length changes from
the pre-installation survey. Additionally, the total changes in volume in the porous groin and
adjacent areas are presented as well as the changes within the groin limits relative to the adjacent
areas. As noted, definitive interpretations of the results were complicated by the natural
undulations in the shoreline, and also by the uncertainties associated with the effects of groin
modifications and repair (when the groins may have not been completely functional) and by the
commencement of removal of the groins at Site 1 on March 20, 2001 and completion of removal
on April 20, 2001.








Table 1
Longshore Locations of Survey Lines
(Notes: The Centerline of the Installation is at 1,800 feet and the Stationing
Increases From East to West)

Survey Station Survey Station Survey Station Survey Station Survey Station
(ft) (ft) (ft) (ft) (ft)
0000 1000 1600 2520 3150

0150 1040 1800 2560 3300

0300 1080 2000 2600 3450

0450 1120 2200 2650 3600

0600 1160 2400 2750

0750 1200 2440 2850

0900 1400 2480 3000

4.1 Shoreline Changes

Figure 2 presents the longshore distribution of shoreline changes for Site 1 and Figure 3 presents
the same information for Site 2. The longshore undulations in shoreline change are evident in
these figures. Also of interest is that the shoreline generally advanced both within the limits of
the groin field and adjacent to the groin field. Tables 2 and 3 present further analysis of the post-
installation shoreline changes. The values without parentheses in these tables represent the
average shoreline changes in the various zones and for the different surveys. For example, the
average shoreline change of the eastern portion of the beach outside of the groin limits for the
January survey was an erosion of 2.5 feet relative to the pre-nourishment survey. The average
shoreline change within the eastern half of the groin receded by 1.9 feet during the same time
period whereas within the western half of the groin the shoreline advanced by 14.2 feet. Still
farther westward, outside of the groin field, the shoreline advanced an average of 32.3 feet.

The values in parentheses within the groin areas are the changes relative to the average of those
adjacent to the installation. It is seen that as of the latest survey (July 2001 for Site 1 and August
for Site 2), the average shoreline within the groin limits had advanced by 9.7 feet at Site 1 and
had advanced by 0.9 feet at Site 2. At Site 1, for the three previous surveys (after the pre-
nourishment survey), the shoreline differences within the groin field ranged from a relative
recession of approximately 9 feet (January survey) to a relative advancement of approximately
21 feet (February survey). At Site 2, for the four previous surveys (after the pre-nourishment
survey), the shoreline differences within the groin field ranged from a relative recession of
approximately 13 feet (July survey) to a relative advancement of approximately 21 feet (January
survey).












100


? 0 60 r .: *, A
Io












(L0mits of Structure
20 7
0






Apr West 2001




20 2001
...- 2 '" .. F'rbrts o c.








-0---8------- July-2001




Longshore Distance (ftR)

Figure 2. Longshore Distributions of Shoreline Changes. Site 1.








200
Project Centerline

SWest


0 100
a" .. , -.' ..








Limits of Structure N January 2001
......... February 2001
.A.-- 2Aprl2001
------- July 2001
-100 --- August 2001
0 1000 2000 3000 4000
Longshore Distance (ft)





Figure 3. Longshore Distributions of Shoreline Changes. Site 2.
0C0020 0040
Logsori stne(t








Table 2
Shoreline Change Characteristics (ft) in Various Longshore Zones. Site 1
(Shaded Cells Denote Zones Occupied by Groins)


Dates of Longshore Zone
Changes
changes 1 2 3 4

Jan-Pre -2.5 -1.9' 14.2 32.3
(-16.8) 4(-0.7)
Feb-Pre 0.7 29.7 42.1 29.9
(14.4) (26.8)

April-Pre 18.0 23.0 21.2 25.7
(1.2) (-0.7)

July-Pre -9.7 7.8 17.6 15.7
(4.8) (14.6)
* Values Without Parentheses Denote Average Shoreline Changes Relative to Pre-Installation Whereas
Values in Parentheses Denote Shoreline Change Differences Between Zones Within Net Field and
Average of Two Adjacent Zones


Table 3
Shoreline Change Characteristics (ft) in Various Longshore Zones. Site 2
(Shaded Cells Denote Zones Occupied by Groins)


Dates of Longshore Zone
Changes
1 2 3 4

Jan Pre -15.3 24.5' 12.3 10.3
(27.0)' (14.8)

Feb-Pre 13.1 66.3 36.5 64.6
(27.5) (-2.4)

April-Pre 24.7 38.3 16.6 52.3
(-0.2) (-21.8)

Jul\-Pre -1.3 19.9 9.6 57.3
_(-8.1) (-18.4)

August -Pre 0.7 20.5 31.9 50.0
t-4.85) (6.55)
* Values Without Parentheses Denote Average Shoreline Changes Relative to Pre-Installation Whereas
Values in Parentheses Denote Shoreline Change Differences Between Zones Within Net Field and
Average of Two Adjacent Zones









4.2 Volume Changes


Figures 4 and 5 present the longshore distributions of volume change for the 150 feet width
defined by the porous groins at Sites 1 and 2, respectively. Figures 6 and 7 present the
distributions for the 150 feet width Gulfward of the groin limits. Tables 4 and 5 present results
for volume changes similar to that in Tables 2 and 3 for shoreline changes.

Referring to these figures and tables, it is seen that on an overall basis, Site 1 performed
considerably better than Site 2. As of the latest survey (July 2001 for Site 1 and August 2001 for
Site 2), the area within the limits of the groin field had gained 7,366 cubic yards at Site 1 and had
gained 8,457 cubic yards at Site 2. However, relative to the areas adjacent to the installations, the
area within the groin limits had gained approximately 4 cubic yards per foot at Site 1, but had
lost approximately 6 cubic yards per foot at Site 2. For the three prior surveys at Site 1, the
relative changes varied from no relative change (January survey) to a gain of 6 cubic yards per
foot (February survey). For the four prior surveys at Site 2, the relative changes varied from a
loss of approximately 8 cubic yards per foot (July survey) to a gain of approximately 2 cubic
yard per foot (January survey). As a basis of comparison, beach nourishments projects add from
approximately 60 cubic yards of sand per foot of beach to 100 cubic yards of sand per foot of
beach and advance the beach by 60 feet to 100 feet, respectively.

From these results it is evident that neither of the two installations achieved the "pass/fail"
criterion of adding 13,000 cubic yards at the 75% level relative to the adjacent shorelines
monitored.

400

300
S, Project Centerlike 3


S100



_-100 ,West

S-200 20
Lits of Structure January 2001
......... February 2001
0 -- -Apr 2001
-300 -- July 2001

-400 1 ,
0 1000 2000 3000 40
Longshore Distance (ft)

Figure 4. Longshore Distributions of Volume per Unit Length
Change Within Net Width. Site 1.















S600

5)
3 400
c

. 200
E
> 0
0,

S-200


-400


1000 2000 3000
Longshore Distance (ft)


Figure 5. Longshore Distributions of Volume per Unit Length
Change Within Net Width. Site 2.


4000


0 1000 2000 3000
Longshore Distance (ft)


Figure 6. Longshore Distributions of Volume per Unit Length
Change Within 150 feet Gulfward of Nets. Site 1.
















800


600 -







/\



-200 Li/ of Stru
I/ January 2001
c ......... February 2001
-400 -- ; ..-- Apri 2001
-.----- July 2001
-- August 2001
-600
0 1000 2000 3000 4000
Longshore Distance (ft)





Figure 7. Longshore Distributions of Volume per Unit Length Change Within
150 feet Gulfward of Nets. Site 2










Table 4


Volumetric Change Characteristics in Various Zones. Site 1
(Shaded Cells Denote Extent of Groins)


Dates of Longshore Zone
Changes
1 2 3 4

Cross- Jan- Pre -2.598 -2.859 2.100 1.436
shore (-3.26) (3.35)
Zone
1 Feb-Pre -2.555 4,166 5,709 3.185
(5.26) (7.31)
April-Pre 778 2,835 3,431 3.659
(1.67) (2.46)
Julv-Pre -1.767 2,257 5.109 3.997
(1.95) (5.75)

Cross- Jan- Pre -8,289 -6,116 -1,404 -297
shore
Zoe Feb-Pre -10,618 -10,504 -5,920 -8,507
Zone
2 April-Pre -9,310 -10,567 -4,010 -1,002

July-Pre -13,960 -11,712 -3,313 -605
Values Without Parentheses are Volume Change in Cubic Yards Whereas Values in
Parentheses Denote Volume per Unit Shoreline Length Change (Cubic Yards per Foot)
Differences Between Zones Within Net Field and Average of Two Adjacent Zones







Table 5


Volumetric Change Characteristics in Various Zones. Site 2
(Shaded Cells Denote Extent of Groins)


Dates of Longshore Zone
Changes 1 3 4
1 2 3 4

Jan Pre 985 3,430' -1 1.708
(3.94)' (-0.64)

Feb-Pre 6.930 7,433 5,172 10.599
Cross- (-1.56) (-1.45)
shore April-Pre 10.155 3,756 2,083 11.187
Zone (4.21) (-6.34)

Jul\-Pre 3.445 1,004 -59 15.364
(-7.62) (-9.03)

Aug Pre 10.605 3,870 4,587 13.255
(-6.20) (-5.25)
Jan- Pre -2,941 1,776 1,381 10,194

Cross- Feb-Pre -2,642 -171 -3865 -537
shore April-Pre -2,641 -3,969 -6,311 1,637
Zone
2 July-Pre 2,707 -2,331 -5,671 12,440
Aug- Pre 3,397 2,892 -5,710 10,108
SValues Without Parentheses are Volume Change in Cubic Yards Whereas Values in
Parentheses Denote Volume per Unit Shoreline Length Change (Cubic Yards per Foot)
Differences Between Zones Within Net Field and Average of Two Adjacent Zones

4.3 Results of Even/Odd Analysis

The results and discussions of the Even/Odd analysis are presented in Appendix A. Even/Odd
analysis is a method which has been developed and applied to assist in interpreting the
interaction between structures, such as the porous groins, and the nearshore processes. For
purposes here, it suffices to note that the results of the analysis presented in Appendix A is
supportive of the results presented in the main body of this text. Additionally, the results
presented in Appendix A indicate that the net longshore sediment transport during the survey
period was to the east which is opposite to the normal net transport direction. However, this does
not affect the analysis nor the interpretation. The analysis also indicates that the porous groins
trap sand from the littoral system and there is no evidence that sand is being drawn from
offshore.









5.0 CONCLUSIONS


Recognizing that the installation at Site 2 appears to have been located at an erosionall trough" of
a natural undulation, and if the relatively poor performance of this installation is discounted and
the performance of porous groins is based solely on the Site 1 installation, it is relevant to
compare the results with those of a representative beach nourishment project. As of the latest
survey, the Site 1 shoreline within the groin limits had advanced approximately 10 feet relative
to the adjacent shorelines. Over the period of installation, the shoreline changes relative to the
areas adjacent to the groin ranged from a relative recession of approximately 9 feet to an
advancement of 21 feet. As of the latest survey, the volume gains within the groin limits were
approximately 4 cubic yards per foot relative to the adjacent areas. Over the period of
installation, the volumetric changes per unit length relative to the areas adjacent to the groin
ranged from approximately no change to a gain of approximately 6 cubic yards per foot. A
typical beach nourishment in Florida places 60 to 100 cubic yards per foot and advances the
shoreline some 60 to 100 feet. Relative to the adjacent shoreline segments monitored, at no time
were either of the installations documented to achieve their "pass/fail" criterion of 13,000 cubic
yards at the 75% level.

The results of the even/odd analysis presented in Appendix A indicate that the porous groins trap
sand from the littoral system and there is no evidence to indicate that this sand has been drawn
from offshore.








APPENDIX A


EVEN AND ODD COMPONENTS OF

SHORELINE AND VOLUME CHANGES







APPENDIX A


EVEN AND ODD COMPONENTS OF
SHORELINE AND VOLUME CHANGES

A.1 INTRODUCTION

This appendix presents results of the even/odd analysis of shoreline and volume changes. Even and
odd components of change provide a method of examining and interpreting the interaction of the
nearshore system with structures. For example, groins placed in an area of strong net longshore
sediment transport cause shoreline advancement on the updrift side and an associated erosion on
the downdrift side. These changes are nearly purely "odd" or antisymmetric in nature. The
even/odd method applied to such data would yield a purely odd signal (the even component would
be zero). A groin field placed in an area of very nearly zero net longshore sediment but a
substantial gross sediment transport would yield a strong even (symmetric) component of shoreline
change with a very small odd component of change. In this case, the shoreline would advance
within the groin field with the possibility of a negative change from the adjacent shorelines.

A.2 RESULTS

A.2.1 Site 1 Shoreline Changes

There are four periods of shoreline change for Site 1. The longshore distributions of the even and
odd components of shoreline change for Site 1 are presented as Figures A.1 and A.2, respectively.
First it is seen that the magnitudes of the even components of shoreline changes are substantially
larger that those of the odd components. Thus, discussion here will focus on the even component.
The even component of shoreline change indicates accumulation within the structure limits;
however, near the outer limits of the survey, the shoreline is also advanced by the same magnitude
except for the February survey when the shoreline advancements within the structure limits are
greater than those near the ends of the survey limits. The pattern of the even component could
either indicate sand drawn from the adjacent beaches by the porous groins or simply an undulating
shoreline. The odd component of shoreline change (Figure A.2) indicates that the groins are
trapping sand from the littoral system and that the net longshore sediment transport during the
survey period is atypical with more sand accumulating on western side of the structure than on the
east side as would be the case for the average annual net longshore sediment transport to the west.

A.2.2 Site 1 Volume Changes

The even and odd components of volume density change for Site 1 are presented in Figures A.3
and A.4, respectively. It is seen that the general patterns for volume density change are similar to
those for shoreline change and the interpretations are the same except the volume increases within
the structure limits are considerably greater than that near the ends of the survey limits. As for the
case of the shoreline changes, the pattern of volume density change indicates sediment transport
from west to east.


A-i






























900 1800 2700


Distance From Eastern End of Survey Limits (ft)



Figure A. 1 Even Components of Shoreline Change. Site 1.


-- January Survey
Projt February Survey
project .-.-.-.- April Survey
CenterlineApril Survey










1 its of Structure V


3 900 1800 2700 36(

Distance From Eastern End of Survey Limits (ft)



Figure A.2 Odd Components of Shoreline Change. Site 1.
Figure A.2 Odd Components of Shoreline Change. Site 1.


A-2


3600
















500
-- January Survey
40 Project Fu..... Survey
------ A prlSu rv ey
300 Centerline-" -





0


UM/iit~s of Structe
-200

300

400


C

()


0
O




0.
0




0
CL
E

o




C
o
o




U


2700


Distance From Eastern End of Survey Limits (ft)




Figure A.3 Even Components of Volume Density Change
Within Groin Width. Site 1.






!00

Project

00
Centerline- /' \ ."' ,














!00
D istane Frm Easten Ed of S y Limits (ft)y
S. : AprSurvey
100 i- ......... Fjuay Su rvey


"'*<.y." |-,, \- its of Structure ,

200 -- -
0 900 1800 2700 3600

Distance From Eastern End of Survey Limits (ft)




Figure A.4 Odd Components of Volume Density Change
Within Groin Width. Site 1.


A-3


1800


3600


5- 00
(









A.2.3 Site 2 Shoreline Changes


There are five periods of shoreline change for Site 2. The even and odd components of shoreline
change for Site 2 are presented as Figures A.5 and A.6, respectively. For Site 2, the magnitudes
of the even and odd components of shoreline change are approximately equal. The even
component of shoreline change indicates accumulation within the structure limits with the
greatest accumulation during the February survey. However, as for Site 1, except for the January
and February surveys, the shoreline advancements within the structure limits are almost equal to
those near the ends of the survey limits. As for Site 1, the odd component indicates a net
eastward longshore sediment transport during the installation period with more sand
accumulating on western side of the structure than on the east side.

A.2.4 Site 2 Volume Changes

The even and odd components of volume density change for Site 2 are presented in Figures A.7
and A.8, respectively. The magnitude of the even component of volume density changes is
substantially greater than that of the odd component. Thus the discussion will focus on the even
component. Except for the January and February surveys, the volume accumulations outside of
the structure limits are substantially greater that those within the structure limits. Comparing
these results with those of the shoreline changes, the only explanation is that whereas the
shoreline advanced, the slope steepened. The odd component of volume density changes is much
more complicated than for Site 1, but is also generally indicative of a net westward transport
during the survey period. However, this indication is not nearly as strong as for the other three
odd components discussed in this appendix.

A.3 SUMMARY OF EVEN/ODD ANALYSIS

The results presented in this appendix are generally supportive of a eastward net transport during
the survey period. Transport reversals from the norm are not unusual nor do they affect
interpretation of the survey results. The odd components indicate that the groins do trap sand
from the littoral system and there is no indication that accumulated sand is brought in from
seaward of the groins.


A-4






























1000 2000 3000
Longshore Distance (ft)


Figure A.5 Even Components of Shoreline Change. Site 2.


1000 2000 3000
Longshore Distance (ft)


Figure 6 Odd Components of Shoreline Change. Site 2.


A-5


Project Centerline



."; ." _,1 '.
." ,S -/. ., ,^
iK, ,,
_u ,- /; "7k '"/ "- "


4000


0 40


0 20
c
20

.- 0
U,

(D -20
CU
-c
S-40


-60


-80


4000



































1000 2000 3000 4000
Longshore Distance (ft)


Figure A.7 Even Components of Volume Density Change
Within Groin Width. Site 2.


1000 2000 3000


Longshore Distance (ft)

Figure A.8 Odd Components of Volume Density Change
Within Groin Width. Site 2.


A-6


M 400


S200

E
0


4 -200
0)
o




-400
C. 400


-600


300


c 200



S100



E


S-100

00
-20
r -200
C-


4000




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