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Independent analysis of porous groun installations at Eglin Air Force Base, Florida

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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
Creator:
Dean, Robert G.
Place of Publication:
Gainesville, Fla.
Publisher:
Coastal & Oceanographic Engineering Dept. of Civil & Coastal Engineering, University of Florida
Language:
English

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University of Florida
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University of Florida
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UFL/COEL-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.,. 4
Department of Civil & Coastal Engineering ---- W.
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 Subama Malakar
Department of Civil and Coastal Engineering
University of Florida Gainesville, FL 32611




TABLE OF CONTENTS
Paize Number
EXECUTIVE SUM M ARY ...................................................... I
1.0 IN TROD U CTION .......................................................... 3
2.0 GENERAL DISCUSSION OF NATURAL PROCESSES ON BEACH SYSTEMS ....... 3
2.1 N atural Changes ...................................................... 3
2.1.1 Longshore Variability .......................................... 3
2.1.2 Seasonal V ariations ............................................ 3
2.1.3 Storm Induced Changes ........................................ 4
2.2 Hum an Related Changes ............................................... 4
3.0 MONITORING AND ANALYSIS PROGRAMS ................................. 4
3.1 M onitoring Program ................................................... 4
3.2 A nalysis Program s .................................................... 5
4.0 RESULTS AND DISCUSSION ............................................... 5
4.1 Shoreline Changes .................................................... 6
4.2 V olum e Changes ..................................................... 9
5.0 C ON CLU SION ........................................................... 13
APPENDIX A
A 1 INTRODU CTION ..................................................... A I
A .2 RE SU LTS ............................................................ A I
A.2.1 Site I Shoreline Changes ......................................... A I
A.2.2 Site I Volum e Changes .......................................... A I
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 M ap ............................................................ 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.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1
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 Pagze 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 postinstallation surveys at Site I 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 i 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 I 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). F or I 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 I 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 I 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 I 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" (erosional 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.
i lis 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 long shore 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 3 3 profile lines were surveyed during some of the various surveys, only the 33 lines listed in Table I 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 LZl 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. Crossshore Zone (CZ) 1 is that within the net confines and CZ2 is the zone extending 150 feet Gulfward of the nets.
Choctawhatchee Bay 1
0 5,000
Scale (ft) Oestin
Site 2
Site I
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) (fi) (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 postinstallation 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 prenourishment 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).




. 4- Project Centerline

:"'"

Units of Structure

60
C
0 40
'f) 40
0
C
0 C 20
0
-- 0
o -20
o>
C C -40 C-)

O0
0 1000 2000 3000 41
Longshore Distance (It)
Figure 2. Longshore Distributions of Shoreline Changes. Site 1.

Project Centerline
West
I0

100 -

Limits of Structure

1000

2000

January 2001
......... February 2001
....- Apri 2001
- July 2001
--- August2001
3000 4000

Longshore Distance (ft)
Figure 3. Longshore Distributions of Shoreline Changes. Site 2.

100

:4..
4 I.

* West
January 2001
......... February 2001
...-. .--- April 2001
... ...... ------- July 2001

-80 -




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

* Values Without Parentheses Denote Average Shoreline Changes Relative to Pre-Installation Wh( 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
Changes 1
Jan -Pre -15.3
Feb-Pre 13.1
April-Pre 24.7
July-Pre -1.3
August Pre 0.7

Longshore Zone
2 3 4
............... ....................... ................
............. .................... ............. .... ..
............. .................... .. I .......... .... ..
...... ............. .... ..
..........
.......... ..........
24. 5 t23
10.3
... ................ .... ..
..... ................ .... ..
..... ............... .... ..
....... .............. .... ..
..... ........
...... ..........
...... ..........
...... ........ ..........
. ......... .......
.... ........ ..........
.............
(27 ..........
..........
..........
..........
... ........................ ..........
..... ....................... ............
... ............
... ...................... I ...................
...............................................
.......................... ............
... ... .... ..............................................
... ... ... .........................................
..............................................
...................... ....
...........
.... .............. ....
............ .... ..............
.................. .............. .....
36- 5 64.6
....................... .
.. ..............
... ....... ....................... ......... ............
. ................
............... ......
.. ...............
.. ..............
P-75 ) ...........
..........................................
................ ................
.. ........
................
..... .... ..................................
....... ........
....... ........ q .. ....................
..........
..........
383 52.3
....... ....
.. . .. ...........
(4 2) ...........
. ...........
...........
....... ....
. ............. %.............................."................
. .. ...........
...........
...........................................
... ...........................................
... ............
.... .. ...... 57.3
.. .. ...... .........
...................... ... ............................. ......
...................... ..........................................
...................... ..........................................
...................... ..........................................
.......... ................................
................
................
................
................
...............
............... .. ................
.............. ......... ............. .................
............... .. ..... ....................................
................ ....................................... .
............... _ ...................................
........... ............ ..........
...................... ............ % ............
...................... ........................
...................... ...............................................
.......... ........
............
...........
50.0
...................... ..........
...............................
.......................... : ... :.. :
..........

*Values Without Parentheses Denote Average Snoreline Unanges Kelaive 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
Project Centerlihe
S200 ,I
100 *., ,
C
0 .. ..Sp i2 0
-300 -. ---- Juy20
~-400 West1
04 -2003004
L itso Dst ctu e (ft)y 00
Figur 4. Lngshoe Disributonsof Distanc pe( UitLegt
Change Within Net Width. Site 1.




600
5,
S400
. 200
E
0
-200
-400

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

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.

1000 2000 3000
Longshore Distance (ft)

4000




800
Project CerdeIine
600
400
200
CD
EO
-200 L6ilti of Stru' ire
C\ V. 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 Changes

Longshore Zone

1 i

4 4

Jan Pre

-2,598

Feb-Pre -2,555
April-Pre 778

July-Pre

Jan Pre

-1,767

-8,289

-6,116

-1,404

4
1,436 3,185 3,659 3,997
-297

Feb-Pre -10,618 -10,504 -5,920 -8,507
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

Crossshore Zone
1

Crossshore Zone
2




Table 5
Volumetric Change Characteristics in Various Zones. Site 2 (Shaded Cells Denote Extent of Groins)
Dates of Longshore Zone
Changes1234
. . .... . .............. .... ............. ....... ... .. ........................
: : : :: : : : : : .: : . . I . . ..:: : : : : : : : : :: : : : : :: :: : : :.... == .=.= = .= = .=.= . . . ..====
.. .. .. .. ...........,...y ...................... . .: .: : .: : .: : .: :.: : ....:: .:: .: : ....::..
C ro s-iJaniii-iiiPreiiii985 1 !! !!4!i 0 i ii .......... i ......~ii~~i~ !!!. 1,708!!! i~iiiiiiii
J u y r 3 4 4 ........................ ......................... . .. .. .................... ................
Aug-Pre ~ ~ ~ ~ ~ ~ ~........ 1060 .......iii iiiiiiiiiiiiiiiiiiii~ iiiiiiiii1,5
i iii i i i i iiii iiii iiiii~i~i! !i!! i iii i ................iiii
Jan Pr -2,941........... 10,19

Crossshore Zone
2

Feb-Pre -2,642 -171 -3865 -537
April-Pre -2,641 -3,969 -6,311 1,637
July-Pre 2,707 -2,331 -5,671 12,440

I I Aug Pre 1 3,397 2,892 -5,710 1 10,108
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
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 "erosional 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 I installation, it is relevant to compare the results with those of a representative beach nourishment project. As of the latest survey, the Site I 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 I 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

3600

Distance From Eastern End of Survey Limits (ft)
Figure A. 1 Even Components of Shoreline Change. Site 1.

- January Survey
Proect......... February Survey
ro j ect ---- April Survey
Centeriine-----. i -- July Survey
VI
V tisof Structure V
D 900 1800 2700 36(
Distance From Eastern End of Survey Limits (ft)
Figure A.2 Odd Components of Shoreline Change. Site 1.

A-2

January Survey
P February Survey
Project ----- April Survey
Centerline... ...... July Survey
Limits of Structure
I I




0 900 1800 2700 3600
Distance From Eastern End of Survey Limits (ft)
Figure A.3 Even Components of Volume Density Change
Within Groin Width. Site 1.
Project
Centedine
30
0
its of Structure
0o
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




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

120
100
80
0
* 60
0
- 40
= 20
0 .r 0 C/)
.E -20
-40
co
o -60
-80
-100

4000

80 60 0 40
E
0 OO
.- 0
a -20
0
-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

-600

300 co 200 F 100
v
E 0
0
-100
-20
.C -200
0D

4000