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

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Title:
Independent cost analysis of porous groin installations at Eglin Air Force Base, Florida
Series Title:
Independent cost analysis of porous groin 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-2003/007

INDEPENDENT COST ANALYSIS OF POROUS GROIN INSTALLATIONS AT EGLIN AIR FORCE BASE, FLORIDA FINAL REPORT
by
Robert G. Dean and
Subarna Malakar

Prepared For:
Bureau of Beaches and Wetland Resources Marjorie Stoneman Douglas Building 3900 Commonwealth Boulevard Tallahassee, FL 32399-3000

July 10, 2003




INDEPENDENT COST ANALYSIS
OF POROUS GROIN INSTALLATIONS AT EGLIN AIR FORCE BASE, FLORIDA
(FINAL REPORT)
July 10, 2003
Prepared For:
Bureau of Beaches and Wetland Resources
Marjorie Stoneman Douglas Building
3900 Commonwealth Boulevard
Tallahassee, FL 32399-3000
Prepared By:
Robert G. Dean and Subara Malakar
Department of Civil and Coastal Engineering
University of Florida Gainesville, FL 32611




TABLE OF CONTENTS
EXECUTIVE SUMMARY ..................................................... ii
1.0 INTRODUCTION .......................................................... 1
2.0 PHOTOGRAPHS .......................................................... 2
3.0 ANALYSIS OF SURVEY DATA .............................................. 4
3.1 Available Survey Data ................................................. 4
3.2 Analysis M ethods ..................................................... 6
3.3 Shoreline Changes .................................................... 6
3.4 Volum e Changes ..................................................... 7
3.5 Site I Shoreline and Volume Changes ..................................... 7
3.5.1 Site 1 Shoreline Changes ....................................... 7
3.5.2 Site I Volume Changes ......................................... 8
3.6 Site 2 Shoreline and Volume Changes .................................... 10
3.6.1 Site 2 Shoreline Changes ...................................... 10
3.6.2 Site 2 Volume Changes ........................................ 11
4.0 COST ANALYSIS .......................................................... 12
4.1 General Discussion .................................................. 12
4.2 Costs of the Porous Groin Installation .................................... 13
4.3 Rationale for Cost Comparisons ........................................ 13
5.0 SUMMARY AND CONCLUSIONS .......................................... 16
6.0 REFEREN CES ............................................................ 17
LIST OF TABLES
Page
Table 1 Characteristics of Survey Data ............................................. 5
Table 2 Average Shoreline Change Characteristics ................................... 8
Table 3 Average Volume Change Characteristics .................................... 9
Table 4 Cost Information for PGS Installations at Sites 1 and 2 ........................ 14




LIST OF TABLES (Continued)
Table 5 Development of Unit Costs of Sand Accumulated ............................ 15
Table 6 Comparison of Costs of Sand by Conventional Methods and by PGS ............. 16
LIST OF FIGURES
Page
Figure 1. Location Map for Two Installation Sites .................................... 1
Figure 2. Aerial Photograph Looking East With Site 2 in Foreground. Destiny Pass in Background. Photograph by Benedict Engineering, March 6, 2001 ....................... 2
Figure 3. Aerial Photograph of Site 1, Looking East. Photograph by Benedict Engineering, M arch 6, 2001 ................................................................ 3
Figure 4. Aerial Photograph of Site 2, Looking West. Photograph by Benedict Engineering, M arch 6, 2001 ................................................................ 3
Figure 5. Schematic of Porous Groin Installation ..................................... 4
Figure 6. Illustrating Case in Which More Than One NGVD Shoreline Exists .............. 6
Figure 7. Average Shoreline Changes Inside and Adjacent to the Porous Groin System. Site 1 7 Figure 8. Average Volume Changes Inside and Adjacent to the Porous Groin System. Site 1 9 Figure 9. Average Shoreline Changes Inside and Adjacent to the Porous Groin. System. Site 2 10 Figure 10. Average Volume Changes Inside and Adjacent to the Porous Groin System. Site 2 11 Figure A. 1. Aerial Photograph Looking East With Site 2 in Foreground. Destiny Pass in Background. Photograph by Benedict Engineering, March 6, 2001 ................... A-2
Figure A.2. Aerial Photograph Looking East With Site 1 in Foreground. Destiny Pass in Background. Photograph by Benedict Engineering, March 6, 2001 .................... A-3
Figure A.3. Aerial Photograph of Site 2, Looking East. Photograph by Benedict Engineering, M arch 6, 2001 ............................................................ A -3
Figure A.4. Site 2, Looking West, December 5, 2000. Photography by Benedict Engineering ......................................... A -4




LIST OF FIGURES (Continued)
Figure A.5. Site 2, Looking West, December 14, 2000. Photography by Benedict Engineering....................................... A -4
Figure A.6. Site 2, Looking East, Photograph Taken on March 22, 2001 by FDEP....... A -5 Figure A.7. Site 2, Looking West, Photograph Taken on May 14, 2001 by FDEP........ A- 5
Figure A. 8. Site 2, Looking East, Photograph Taken on May 14, 2001 by FDEP .........A -6
Figure A.9. View of Configuration of Porous Groins at Site 2. Photograph Taken Mayl14, 2001 by FDEP ............................................ A-6
Figure A. 10. Site 2, Looking East, Photograph Taken August 16, 2001 by FDEP. Tropical Storm Barry Made Landfall at Destin on August 6, 2001...................A -7
Figure A. 11. Site 2, Looking West, Photograph Taken August 16, 2001 by FDEP. Tropical Storm Barry Made Landfall at Destin on August 6, 2001...................A -7
Figure A. 12. View Looking East as Site 2.
Photograph Taken by PBS&J on October 25, 2001.............................. A -8
Figure A. 13. View Looking West as Site 2.
Photograph Taken by PBS&J on October 25, 2001.............................. A -8
Figure A. 14. Site 2. Looking East, Photograph Taken in December 2001 .............. A -9
Figure A. 15. Site 2. Looking West, Photograph Taken in December 2001.............A- 9




EXECUTIVE SUMMARY
This report presents an analysis of shoreline and volume changes at the two Porous Groin System (PGS) installation sites on Eglin Air Force property in western Florida and a cost comparison of the PGS methodology and more conventional nourishment methodology. The groins were installed at two sites. Site 1 was located at the Eglin Air Force Beach Club and Site 2 is at a radar base some two miles west of Site 1. The PGSs were installed in November 2000 and the system was removed from Site 1 in April 2001 and removed from Site 2 in March 2002. A total of sixteen surveys are available commencing in December 2000 and extending to November 2002. The porous groin installations consisted of sixteen shore perpendicular groins, spaced at 100 feet, thereby occupying a longshore length of 1,500 feet. The total surveyed longshore length was 3,600 feet at each site including a longshore length of 1,050 feet on either side of each set of PGS. The areas adjacent to the groins serve as "controls" for comparison purposes.
The shorelines and volume changes were averaged over the 1,500 feet longshore length of the PGS installation and the 150 feet length of the individual groins. These results are compared with corresponding quantities in the adjacent control areas.
The data suggest that the PGSs were installed when the beaches were in an eroded condition as the shorelines and volumes generally increased both within and adjacent to the groins during the surveyed period. Comparison of the average shoreline and volume changes did not reveal a strong, clearly identifiable effect of the groins with the increases within the groin field at some locations and times being greater than in the control areas and in other locations or times, less. Rather, the comparison was more indicative of irregular shoreline and volume changes superposed on natural seasonal shoreline and volume changes. Thus, on this basis, it is difficult to attribute a volume gain or loss to the PGS. Three volume increase bases were adopted with the most generous being the average increase within the groin limits irrespective of those in adjacent areas.
Costs for nourishment were based on trucking since, by any definition, volume increases within the groin field were small and would not justify mobilization of a dredge. A range of trucking costs from $ 12.00 per cubic yard to $ 15.00 per cubic yard was considered. Several costs for the installations had been developed by others and were employed herein. Using the most generous definition of the volume increases, the costs of truck haul nourishment were less than those for the PGS. Additionally, in evaluating these results, it should be recalled that truck haul introduces additional sediment into the nearshore system whereas a PGS installation can, at best, simply rearrange the sediment residing within the active nearshore system.




INDEPENDENT COST ANALYSIS OF POROUS GROIN INSTALLATIONS
AT EGLIN AIR FORCE BASE, FLORIDA (FINAL REPORT)
1.0 INTRODUCTION
This report completes the data analysis and cost evaluation of the two porous groin installations at Eglin Air Force Base, FL. The two sites are located as shown in Figure 1 and include Site 1 which was located at the Eglin Air Force Base Beach Club and Site 2 located at a radar site approximately 2 miles west of Site 1. These porous groin systems (PGS) were installed in November 2000 and removed at Site 1 on April 27, 2001 and removed at Site 2 in early March 2002. A previous interim report has been published by Dean and Malakar (2001).
The purpose of the present report is to present: (1) An updated analysis of the survey data, and
(2) The results of a cost analysis comparing the PGS with more conventional approaches in which sand is added to the system through beach nourishment which could be by either truck haul or dredging.

1 Jv

Choctawhatchee Bay
0 5,000
Scale (ft)

Destin

Site 2

Site 1

Figure 1. Location Map For Two Installation Sites.




2.0 PHOTOGRAPHS

Photographs can provide qualitative information useful in supplementing the analysis results of the survey data. Figure 2 is an aerial photograph looking east with Site 2 in the immediate foreground. Figures 3 and 4 show Sites I and 2 respectively. Appendix A presents a series of photographs depicting the site conditions at various times.

Figure 2. Aerial Photograph Looking East With Site 2 in Foreground. Destiny Pass in Background. Photograph by
Benedict Engineering, March 6, 2001.




Figure 3. Aerial Photograph of Site 1, Looking East. Photograph by Benedict Engineering, March 6, 200 1.

Figure 4. Aerial Photograph of Site 2, Looking West. Photograph by Benedict Engineering, March 6, 2001.




3.0 ANALYSIS OF SURVEY DATA

This section presents the results of the survey data analysis and will be used in the second major task which is the cost comparison.
3.1 Available Survey Data
Table 1 summarizes the available survey data. It is seen that a total of 16 surveys were conducted with some of these surveys encompassing both sites and others only one site. The PGS consisted of 16 groins at each site and occupied an alongshore length of 1,500 feet and the surveys included this region and extended 1,050 feet on either side of the groins for a total surveyed length of 3,600 feet. The 1,050 sections on either side of the groin are considered here as "control regions", which on average, are not affected by the groin installation. Figure 5 presents a schematic of the installations. Each porous groin is 150 feet long.
4( 3,600 Feet Surveyed Area
Figure 5. Schematic of Porous Groin Installation.
It is seen from Table 1 that the number of profiles surveyed during the various surveys ranged from 21 to 43. The method of analysis employed in the previous report (Dean and Malakar, 2001) required use of the same profile lines for comparison. For purposes here, all 16 surveys were analyzed by a method that did not require the use of common lines for all surveys. In some cases, the profile lines extended gulfward a shorter distance than 300 feet, the nominal distance to which profile lines had been analyzed in previous reports. These profiles were extended approximately and analyzed in the cross-shore distance to 300 feet; however, the confidence in the results is reduced due to the lack of adequate survey data. Therefore, the cross-shore analyses are only presented for the 150 foot length encompassed by the groins.




Survey Date Survey Purpose T Surveyed Number of Profiles Surveyed
December 2000 Pre-Installation Sites 1 and 2 Site 1: 42; Site 2:42
January 2001 Document Changes Sites 1 and 2 Site 1: 43; Site 2:43
February 2001 Document Changes Sites I and 2 Site 1: 42; Site 2:42
April 2001 Document Changes Sites I and 2 Site 1: 33; Site 2:33
July 2001 Document Changes Sites 1 and 2 Site 1: 42; Site 2:42
August 2001 Document Changes Site 2 Only Site 2:43
October 2001 Document Changes Sites 1 and 2 Site 1: 43; Site 2:43
March 2002 Document Changes Site 2 Only Site 2:43
April 2002 Document Changes Site 2 Only Site 2:43
May 2002 Document Changes Site 2 Only Site 2:33
June 2002 Document Changes Site 2 Only Site 2:21
July 2002 Document Changes Site 2 Only Site 2:21
August 2002 Document Changes Site 2 Only Site 2:33
September 2002 Document Changes Site 2 Only Site 2:21
October 2002 Document Changes Site 2 Only Site 2:21
November 2002 Document Changes Site 2 Only Site 2:32

Table 1

Characteristics of Survey Data




3.2 Analysis Methods

As noted, a previous report (Dean and Malakar, 2001) relating to the porous groin installations at Eglin Air Force Base has presented analysis results including shoreline and volume changes and the patterns of these changes. The patterns can assist in determining the processes that caused the shoreline and volume changes, in particular the differential effect in the installation areas as compared to the adjacent shorelines. Because the purpose of the present report is to establish overall performance of the installations at the two sites, the emphasis will be on total volume and shoreline changes inside and adjacent to the regions occupied by the porous groin systems. As noted, this allows use of more of the survey data than was possible for the study of patterns of changes. Thus, the patterns of shoreline and volumetric change are not the focus here and are not presented in this report. Common to both shoreline and volume changes, the analysis determined the averages within the 1,500 feet shoreline segment encompassed by the nets and the 2,100 feet segment adjacent to the nets. The volume changes accounted for the 150 feet lengths (perpendicular to the shoreline) of the individual groins. In the control areas, the volumes were computed over the Gulfward 150 feet from the baseline.
3.3 Shoreline Changes
The shoreline changes are based on NGVD elevations. In some cases, a bar was present which resulted in multiple locations of this shoreline as shown in Figure 6. A limited comparison (12 surveys) of shoreline changes was conducted for the most gulfward and the most landward shoreline positions. It was found that the average of the most gulfward positions could be significantly greater than the average most landward shoreline positions. However, the overall average within groin field shoreline changes minus adjacent average control shoreline changes was within 5.1 feet for the most landward and seaward shoreline positions. Therefore the results presented here are based on the more landward shoreline positions. Shoreline changes were determined by subtracting the shorelines for the December survey from the shorelines for each subsequent survey being considered
Most Shoreward NGVD Shoreline
Figure 6. Illustrating Case in Which More Than One NGVD Shoreline Exists.




3.4 Volume Changes
As noted, the average volume changes were determined within: (1) The 1,500 feet longshore and the 150 feet cross-shore dimension of the groin field, and (2) The 2,100 feet longshore dimension of the control areas and a cross-shore distance of 150 feet from the baseline. Volume changes were determined by subtracting the volumes for the December survey from the volume for each subsequent survey being considered.
Shoreline and volume change results are presented in the following sections.
3.5 Site 1 Shoreline and Volume Changes
3.5.1 Site 1 Shoreline Changes
The average shoreline positions within the 1500 feet longshore distance of the groin field and within the 2,100 feet longshore distance of the adjacent control areas are presented for Site 1 in Figure 7 over the period of surveys at Site 1. It is seen that the average shorelines both inside the limits of the groin fields and in the adjacent control areas increased after installation with the shorelines inside the groin field generally increasing more than outside the groin field. The average shoreline inside the groin commenced retreating prior to removal of the groins and the shorelines inside and outside of the groin field continued to decrease after groin removal.

60
~50
0) 40
C o30
~20
0 Cl) 10
(D 0) E2 0
()

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Years After Installation Figure 7. Average Shoreline Changes Inside and Adjacent to the Porous Groin. Site 1.

. . ..... ..... ........
.. .. .... .. . . . ... . . . .. . . .
El
. ..... ......
Inside GroinmUrn

LI~




In interpreting these overall shoreline changes with time, it appears that the PGS was installed when the shoreline was in a recessed condition (November 2000). The generally close tracking of the two average shorelines suggests that the changes were due primarily to natural effects and not to the groins although at one time (February 2001), the average shoreline inside the groin field had advanced 20 feet more than the average shoreline adjacent to the groin field.
Table 2 presents the time averaged shoreline change results including the changes inside the groin field and outside the groin field (2,100 foot control area) over the period of groin installation and the average at the time of groin removal. For Site 1, it is seen that the averages over the period of installation are 20.1 feet and 14.9 feet advancement within and outside of the groin limits, respectively. At the time of removal, the averages are 21.9 feet advancement both within and outside of the groin limits.
Table 2
Average Shoreline Change Characteristics
Average Shoreline Change Over Average Shoreline Change at Time Period of Installation of Groin Removal
(feet) (feet)
Site Within Groin Within Control Within Groin Within Control
Field Areas Field Areas
1 20.1 14.9 21.9 21.9
2 30.4 22.8 47.7 20.0
3.5.2 Site I Volume Changes
The Site I volume changes, presented in Figure 8, parallel to some degree the shoreline changes at this site and are suggestive of a seasonal cycle with the volumes within the groin field increasing in the summer season and decreasing (sediment moving seaward of the 150 feet crossshore dimension of the groins) in the winter season. In this case, the volume increases outside the groin field were generally slightly greater than within the 1,500 feet occupied by the groin field.
Table 3 presents the time averaged volume change results including the changes inside the groin field and adjacent areas (2,100 foot control area) over the period of installation and the average at the time of groin removal. For Site 1, it is seen that the averages over the period of installation are 4.6 yd 3/foot and 5.0 yd 3/foot increase within and outside of the groin limits, respectively. At the time of removal, the averages are increases of 6.4 yd 3/foot and 9.7 yd 3/foot within and outside of the groin limits, respectively.




16 .
................. ................. .....
14 ... .......... ..... : ..... .. . .
Cf) M............... ........... .......... ......
... .......... ....................... ...............
(D ..... :................... . ...
-2
8Years After IG i-atton
Figure~~~~~~~~~ 8..... Avrg oueCagsIsd n daetth Outsid Groin Sysem
Sites A
...........v e.................e............A d ....n ........... r ............... m
6ie1

Table 3
Average Volume Change Characteristics

Average Volume Change Over Average Volume Change at Time of
Period of Installation Groin Removal
(yd3/foot) (yd3/foot)
Site Within Groin Within Control Within Groin Within Control
Field Areas Field Areas
1 4.6 5.0 6.4 9.7
2 4.8 10.0 7.5 8.4




3.6 Site 2 Shoreline and Volume Changes
3.6.1 Site 2 Shoreline Changes
The Site 2 shoreline change results are presented in Figure 9. The results are quite irregular with the shoreline inside the groin field advancing more than that outside for the first two months, but for the next seven months, the shoreline outside the groin field was more advanced, followed by the remaining six months of groin installation during which the average shoreline inside the groin field remained more advanced than outside the groin field. Also, of interest, the shoreline generally continued to advance even after removal of the groins with average advancement greater within the (previous) limits of the groin field than outside.

100
'~80 ci)
C CU0
0
a)
0)
C
a)
< 0

!)A I

,)A

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Years After Installation Figure 9. Average Shoreline Changes Inside and Adjacent to the Porous Groin System. Site 2.
10

.. ... .. . > . ... .......
Inside Groin Limits 0. .
...... Outside Groin Limits Cl ...:...
I I I IN




..... ....................... .......
>
................ ..... ................ .. .....................
0
C
......................
..................................................... A 0 4 ..... ............
. 4 ....... ..
.......... ............... t ................ ................ ..............
Co
................. ..........
.................. ...........
..................
....... .........................
................... ....... .................. ............. ............. .
........... ...... ......... ..... ........................................................... .....
.......... ....... ... I ..... ...... .... I ..... .......... .....
.............. .. ..... ........... .......... .........................
Inside Groin Limits
................ ........ ................ ......
......... Outside Groin Limits' ...... ............... ................ ........................................................ ........
........... .......... ....... ...... ....

Table 2 has presented the average shoreline change results including the changes inside the groin field and outside the groin field (2,100 foot control area) over the period of installation and the average at the time of groin removal. For Site 2, it is seen that the averages over the period of installation are 30.4 feet and 22.8 feet advancement within and adjacent to the groin field, respectively. At the time of removal, the averages are 47.7 and 20.0 feet advancement within and adjacent to the groin limits, respectively.
3.6.2 Site 2 Volume Changes
The volume change results for Site 2 are presented as Figure 10 and differ somewhat from the shoreline change results (Figure 9). It is seen that the volumes generally increased both inside and outside of the groin field with the volumes outside the groin field being greater than inside the groin field, although the two volume changes start to converge before the groin removal in March 2002. Subsequent to groin removal, both volume changes were approximately the same, increasing from March 2001 to July 2001 and then decreasing, consistent with natural seasonal changes.

4= 14 >' 12 C: 10
8
(D
E
2 6 .0
ci) 4
2 0

-2
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2A Years After Installation Figure 10. Average Volume Changes Within and Adjacent to the Porous Groin System.
Site 2




In interpreting these results, it is difficult to identify conclusively an effect of the groin field. It appears that most of the relative differences within and adjacent to the groin field are due to natural changes in the system and the strongest case that can be made is for the changes being a result of noise in the natural system combined with the seasonal effects. As discussed in previous reporting of the survey results of this project, this general shoreline is known to be "noisy"~, that is there are substantial natural undulations or oscillations of the shoreline and the differences in Figure 10 are most likely dominantly due to these natural effects with any effects due to the groin field being secondary. Aerial photographs (Figures 2 and 4) confirm that the Site 2 groin installation area coincided with an erosional "trough" 'in the beach planform. Nevertheless, in this case, the groin system was unable to stabilize the shoreline against these natural forces.
Table 3 has presented the average volume change results including the changes inside the groin field and adjacent to the groin field (2,100 foot control area) over the period of installation and the average at the time of groin removal. For Site 2, it is seen that the averages over the period of installation are 4.8 yd3/foot and 10.0 yd3/foot increase within and outside of the groin limits, respectively. At the time of removal, the averages are increases of 7.5 yd3/foot and 8.4 yd3/foot within and outside of the groin limits, respectively.
4.0 COST ANALYSIS
4.1 General Discussion
In developing an appropriate basis for a cost analysis and comparison with the more conventional methods discussed earlier, it is necessary to consider the processes induced by the porous groins which could be considered appropriate for crediting the porous groin system with volume and/or shoreline changes.
Beach nourishment, whether by dredge, truck haul, or other means adds sediment to the active nearshore system from outside this system. The seaward limit of this active portion of the nearshore system is usually defined approximately in terms of this closure depth and thus efforts are made during nourishment operations to not remove sand from areas landward of this depth limit. Otherwise, the sand will tend to return to the area from which it is removed. Estimates of the closure depth have been developed for the Florida peninsula and, for the Florida Panhandle areas are on the order of 13 to 17 feet (Dean and Grant, 1989). By contrast, any sand accumulated within the PGS is removed from the active system and thus, this can be considered as a zero sum process. Therefore, considerations of the cost effectiveness should recognize this difference between beach nourishment which adds "new" sand to the system and a groin system which sequesters sand from the active system. One could argue that dredging sand from seaward of the closure depth isn't really adding new sand to the system and that over a very long time frame (many decades to centuries) some of the nourishment sand will return to the deepened borrow areas. However, it is the differences in degree of sediment transport activity in the areas from which the sand was removed and the time frames for the sand to return that differs markedly for these two methods of addressing local beach erosion.




The claim of the proponents of the porous groin system is that any sand deposited within the groin field originates from offshore and therefore does not diminish the sand volume in the nearshore system. This claim cannot be supported based on nearshore coastal engineering or coastal science knowledge or principles. In order for the system to draw sand from offshore, the portion of the system from which the sand is drawn must be active by definition and thus if sand is removed from this active area, this portion of the profile would remove sand from adjacent portions of the profile where the groins are not present and thus, based on well-accepted and field proven concepts of equilibrium beach profiles, those portions of the beach system where the groins were not present would experience erosion. In sum, the beach system is interconnected (geologists call it a "sand sharing system") and if sand is removed from one portion of the active system, another part of this sand sharing system will experience an equivalent loss. Thus, even allowing the most generous interpretation of the mechanics by which the porous groin system functions, but still retaining well-established physical fundamentals of nearshore processes, the system still functions as a groin as indicated by its designation "Porous Groin System".
With the previous paragraphs as background, in order to conduct cost comparisons at all, it is necessary to attribute some volume gain to the porous groin system. Inspection of Figures 8 and 10 combined with the foregoing discussions does not support a finding that the system has caused the accumulation of sand from any source. The original contention was that the system would accumulate sand from offshore and would not remove sand from the active nearshore system. Nevertheless, in order to continue with the goal of developing cost comparisons, three bases for "crediting" the PGS for volumetric increases will be considered with the first being the general difference between the volumetric accumulation per unit length of beach within the PGS relative to the adjacent control area and the second, to consider the average volume changes within the limits of the PGS over the period of installation without regard to the adjacent control area. The third basis is the volumetric increase within the groin field at the time of the groin field removal.
4.2 Costs of the Porous Groin Installations
Attempts were made to summarize the available cost information for the two Eglin porous groin installations. These data were obtained from the Florida Department of Environmental Protection and Benedict Engineering, Inc. and reflect best efforts to include all costs which could be documented. Table 4 summarizes the available estimated and actual cost information.
4.3 Rationale for Cost Comparisons
As noted, there are two issues which arise in the selection of an appropriate basis for comparison of costs of the porous groin installation versus the more traditional method of beach nourishment: (1) The volume or shoreline "credit" that should be assigned to the groin installation based on the results of the monitoring data, and (2) The costs which should be considered in the cost comparison. The volume credit issue has been addressed in Section 4. 1. The rational for selecting each of the cost bases is discussed below.




The total costs for the porous groin installations, which were to some extent experimental, obviously included engineering, development and monitoring costs that are unique to this type of project. Engineering and monitoring costs are also associated with more traditional nourishment methods. For purposes here, the four cost estimates presented in Table 4 excluding monitoring and reporting costs will be used as a basis.
Table 4
Cost Information for PGS Installations at Sites 1 and 2
Estimate Type of Cost
Number __ _ _ _ _ __ _ _ _ __ _ __
and Basis Engineering Monitoring Materil Labor Contingency Total for Estimate $ and $ $ $ $
_________[Reporting
Estimate 1 186,000 143,000 138,424 100,000 57,214 624,638
Estimated
Costs for 481,638**
Both Sites (Original Test Plan)'*
Estimate 2 230,790 152,059 202,312 109,280 NA 694,440
Actual Costs
for Both 542,3 8 1
Sites*
Estimate 3 213,380 184,404 17,331 26,394 NA 441,509
Actual Costs
for Radar 257,105 **
Site*
Estimate 4 166,900 96,900 35,235 60,725 NA 359,760
Projected
Costs for 262,860~
One Site* ______ _____ ____ ______ ____*Cost Estimates Provided by FDEP and Benedict Engineering. "*Excluding Monitoring and Reporting Costs




Table 5 presents a summary of the costs without monitoring and, the volume credit adopted, and the resulting costs per cubic yard associated with the most generous acceptance of volume accumulated by the PGS. The costs per cubic yard were calculated by dividing the costs in Column 2 of Table 5 by the total PGS length (3,000 feet for two sites and 1,500 feet for one site). The costs of trucking in small amounts of good quality sand will be taken as the range from $ 12.00 per yd' to $ 15.00 per yd.
Table 5
Development of Unit Costs of Sand Accumulated
Costs Amount of Volume Costs per cubic yard
Based on Cost (Without Increase Attributable to M$
Estimate Monitoring PGS
(See Table 4) Costs, See (yd 3/foot)______Table 2) Minimum Maximum Maximum Minimum
M$
1 481,638 Nil 7.5* Not Possible to
Two Sites. Total Calculate, Very 21.41
PGS Length =High
3,000 feet ____2 542,381 Nil 7.5* Not Possible to
Two Sites. Total Calculate, Very 24.11
PGS Length =High
3,000 feet ______3 257,105 Nil 7.5 Not Possible to 22.85
One Site. Total Calculate, Very
PGS Length =High
1,500 feet
4 262,860 Nil 7.5 Not Possible to 23.37
One Site. Total Calculate, Very
PGS Length =High
1,500 feet __ _ _ ________________ _
*Taken as the Maximum of Sites 1 and 2 in Table 3




Table 6 compares the range of trucking costs per cubic yard with those developed for the four cost estimates for the PGS. It is seen that with the most generous interpretation of volume accumulation by the PGS, trucking is still less expensive. Additionally, as noted earlier, trucking adds "new" sand to the nearshore system.
Table 6
Comparison of Costs of Sand by Conventional Methods and by PGS
Based on Cost Trucking Nourishment Porous Groin Costs
Estimate Costs ($/yd3) ($/yd3)
(See Table 2) Minimum Maximum Minimum Maximum
1 12.00 15.00 21.41 Not Possible to Calculate,
Very High
2 12.00 15.00 24.11 Not Possible to Calculate,
Very High
3 12.00 15.00 22.85 Not Possible to Calculate,
Very High
4 12.00 15.00 23.37 Not Possible to Calculate,
Very High
5.0 SUMMARY AND CONCLUSIONS
The monitoring data from the porous groin installation do not support the contention that the porous groin system has had a measurable beneficial effect in terms of volume accumulation over and above the control area which comprised the 1,050 feet segments immediately adjacent to and on either side of the Site 1 and Site 2 Eglin Air Force Base PGS installations. As discussed in our previous report (Dean and Malakar, 2001), this may be due, in part, to the well-known "noisy" character of the shorelines in the Panhandle area of Florida. Regardless, even ascribing the most generous volume increases to the PGS, the costs of sand accumulation by the PGS is still greater than by trucking from an interior source. Three additional points worth noting are: (1) Even if the PGS did trap sand, there is no supporting evidence that this sand did not originate from within the nearshore active zone. In fact, all accepted coastal engineering and science knowledge supports the position that this accumulated sand did originate within the active nearshore system and, as for any other groin system, will cause a deficit elsewhere, (2) Nourishment is normally carried out through accessing sand that is well outside of the normal active nearshore zone and thus does not incur a deficit within the active nearshore zone, and (3) The maximum amounts which could possibly be ascribed to the PGS are much smaller that those associated with a substantial beach nourishment project which are on the order of 100 yd3/ft as compared to the approximately 8 yd3/ft, which is the upper limit for the PGS.




6.0 REFERENCES

Dean, R. G. and J. Grant (1989) "Development of Methodology for Thirty-Year Shoreline Projections in the Vicinity of Beach Nourishment Projects", UFL/COEL-89/026, Coastal and Oceanographic Engineering, University of Florida, Gainesville, FL.
Dean, R. G. and S. Malakar (2001) "Independent Analysis of Porous Groin Installation at Eglin Air Force Base, FL; Interim Report", UFL/COEL-2001/013, Civil and Coastal Engineering Department, University of Florida, Gainesville, FL.




APPENDIX A
SELECTED PHOTOGRAPHS OF THE EGLIN AIR FORCE BASE INSTALLATIONS

A-1




A.1 Introduction

This appendix presents selected photographs of the porous groin installations at the two Eglin Air Force Base sites. The first three photographs are the aerial photographs presented as Figures 2, 3 and 4 in the main body of this report. The remainder are ground views looking east and west from the two sites, where such photographs are available.

Figure A. 1. Aerial Photograph Looking East With Site 2 in Foreground. Destin Pass in Background. Photograph by Benedict Engineering, March 6, 2001.

A- 2




Figure A.2. Aerial Photograph of Site 1, Looking East. Photograph by Benedict Engineering, March 6, 2001.

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Figure A.3. Aerial Photograph of Site 2, Looking West. Photograph by Benedict Engineering, March 6, 2001.

A- 3




Figure AA Site 2, Looking West, December 5, 2000. Photography by Benedict Engineering.

Figure A.5. Site 2, Looking West, December 14, 2000. Photograph by Benedict Engineering.

A- 4




Figure A.6. Site 2. Looking East. Photograph Taken on March 22, 2001 by FDEP.

Figure A.7. Site 2. Looking West. Photograph Taken May 14, 2001 by FDEP.

A-5




Figure A.8. Site 2. Looking East, Photograph taken on May 14, 2001 by FDEP.

Figure A.9. View of Configuration of Porous Groins at Site 2.
Photograph Taken May 14, 2001 by FDEP.

A-6




Figure A. 10. Site 2. Looking East. Photograph Taken August 16, 2001 by FDEP. Tropical Storm Barry Made Landfall at Destin on August 6, 2001.

Figure A. 11. Site 2. Looking West. Photograph Taken August 16, 2001 by FDEP. Tropical Storm Barry Made Landfall at Destin on August 6, 2001.

A-7




Figure A.12. View Looking East at Site 2. Photograph Taken by PBS&J on October 25, 2001.

Figure A. 13. View Looking West at Site 2. Photograph Taken by PBS&J on October 25, 2001.

A- 8




Figure A. 14. Site 2. Looking East, Photograph Taken in December 200 1.

Figure A. 15. Site 2. Looking West, Photograph Taken in December 200 1.

A- 9