Agenda 02/12/2013 Item #16A20Proposed Agenda Changes
Board of County Commissioners Meeting
February 12, 2013
Move Item #16A20 to Item #IIG: Recommendation to approve
$350,000 in eligible costs for the FY13 Hideaway Beach erosion control
structure project based on a January 16, 2013 Proportionality Analysis
conducted by Coastal Engineering and reviewed by Collier County staff,
make a finding that this item promotes tourism and approve necessary
budget amendments. (Commissioner Henning's request)
Continue Item #16A18 to the February 26, 2013 BCC Meeting: Recommendation to approve
disposal of surplus property associated with the Gateway Triangle Stormwater Improvements
Phase II, Contract #10 -5366. (County Attorney's request)
Add Item #4D: Proclamation designating February 12, 2013 as the Frank Oakes Day of
Remembrance in Collier County, in recognition of his contributions of the community. To be
accepted by family members. Sponsored by Commissioner Hiller.
Continue Item #11E to the February 26, 2013 BCC Meeting: A Resolution authorizing
acquisition by gift, purchase or condemnation of those perpetual and temporary easement
interests necessary for construction of stormwater improvements known as the "Haldeman
Creek and Crown Pointe Weirs" segment of the LASIP Project. (County Attorney's request)
Continue Item #16A17 to the March 12, 2013 BCC Meeting:
Recording the final plat of Camden Lakes, Application Number
PPL- PL20120000747 approval of the standard form Construction and Maintenance Agreement
and the amount of the performance security. (Applicant's request)
Continue Item 916118 to the February 26, 2013 BCC Meeting: Commissioner Hiller requests
Board Approval for Payment to Attend a Function Serving a Valid Public Purpose. She will
attend the Beach Ball Gala for Children's Advocacy Center on February 23, 2013. (Staff request)
Move Item #17A to Item #911: This item continued from the January 22, 2013 BCC Meeting.
Recommendation to adopt an ordinance which would establish limitations, in addition to those
set forth in Chapter 538, Part I, Florida Statutes, on the sale and /or purchase of secondhand
goods (secondhand dealers). (County Attorney's request)
Note:
Item #16A16: With respect to Staff Clarification 06 -05 which restricts fuel tanks or fuel trucks
of over 250 gallon capacity from all residential and estates zoned property; staff makes further
clarification that non -fuel tanker trucks or traditional semi trucks with a fuel capacity over 250
gallons are not prohibited from estates zoned property.
2/12/2013 16.A.20.
EXECUTIVE SUMMARY
Recommendation to approve $350,000 in eligible costs for the FY13 Hideaway Beach
erosion control structure project based on the January 16, 2013 Proportionality Analysis
conducted by Coastal Engineering Consultants and reviewed by Collier County staff,
make a finding that this item promotes tourism and approve necessary budget
amendments.
OBJECTIVE: Approve the eligible costs associated with Hideaway Beach FY 13 Erosion
Control Project.
CONSIDERATIONS: The Board of County Commissioners directed that a Proportionality
Analysis be performed by the ' City of Marco Island through the Hideaway Beach District to
determine the effectiveness of the proposed FY 13 Erosion Control structures in preventing
and /or minimize shoaling inside the entrance channel of Collier Bay.
The analysis was conducted by Coastal Engineering Consultants on January 16, 2013 and
recommended a proportional public benefit of $730,000. Collier County staff reviewed this
analysis with Coastal Engineering Consultants, the Hideaway District and the City of Marco
Island and have agreed on a proportionally benefit of $350,000 for the following reasons:
1.
The actual dredging of Collier Creek occurred in 2001 and 2012. This represents an
eleven (11) year dredging cycle and not every six (6) years as noted in the report.
2.
The single most significant event that occurred in this area in recent years is the
disintegration of Coconut Island that served as a natural erosion barrier to this area. This
occurred in 2006/07 and served to make the entire area more ephemeral.
3.
Staff review is based on actual monitoring reports and physical data provided by Coastal
Engineering Consultants for the past five (5) years. No modeling analysis was used in
staff's analysis.
4.
Monitoring reports indicated 1,300 Cubic Yards (CY's) per year filling in Collier Creek.
9,600 CY's of material was dredged from Collier Creek in 2012 and this permitted
template will be used for future dredging events. This yields duration between dredging
events without erosion control structures for Collier Creek of 7.4 years (9,600 CY's
divided by 1,300 CY's per year). This serves to justify the shorter duration between
dredging events since the destruction of Coconut Island.
5.
Monitoring reports over the last ten (10) years indicate that 76% of the original fill
volume is retained by the erosion control structures. This would increase the time
between dredging events in Collier Creek if structures were in place to thirteen (13) years
(7.4 years multiplied by 1.76).
6.
Considering a 25 year project life, two (2) dredging events would be required if structures
were in place and three dredging events would be required if no structures were installed.
This saves one (1) dredging event if structures were installed.
7.
The total cost of the 2012 dredging event was $336,000. This includes the construction,
design and monitoring. It is realistic to expect that between $300,000 and $400,000 will
be saved over the next 25 years in dredging cost if structures are installed. Staff is
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2/12/2013 '16.A.20.
recommending $350,000 in savings as a result of the analysis. This complements the
2012 actual project cost of $336,000.
8. Collier County staff, Coastal Engineering Consultants, the Hideaway District and the
City of Marco have reviewed this recommendation and are in agreement with the revised
analysis and costs.
FISCAL IMPACT: Funding for the project under discussion is not presently budgeted. The
proposed source of funding is Tourist Development Tax Beach Renourishment Fund (195). If
the project is approved a budget amendment in the amount of $350,000 reducing reserves and
establishing the project budget will be necessary.
GROWTH MANAGEMENT IMPACT: No impact to the growth management plan would
result from this Board action.
LEGAL CONSIDERATIONS: This item has been reviewed by the County Attorney's Office,
requires simple majority vote, and is legally sufficient for Board action. — CMG
RECOMMENDATION: Approve $350,000 in eligible costs for the FY13 Hideaway Beach
erosion control structure project based on the January 16, 2013 Proportionality Analysis
conducted by Coastal Engineering Consultants and reviewed by Collier County staff, make a
finding that this item promotes Tourism and approve necessary budget amethdments.
Prepared By: J. Gary McAlpin, P.E., Coastal Zone Management, Natural Resources Department
Attachments: A) Coastal Engineering Consultants Proportionality Analysis dated January 16,
2013.
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2/12/2013 16.A.20.
'-N COLLIER COUNTY
Board of County Commissioners
Item Number: 16.16.A.16.A.20.
Item Summary: Recommendation to approve $350,000 in eligible costs for the FY13
Hideaway Beach erosion control structure project based on the January 16, 2013
Proportionality Analysis conducted by Coastal Engineering Consultants and reviewed by Collier
County staff, make a finding that this item promotes tourism and approve necessary budget
amendments.
Meeting Date: 2/12/2013
Prepared By
Name: HambrightGail
Title: Accountant,Coastal Zone Management
1/31/2013 11:34:15 AM
Approved By
Name: McAlpinGary
Title: Director - Coastal Management Programs,Coastal Zon
Date: 1/31/2013 11:47:49 AM
Name: LorenzWilliam
Title: Director - CDES Engineering Services,Comprehensive
Date: 1/31/2013 4:31:22 PM
Name: PuigJudy
Title: Operations Analyst, GMD P &R
Date: 2/1/2013 10:50:44 AM
Name: LaPierreBarbara
Title: Management/Budget Analyst,Transportation Administr
Date: 2/1/2013 2:37:09 PM
Name: MarcellaJeanne
Title: Executive Secretary,Transportation Planning
Date: 2/1/2013 3:27:51 PM
Name: GreeneColleen
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Title: Assistant County Attomey,County Attorney
Date: 2/4/2013 8:48:34 AM
Name: FinnEd
Title: Senior Budget Analyst, OMB
Date: 2/4/2013 3:59:06 PM
Name: KlatzkowJeff
Title: County Attorney
Date: 2/4/2013 4:25:54 PM
Name: OchsLeo
Title: County Manager
Date: 2/5/2013 9:28:57 AM
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Hideaway Beach Erosion Control Project
Introduction
Attachment A 2/12/2013 16.A.20.
Proportionality Analysis
The City of Marco Island's northern beach area has been experiencing significant erosion in the
wake of recent storms including Tropical Storm Fay and coastal processes (winds, waves, tides
and currents). The upland development and infrastructure are threatened by the continuing
erosion. Based on these measured near -term erosion rates, it is expected the building foundations
will soon be under direct wave attack as the remaining dune and wetland habitats and upland
vegetated lawn areas will be lost to erosion. The Project is located along the City of Marco
Island's northern beach area adjacent to the Big Marco River and Gulf of Mexico, Marco Island,
Collier County, Sections 5, 6, and 7, Township 52S, Range 26E, Class III Waters. A location
map is presented in Figure 1.
Figure 1. Project Location Map.
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January 16, 2013
Attachment A
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Hideaway Beach Erosion Control Project Proportionality Analysis
2 Project Purpose
To address this critical erosion area, the City through its consulting contract with Coastal
Engineering Consultants and Coastal Technology Corporation has completed a detailed model
study and design, has received the FDEP permit and USFWS Biological Opinion (draft), and is
currently processing the last permit required from the USACE for installation of three erosion
control structures (T- groins) and placement of up to 25,000 cubic yards of beach compatible
sand. The sand sources include the previously utilized Nearshore Borrow Area (2010 project)
and Collier Bay Entrance Channel (2001, 2005 and 2012 projects). A third sand source, the
Capri-Big Marco Pass Borrow Area (2005 project) is also permitted and will be available for
future renourishment events.
The purpose of the beach fill and erosion control structures is to address significant erosion along
this beach segment providing a mechanism to offset historical erosion, restore recreational beach,
provide storm protection to the upland properties, provide and preserve sea turtle nesting sites,
and restore coastal habitat for other threatened and endangered species.
One public benefit realized by the Project is to reduce the maintenance dredging costs of the
Collier Bay Entrance Channel which addresses the navigation needs for the boating community.
Installation of the structures is expected to hold the sand placed along this critically eroded beach
segment, thereby reducing Project related costs and future maintenance costs.
This proportionality analysis has been completed in support of the City of Marco Island's Tourist
Development Council's Grant Application in the amount of $925,000 to offset the materials and
installation costs of the three (3) T -groin structures. Utilizing the consulting team's coastal
processes analysis and detailed model study completed in support of the Project design and
permitting, Collier Bay Entrance Channel maintenance history, and Project related monitoring
surveys, the costs for maintenance dredging "without" and "with" the T- groins was estimated
throughout the Project life which was defined as the expected life of the erosion control
structures estimated to be 20 to 25 years. It is noted that no new data collection or numerical
modeling was conducted due to the time constraint.
3 History of Management Activities (1997 to present)
1997
• Two (2) temporary geotextile T- groins were constructed at South Point
• Three (3) temporary geotextile T- groins were constructed at Royal Marco Point
2001
• Survey (December) from Royal Marco Point to Collier Bay
• Dredging of Collier Bay entrance (May through July); 24,100 cubic yards were
removed and placed along the beaches extending up to the Royal Marco Point T-
groin field
• Two (2) additional temporary geotextile T- groins were constructed
• Ville de Marco initiated seawall and dock repairs along Collier Creek (construction
suspended due to contractor issues)
2 January 16, 2013
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Attachment A 2/12/2013 16.A.20.
Hideaway Beach Erosion Control Project Proportionality Analysis
2002 -2003
• 500 -foot section of seawall and 10 finger piers along Collier Creek were replaced by
Ville de Marco West (VDMW) in 2002 as result of channel scour. Concrete armor mat
was installed along entire property fronting Collier Creek to protect finger piers and
seawall from future scour. 220 -foot long steel sheet pile toe wall was installed along
northwestern corner of property to protect seawall and observation pier from future
scour. Sheet pile were 19 -foot long PZ -27 sections driven 17 feet into channel bottom.
2005
• Pre - construction survey (April) of Collier Bay and Hideaway Beach
• Seven (7) temporary geotextile T- groins constructed were removed
• 136,350 cy were placed along 2,800 ft of shoreline at South Point
• 180,420 cy were placed along 3,000 ft of shoreline at Royal Marco Point
• Five (5) T- groins were constructed at South Point
• Five (5) T- groins were constructed at Royal Marco Point
• Terminal jetty was constructed at the entrance to Collier Bay
• Post- construction survey (December) of Collier Bay and Hideaway Beach
2006
• Monitoring surveys (June and December) of Collier Bay and Hideaway Beach
2007
• Monitoring survey (July) of Collier Bay and Hideaway Beach
2008
Monitoring surveys (September) of Collier Bay and Hideaway Beach
Emergency revetment was constructed (September) between the South Point and Royal
Marco Point T -groin fields
2010
• Survey (May) of Collier Bay and Hideaway's North Beach
• Pre - construction survey of Collier Bay and Hideaway Beach
• Approximately 122,000 cy were placed along 2,500 ft of shoreline
• Six (6) T- groins were constructed
• Post - construction survey (December) of Collier Bay and Hideaway Beach
2011
Survey (April) of Collier Bay and Hideaway's North Beach
Tide, current and wave gauge deployment (March -April)
Monitoring surveys (August) of Collier Bay and Hideaway Beach
2012
• Collier Bay Entrance Channel was dredged (January), approximately 9,300 cubic
n yards (total) were excavated and placed in nearshore between H12 and H14
January 16, 2013
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Hideaway Beach Erosion Control Project
2013
Attachment A
2/12/2013 16.A.20.
Proportionality Analysis
Monitoring surveys (July) of Collier Bay and Hideaway Beach
Bid Documents prepared for Hideaway Beach Erosion Control Project — Phase III to
include 25,000 cubic yards between approximately H -12 and H -14 plus three new T-
groins tapered to replicate the 1990 mean high water shoreline
Bids received for the Project. Apparent low bidder priced the three erosion control
structures equal to $994,952 including mobilization, materials, installation, and
demobilization along with 50% of the environmental protection bid item ($7,500). It is
noted the environmental protection bid item was for the whole Project including both the
dredging/filling operations and the structures. The bid tabulation sheet prepared by City
Purchasing is included in Attachment 1. It is noted this bid is approximately 4% under the
Engineer's Opinion of Cost for the structures (same bid items) equal to $1,036,370.
4 Terminal Jetty
The existing terminal jetty located along the west side of the entrance to Collier Bay was
constructed by the County in 2005. The jetty was placed within Sovereign Submerged Lands
Easement No. 40548, BOT File No. 110337105. A 2001 to 2005 project components map is
presented in Figure 2.
5 Collier Bay Entrance Channel
5.1 Introduction
The Collier Bay Entrance Channel is located at the junction of the Big Marco River with the
entrance channel to Collier Bay, locally known as Collier Creek. The dredge area was placed
within a Sovereign Submerged Lands Easement No. 30622, BOT File No. 110222775. The
design cut depth is to elevation -11.3 feet NAVD with a 1 -foot overdredge tolerance to -12.3 feet
NAVD. The design cut width is 80 feet; however, due to the presence of the existing terminal
jetty, between approximate Stations 2 +00 and 4 +50, the dredge cut width reduces by 10 feet (70
feet) to 38 feet (42 feet).
Based upon field observations and review of the multiple monitoring surveys, the terminal jetty
has filled to capacity by natural sand transport and bypassing is occurring into the channel
resulting in a constriction of the Collier Creek waterway. This narrowing has increased the
current velocities in the Creek resulting in significant scour along the eastern side of the channel
adversely impacting the upland development on the opposite shoreline. The 2012 dredging
project, FDEP Permit No. 0305112- 001 4C, was completed by the City (design and permitting)
and County (construction and construction management) to temporarily alleviate this condition.
4 January 16, 2013
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Attachment A
Hideaway Beach Erosion Control Project
Figure 2.2001— 2005 Project Components Map
5.2 Entrance Channel Maintenance History
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Proportionality Analysis
Details of the entrance channel maintenance projects are presented in Table 1. The volumes for
each dredging event, costs for each construction project, and volumes within the dredge cut for
various condition surveys are presented therein.
Table 1. Collier Bay Entrance Channel Volume Chronology
Description
Volume In Permitted
Template (CY)
2001 Original Dredging
24,100
2005 Terminal Jetty
Unreported
April 2011 Condition Survey
9,900
2012 Maintenance Dredging
9,300
July 2012 Condition Survey*
> 6,000
* Limited number of surveyed channel cross sections
With respect to computing the average dredge volume, it is noted that the terminal jetty was
placed within the original dredge cut limits; no volume was recorded for the 2005 event that
CEO's research was able to discern. To that end, the condition survey in 2011 and maintenance
dredge project in 2012 yielded 9,600 cubic yards plus or minus 300 cubic yards in the permitted
5 January 16, 2013
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Attachment A 2/12/2013 16.A.20.
Hideaway Beach Erosion Control Project Proportionality Analysis
dredge cut. This indicates that once the channel infills to this approximate volume, no additional
shoaling within the permitted dredge limits occurs. Rather, at this point the shoaling into the
channel deflects the currents which then scour the sediment along the opposite shoreline as
evidenced by the monitoring results described herein. Based on these data, the design
maintenance dredge volume shall be set equal to 9,600 cubic yards.
Based on the construction events (2000, 2005 and 2012), inlet maintenance has been completed
on average every 6 years. However, based on the monitoring surveys and observed infilling /
scouring trends, the entrance channel fills in more rapidly than every 6 years (as evidenced in the
proceeding sections) suggesting the appropriate maintenance interval may be less than 6 years.
Based on the coastal processes analysis and annual monitoring surveys /reporting, the
maintenance dredge interval is primarily a function of episodic events which are the predominant
coastal forcing function transporting sediment along the shoreline and into the inlet mouth.
6 Coastal Processes Assessment
6.1 Historic Shoreline and Volume Changes
Bathymetric /topographic survey data and aerial photographs collected between 1990 and 2010
were used to analyze and compute historic shoreline changes. Figure 3 presents a summary of
historic shoreline change rates at Mean High Water (MHW) within the Project area for four
periods between 1990 and 2010. The rates indicate that the 20 -year trend (1990 -2010) within the
Project area between approximately H -12 and H -14 was erosional with erosion rates ranging
from 2 feet per year to 6 feet per year. Immediately outside the Project area the shoreline during
this period was stable to accretional. Further, there is a significant shift in trends from the 1997-
2005 period when the shoreline within the Project area was stable to the most recent 2005 -2010
period when erosion rates ranging from 8 feet per year to 20 feet per year occurred.
Bathymetric /topographic survey data collected in December 2005 and December 2010 were used
to analyze and compute historic volumetric changes. Figure 4 presents a contour map of the
changes with three (3) volume cells identified. Cell 1 approximately delineates the Project area
experiencing erosion, Cell 2 represents the area updrift of the existing terminal jetty, and Cell 3
covers the entrance to Collier Creek and the creek interior. Seaward limits for Cells 1 and 2 were
determined based upon comparison between the 2005 and 2010 profiles and defined as an
approximate location of profile closure seaward of which cross -shore sediment movement did
not occur.
Based on the volumetric calculations, Cell 1 lost approximately 17,700 cubic yards between
2005 and 2010, Cell 2 gained approximately 4,900 cubic yards, and Cell 3 gained approximately
6,500 cubic yards.
6 January 16, 2013
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Attachment A
Hideaway Beach Erosion Control Project
2/12/2013 16.A.20.
Proportionality Analysis
Figure 3. North Hideaway Beach Historic Shoreline Change Rates.
Figure 4. Hideaway Beach North Segment Historic Volume Changes.
% January 16, 2013
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Attachment A 2/12/2013 16.A.20.
Hideaway Beach Erosion Control Project Proportionality Analysis
6.2 Sediment Budget
The historic volumetric changes presented in the previous section were annualized and a local
sediment budget was developed. It is presented in Figure 5. A negligible amount of sand was
measured transporting from the existing T -groin field into Cell 1 (North Beach segment). The
amount of sediment transported out of Cell 1 to the northeast was on the order of 3,500 cubic
yards per year. The fillet formed updrift of the jetty at an average rate of 1,000 cubic yards per
year attributed to the erosion from Cell 1. The net change in Cell 3 including the deposition into
the channel and scouring on the opposite shoreline was approximately 1,300 cubic yards per
year, again attributed to the erosion from Cell 1.
A detailed coastal processes analysis was prepared on behalf of the City and submitted to the
FDEP and USACE in support of the Project design and permitting (CEC, 2011).
Figure 5. North Hideaway Beach Sediment Budget.
The results of the sediment budget indicate the majority of the sediment transporting off the
North Beach segment either deposits on the beach updrift of the jetty or infills the channel.
January 16, 2013
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Attachment A 2/12/2013 16.A.20.
Hideaway Beach Erosion Control Project Proportionality Analysis
6.3 Current Conditions
Examining the sediment budget for Cells 2 and 3 (Figure 5) and noting that the jetty fillet is at
capacity under current conditions, the 1,000 cubic yards per year is likely bypassing the jetty and
when combined with the 1,300 cubic yards per year, equates to a potential shoaling rate of
approximately 2,300 cubic yards per year. Based on the design maintenance dredge volume of
9,600 cubic yards and the average annual shoaling rate, the design maintenance dredge interval
equals approximately 4.2 years.
Utilizing the limited number of inlet cross sections collected as part of the July 2012 monitoring
survey provided by the City through their outside consultant, Humiston and Moore (H &M), it is
estimated that over 6,000 cubic yards of sand is within the permitted dredge cut. This deposition
occurred within 6 months of the 2012 maintenance event. It is noted that Tropical Storm Debby
struck the Southwest Florida coastline during this timeframe impacting the Project area and
contributing to this significant deposition rate compared to the five year average. Because the
terminal jetty fillet remains filled to capacity, the significant majority of sand eroding off of
North Beach was transported alongshore and deposited in the channel.
7 Numerical Modeling Study
The main objective of the Numerical Modeling Study was to predict, using numerical model
simulations, the sediment transport magnitude and directions, bathymetric changes, beach fill
diffusion, and channel sedimentation rates for each alternative carried forward from the Plan
Formulation Phase of the Project; and to compare the relative performance of the alternatives in
order to select the recommended design.
DHI's MIKE21 model was implemented in this Study. The model is state -of -the -art with features
capable of simulating the processes driving morphologic changes in the Project area. MIKE21 is
a fmite volume model based on unstructured mesh. Computational grids were created to include
three (3) offshore (north, west, and south) and three (3) inland open boundaries. The morphology
module, which computes both bed -load and suspended load transport of non - cohesive sediments,
was activated and coupled with the flow module. The wave module was activated because wave
action is an important process causing morphologic changes in the Project area. The
computational grid used in the flow module was also specified in the wave module for
simplicity. The coupling of flow, waves, and sediment transport was done dynamically.
The primary forces behind processes within the Project area are wave action and tidal currents
associated with the inlet system. Therefore, the flow, wave, and sediment transport modules were
dynamically coupled within the model. The calibration and validation steps were performed for
two independent time periods and utilized different input data.
The consulting team concluded that the calibration and validation program was sufficient for
utilization in modeling the defined beach and inlet management alternatives, specifically for
comparative assessment and ranking of the performance of each alternative. As part of the
alternatives analysis, a detailed modeling report was prepared on behalf of the City and
submitted to the FDEP and USACE in support of the Project design and permitting (CEC, 2011).
9 January 16, 2013
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Attachment A
Hideaway Beach Erosion Control Project
8 Alternatives Analysis
8.1 Introduction
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Proportionality Analysis
The next step in the design and permit process was to model several alternatives and compare
and contrast the results. The alternatives were simulated using the calibrated and validated
MIKE21 model. These alternatives included but were not limited to:
1) No Action
2) Beach fill with T- groins (Figure 6). The T- groins are cited such that their T -heads are aligned
with the 1990 shoreline position in an effort to restore the shoreline to pre- erosion control
management implementation on Hideaway Beach as well as prior to the loss of Coconut
Island which afforded protection to this shoreline segment. Further, according to the analysis
of historic shoreline trends, North Beach was stable between 1990 and 1997. The toe of the
fill is located approximately 20 feet landward of the steep river slope to avoid direct losses of
the fill into the channel.
Figure 6. Beach Fill with T- Groins Alternative Design Plan.
10 January 16, 2013
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Attachment A
Hideaway Beach Erosion Control Project
8.2 Model Results
2/12/2013 16.A.20.
Proportionality Analysis
The No Action Alternative was chosen as a baseline alternative to which model results of the
other alternatives were compared. It should be noted that due to model instabilities,
approximately 10 months of the 1 -year simulation period were achieved. Figure 7 presents the
comparison of morphologic elevations and volume change quantities within the beach fill
between the two alternatives at the end of the 10 -month simulation. This comparison was created
by subtracting the 10 -month modeled surfaces. The comparison indicates that for the No Action
Alternative there was a loss of approximately 5,400 cubic yards of sand within the beach fill
template; and that for the Beach Fill with T- Groins Alternative there was a loss of approximately
4,200 cubic yards of sand within the beach fill template. Based on the model results, Beach Fill
with T- Groins Alternative reduced the losses from the beach fill by approximately 22 %.
Figure 7. Analysis of Morphologic Changes and Volumetric Quantities.
11 January 16, 2013
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NO ACTION ALTERNATIVE
8
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Figure 7. Analysis of Morphologic Changes and Volumetric Quantities.
11 January 16, 2013
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Attachment A 2/12/2013 16.A.20.
Hideaway Beach Erosion Control Project Proportionality Analysis
Numerical modeling of the No Action Alternative resulted in deposition of approximately 1,800
cubic yards of sand within the permitted borrow area limits over a 10 -month simulation period,
which is equivalent to a shoaling rate of approximately 2,200 cubic yards per year. Comparing
this to the potential shoaling rate taken from measured results (Section 6.3), the model results are
very realistic, and confirm the design maintenance dredge interval.
9 Proportionality Analysis
9.1 Benefits Analysis
Two methods are examined to predict the reduction in the entrance channel infilling from
installation of the three T- groins along the North Beach segment.
9.1.1 Numerical Modeling Approach
First, the results of the numerical model study developed by the consulting team for the design
and permitting were examined to compare the No Action Alternative to the Beach Fill with T-
groins Alternative. The model results predicted the structures will reduce the beach fill losses by
approximately 22 %. It is noted that due to the time constraint in preparing this analysis, a model
run with beach fill only (i.e. no structures) was not achievable. It is suggested that the placement
of beach fill without structures compared to the beach fill with structures would show similar
results or quite possibly show that the structures have a higher percent retainage of fill. Thus the
22% is assumed to be the minimum benefit afforded by the structures for reducing the infilling
into the entrance channel.
9.1.2 Empirical Approach
Second, the performance of the existing T -groin field was reviewed to quantify the benefits the
T- groins provide in retaining the sand within the fill template. Humiston and Moore (H &M)
have completed long -term monitoring surveys and reports for the T -groin projects along
Hideaway Beach for over a decade. As part of the post - construction report of the 2010 project,
H &M (2011) reported that the T -groin field constructed in 2005 along Royal Marco Point
retained approximately 76% of the original fill volume after four years and approximately 81%
of the original fill volume after five years noting that 3,000 cubic yards had been added to this
segment by virtue of the 2010 construction project. The current Project utilizes the same design
principals as the 2005 and 2010 projects, and the performance of the T -groin field along North
Beach is predicted to perform similar to the rest of the T -groin field. Thus the 76% is assumed to
be the maximum benefit afforded by the structures for reducing the infilling into the entrance
channel.
9.2 Dredge Cycles
Table 2 presents a summary of dredge cycles and number of events computed for the Project life
defined as the life of the structures which is equal to 25 years. The maintenance years are
computed from 2012, the date of the last maintenance event. The 25 -year period begins in 2013,
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Attachment A 2/12/2013 16.A.20.
Hideaway Beach Erosion Control Project Proportionality Analysis
corresponding to the new T -groin installation, and ending in 2038. Based on the design
maintenance dredge cycle of 4.2 years, the summary begins with the 4 -year cycle.
Table 2.25 -Year Period Summary of Dredge Cycles and Number of Maintenance Events
Cycle
Maintenance Years *
Number of Events **
4 -Year
2016, 2020, 2024, 2028, 2032, 2036
6
5 -Year
2017, 2022, 2027, 2032, 2037
5
6 -Year
2018, 2024, 2030, 2036
4
7 -Year
2019, 2026, 2033
3
8 -Year
2020, 2028, 2036
3
9 -Year
2021, 2030
2
* Measured from 2012 — date of last maintenance dredge event
** Within 25 -year project life (2013 -2038)
Based on the two approaches, the benefits the structures will provide ranges from a 22%
reduction to a 76% reduction in erosion off North Beach and alongshore into the channel.
Applying these percent reduction rates, a four year dredge cycle (6 events) would extend to 4.9
years (5 events) and 7.0 years (3 events) respectively. This equates to a reduction of one to
possibly three maintenance events within the period of analysis.
Similarly, a five year dredge cycle (5 events) would extend to 6.1 years (4 events) and 8.8 years
(2 events) respectively. This equates to a reduction of one to possibly three maintenance events
within the period of analysis.
9.3 Cost Savings
The construction cost for the 2012 dredging project was $262,000. The design and permit costs
were approximately $50,000. The construction administration and monitoring /reporting costs
were $20,000. This equates to a total project cost of $332,000 in 2012 dollars. Future
maintenance dredge costs are presumed to be slightly less than the 2012 project noting the design
and permitting tasks will be able to take advantage of the extensive work completed to permit the
project as well as the Erosion Control Project. It is assumed the maintenance event costs will be
$315,000 in 2012 dollars.
Applying the reduction in the number of maintenance events computed above, ranging from one
to possibly three events, the cost savings from installation of the T- groins ranges from $315,000
to $945,000. The scenarios analyzed above include the likelihood of reducing the number of
events by two within the 25 -year period of analysis. Therefore, the recommended proportionality
analysis is a cost savings to the future maintenance dredge program of $630,000.
It is noted that the City has borne the cost of the design and permitting for the Project, on the
order of $300,000. There are three major components to the Project: beach fill, structures, and
borrow areas. Using a simple assumption of equality, the assumed cost for the design and
permitting of the structures is $100,000.
11—IN Thus the proportional public benefit is recommended as $730,000.
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Hideaway Beach Erosion Control Project
10.0 Conclusion
Attachment A 2/12/2013 16.A.20.
Proportionality Analysis
A Proportionality Analysis was completed in support of the City of Marco Island's TDC funding
application for erosion control structures. The analysis was based on existing data, analyses,
modeling results, and experience of the consulting team and City representatives.
To date three maintenance projects have been completed by the County at the Collier Bay
Entrance Channel. The dredge quantity ranged from 9,300 cubic yards to 24,100 cubic yards and
one event included installation of the terminal jetty.
Based on the coastal processes assessment, the design maintenance dredge volume and dredge
interval are 9,600 cubic yards and 4.3 years respectively.
Some of the results from the detailed numerical model study developed by the City's consulting
team in support of the Project design and permitting were utilized in the analysis. The channel
shoaling rate and thus the dredge interval were verified through comparisons with the measured
data. The minimum benefits to be derived from installation of the structures were quantified
through the modeling results which predicted a 22% reduction in the beach fill erosion rate when
compared to the No Action Alternative. The maximum results were set based on the historic
monitoring and reporting by the City's outside consultant (H &M) who demonstrated that the
existing T -groin field as retained over 76% of the original beach fill volume after 4 to 5 years.
Applying these benefits to the design dredge interval, it is predicted that the dredge cycle will
increase from one to possibly four years; equating to a reduction in the number of maintenance n
events from one to possible three events within the Project life defined as 25 years.
The reduction in the number of maintenance dredge events equates to cost savings. Based on the
2012 maintenance dredge event total project cost, the estimated savings for one event is
$315,000 and for three events is $945,000. Using averages and including one -third of the design
and permitting costs, the proportionality analysis yields a recommended total cost for the public
benefit equal to $730,000.
11.0 References
Coastal Engineering Consultants (CEC). 2011. Joint Coastal Permit Application, Attachment XI
"Coastal Systems Assessment" and Attachment XII "Alternatives Analysis." Submitted to FDEP
and USACE in support the Hideaway Beach Erosion Control Project.
Humiston and Moore Engineers (H &M). 2011. Hideaway Beach Nourishment & T -Groin
Erosion Control Project Phase II, One Month Post Construction Monitoring Summary Report 1,
DEP Permit 0222764 - 006 -EM, March 2011.
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