Thursday, January 15, 2015

Stump Pass 10-Year Beach & Inlet Management Plan

We'd like to thank Robin Madden for sending the following report regarding the local erosion control program that has been ongoing since 2001.

Stump Pass 10 YR Beach and Inlet Management Plan 5/20/14


1. Introduction ....................................... 1
2. Project History.................................... 2
3. Way Ahead ......................................... 4
4. Project Status ..................................... 5
5. Projected Timeline ............................. 5
Figure 1. Project Location Map. ............. 6

1. Introduction

The Project includes providing erosion control and shoreline stabilization measures including beach nourishment, maintenance dredging and bypassing, and stabilizing structures for six miles of eroding gulf and inlet shorelines within the Manasota Barriers, Charlotte County utilizing inlet channel, nearshore, and offshore borrow areas. A Project location map is presented in Figure 1.
The northern Project Boundary shall be Chadwick Park, the County’s public beach park, located approximately 100 feet south of Florida Department of Environmental Protection (FDEP) Reference Monuments R-9 extending south and encompassing the Stump Pass Beach State Park to Stump Pass. The Project continues on Palm-Knight-Bocilla-Don Pedro Islands extending from approximately 1300 feet northeast of R-22 along Stump Pass’ southern inlet shoreline and then along the gulf-front shoreline to the southern end of the development. The southern Project Boundary shall be the north limit of the Don Pedro State Park located approximately 600 feet south of R-40.
The Project features include the following components:
Initial Construction:
• Restore critically eroding beaches on Manasota Key (Updrift Beach Fill-UBF), Palm Island (North Beach Fill-NBF), and Knight-Don Pedro Islands (South Beach Fill-SBF) utilizing offshore sand resources and inlet channel bypassing; and
• Install stabilizing structure on the south end of the Stump Pass Beach State Park to mitigate for inlet maintenance impacts.
Future Construction and Adaptive Management Plan:
• Maintenance dredge Stump Pass for navigation purposes;
• Bypass sand from maintenance dredging onto the NBF and backpass available sand from maintenance dredging to UBF for the purposes of offsetting erosion of the adjacent shorelines, balancing the sediment budget between the inlet and adjacent shorelines, and maintaining the location and hydraulic stability of the navigation channel;
• Install stabilizing structures on the NBF in the event future monitoring depicts beach renourishment and sand bypassing from maintenance dredging does not stabilize this segment of shoreline or provide necessary storm damage reduction benefits for the upland properties as part of the Adaptive Management Plan;
• Place sediment on the ebb shoal in the event the physical monitoring results determine additional sediment will contribute its reformation as part of the Adaptive Management Plan;
• Additional adaptive management activities including adjusting permeability of stabilizing structure on UBF, minor stabilizing structure repairs, filling scour holes adjacent to the stabilizing structures, sand sharing (transferring sand from accretional areas to erosional areas), and maintaining water quality in Rum Cove lagoon; and
• Maintain the UBF, NBF and SBF through renourishment using offshore sources.

2. Project History

Beach Erosion Study (BES), Joint Project between Sarasota and Charlotte County, 2001-2003
Sarasota and Charlotte Counties teamed together to conduct a regional study on beach erosion and develop alternatives to address identified erosion problems. The Consulting Team comprised of Coastal Technology Corporation (CTC) and Coastal Engineering Consultants (CEC) provided the engineering, geotechnical, survey, and environmental services. The BES scope included the following: severity of erosion analysis, risk assessment, alternatives assessment, conceptual designs, and funding analyses (CTC & CEC, 2003).

The severity of erosion analysis examined the accretion and erosion trends and yielded a sediment budget extending from the north county line for Sarasota County to the south county line for Charlotte County for the time period of 1974 to 2001. Specific to this Project, the sediment budget defined the Stump Pass inlet impact on the order of 35,000 cubic yards per year (CY/YR) comprised of the ebb shoal, flood shoal, and Manasota Key spit growth rates noting the
Inlet Management Study (IMS) completed by CEC (2001) determined the bypass quantity around the inlet was negligible and listed published rates for the net longshore transport rate ranging from 30,000 to 50,000 CY/YR.

Utilizing the cross-shore sediment transport model, SBEACH, a risk assessment was completed for the 10, 20 and 50 year return period storm events for each critical erosion area. Specific to the Project area, the estimated storm damages for Knight – Don Pedro gulf-front properties ranged from $13.4 Million (10-Year) to $14.8 Million dollars (50-Year) in 2003 dollars.

Specific to the Knight Island – Don Pedro Island Planning Area, conceptual plans were developed for two alternatives. Both included beach restoration of the NBF and SBF. The first alternative was consistent with the recommendations of the IMS (CEC, 2001); the second alternative included an enhanced storm protection component and extended the fill to the south to include a third critical erosion area on Little Gasparilla Island.

Erosion Control Projects, 2003-Present:

Utilizing the same Consulting Team, between 2002 and 2003, Charlotte County applied for and obtained permits to conduct beach restoration of the critically eroding beaches adjacent to Stump Pass utilizing inlet and nearshore borrow area sources. The original Joint Coastal Permit (JCP) Application included the recommended alternative from the 2001 IMS / first alternative from the 2003 BES. During the permit process the emphasis of the project changed from one of navigation to one of erosion control / beach restoration; thus the application was modified to include the enhanced storm protection component for the NBF and SBF. Further, a dune system was incorporated into the SBF design to address concerns from the Florida Fish and Wildlife Conservation Commission.

Due to the increase in volume to be dredged from the inlet sources to accomplish the enhanced project, an advanced mitigation component was developed among the FDEP, Florida Park Service (FPS), Charlotte County, and Consulting Team. Specifically, place the necessary volume of sand on the UBF to offset the erosion losses on the Stump Pass Beach State Park directly attributable to the project’s excavation of the primary borrow area. As part of the permit process, the Consulting Team defined the average annual net longshore transport rate of 30,000 to 35,000 CY/YR at Stump Pass. The advanced mitigation component was then set equal to 100,000 CY equal to approximately three years times the average annual rate.

Initial construction of the County’s Erosion Control Project was completed in 2003. A total of approximately 925,000 CY of sand were excavated and placed in the three permitted beach fill areas including the advanced mitigation component of 100,000 CY on the UBF. Dunes were constructed on a portion of the updrift beach fill and south beach fill. The sand placement created acres of sea turtle and shorebird nesting habitats. Dredging of a hydraulically efficient inlet channel increased the cross-sectional area and tidal velocities, restoring the tidal prism to historic levels measured in the early 1980s.

In 2006, Charlotte County received authorizations for and completed construction of their Post-Storm Recovery & Maintenance Project to offset significant erosion losses attribute to the hurricanes of 2004 and 2005. The Project restored three critically eroding beach segments totaling 3.2 miles along Manasota Key, Knight Island and Don Pedro Island, using approximately 450,000 CY of sand including the advanced mitigation component of 145,000 CY on the UBF. Dunes were restored on portions of the south beach fill. An improved project was completed and FEMA reimbursement was received for the eligible costs associated with the 2004 hurricane damage.

In 2010/2011, Charlotte County received authorizations for and completed construction of their Post-Storm Recovery & Maintenance Project to offset erosion losses from recent storm events (e.g. Tropical Storm Fay) and to implement the permit required advanced mitigation requirement. A secondary component of the project was to restore the hydraulic efficiency of the inlet by placing additional sand along the north beach fill, forcing tidal flow through the dredged alignment. The project restored three critically eroding beach segments totaling 3.2 miles along Manasota Key, Knight Island and Don Pedro Island, using approximately 374,000 CY of sand including the advanced mitigation component of 156,000 CY on the UBF. Dunes were restored along the south beach fill. Over 4 acres of shorebird habitat were created including placement of 12,000 CY of sand to enhance low-lying beach area adjacent to the existing lagoon. An improved project was completed and FEMA reimbursement was received for the eligible costs associated with the storm damage.

3. Way Ahead

In April 2009, representatives of the County, FPS and FDEP met on site and discussed the opportunity to partner on a feasibility study for the stabilization of South Manasota Key. FPS’ preference is to maintain the natural system to the extent possible recognizing that the southern segment of the Stump Pass Beach State Park will continue to be affected by the presence of the inlet and management thereof, thus some type of stabilizing influence may be necessary. Based on the draft scope of work for such a study prepared by FPS in March 2007, the discussions from the 2009 meeting, discussions from the subsequent meeting (January 2010) held in conjunction with the permit processing of the 2011 project, and recent meetings and discussions among the County, Beach Committee, and FPS; it was recommended that the study include an analysis of modifying the Primary Borrow Area via channel size, shape, alignment and depth revisions; analysis of stabilizing influences such as a terminal structure or groin field, and evaluation of the structural complements utilizing the following parameters:

• stabilizes the southern tip of Manasota Key,
• is minimally intrusive,
• requires minimal maintenance,
• is adjustable if possible,
• increases dredging interval and thereby is cost effective, and
• possibly even creates some habitat.

The County has expressed its commitment to partner with the FPS and FDEP. To that end, the County has embarked on the next 10-Year Management Plan utilizing its local dedicated funding sources to fund the Study. The County and its Consulting Team (CEC and CTC) have held numerous stakeholder meetings including two with the FDEP and FPS staff to date to keep them apprised of the progress of the work and seek input and recommendations as to formulation of alternative plans and approaches. Further, the County is pursuing an Offshore Sand Source Search for the purpose of identifying beach compatible sand sources as an alternate to using Stump Pass and ebb shoal complex to address the County’s long-term sand needs. This work follows the 2003 BES desktop analysis of potential sand sources.

The County has undertaken extensive stakeholder outreach as an integral component of developing the new long-term management plan. Together with the Consulting Team, the County has arranged, prepared for, and attended over a dozen major stakeholder meetings comprised of the kick-off meeting, Board of County Commissioner meetings, County advisory committee meetings (Beaches and Shores, Parks and Recreation, Marine Advisory), resident and stakeholder meetings (Manasota Key, Palm-Knight-Don Pedro Island), and meetings / webinars with the state agencies (FDEP, FPS). The County has also posted on their website all of the published reports and milestones for access by the general public. Lastly, the County has shared the details with the local media who have published newspaper articles on the progress.

4. Project Status

A Joint Application has been submitted in May 2014, that through development of a stabilizing structure for the south end of Manasota Key and the identification of offshore sand sources, will redefine the next 10-Years of management for Sump Pass, eliminating the need for advanced mitigation, and making Manasota Key an integral part of the overall County Erosion Control Project.

5. Projected Timeline

• May 2014- April 2015 Permit Processing with FDEP & USACE
• June 2015 FDEP Permit complete
• July 2015 USACE Permit complete
• July - October 2015 Bid Process, Contract Procurement & Mobilization
• November 2015 - Commence Construction

6. Updates Online
Link to State Permit Application Site

Figure 1. Project Location Map.

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