MOUNT PLEASANT, S.C. (Dec. 1, 2020) - The Town of Mount Pleasant is coordinating with South Carolina Department of Natural Resources and South Carolina Emergency Management Division to apply for non-disaster Hazard Mitigation Assistance funding through the Federal Emergency Management Administration’s Flood Mitigation Assistance and Building Resilient Infrastructure and Communities grant programs.
As part of the application process and in accordance with Executive Order 11988 and 44 CFR §9.12, final public notice is hereby given for the Town of Mount Pleasant’s proposed project which contains actions in or affecting the floodplain and/or wetlands. The project will conforms to applicable state and local floodplain protection standards
Funding for the proposed project will be conditional upon compliance with all applicable federal, tribal, state and local laws, regulations, floodplain standards, permit requirements and conditions.
Applicant: The Town of Mount Pleasant
Project Title: Old Village – Edwards Park Storm Water Basin
Location of Proposed Work: The proposed work will be in the Edwards Park storm water drainage basin. The Edwards Park basin drains approximately 131 acres. This basin serves approximately 434 residential properties and 3 commercial properties. The proposed drainage improvements will generally maintain the overall drainage patterns in the basin, however, a second outfall is being proposed as part of the improvements. Currently, stormwater is directed south towards Edwards Park where it flows into a stormwater pump station and is pumped down Ferry Street where it discharges into the marshes of the Charleston Harbor. The existing pump station is undersized to meet the design storm (10-year), and therefore an alternate gravity outfall corridor was identified that will divert approximately 3/5 of the contributing area from the existing pump station to a new outfall and allow the pump station to function at the intended design level. This new outfall will be located at the end of Queen Street, one block east of the existing pump
Planning Factors and Considerations:
Several significant factors were considered as part of this project, including, but not limited to:
- Impacts to the natural environment including changes to the floodplain and base flood elevation as well as natural habitats and native animal species;
- Consistency with local goals and initiatives to reduce impacts from natural hazards;
- The economic impact to the community
- Legal constraints that may impact project execution.
Proposed Work and Purpose: The purpose of this project is to mitigate the continuous flooding in the Edwards Park drainage basin. The required improvements in the Edwards Park basin will be approximately 12,617 linear feet of pipe and box culvert improvements/extensions; approximately 172 replaced/new structures (inlets, junction boxes, conflict structures, etc.); improvements related to delayed maintenance (mainly associated with swales and small driveway culverts); and pump station rehabilitation. The new gravity outfall will consist of a box culvert discharging into a plunge pool. The plunge pool will be armored with articulated concrete block matting and riprap. Many of the roads in the Old Village do not exhibit the originally intended typical road sections which included shallow roadside drainage swales. As the proposed infrastructure is installed and the right-of-way stabilized, part of the planned improvements will be to rehabilitate the road sections. The rehabilitation would aim to re-establish the roadside swales and provide positive drainage. Off-street parking within the right-of-way will be removed and driveways replaced with inverted sections to allow for positive drainage. Mitigation is achieved through this action and the avoidance of continuous flooding and damages to existing storm water structures and residential/commercial properties.
Option/Alternative #1 – The existing pump station at Edwards Park was to be expanded to 5 pumps instead of the 2 currently in place. This would have increased our capacity for stormwater conveyance to meet the 10 year storm event but would have increased our dependence on a mechanical system (pumps), increased maintenance costs and would have directed a significant amount of additional stormwater to one location that requires pumps.
Option/Alternative #2 – A second outfall was located which allowed 60% of the stormwater water to be taken off of the pump system required in Option/Alternative #1. This allowed us to reduce the improvements needed for the existing pump station by providing a piped, gravity system that is not dependent on pumping to move the water. Option/Alternative #2 was chosen because it eliminates the need for additional pumps, reduces the costs for pump maintenance, reduces the amount of water going to one location and moves a majority of the stormwater in the basin by gravity without relying on a mechanical system.
Comment Period: The comment period is from December 1, 2020 through December 16, 2020. Comments are solicited from the public; local, state or federal agencies; and other interested parties in order to consider and evaluate the impacts of the proposed project. The comments can be made in writing and addressed to Amanda Knight, 100 Ann Edwards Lane, Mount Pleasant, SC 29464 or by email to firstname.lastname@example.org. Comments are due by close of business on December 16, 2020.
Maps: A map of the project areas is attached and is also available for public inspection at 100 Ann Edwards Lane, Mount Pleasant, SC 29464
Point of Contact: For additional information, please contact: Amanda Knight, Emergency Management and Resilience Officer at email@example.com or 843-996-0030