Isle of Palms BRIC Grant Application - Public Notice
The Federal Emergency Management Agency (FEMA) and South Carolina Emergency Management Division (SCEMD) have received the City of Isle of Palms’ application for Federal grant funding through the Building Resilient Infrastructure and Communities Program (BRIC).
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 City of Isle of Palms’ proposed project which contains actions in or affecting the floodplain and/or wetlands. The project will conform 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: City of Isle of Palms
Project Title: 41st Avenue Outfall & Waterway Boulevard Pathway Improvements
Location of Proposed Work: The proposed work will extend from 21st Avenue to 41st Avenue for approximately 1.68 miles, and along 41st Avenue and Waterway Boulevard.
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; and
- Legal constraints that could have impacted project execution.
Proposed Work and Purpose:
The City of Isle of Palms is experiencing increased occurrences of flooding due to heavy rainfall events, extreme high tides, sea level rise, high-water table conditions, and more intense coastal storms. These conditions, combined with an inadequate drainage system, have created flooding conditions throughout the City. In response, the City intends to implement a stormwater improvement project in two areas:
Project Area 1: Phase 3 Drainage Outfall Improvements – 41st Avenue Outfall
The 41st Avenue basin serves approximately 93 acres and consists of mainly residential with some commercial area and includes a fire station. The proposed drainage improvements will maintain existing drainage patterns which convey stormwater under Waterway Boulevard., along 41st Avenue, and discharge to the to the Intracoastal Waterway. The improvements will include approximately 218 LF of pipe improvements, channel improvements, 4 replaced/new structures, riprap outfall and erosion protection, and tide backflow prevention.
The total project disturbed area is 1.0 acres. Portions of the proposed improvements are located within SCDOT right-of-way including Waterway Boulevard. and a portion of 41st Avenue. The remaining portions of the proposed improvements ae located along the locally owned portion of 41st Avenue from Waterway Boulevard. to the Intracoastal Waterway.
The project is located in FEMA Flood Zone AE, which covers nearly the entire City of Isle of Palms. The project site is located in a tidally influenced roadside ditch that drains to the Atlantic Intracoastal Waterway. This roadside ditch is designated as Section 404/ Section 10 / SCDHEC-OCRM Critical area. The proposed improvements will take place within the existing roadside ditch, which serves as the outfall for the contributing drainage system. The proposed improvements are required order to provide the necessary capacity for the stormwater system. The impacts represent the minimum necessary to meet the project purpose.
The proposed impacts include channel excavation; minor fill resulting from the installation of the new junction box, pipes, and riprap; and draining roadside ditch (elimination of tidal influence) from the installation of backflow prevention measures. The backflow prevention measures will provide protection from tidal flooding of key infrastructure upstream including roads, a fire station, and private residences. Stormwater best management practices will be used during construction.
The City plans offset the impacts to the vegetated portions of the ditch through the purchase of third-party mitigation credits from an approved mitigation bank servicing the site location.
Project Area 2: Waterway Boulevard. Pathway Improvements
The City intends to improve the Waterway Boulevard. Pathway to serve as a flood barrier to provide protection from tidal intrusions from the Intracoastal Waterway (north) side of the island.
This project corridor extends from 21st Avenue to 41st Avenue and is approximately 8,850 LF (1.68 miles). The proposed pathway improvements include raising the pathway to elevation 6.0’ (NAVD88) to provide protection from extreme tides and sea level rise. Portions of the existing pathway are below elevation 5, and as low as 4.27 and have experienced overtopping from extreme tide events on numerous occasions. The proposed target elevation was selected because it reduced the annual probability of exceedance (overtopping) from 100% to 3.7%. This is based on the historical data for the NOAA Tide Gage in the Charleston Harbor (Station 8665530).
The proposed pathway will also be widened from 5’ to 8’ to be improved from a standard sidewalk to a multi-use pathway. Additional improvements include localized drainage improvements to convey stormwater runoff captured along Waterway Boulevard. under the pathway. Proposed improvements also include the installation of in-line check valves on all pipes along the corridor that discharge under the pathway to the Intracoastal Waterway. The check valves will serve to prevent tidal backflow in the drainage system and eliminate sunny day flooding as well as preserve the capacity in the drainage system.
Most of the proposed pathway improvements are located within SCDOT right-of-way along Waterway Boulevard. Some portions of the proposed improvements will be in drainage easements on Wild Dunes Golf Course Property.
The project is located in FEMA Flood Zone AE, which covers nearly the entire City of Isle of Palms. This project results in no impacts to wetlands.
The proposed improvements will require localized fill within the FEMA floodplain, along the project corridor, to provide a protective barrier for rising sea levels and tidal intrusion. This project will not result in adverse impacts to any adjacent properties.
No mitigation is required for this project.
Project Area 1: Five alternatives were considered for this project: 1) Do nothing; This alternative was not chosen because, while the total project cost was lower; it would not alleviate the flooding in the project area; 2) Incorporate regional detention facilities; This alternative was not chosen because of the densely developed study area elevation of the ground water 3) Install storm water pump stations; This alternative was not chosen because it is very expensive and relies on electricity which may be lost during a severe storm event 4) Design the project with a lower year storm event (10-year); This alternative was not chosen because although cheaper, it did not provided the necessary capacity required to meet local regulations for permitting; and 5) Design the project with a higher design year storm event (25-year). This alternative was selected because it would alleviate flooding in the project area for the design storm. Additionally, Charleston County and SCDOT require the 25-year storm event; otherwise, the City would not be able to obtain approval for the required permits. Therefore, Alternative 5 was chosen.
Project Area 2: Six alternatives were evaluated for this project: 1) Do nothing; 2-6) Raising the pathway to elevations 5, 5.5, 6., 6.5, and 7 (NAVD88) was evaluated for effectiveness, feasibility, permit ability, and constructability. The do nothing alternative would cost nothing but would allow for continued tidal flooding of roads and residential structures numerous times each year, with increasing occasions as sea levels continue to rise. It was determined that raising the pathway to elevation 6 (9.14 ft. gage) was feasible while providing the most cost-effective level of protection. The selected target level of protection corresponds to approximately the 25-year event. This target elevation eliminates nearly all sunny-day flooding currently experienced.
The comment period is from October 28, 2021, through November 12, 2021. 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 Desirée Fragoso, 1207 Palm Boulevard, Isle of Palms, SC 29451
or by email to firstname.lastname@example.org. Comments are due by close of business on November 12, 2021.
A map of the project areas is available here and is also available for public inspection at 1207 Palm Boulevard, Isle of Palms, SC 29451.
Point(s) of Contact:
For additional information, please contact: Desirée Fragoso, City Administrator at email@example.com or (843) 886-6428.