30 Minute Presentation
Caswell Beach Dune Infiltration System: An Innovative Approach to Address Road Flooding for Coastal Towns
The only accessible roadway serving the majority of Town of Caswell Beach, Caswell Beach Road, experiences significant flooding during moderate rain events and becomes impassable to low-clearance vehicles for up to 8 hours. In severe rain events, this access becomes impassable to even high-clearance emergency vehicles, presenting a public safety concern during storm events. While the Town currently utilizes a portable pump attached to a fire truck to pump this stormwater to the adjacent sound, this process is very time and labor intensive and is estimated to occur at a frequency of at least four times per year. This road flooding also presents a significant economic impact to the Town, as the Town relies heavily on beach tourism and wants to maintain visitor access to the main tourist destinations, including the Oak Island Lighthouse, North Carolina Baptist Assembly and several public beach accesses.
By utilizing a similar approach developed by the NCDOT and NCSU at Kure Beach, WK Dickson is assisting the Town with planning, designing and constructing a Dune Infiltration System (DIS) that will accept and infiltrate this stormwater. The infiltration site, located on a Town-owned parcel adjacent to the Oak Island Lighthouse, will contain approximately 525 square feet of buried infiltration high-density polyethylene chambers (approximately 105 chambers) that can store the stormwater until it can absorbed by the groundwater after filtering through the dune sand. The DIS will be buried at least five feet within the primary dune system and dunes will be rebuilt on top of the chambers and revegetated accordingly. This new system will allow the Town to pump out the low points along their primary road, increasing the ability for the Town to respond to emergencies during and immediately after storm events and provides an opportunity to safely infiltrate stormwater runoff.
A groundwater mounding analysis was also evaluated as part of this project to ensure that the infiltration stormwater did not have an adverse impact on adjacent properties, specifically impacting existing septic fields. Existing soil infiltration rates and depth to Seasonal High-Water Table (SWHT) was incorporated into this mounding analysis to ensure that the appropriate groundwater flux would match or exceed the proposed stormwater inflow to the DIS chambers. This mounding analysis ensures that this infiltrated water would not backflow into the chambers or cause lateral flooding back onto the primary roadway.
This case study will review the main design considerations and site constraints that a community should consider when determining the installation feasibility of these systems.