Coastal infrastructure is threatened by increased erosion associated with rising sea levels and coastal subsidence and is exacerbated by major meteorological events such as Hurricane Sandy in 2012.
Beach replenishment via the placement of sand (from borrow sources) is the predominant method for mitigating coastal erosion and is extremely expensive. Borrow sources are finite and the use of sand dredged or pumped from borrow sources is not sustainable in the long term. BMT Designers & Planners is evaluating the use of innovative alternatives for the mitigation of coastal erosion including passive dewatering systems.
Passive dewatering systems allow the water in the subsurface of the beach to drain more rapidly than a beach without the system. Pore fluids, in this case groundwater or sea water, occupy pore space between sand grains in the subsurface of the beach. These pore fluids exert a pressure (pore pressure) on the surrounding sand grains. This pressure reduces the sheer stress and normal stress between sand grains that hold the sloped beach together. The reduced stress between grains makes them more susceptible to erosion (less energy is required to erode the sand). Passive dewatering systems can be effective in reducing beach erosion and in some cases result in the accretion of sand; however, the effectiveness of these systems has not been evaluated in the Mid-Atlantic States.
The evaluation and demonstration of the technology is considered essential to the advancement of the passive dewatering system technology in the Mid-Atlantic. BMT Designers & Planners is proposing to conduct Pilot Studies to collect beach specific information to assess the potential for passive dewatering system effectiveness. Upon favorable results, BMT Designers & Planners would recommend a larger scale passive dewatering system to quantify the effectiveness of the passive dewatering system. The Passive dewatering systems have the potential to mitigate coastal erosion at a fraction of the cost of traditional beach replenishment projects.