This project will initiate the development of a stormwater quantity and quality assessment method in watersheds with shallow water tables that are undergoing land-use change in southeastern US coastal landscapes. In coastal areas with shallow water tables and low gradient topography, surface and groundwater coupling complicates the feasibility of pre- and post-development flow prediction, including peak flow rates, using the Soil Conservation Service curve numbers (CN) method. This interaction also potentially diminishes the effectiveness of wet detention ponds for water quantity and quality management due to groundwater influence while reducing the potential soil water storage and, consequently, the effectiveness of infiltration practices due to shallow soil saturation and impeded percolation. In short, groundwater-surface water interactions (pathways and contributions of each during a storm event) in coastal areas with shallow water tables are not appropriately considered in current pre- and post-development flow assessments and in the stormwater management practice selection and design process.
There are five objectives of this proposed work (1) to quantify hydrologic interactions (surface and groundwater) and develop storm hydrograph separation techniques for two comparable headwater streams draining coastal watersheds using natural hydrologic tracers (geochemical end-member mixing analysis), (2) to compare and contrast the interactions within and between the two comparable watersheds (one is slated for and is partially comprised of existing development, the other has no existing or planned development), (3) to determine feasibility of assigning SCS CN within these watersheds for rainfall-runoff estimates, (4) to determine the general feasibility of installing infiltration practices versus wet detention ponds based on hydrologic interactions, and (5) to disseminate these results to regulatory agencies, local county and municipal officials and planning and public works staff, and other professional decision-makers, such as developers, engineers, and landscape architects.