Johns Island Flood Risk Assessment & Drainage Study

The City of Charleston commissioned Davis & Floyd to develop an island wide, 2D hydraulic model to quantitatively characterize site-level flood risk for existing and proposed developments. The overall project goal was to bridge the gap between site and regional scale stormwater while considering riverine and tidal flooding to prevent/alleviate site-scale flooding. We investigated impacts of sea level rise on the island.

We also developed a hydrologic & hydraulic model to investigate the causes of significant, frequent flooding of neighborhoods located in an approximately 500-acre drainage basin on Johns Island.

Johns Island Flood Risk Assessment

Davis & Floyd developed a 2D surface flow model (‘rain-on-grid’) to assess the potential flood risk for the island and used geospatial tools to identify significant watersheds on the island. We also developed flood risk zones for the 2-, 10-, 25-, 50-, 100-year, and 24-hour design rainfall events. Our team worked with the city to identify existing flooding concerns, proposed development, and areas of future growth to prioritize the basins for more detailed 1D/2D watershed assessment models. In addition, we completed GIS mapping and web applications to facilitate client communication, public outreach, and planning reviews for proposed development.

Barberry Woods Drainage Study

Davis & Floyd developed a dynamic hydrologic & hydraulic study using ArcMAP GIS tools, PCSWMM modeling software, historical rainfall records, and documented past flooding events to perform sensitivity analyses on the model. Our team coordinated with property owners and city stakeholders to compare the results of the model with observed flooding conditions. We modeled and identified solutions aimed at alleviating the flooding impacts while improving water quality.