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Stormwater

Johns Island Flood Risk Assessment / Barberry Woods Drainage Study

The City of Charleston engaged us 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 in order to prevent/alleviate site-scale flooding. Impacts of sea level rise on the island also were investigated. GIS web mapping tools were developed to aid the City in stormwater reviews and identify the need for drainage improvement projects. We also developed a hydrologic and hydraulic model to investigate the causes of significant, frequent flooding of neighborhoods located in an approximately 500-acre drainage basin on Johns Island.

Solutions

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 U=used geospatial tools to identify significant watersheds on the island. The team also developed flood risk zones for the 2-, 10-, 25-, 50-, 100-year, and 24-hour design rainfall events. They 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, the team developed GIS mapping and web applications to facilitate client communication and public outreach and planning reviews for proposed development.

Barberry Woods Drainage Study:

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

Services Provided

  • Drainage Study
  • Stormwater Master Planning
  • Hydrology & Hydraulic Design
  • Surveying
  • GIS Mapping
  • Public Involvement & Stakeholder Communication