Name
Rock Hill, SC - 1-D and 2-D hydraulic modeling to support flood mitigation
Date & Time
Wednesday, September 28, 2022, 11:00 AM - 11:30 AM
David Dickson
Description
Rock Hill, SC completed a city-wide watershed modeling initiative with the primary goals of identifying flood prone areas and creating a prioritized Capital Improvement Project program. The watershed modeling efforts include the development of hydraulic and hydrologic models for over 36,000 acres and hydraulic models for over 76 miles of stream. Data used included aerial photography, LIDAR topography, as-built plans, and field surveying. Hydrologic models were based on the NRCS methodologies within the Pond Pack platform. Hydraulic models (one-dimensional computations) were based on standard-step backwater computations within the HEC-RAS model. Floodplain mapping was performed using the HEC-GeoRAS platform. The Capital Improvement Project evaluation resulted in over one-hundred (100) projects. Typical solutions included infrastructure improvements such as pipe/culvert replacement and stream restoration/enhancement. Some project solutions included the conventional mitigation strategy of building removal from flood prone areas. For example, the solution recommendations for the College Downs Stormwater Improvement project included a combination of pipe/culvert improvements, floodplain improvements, stream enhancements, roadway removal and re-routing, and building purchase/removal. The Rock Hill mitigation strategy of building purchase/removal is voluntary. Rock Hill does not use the condemnation process to support building purchase/removal. Experience shows that property owners of buildings that suffer significant and frequent flood damage are willing participants; property owners of buildings that experience moderate flood damage elect to not participate. An accurate understanding of flood damages (depth, velocity, and floodway limits) for a stream reach and/or group of buildings is needed to focus the mitigation efforts. Buildings that experience significant flood damage are considered top priority and actively contacted. Buildings that do not experience significant flood damage are considered lower priority and are only notified via a mass mailing. For the College Downs project, the one-dimensional HEC-RAS model results were used initially to estimate flood depth and velocity and also define the floodway limits. Because the floodplain/floodway is relatively wide and flat, a two-dimensional model was developed to provide more detailed results. A comparison of the one- and two-dimensional modeling for flood depth, velocity, and floodway limit was completed. A building purchase/removal priority list was developed using both sets of model data. The model results were validated during discussions with property owners that recorded severity of flood damage and willingness of the property owner to participate in Rock Hill’s building removal mitigation program.
Location Name
National Harbor 4
Full Address
Gaylord National Resort & Convention Center
201 Waterfront St
Fort Washington, MD 20745
United States