The Hampton Roads Sanitation District (HRSD) provides wastewater services to 1.7 million people in southeast Virginia. The low topography, regional climatology, and coastal proximity of this region make many of HRSD’s pumping and treatment facilities vulnerable to flooding. This vulnerability is increasing with climate change and rising sea levels, increased storm surge, and greater rainfall recurrence frequency. HRSD facilities are located over a wide expanse of over 3,000 sq. miles, posing a significant challenge to accurately determine flood elevations. To make these large-scale analyses both accurate and practicable, a tiered framework of flood risk evaluation was adopted to account for susceptibility to coastal, pluvial, and/or fluvial flooding. Based on flooding type, site-specific exposure was computed using hydrodynamic models. Storm surge elevations utilized the high-fidelity models employed by USACE for the North Atlantic Coast Comprehensive Study. Pluvial and fluvial flood elevations were determined using two-dimensional hydraulics in HEC-RAS and by expanding on available base flood elevations published by FEMA, respectively.

 

The flooding exposure evaluations completed as part of the HRSD Climate Change Planning Study are intended to support subsequent vulnerability assessment and mitigation analysis planning tasks. The completed analyses can be updated in the future to include additional detail for designing and implementing site-specific mitigation measures.