Coupled Coastal and Riverine Risk Modeling - TNC Northcoast Project

The North Coast project in Georgetown and Horry Counties (SC) grew from TNC’s Coast Summit in 2016 where riverine flooding was highlighted as a problem that held opportunity for nature based mitigation projects. Geoscience Consultants was hired to provide an understanding of localized flood risk at present and under future climate change. This information will help community stakeholders identify locations where green infrastructure can be used to mitigate increasing flooding issues.

Four separate products were developed to inform the stakeholders in each county. Hindcasted flooding maps from Hurricanes Joaquin and Mathew depicted the extents of flooding that played a large part in developing the needs of the project. The ‘historical’ flooding extents were developed from high resolution elevation data and empirical data collected during these storms. Predicted and projected future flooding risk maps built on the empirical data and included time series information from tide and stream gages along with projections for sea level changes and extreme rain events. This information was analyzed using a z-score technique originally developed for use in NOAA’s SLR Viewer. The extents of the risk envelop are similar to FEMA’s special flood hazard zones but the technique provides results in discreet scores adding context. To help inform project ideas a ‘hydro land cover’ product was developed that includes flooding pathways and habitats where flooding is likely now and in the future. Finally, for emergency management, a storm surge risk product was developed from 64 Category 1 SLOSH outputs.

This is a significant amount of information for stakeholders to digest and use in developing ‘shovel ready projects’. To help, TNC is holding county-wide stakeholder meetings and has included the data in their online mapping portal.

See the Coastal Geotools ‘19 presentation

Example 2035 Flood Risk Map - Cool tones highlight more chance for inundation