Monitoring, Modeling, and Mapping Flood Events for Rivers into Winyah Bay D. R. Hitchcock, T. M. Williams, T. O’Halloran, B. Song Belle W. Baruch Institute of Coastal Ecology and Forest Science Clemson University Project Objectives • Collect available flood stage information from extreme storms • Develop/calibrate models for flood stages/volumes with the available data • Use predictive models explain flood stages/volumes where data do not exist • Quantify parameters for a model that fits measured and statistically estimated data • Develop outputs and tools for decision-makers and citizens • Deliver products to appropriate audiences 2015 - Joaquin brought highest historic rainfall event ever measured in coastal SC locations 2015 - More rainfall with Matthew 2018 - Florence delivered 150% of Matthew rainfall in many locations Winyah Bay Surface Water Sources USGS Gaging Stations From Dr. Tom Williams Clemson – Baruch Institute and USGS Realtime Water Data https://waterdata.usgs.gov/nwis/rt T T T T Low flow tidal limit Joaquin 2015 Matthew 2016 Florence 2018 All USGS gaged water levels adjusted to same datum (NAVD88) Major flood response on Black River from Joaquin Rainfall distribution greatly affects differences in Little Pee Dee and Waccamaw stage/flows 3 What Did We Observe? • Dampened or decreased river stages for Pee Dee and Waccamaw downstream of Bucksport • Downstream channel widens and more expansive floodplain areas between the Pee Dee and Waccamaw • Downstream tidal effects dissipate peak flows • Floodplain and wetland areas helped buffer peak flows • Timing is everything! • We are all still learning from these unprecedented events to help us better predict future flooding and storm impacts Matthew vs. Florence Flooding Above Bucksport Great Pee Dee River Little Pee Dee River Lynches River Waccamaw River USGS Gauge What Have We Learned So Far? ▪ Winyah Bay estuarine and tidal river system flooding have both riverine and tidal components ▪ Discerning the point of flow stagnation where upstream tidal flow balances downstream river discharge determines flooding depths ▪ Subtle differences in floodplain geomorphology resulted in vast differences in flood attenuation between Hurricanes Matthew and Florence ▪ Data on channel and floodplain morphology will be most important to accurately forecast future flooding Where Do We Go From Here? • Continue HEC-RAS model - channel estimation in tidal river sections. Model output to be incorporated into visual communication tools • SC Water Resources Journal article (draft shared with USFWS, TNC with interest in regional flood attenuation by natural land management) • Continue to work with Georgetown County GIS department on county flood preparations • Seek funding for long term data collection on stage/discharge in Lower Pee Dee Basin. To our knowledge, NO discharge data were collected in Georgetown County during these historic storm events Acknowledgements • Funding from Clemson Public Service and Agriculture (PSA) • Support from SC Water Resources Center • Brian Williams – GIS technician, Clemson – Baruch Institute • USGS Realtime Water Data - https://waterdata.usgs.gov/nwis/rt • Georgetown County GIS Department THANK YOU!!! For more info, please contact me: [email protected] Also visit: www.clemson.edu/baruch.