Water and Nutrients Exports during an Extreme Flooding Event in South Carolina
Monday, 23 January 2017
Ballroom II (San Juan Marriott)
Shaowu Bao1, Hongyuan Zhang1, Martin Tsz-Ki Tsui2, Alexander Ruecker3, Habibullah Uzun4, Tanju Karanfil4 and Alex T Chow3, (1)Coastal Carolina University, School of Coastal and Marine Systems Science, Conway, SC, United States, (2)University of North Carolina Greensboro, Greensboro, NC, United States, (3)Belle W. Baruch Institute of Coastal Ecology and Forest Science, Georgetown, SC, United States, (4)Clemson University, Clemson, SC, United States
Abstract:
In October 2015, a torrential rain event caused extensive flooding in a short period in the coast of South Carolina, resulting in a large volume of water flushing nutrients, such as dissolved organic carbon (DOC) and total Hg (THg), from the forested coastal wetlands into the coastal rivers, and eventually exporting to the ocean. To estimate the total water discharge and nutrients exports from this flooding event, we applied a hydrological model, WRF-Hydro, to simulate the flooding event with a focus on Winyah Bay, South Carolina, which is the third largest watershed in the east coast of the US. Precipitation rate derived from radar reflectivity was used as the main meteorological forcing input, along with near surface air temperature, humidity, and wind speed, pressure and incoming shortwave and longwave radiations data from NASA’s Land Data Assimilation Systems (NLDAS). A high-resolution terrain routing grid was created using the National Hydrography Dataset (NHD). Surface flow due to surface runoff, baseflow due to underground runoff, and the stream flow rate on the routing grid along rivers were modeled validated with USGS measurement data.
In addition, we also collected water samples along the hydrograph of the flooding event in Waccamaw River. The first water samples were collected on Oct 4, 2015, representing the rising limb of the hydrograph. Since then, samples were collected daily for the first week and several times per week in the following weeks. Samples were promptly analyzed for general water chemistry, DOC and THg. We observed that concentrations of DOC and THg started to rise with the river discharge in an unsynchronized pattern, reaching the highest (32 mg/L and 7.5 ng/L, respectively) a few days after the peak flow.
Based on the model simulation and field sample collection, we estimated loadings of DOC and THg exported from this extreme flooding event. The findings of this study revealed the impact of extreme flood events on the balance of DOC, THg in the southeastern US coastal regions.
