Date of Award

5-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Biosystems Engineering

Advisor

Hitchcock, Daniel R

Committee Member

Jayakaran , Anand D

Committee Member

Williams , Thomas M

Abstract

Toward the goal of the assessment of the rainfall response on forested headwater catchments in the Lower Coastal Plain (LCP) of South Carolina, rainfall, streamflow, and groundwater elevation were monitored on two similar streams. Upper Debidue Creek (UDC) in coastal Georgetown County, South Carolina is slated for development and Watershed 80 (WS80) in the Francis Marion National Forest serves as an undeveloped reference watershed. Spatial rainfall variability was assessed at UDC and it was concluded that a single gage was sufficient to accurately measure rainfall for this watershed. Throughfall measurements at UDC indicate a seasonal difference that may influence seasonal trends in streamflow. The rainfall response on the two watersheds was measured as total storm flow and direct runoff components of watershed outflows. Storm event runoff was determined by a graphical hydrograph separation method that takes into account the unique mechanisms of runoff generation in the LCP related to low topography and shallow water table. Variability in runoff generation at UDC and WS80 was related to seasonal trends of evapotranspiration that determine soil moisture conditions and are related to seasonal fluctuations in groundwater elevation. Break point water table elevations were determined for each watershed above which runoff generation was observed to increase sharply. The SCS Curve Number method for runoff modeling was compared to measured rainfall and runoff for storm events on both watersheds. Parameter selection by the accepted methodology does not appear to accurately model runoff generation on these LCP headwater catchments. The strong relationship between groundwater elevation and runoff generation should be considered for applications of the Curve Number method in similar watersheds. The effect of seasonal trends in groundwater elevation on the rainfall response for similar streams in the LCP may not be well modeled by the median measure for runoff generation that is typically used due to fluctuating moisture conditions.

Included in

Hydrology Commons

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