Seasonal rainfall–runoff relationships in a lowland forested watershed in the southeastern USA

Authors

  • Ileana B. La Torre Torres,

    1. Environmental Studies Program, College of Charleston, 66 George Street, Charleston, SC 29424, USA
    Current affiliation:
    1. Berkeley-Charleston-Dorchester Council of Governments, 1362 McMillan Ave. Suite 100 North Charleston, SC 29405, USA.
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  • Devendra M. Amatya,

    Corresponding author
    1. USDA-Forest Service, Center for Forested Wetlands Research, 3734 Hwy 402, Cordesville, SC 29434, USA
    • USDA-Forest Service, Center for Forested Wetlands Research, 3734 Hwy 402, Cordesville, SC 29434, USA.
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    • The contributions of Devendra M. Amatya and Ge Sun to this article were prepared as part of their official duties as United States Federal Government employees.

  • Ge Sun,

    1. USDA-Forest Service, Eastern Forest Environmental Threat Assessment Center, 920 Main Campus, Venture II, Suite 300, Raleigh, NC 27606, USA
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    • The contributions of Devendra M. Amatya and Ge Sun to this article were prepared as part of their official duties as United States Federal Government employees.

  • Timothy J. Callahan

    1. Department of Geology and Environmental Geosciences, College of Charleston, 66 George Street, Charleston, SC 29424, USA
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Abstract

Hydrological processes of lowland watersheds of the southern USA are not well understood compared to a hilly landscape due to their unique topography, soil compositions, and climate. This study describes the seasonal relationships between rainfall patterns and runoff (sum of storm flow and base flow) using 13 years (1964–1976) of rainfall and stream flow data for a low-gradient, third-order forested watershed. It was hypothesized that runoff–rainfall ratios (R/P) are smaller during the dry periods (summer and fall) and greater during the wet periods (winter and spring). We found a large seasonal variability in event R/P potentially due to differences in forest evapotranspiration that affected seasonal soil moisture conditions. Linear regression analysis results revealed a significant relationship between rainfall and runoff for wet (r2 = 0·68; p < 0·01) and dry (r2 = 0·19; p = 0·02) periods. Rainfall-runoff relationships based on a 5-day antecedent precipitation index (API) showed significant (r2 = 0·39; p < 0·01) correspondence for wet but not (r2 = 0·02; p = 0·56) for dry conditions. The same was true for rainfall-runoff relationships based on 30-day API (r2 = 0·39; p < 0·01 for wet and r2 = 0·00; p = 0·79 for dry). Stepwise regression analyses suggested that runoff was controlled mainly by rainfall amount and initial soil moisture conditions as represented by the initial flow rate of a storm event. Mean event R/P were higher for the wet period (R/P = 0·33), and the wet antecedent soil moisture condition based on 5-day (R/P = 0·25) and 30-day (R/P = 0·26) prior API than those for the dry period conditions. This study suggests that soil water status, i.e. antecedent soil moisture and groundwater table level, is important besides the rainfall to seasonal runoff generation in the coastal plain region with shallow soil argillic horizons. Copyright © 2011 John Wiley & Sons, Ltd.

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