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Hydrologic Relationships of a Paired Coastal Watershed on the Santee Experimental Forest for Evaluating Watershed-scale Effects of Longleaf Pine Restoration on Water Yield
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  • Devendra Amatya,
  • Herbert Ssegane,
  • Carl Trettin,
  • Mohammad Daud Hamidi
Devendra Amatya
USDA Forest Service
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Herbert Ssegane
Oshkosh Corp
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Carl Trettin
USDA Forest Service
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Mohammad Daud Hamidi
Durham University
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Abstract

We analyzed hydrology of 1st order paired watersheds (155-ha WS77 (treatment) and 160-ha WS80 (control)) in anticipation of a study to assess the hydrologic response to restoring longleaf pine (Pinus palustris) on the Santee Experimental Forest in coastal South Carolina. Rainfall, streamflow (runoff), water table, and other watershed parameters measured during 2011-2019 were used as the basis of comparison with earlier studies. The objective is to affirm hydrologic relationships between the two watersheds by testing the hypotheses that the a) mean annual runoff coefficients (ROC) are not different between the pair and b) paired mean annual ROCs, mean monthly runoff difference and calibration regression are not different (α = 0.05) from the respective ROCs, runoff difference, and regression reported for historic 1969-1978 and 2004-2011 forest regeneration periods, and c) the calibration regression is also indifferent from both periods and statistically significant (α = 0.05). Annual ROCs were not statistically different (p > 0.17) between the WS77 (0.24) and WS80 (0.19) for 2011-2019 and the ROC pair was also not different (p > 0.20) from 2004-2011 (WS77 (0.18); WS80 (0.14)), nor (p > 0.8) from the 1969-1978 period (WS77 (0.25); WS80 (0.18)). The mean monthly runoff difference (WS80-WS77) of – 7.54 (±1.68) mm was not different (p = 0.41) from -8.57 (±1.66) mm for the 1969-1978 period but different from -3.89 (±1.09) mm for 2004-2011 period. The inherently higher WS77 runoff than WS80 was attributed to its > three times smaller surface storage than WS80 and its land morphological characteristics defined by higher hypsometrical integral. The monthly runoff calibration relationship (WS77 = 1.03*WS80 + 7.00; R2 = 0.83; p = 0.0005), without an extreme October 2015 runoff (outlier), was significantly different (α = 0.05) from the historic 1969-1978 relationship, but not from the recent 2004-2011 one with similar climate regime.