Hydrologic Relationships of a Paired Coastal Watershed on the Santee
Experimental Forest for Evaluating Watershed-scale Effects of Longleaf
Pine Restoration on Water Yield
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.