Jr. Peterson et Jm. Hamlett, HYDROLOGIC CALIBRATION OF THE SWAT MODEL IN A WATERSHED CONTAINING FRAGIPAN SOILS, Journal of the american water resources association, 34(3), 1998, pp. 531-544
The Soil and Water Assessment Tool (SWAT) model, designed for use on r
ural ungaged basins and incorporating a GRASS GIS interface, was used
to model the hydrologic response of the Ariel Creek watershed of north
eastern Pennsylvania. Model evaluation of daily flow prior to calibrat
ion revealed a deviation of runoff volumes (D-v) of 68.3 percent and a
Nash-Sutcliffe coefficient of -0.03. Model performance was affected b
y unusually large observed snowmelt events and the inability of the mo
del to accurately simulate baseflow, which was influenced by the prese
nce of fragipans. Seventy-five percent of the soils in the watershed c
ontain fragipans. Model calibration yielded a D-v of 39.9 percent and
a Nash-Sutcliffe coefficient of 0.04, when compared on a daily basis.
Monthly comparisons yielded a Nash-Sutcliffe coefficient of 0.14. Snow
melt events in the springs of 1993 and 1994, which were unusually seve
re, were not adequately simulated. Neglecting these severe events, whi
ch produced the largest and third largest measured flows for the perio
d of record, a D-v of 4.1 percent and Nash-Sutcliffe coefficient of 0.
20 were calculated on a daily comparison, while on a monthly basis the
Nash-Sutcliffe coefficient was 0.55. These results suggest that the S
WAT model is better suited to longer period simulations of hydrologic
yields. Baseflow volumes were accurately simulated after calibration (
D-v = -0.2 percent). Refinements made to the algorithms controlling su
bsurface hydrology and snowmelt, to better represent the presence of f
ragipans and snowmelt events, would likely improve model performance.