EFFECTS OF SUBBASIN SIZE ON TOPOGRAPHIC CHARACTERISTICS AND SIMULATEDFLOW PATHS IN SLEEPERS RIVER WATERSHED, VERMONT

The effects of subbasin size on topographic characteristics and simula ted flow paths were determined for the 111.5-km(2) Sleepers River Rese arch Watershed in Vermont using the watershed model TOPMODEL. Topograp hy is parameterized in TOPMODEL as the spatial and statistical distrib ution of the index ln (a/tan B), where In is the Napierian logarithm, a is the upslope area per unit contour length, and tan B is the slope gradient. The mean, variance, and skew of the ln (a/tan B) distributio n were computed for several sets of nested subbasins (0.05 to 111.5 km (2)) along streams in the watershed and used as input to TOPMODEL. In general, the statistics of the ln (a/tan B) distribution and the simul ated percentage of overland flow in total streamflow increased rapidly for some nested subbasins and decreased rapidly for others as subbasi n size increased from 0.05 to 1 km(2), generally increased up to a sub basin size of 5 km(2), and remained relatively constant at a subbasin size greater than 5 km(2). Differences in simulated flow paths among s ubbasins of all sizes (0.05 to 111.5 km(2)) were caused by differences in the statistics of the ln (a/tan B) distribution, not by difference s in the explicit spatial arrangement of ln (a/tan B) values within th e subbasins. Analysis of streamflow chemistry data from the Neversink River watershed in southeastern New York supports the hypothesis that subbasin size affects flow-path characteristics.