DO PAIRED WATERSHED STUDIES WORK?

The ability to quantify change in a watershed depends on understanding the basin’s baseline behavior.  If baseline information is not available, many studies rely on other basins in close proximity to approximate the initial conditions.  In some cases, it is assumed that basin hydrology is similar if two basins are in close proximity and they have similar areas.  However, basin hydrology depends not only on basin size, but also bedrock and surficial geology, land use, hypsometry, and precipitation distribution.

In order to test the baseline hydrology of proximal basins we measured discharge from September to November 2003 (n=15) in the East Brach Kayderosseras Creek, (EBK) and Sturdevant Creek, Saratoga County, New York.  We divided the EBK into two sub-basins (3 and 16 km²) and Sturdevant Creek into three sub-basins (3, 7, and 20 km²).  Both basins have a similar bedrock geology, land use pattern, and hypsometry.  Three recording tipping bucket rain gauges, placed at different elevations in the basins, have a high correlation (r² > 0.9, trendline slopes close to 1.0) suggesting a weak orographic effect and no small-scale (< 5 km²) precipitation events during the collection period.  The main difference between the two basins is the surficial geology and their associated infiltration capacities.  The surfical geology of each basin (based on the Hudson-Mohawk Surficial Geology Quad, 1:250,000), is a patchwork of bedrock, till, and kame moraine (and some swamp in Sturdevant Creek basin).  The area of kame moraine in EBK is ~2x larger than in Sturdevant Creek.

In general, discharge increases at larger sub-basin sizes.  However, the EBK increases in discharge at a lower rate than Sturdevant Creek in 14 of the 15 data sets.  Such lower increase in discharge (EBK) is most likely due to a higher percentage of “kame moraine” and the associated slower release of groundwater to the creek.  In 11 of the 15 data sets, the EBK had higher discharges at small basin areas (<3 km²) while Sturdevant Creek had higher discharges at larger basin areas (>16 km²).  Similar discharges from 3 to 16 km² suggest the range where the paired watershed method is effective for the EBK and Sturdevant basins.  Overall, our results show that the paired watershed is strongly dependent on basin geology in addition to basin area.