Use of spot measurements to improve the estimation of low streamflow statistics.

Abstract:

Despite substantial efforts to improve the modeling and prediction of low streamflows at ungauged river sites, most models of low streamflow statistics create estimators with large errors. Often this is because the hydrogeologic characteristics of a watershed, which can strongly impact low streamflows, are difficult to characterize. One solution is to take a nominal number of streamflow measurements at an ungauged site to either estimate improved hydrogeologic indices or correlate with concurrent streamflow measurements at a nearby gauged river site. Past results have indicated that baseflow correlation performs better than regional regression when 4 or more streamflow measurements are available, even when the regional regression models are augmented by improved hydrogeologic indices. Here we revisit this issue within the 19,800 square mile Apalachicola-Chattahoochee-Flint watershed, a USGS WaterSMART region spanning Geogia, southeastern Alabama, and northwestern Florida. This study area is of particular interest because numerous watershed modeling analyses have previously been performed using gauged river sites within this basin. Initial results indicate that baseflow correlation can produce improved estimators when spot-measurements are available, but selection of an appropriate donor site is problematic, especially in regions with a small number of gauged river sites. Estimation of hydrogeologic indices do improve regional regression models, but these models are generally outperformed by baseflow correlation.