A Decision-Support System to Assess Surface-Water Resources in Massachusetts

Federal, State and local water supply, regulatory, and planning agencies require easy-to-use, technically-defensible, decision-support (DS) applications that can evaluate impacts of proposed water withdrawals, determine baseline streamflow conditions needed for sustainability of aquatic habitat, and estimate inflows to drinking-water-supply reservoirs for safe yield analyses at ungaged locations. An interactive, point-and-click DS application is developed in combination with a geographic-information system to address these needs. The DS application estimates unimpacted daily streamflow at any user-selected location — gaged or ungaged — on a perennial stream in Massachusetts. A new method is proposed to estimate a daily flow-duration curve at an ungaged site by exploiting the strong structural relationship among streamflow quantiles. This method offers improvement — particularly for low flows — over traditional regression-based approaches that relate flows at selected flow quantiles to measurable basin characteristics. A time series of daily flows is then created by transferring the timing of the daily flows at an index gage to the ungaged site at equivalent exceedance probabilities. Estimated daily streamflows show remarkably good agreement with observed daily flows and are generally comparable to the agreement obtained from a calibrated rainfall-runoff model. A jack-knife cross-validation experiment indicates that the agreement between observed and estimated flow series at an ungaged site is also remarkably good.