Many investigators have sought to develop regional multivariate regression models which relate low-flow statistics to watershed characteristics. Normally, a multiplicative model structure is imposed and multivariate statistical procedures are employed to select suitable watershed characteristics and to estimate model parameters. Since such procedures have met with only limited success, we take a different approach. A simple conceptual stream-aquifer model is extended to a watershed scale and evaluated for its ability to approximate the low-flow behavior of 23 unregulated catchments in Massachusetts. The conceptual watershed model is then adapted to estimate low-flow statistics using multivariate regional regression procedures. Our results indicate that in central western Massachusetts, low-flow statistics are highly correlated with the product of watershed area, average basin slope and base flow recession constant, with the base flow recession constant acting as a surrogate for both basin hydraulic conductivity and drainable soil porosity. INTRODUCTION Estimates of low-flow statistics are needed in water quality management and water supply planning and for the determination of minimum downstream release requirements from hydropower, irrigation, water supply, cooling plant and other facilities. Water quality management applications of low-flow statistics include the determination of wasteload allocations, discharge permits, and the siting of treatment plants and sanitary landfills. Many investigations have attempted to develop regional hydrologic models for the purpose of estimating low-flow statistics at ungaged sites from readily available geomorphic, geologic, climatic and topographic parameters. For example, Thomas and Cervione [1970], Tasker [1972], Parker [1977], Dingman [1978], Male and Ogawa [1982], Cervione et al. [1982], Downer [1983], Fennessey and Vogel [1990], and Vogel and Kroll [!990] have developed regional low-flow models in the New England region. Usually such models take the form Qd, T bo J•b•Yb2Yb3 ' ' ' = 1 •2 •'•3 (1) where Qa, r is the d-day, T-year low-flow statistic obtained from gaged flow records, the Xi are measurable drainage basin characteristics and the b i are parameter estimates obtained from multivariate regression procedures. Such models are generally developed using long-term streamflow data and associated basin characteristics from many sites. Regional statistical models of this type, frequently referred to as "state equations," are used widely in the United States for estimating flood flow statistics at ungaged sites. Newton and Herrin [1983] recommend such statistically based regional regression equations over the use of deterministic watershed models for estimating flood flows at ungaged Copyright 1992 by the American Geophysical Union. Paper number 92WR01007. 0043-1397/92/92 WR-01007 $05.00 sites. Their recommendations are based upon a large nationwide comparison of alternative methods for estimating flood flows at ungaged sites developed by several federal agencies. Unfort...
