A Procedure for the Preliminary Assessment of Water Supply Availability

Abstract

Of the factors that determine development potential in a given geographic area, the availability of water for residential, commercial, and industrial purposes is a primary indication of prospective growth. Governmental bodies at the regional, state and federal levels often need to identify water supply availability in order to identify growth potential.

To address this need, a procedure for the preliminary assessment of water supply availability has been developed that can potentially be applied to any geographic area in the United States. The procedure uses the USGS demand cataloging unit as the basic planning area, with supply estimates from streamflow parameters at USGS gage locations and demand estimates from USGS demand reports. By comparing known supply and demand estimates in a base year, an overview of water supply availability in the region can be determined.

With supply and demand data in a base year, projections of future water supply availability can then be made. Detailed projection of future water demand must account for changes in the amount of water use activities and the rates of water use within those activities, but a simplified procedure is applied here. Total offstream water use is averaged over the population in the base year to determine per-capita offstream use, which is assumed to remain constant in the future in this preliminary assessment procedure. Population is then projected and demand is forecast as a function of the projected population. The supply quantity is projected assuming each flow parameter derived from the historical record will remain constant in the future year. By comparing projected supply and demand estimates, water supply availability in future years can be anticipated in the planning area.