A STATEWIDE ANALYSIS OF WATER SUPPLY AND DEMAND IN MAINE AS A STEP TOWARD SUSTAINABLE WATER USE

Increasing demand for water resources and concern for potential affects of climate change on these resources have led Maine policy makers to consider the sustainability of use in policy deliberations. To facilitate these discussions we conducted a first-order analysis intended to answer this basic question: does Maine have a statewide issue with sustainable water use, or are there specific watersheds of concern?

We assembled existing statewide datasets to conduct this analysis using the NRCS 12-digit Hydrologic Unit Code (HUC) watersheds of which there are 973 in Maine. For each watershed we constructed a water balance equation comparing mean annual runoff to the sum of minimum required instream flows and consumptive water use. A regional regression equation from Dudley (2004) was used to compute mean annual runoff: Q_ann = 1.151(A^0.991)(10^0.023*pptW), where Q_ann is the annual runoff in cubic feet per second (CFS), A is the watershed area in square miles, and pptW is the mean winter precipitation in inches of water. Consumptive water use was compiled from databases of reported water use (including agricultural and industrial), public water system records, and use coefficients for population on private wells (40%). Stream flow requirements to support habitat were based on rules adopted by the Maine Department of Environmental Protection which define flow thresholds for six seasons. In aggregate over the defined seasons, the required flows approximated 65% of annual flow, which was used throughout the analysis. A “watershed-at-risk” was defined as a watershed where the sum of the minimum required in-stream flows plus the estimated consumptive water use was equal to or greater than some threshold percent (90% for this analysis) of the estimated mean annual runoff generated in the watershed. Our analysis found 12 such basins. We are now conducting detailed investigations in several watersheds to better refine their water resource information and guide resource management. For the next stage of statewide analysis we will consider the seasonality of watershed flows and water uses.

Dudley, R.W. (2004), U. S. Geological Survey, Scientific Investigations Report SIR 2004-5026, 22 p.