2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 9
Presentation Time: 4:00 PM

Use of Probability-Based Streamflow-Depletion Criteria to Constrain Optimal Ground-Water Withdrawals

GRANATO, Gregory E. and BARLOW, Paul M., U.S. Geol Survey, 10 Bearfoot Road, Northborough, MA 01532, ggranato@usgs.gov

Increased demands for water to meet human and ecosystem requirements are creating a need for improved methods for planning reliable water supplies while meeting environmental-protection goals. Streamflow depletion caused by ground-water withdrawals can be an environmental problem when such depletions reduce streamflow below minimum levels required to sustain healthy ecosystems. The approach to water-supply management taken in this work is to use probability based streamflow-depletion criteria that account for natural variability in streamflow, as quantified by monthly streamflow-duration curves. In this approach, ground-water withdrawal schedules are determined using simulation-optimization models that maximize ground-water withdrawals while simultaneously meeting maximum allowable streamflow-depletion rates that are based on specified monthly low-flow probabilities. The resulting optimal withdrawal schedules provide water suppliers with an assured maximum supply of water each month for a given level of maximum streamflow-depletion risk. For example, the water supplier and environmental regulators may decide to allow streamflow to be reduced to some percentage of the natural period-of-record minimum monthly one-day streamflow for each month of the year. These minimum monthly one-day streamflows correspond approximately to a one-percent probability that the minimum monthly streamflow criteria will actually be realized over a long period of withdrawal. The optimal withdrawal schedules determined for a given constraint set will result in new monthly streamflow-duration curves that are shifted downward relative to the natural streamflow-duration curves but are constrained to lie above each of the minimum monthly required flows.