ESTIMATING GROUNDWATER-WITHDRAWAL EFFECTS ON STREAMS

ABSTRACT- Numerical groundwater-model simulations can estimate effects of proposed groundwater development and help find solutions to balancing the water needs of humans with the needs of natural stream environments. Such estimates are critical where significant connection exists between groundwater and small streams, such as those in the southern Lihue Basin. Model simnlations of the basin indicate that a proposed increase in withdrawal of only 1.16 million gallons per day could cause groundwater discharge to certain small streams to decrease by as much as 18 percent within 20 years. Because streams are numerous and the groundwatdstream connection is significant in the basin, the effect on streams as a whole cannot be substantially reduced without a corresponding reduction in proposed withdrawal. However, model simulations of various alternative well distributions indicate that well placement can help mitigate the effects the proposed withdrawal may have on individual small streams. KEY TERMS: groundwatdsurface-water relations; pumping effects; groundwater modelin