Drought Mitigation and Effect on Perennial and Deferred Perennial Yield Strategies, Case Study: Cache Valley

Groundwater users are often the last to be affected by drought. Also, groundwater users are the last to experience a return to normal water levels. Less than average precipitation will affect the sustainability of the aquifer use and the hydraulically connected surface water. We examine the effect of drought on perennial and deferred perennial yield strategies developed for long-term average conditions. An optimal perennial yield strategy gives areal distribution of groundwater pumping rates that will cause acceptable consequences to the aquifer and hydraulically connected surface water bodies. Such strategies have relatively constant annual pumping rates and check for annual average conditions. Deferred perennial yield strategies differ from perennial yield strategies in that pumping rates can initially be high while aquifer mining is allowed for hydrological or economic reasons. Afterwards, pumping rates are reduced allowing for aquifer recovery. Reconnaissance optimization problems or scenarios are constructed to help explore the options for mitigating drought (less than average) effect on groundwater. One scenario computes the maximum allowed junior water rights to be granted if less-than average precipitation exists. Another scenario will be invoked if junior rights can not be granted and unacceptable consequences are still noticed. This scenario computes an optimal unified reduction percentage in background pumping or shaving groundwater senior water rights. The third scenario will reduce senior water rights by an optimal proportion and prevent junior water rights from pumping more than their perennial yield pumping rates. Cache Valley aquifer system will be used as a representative aquifer to evaluate the results of the three scenarios. Drought with PDSI (Palmer Drought Severity Index) of -1 or less (absolute value \u3e 1) has not hit Utah for hundreds of years. However, normal fluctuation in climatic conditions can be observed in Cache Valley. Precipitation depth between 11 and 21 inches has a cumulative distribution of 81%. Such statistics will be used in conjunction with a USGS Cache Valley transient simulation model to test the effect of using less-than-average conditions on a previously developed perennial yield strategy. Bassel Timani and Richard C. Peralt