Middle Carson River Basin Evaluation

County and other land-management agencies are concerned that increased ground-water pumping from existing and new wells in the Carson River Basin could impact streamflow in the Carson River by reducing the amount of ground-water discharge to the river. Rapid growth and development in the Dayton and Churchill Valleys has caused concern over whether water resources in these valleys will be able to sustain the projected growth into the future. Land presently used for agriculture will be urbanized to support population growth, and consequently, ground-water pumping will increase and the location and distribution of pumping will change. These changes may decrease streamflow in the Carson River and, in turn, decrease river water availability to downstream communities that rely on the river to meet their water needs, especially during the summer and fall periods.

Objectives

Develop estimates of the spatial and temporal distribution of ground-water recharge for the Dayton and Churchill Valley hydrographic areas, determine hydrogeologic controls on ground-water flow in the middle Carson River basin, develop and calibrate a ground-water/surface-water flow model of the Carson River Basin between Carson Valley and Lahontan Dam with a model grid resolution that is appropriate to address local-scale water-resources issues, and evaluate potential impacts on streamflow in the Carson River caused by present and future ground-water pumping in Eagle, Dayton, and Churchill Valleys.

Strategy and Approach

The project consists of two overlapping phases of work that are divided into nine main tasks. Tasks to be completed in Phase I include (1) develop watershed models for the mountain blocks surrounding the Dayton and Churchill Valley hydrographic areas; (2) determine hydrogeologic controls on ground-water flow in the middle Carson River basin; (3) develop hydrogeologic conceptualizations and preliminary regional ground-water flow models of the basins; (4) compile and analyze existing aquifer test data and conduct additional aquifer tests; (5) publish reports summarizing results of watershed and ground-water flow modeling. Tasks to be completed in Phase II will begin in Fiscal Year 2010 and include (6) develop and calibrate a steady-state model, and design a higher resolution model grid imbedded within the larger model grid that surrounds important areas of the model; (7) develop and calibrate a transient model; (8) simulate selected development scenarios; and (9) prepare and publish reports documenting model development and summarizing simulation results.

Relevance and Benefits

The proposed study is relevant to issue 1 of the USGS Water Resources Discipline Strategic Directions, which is to evaluate effects of urbanization on water resources and the study is consistent with the goal of the USGS Strategic Plan of providing water-resource managers with accurate, reliable, and impartial scientific information. The flow model will provide a tool for stakeholders and other interested parties to assess ground-water management and water-use issues that have the potential to affect streamflow in the Carson River.