Basic hydrologic studies for assessing impacts of flow diversions on riparian vegetation: examples from streams of the Eastern Sierra Nevada, California, USA

The geomorphic and hydrologic characteristics of a site would be needed to determine the effect of streamflow reduction on riparian vegetation. Several types of hydrologic data relevant to impact analysis and their collection are described. The methods were applied to 7 streams affected by proposals for small hydroelectric projects. Geomorphic features were mapped from aerial photographs. Existing groundwater data was gathered after identifying existing wells along or near the study reaches. Synoptic flow measurements were carried out to identify zones of groundwater recharge and discharge, and to measure gains and losses if flow along the reaches proposed for diversion. Results of the studies on the largest stream and the 2 smallest are presented. Groundwater contributions controlled by local geomorphology caused flow increases of up to 275 per cent on 1 stream indicating less water available for diversion upstream than had been thought. This raised questions as to the economic viability of the proposed hydroelectric project.