COMPARISON OF HEAT WITH CHLORIDE AND SPECIFIC CONDUCTANCE AS GROUND-WATER TRACERS NEAR STREAMS

Chloride and specific conductance were compared to heat as tracers of stream-water /ground-water exchange along the Russian River, CA over a two year period. Stream-water temperature and specific conductance data were collected continuously and stream-water chloride was sampled quarterly. In wells adjacent to the stream, temperature, chloride and specific conductance data were collected quarterly. Strong seasonal variations in stream-water temperature and specific conductance data were observed. In wells where temperature response correlated to stream-water temperature, chloride and specific-conductance values were similar to stream-water values, indicating significant stream-water exchange with ground water. Where ground-water temperature fluctuations were negligible, neither chloride and/or specific-conductance values correlated to stream-water values, indicating insignificant stream-water/ground-water exchange. At two sites best fit simulation modeling was performed to derive temperature-based estimates of hydraulic conductivity (K) values of the alluvial sediments between the stream and wells. Simulations showed that K values varied both seasonally and annually as a result of scouring or clogging of the streambed, and temperature changes. These K estimates were then used in solute transport simulations to compare measured and simulated values for chloride and specific conductance. Specific conductance fits were good, while chloride data were difficult to fit due to the infrequent (quarterly) stream-water measurements. Combined analyses of temperature, chloride and specific conductance led to improved quantification of the spatial and temporal variability of stream-water exchange with shallow ground-water along the Russian River.