Stream gauging, groundwater monitoring and isotopic analysis in Big Chico Creek, California

The sources of the water that keep Big Chico Creek flowing during the dry\ud summer months were previously unknown. It was hypothesized that the water flowing in\ud the creek during the summer months was largely contributed by melted snow from the\ud mountains in Butte Meadows. Three study elements were employed to investigate Big\ud Chico Creek between January 30 and August 28, 2011. Stream gauging was performed\ud and the depth of the water table along a portion of Big Chico Creek was monitored, indicating\ud whether the creek was gaining or losing to groundwater. Stream gauging and water\ud table monitoring indicated that baseflow did not contribute to the creek over the course of\ud the study. Additionally, samples of snowmelt, rainwater, spring water, groundwater, and\ud water from Big Chico Creek were collected and subjected to isotopic analysis to determine whether Big Chico Creek assumes an isotopically depleted signature consistent\ud with snowmelt. Water from Big Chico Creek did become more depleted over the summer\ud and adopted an isotopic makeup more consistent with that of the snow collected from\ud Butte Meadows. Rainwater sources, water from a natural spring and groundwater sources\ud were relatively enriched compared to Big Chico Creek and snow from Butte Meadows\ud To determine the relative contributions from the various sources, a variety of\ud statistical applications, such as cross correlation between creek water elevation and the\ud water table elevation, an analysis of variance to establish statistically significant differences\ud in isotope ratios across the different locations and collection dates, a crosscorrelation\ud between the creekflow and depletion of 18O and 2H isotopes, a crosscorrelation\ud between isotope ratios of creekwater and snowmelt, rainwater, spring water,\ud and groundwater, and a runs test to determine that the changes in isotope ratios were nonrandom\ud in nature were performed. Cross-correlation showed strong correlations between\ud the water table elevation at individual monitoring points and the creek elevation, with no\ud lag detected. An analysis of variance revealed that significant differences in ??18O and ??2H\ud values did exist between different sample sites, but no significant difference was found\ud between different sampling dates. Cross-correlation found a strong correlation between\ud low creek levels and waters depleted in 18O and 2H isotopes, while no correlation was\ud seen between the creek and any one particular sampling site. A runs test showed that nonrandom\ud variation was present in all samples.\ud Monitoring of creek discharge, groundwater levels in the vicinity of the creek,\ud and isotopic composition of the water all suggest that Big Chico Creek is consistently losing to groundwater year-round and only maintains flow due to the contribution of\ud snowmelt in the headwaters. Failure to reach statistically significant differences within\ud the analysis of variance may have been due to the evaporative enrichment endemic to the\ud dry summer months, dulling the depleting effect of the melting snow contributing to the\ud creek. Additionally, the early summer months featured higher than average precipitation,\ud further enriching the creek water.CSU, Chic