Similar watershed cross-correlation and climate stationarity, Cherry Creek, California

Graduation Date

2014

Document Type

Project

Program

Other

Program

Project (M.S.)--Humboldt State University, Environmental Systems: Environmental Resources Engineering, 2014

Committee Chair Name

Margaret Lang

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

HEC-RAS, Cross-correlation, Streamflow, Stationarity, Stream gauging, Climate change, Hydrology, Humboldt State University -- Projects -- Environmental Resources Engineering

Abstract

The Hetch Hetchy system in Yosemite National Park including Cherry Lake stores over 80% of San Francisco's municipal water. This system consists of Hetchy Reservoir on the Tuolumne River and Lake Eleanor and Cherry Lake on Eleanor and Cherry Creeks respectively, two main tributaries to the Tuolumne. All three reservoirs are on separate waterways with Hetch Hetchy surface elevation at 3,783 feet, Eleanor Lake at 4,657, and Cherry Lake at 4,659 feet. Due to Cherry Lake and Eleanor Lake's being adjacent watersheds with similar elevations, they are connected with large pipes which allow for moving water between the two reservoirs. The water can be moved in either direction based on water elevation being higher in one reservoir or the other. These reservoirs are mainly fed by snow melt from high peaks on the west slope of the Sierra Nevada. The potential impacts of global climate change on the snowpack that provides the majority of inflow to these reservoirs are of concern to water managers. The general hypothesis is that warmer temperatures and shifts in the El Niño Southern Oscillation will cause more rain than snow in alpine climates, such as the Cherry Creek watershed, producing earlier peak flows. The possible changes are important for water managers to understand because current reservoir management frameworks may not apply in the future climate. The purpose of this study is to evaluate these potential climatic effects on the Cherry Creek and the Cherry Lake system, determining if these effects can be observed in the historical hydrological record, and to provide analyses to be used in future reservoir management. These analyses include evaluating historic data to identify changes in streamflow timing and peak volume. Non-parametric statistical tests, Kendall and Spearman's Rho, are used to quantify statistical evidence of trends in the streamflow record. Cherry Creek's existing record is not long enough for this non-parametric analysis so watershed cross-correlation with nearby Falls and Eleanor creeks was used to produce a longer record. Results from this correlation show Falls Creek to give the best correlation for extending the Cherry Creek flow record. Non-parametric tests show the longer Cherry Creek record created from cross-correlation to have a declining trend in peak streamflow timing at the 5% significance level. This result supports to the hypothesis that peak flow is occurring earlier in the water year. Significant trends were also found in all other streamflow statistics, with the exception of hydrograph volume. Evaluating these statistics allows for water managers to account for earlier run-off and lower snow volume, and releases can be adjusted to fill the reservoir appropriately. Additionally, a real-time streamflow gauge was installed on Cherry Creek to collect flow data to further monitor climatic trends in the future. The streamflow gauge is installed and collecting real-time data for future use.

https://scholarworks.calstate.edu/concern/theses/2801pj72r

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