Date of Award

6-2020

Degree Name

MS in Civil and Environmental Engineering

Department

Civil and Environmental Engineering

College

College of Engineering

Advisor

Misgana Muleta

Advisor Department

Civil and Environmental Engineering

Advisor College

College of Engineering

Abstract

The Santa Rosa Creek Watershed is an approximately 48 mi2 large watershed located on the central coast of California. This watershed drains to the Pacific Ocean through Santa Rosa Creek as it passes through agricultural land and the town of Cambria. Historically the groundwater within the Santa Rosa Creek Watershed has been used for irrigation, municipal and domestic uses, and the creek is critical habitat steelhead trout. During dry years, there is less water for all uses. When low groundwater levels occur, water can be drawn out of the creek and into the soil, drying out steelhead habitat. Seven agricultural operators within the Santa Rosa Creek Watershed are working with a local non-profit to improve sustainability of the aquifer through artificial groundwater recharge. One of these projects includes the use of a recharge basin. This study was conducted to understand the impacts of that recharge basin on the groundwater surrounding it as well as to evaluate the site’s potential for other recharge methods. The groundwater within the site of interest was modeled using GMS to calculate head values, to determine flow directions, and to determine timings. Three different hydrogeologic layers were used to simulate an upper unconfined zone, a clay confining layer, and a confined zone. The model was calibrated to known groundwater head values throughout the site. ArcMap was used to organize and preprocess data that went into the GMS model. Elevation, hydrologic soil characteristics, boundary heads, recharge rates, evapotranspiration rates, and well locations and pumping rates datasets were all preprocessed and imported into GMS. The model showed that the water from the recharge basin does not percolate into the underlying groundwater aquifer, but it flows out of the upper unconfined layer and into the creek over time. This is caused primarily by a low hydrologic conductivity confined aquifer in the northern section of the site as well as a confining clay layer underneath the unconfined top layer. According to the model, the site may not be feasible for artificial groundwater recharge in the northern portion, but there is potential for recharge in the southern area. Further data collection could improve the model to support or dispute these findings.

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