Date of Award

6-2021

Degree Name

MS in Civil and Environmental Engineering

Department/Program

Civil and Environmental Engineering

College

College of Engineering

Advisor

Misanga Muleta

Advisor Department

Civil and Environmental Engineering

Advisor College

College of Engineering

Abstract

A model was developed to simulate the groundwater of 8,300 acres of the Northern Cities Management Area (NCMA), which encompasses the northern portion of the Arroyo Grande Watershed and a small subset of the Santa Maria Valley Groundwater Basin. This watershed and groundwater basin is located on the coast and contains Oceano and the Cities of Arroyo Grande, Grover Beach, Pismo Beach. Groundwater in the NCMA is used heavily for agricultural irrigation in the southern portion and municipal applications in the northern portion. Up to 18 of these municipal wells and over 50 irrigation wells are drawing groundwater at any time. Due to the critical nature of both uses, and location on the coastline, both supply and quality is a significant concern. The objective of this research was to improve an existing groundwater model with a longer model duration, a more detailed and discretized recharge estimation, and incorporation of addition municipal well data. Some data was preprocessed in ArcMap. Groundwater modeling was accomplished with Aquaveo GMS using MODFLOW-NWT upstream weighting package (UPW). Elevation, hydrologic soil conditions, stream gauge heights and flows, recharge rates, fault locations, well locations and pumping rates, and transient head boundaries were created via coverages in GMS and mapped to MODFLOW. The model was calibrated using Parameter Estimation (PEST) with Singular Value Decomposition-Assist (SVD-Assist) to observation data in six select monitoring wells and fifteen Sentry wells. The model showed outflow from the domain to the ocean with groundwater flows shifting to parallel the coast following dry periods and significant simulated drawdown from one particular municipal well. These trends can provide water purveyors in the area with additional information on groundwater trends and effects of pumping rates on formation drawdown.

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