ASR Program Development and Modeling, Davis-Woodland Water Supply Project
Woodland-Davis Clean Water Agency, California

The Woodland-Davis Clean Water Agency is a Joint Powers Authority representing the water supply interests of the cities of Davis and Woodland. Under the Aquifer Storage and Recover (ASR) Program, the City of Woodland is implementing a comprehensive ASR Program to help address its water supply needs during periods of peak demand and/or drought. The City of Davis may also choose to undertake its own ASR Program. As part of the ASR Program, West Yost team members used the California Department of Water Resources (DWR) Modeling Support Branch’s Integrated Water Flow Model (IWFM) to develop a three dimensional groundwater flow model for Yolo County. The model was then used to assess six scenarios for current (2014) and future (2040) ASR operational conditions in both cities.

Key modeling challenges and work elements included developing 3-D representations of the subsurface geology and assigning pumping rates in agricultural and rural residential areas, where pumping records are very limited or nonexistent. The West Yost team developed a groundwater data management system (DMS) for Yolo County to support development of the model. The DMS was developed as an Arc Hydro for Groundwater Geodatabase and contains detailed geologic, land and water use mapping; well construction details; borehole lithology information; pumping and diversion records; and groundwater quality data. GIS tools were applied to the geologic data to create 2- and 3-D representations of the aquifer system. The 3-D representations of the subsurface geology were developed by applying GIS tools and expert geologic knowledge of the study area to published geologic mapping, available well log information, and digital elevation models of the study area. Pumping rates in agricultural areas were estimated with DWR’s IWFM Demand Calculator using DWR land use and NRCS soils mapping as model inputs. Rural residential pumping was estimated based by Census Tract information using estimated per capita rates. These efforts led to successful model development and simulation of future ASR operations.

The modeling results for the six ASR scenarios were documented in a comprehensive report on the ASR Program.In addition, the report addressed:

  • Groundwater modeling of ASR scenarios
  • Groundwater basin characterization
  • Baseline water quality evaluations
  • Geochemical analysis and modeling

The report supported and led to the recent adoption of a Supplemental Environmental Impact Report for the ASR Program, which enables the ASR Program to be implemented. West Yost is currently supporting the City of Woodland to implement ASR.