Colusa Subbasin Groundwater Sustainability Plan Revisions

Client: Colusa Groundwater Authority and Glenn Groundwater Authority

Funder: Colusa Groundwater Authority and Glenn Groundwater Authority

Location: Colusa Subbasin, Colusa and Glenn Counties, CA

Date: 2023-2024

In fall 2023, Davids Engineering, Inc. (DE) was contracted by the Colusa Groundwater Authority (CGA) and the Glenn Groundwater Authority (GGA) to support their revisions to the Colusa Subbasin Groundwater Sustainability Plan (GSP) in response to comments received from the California Department of Water Resources (DWR). In DWR’s October 2023 “incomplete” determination for the Colusa Subbasin GSP, DWR identified three deficiencies pertaining to: (1) the overdraft estimate and overdraft mitigation strategy for the Colusa Subbasin, (2) the sustainable management criteria (SMC) and mitigation strategy for chronic lowering of groundwater levels, and (3) the SMC, monitoring approach, and mitigation strategy for subsidence.

Over the remainder of the 180-day period from December 2023 to April 2024, DE supported the GSAs in developing and implementing a strategy for the GSP revisions and consulting with DWR staff to discuss and verify that the revisions were on track toward approval. DE led and supported the GSAs in navigating the revisions process through biweekly coordination meetings, monthly Technical Advisory Committee and Board meetings, five formal consultation meetings with DWR, and other touchpoints to work through the many technical and policy decisions involved in the GSP revisions. DE also teamed with West Yost Associates to complete various technical analyses and revisions to the GSP document related to these discussions and decisions.

During the GSP revisions process, DE supported the GSAs in the initial development of a demand management program and domestic well mitigation program to address and mitigate sustainability concerns in the Colusa Subbasin related to overdraft, groundwater level decline, and subsidence. As an outcome of this work, the GSAs have developed and signed an agreement for each program that outlines the terms and approach for implementing the programs over the next several years. DE’s efforts also helped to create a clear timeline and strategy for GSP implementation over the next five years to ensure that the GSAs remain on track to reaching sustainability in the Colusa Subbasin.

All Projects

Tehama County Groundwater Sustainability Plan Implementation 

Colusa Subbasin Groundwater Sustainability Plan Revisions

Madera Subbasin Groundwater Sustainability Plan Revisions 

Chowchilla Subbasin Groundwater Sustainability Plan Revisions

Moore Siphon Replacement Project

Dos Rios Ranch SB88 Compliance and Crop Planning Analysis

Hart Ranch On-Farm Irrigation Efficiency Improvements

Orland Project Distribution System Modernization

Water Management Plan Compliance Mapping

Agricultural Development Feasibility Assessment

Analysis of Effects of Water Management on Evapotranspiration from Managed Wetlands

Garden Highway Mutual Water Company Water Control Projects

Richvale Irrigation District Phase I Infrastructure Modernization

Joint Water Districts Board SCADA

Sutter Mutual Water Company Modernization Support

Shasta Valley Groundwater Monitoring

Time Series Evapotranspiration and Applied Water Estimates from Remote Sensing

Customer Delivery Measurement Data Collection and Accounting (RemoteTracker Implementation)

SGMA Technical Support Services and Prop 1 Stressed Basin Grant Project

Efficiency Conservation Definite Plan and Conservation Program

Boundary Outflow Measurements

Oakdale Irrigation District Agricultural Water Management Plan

Yuba Water Agency Agricultural Water Managment Plan

Feather River Agricultural Water Management Plan (FRRAWMP)

Colusa Subbasin Groundwater Sustainability Plan Development

Madera and Chowchilla Subbasins Groundwater Sustainability Plans

2022 Verification Project for Madera County GSAs

Little Shasta River Efficiency Study

Mill Creek Flow Measurement Improvements

Kettle Spring Improvement Project

Antelope Creek Fish Passage Improvement Project

Conservation Planning and Operations Decision Support