Tuolumne River Flood Management Feasibility Study

Project Lead: Stanislaus County

Potential Project Partners:
City of Modesto, USACE

Short Project Description:
Complete a USACE Feasibility Study, or a study similar in scope, that evaluates how the management of the Tuolumne River could be revised to improve flood control, enhance aquatic habitat, and improve water quality.

Long Project Description:
The Northern California Streams, Tuolumne River, California, Reconnaissance Study, Section 905(b) Analysis was prepared by the USACE and published in October 1998. The purpose of the investigation was to document flooding and related problems, and to identify potential opportunities for flood protection and environmental restoration in the Lower Tuolumne River Watershed. Stanislaus County and the City of Modesto were identified as potential non-federal sponsors of the feasibility analysis, which is the next phase of analysis per the USACE protocol. Several measures were identified during the process that were deemed worthy of further analysis at the feasibility level to be included as part of this project. These measures included the evaluation of 1) detention/wetland habitat basin along Dry Creek; 2) a potential site for small off-stream multi-purpose reservoir along the Tuolumne River for flood control storage, habitat, and water supply below La Grange Dam; 3) the construction of levees from below the City of Modesto Wastewater Treatment Plant to approximately two miles east of the airport along the Tuolumne River for flood control and environmental restoration; 4) the riparian corridor from below La Grange Dam to the confluence of the San Joaquin and Tuolumne Rivers (approximately 52 miles); 5) a low-flow meandering channel within the riparian corridor; 6) non-structural measures such as flood flow easements, relocation, elevating structures, ring levees, floodwalls, and floodplain management restrictions along Tuolumne River and Dry Creek; 7) channelization of the Tuolumne River at and downstream of the 9th Street Bridge in Modesto to relieve the Tuolumne River floodwater backwater effect in Dry Creek; and 8) the need to increase the channel capacity of the Tuolumne River at the 9th Street Bridge from 9,000 to 20,000 cubic feet per second (cfs).

Since publication of the Northern California Streams, Tuolumne River, California, Reconnaissance Study, Section 905(b) Analysis, the need for at least one additional analysis has been identified and is included as part of this project. A hydraulic analysis of current conditions is needed to identify any existing constrictions or structures at risk of flood damage along the Tuolumne River. The hydraulic analysis should analyze flood releases of 9,000-15,000 cfs with Dry Creek flows of 5,000-6,000 cfs. With this information in hand, agencies responsible for flood management would be better able to focus future flood damage reduction projects while also improving flood operations of Don Pedro Dam. Other necessary analyses may be identified in the reevaluation of the scope of the feasibility study, which would be necessary given that the reconnaissance study was published more than 15 years ago in 1998.

Unique Project Characteristics:
This project would protect human life and property. It marries flood management and habitat restoration.

Project Status Dormant
Project Cost $3,000,000
Project Timeframe Approximately 5 years
Cost-sharing USACE, Stanislaus County, and City of Modesto
Multi-benefit Project Yes
Types of benefits The project would improve flood risk management and institutional support.
Source of Project USACE


Background Information:
See the Northern California Streams, Tuolumne River, California, Reconnaissance Study, Section 905(b) Analysis (October 1998)