The Twain Harte School project, completed December 2025, is one component of the larger, community-scale Twain Harte Community Stormwater Enhancement Project (THCSEP). The THCSEP is Prop 1 funded grant awarded from the California State Water Resources Control Board to the Twain Harte Community Services District (THCSD). The Tuolumne County Resource Conservation District (TCRCD)is managing the portion of the project at Twain Harte School THS.
The THCSEP was a collaborative effort to plan and implement hydrologically connected stormwater treatments necessary to address existing deficiencies and increase resilience to future conditions. The project area historically experienced flooding and water quality problems associated with its high-water table, impervious surfaces, steep surrounding topography, and aging stormwater infrastructure.
Extreme precipitation events associated with ongoing climate change has exacerbated these hazards.
The goals of the THCSEP and Twain Harte School project were to mitigate the hazards presented and provide multiple benefits to the surrounding region. These multi-benefit goals include:
- Increased treatment of stormwater runoff
- Increased water supply reliability
- Improvement and protection of environmental habitat
- Improvement of stormwater system capacity (flood management)
Project benefits are not limited to the project area. Twain Harte Creek is a tributary of Sullivan Creek and Phoenix Lake. As such, the project will provide multiple downstream benefits. Phoenix Lake is the Tuolumne Utility District’s (TUD) primary storage facility for drinking water that serves downstream disadvantaged communities including Sonora, Jamestown, and Columbia. Implementation of this project will reduce sediment and pathogen loads from upstream of this critical water storage facility and help to reduce future maintenance cost.
Twain Harte School is an approximately 8-acre property located in the heart of the Twain Harte community. The site consists of a large asphalt play area roughly 20,000 square feet insize,withbuildingsandfacilitiesonitsperimeter.
Hydrologically, stormwater flows from northeast to southwest through the site. A large drainage inlet located between the school and the turf field drains stormwater into a 42-inch reinforced concrete pipe (RCP) to the western edge of the site where it continues downstream eventually discharging at Twain Harte Creek. Stormwater not collected in the storm drain system travels across the site and onto the asphalt. Some areas of the school are prone to flooding in low points as well as consistently “wet” zones which are subject to freezing in the winter.
The project will:
- Install a rainwater collection tank with a storage capacity of three thousand (3,000) gallons to capture runoff from rooftops for irrigation to an existing garden.
- Convert a minimum of 12,768 square feet of existing asphalt into bioretention basin to include drought tolerant landscaping.
- Install 6,145 square feet of bioswales to include drought tolerant landscaping.
- Install 675 square feet of raingardens to include drought tolerant landscaping.
Installation of the bio retention basin, bioswales and raingarden was completed August 2025. Landscaping was completed in December 2025 with the help of Community Volunteers. A bit Thank You to those who helped out!
For more information, please contact Tricia at Tricia@TCRCD.org or Renata at Renata@TCRCD.org