The Green Valley Flood Control Project is located in the Cordelia area. The watershed area for the Green Valley Project ranges from the hills between Vallejo and Fairfield to the Suisun Marsh. Construction for the Green Valley Project was completed in 1962. The United States Army Corps of Engineers designed and constructed the Project. After completion of the Green Valley Project the Project was turned over to SCWA for operations and maintenance.
When the Green Valley Project was first built, the service area was unincorporated and largely undeveloped. The Green Valley Project was designed to control a storm with a 40-year recurrence level, meaning the Project was designed to handle a storm that occurs on an average of once in every 40 years. Flood control protection in an urban area is usually a 100-year recurrence level. Portions of the Green Valley Project within the City of Fairfield have been upgraded to a 100-year protection level. The channels are almost entirely on private property with easements granted to SCWA for operations and maintenance access. The Corps of Engineers inspects the Green Valley Project once a year and reviews any plans for major modifications or improvements to the Project. SCWA is responsible for all maintenance and capital improvements. The channels of the Green Valley Project are unlined earth channels where some vegetation is allowed to grow for slope protection. Trees and woody vegetation are cleared annually to ensure adequate flood control capacity. The channels are dredged as needed and some plant growth is controlled by chemical herbicides. As development in the watershed of the Green Valley Project continues, SCWA must ensure that there is adequate capacity for additional runoff created. SCWA works closely with the City of Fairfield to ensure that development projects adequately mitigate their storm water runoff impacts. Part of the long-term maintenance program includes monitoring the channels to ensure that they retain the capacity to carry the flows the Green Valley Project was designed for.