Lake Solano Sediment Management Study

A comprehensive basin-wide sediment management assessment of Lake Solano in Northern California identified affordable solutions to operation and maintenance problems caused by sedimentation. The Solano County Water Agency (Agency or SCWA) sponsored studies in 1997 and 1998 to develop a sediment management program for Lake Solano, an 888,000 cubic meter (720 acre-feet) diversion reservoir supplying water to Sacramento Valley farms and municipalities via the Putah South Canal (Northwest Hydraulic Consultants, 1998). The reservoir and canal are part of the U.S. Bureau of Reclamation (USBR) "Solano Project" completed in 1958. (Figure 1) The Project includes Monticello Dam and Lake Berryessa, which provides 1.93 billion cubic meters (1.6 million acre feet) of water storage. The drainage basin for Lake Solano downstream of Monticello Dam is approximately 98 square kilometers (38 square miles) and is the primary source of sediment deposited in the lake. Since construction, approximately 191,000 cubic meters (250,000 cubic yards) of sediment have accumulated in Lake Solano, infilling approximately 20 percent of the reservoir's initial capacity. The sediment affects the operation of the water diversion system. The most significant problem is flow restriction through the trashrack at the canal headworks due to a combination of trashrack corrosion and accumulation of organic debris and sediment. There also were perceptions by Agency operating staff and municipal water customers that sediment deposits degrade water quality by increasing turbidity while promoting aquatic weed growth and algae blooms responsible for bad tastes and odors that require additional water treatment. The Agency initially believed extensive dredging would be required to restore the operating capacity of Lake Solano, reduce turbidity, and retard the growth of rooted aquatic plants. A comprehensive investigation was conducted for the Agency to develop methods for removing and managing sediment accumulations and for reducing the delivery of sediment from the watershed to the reservoir. The approach and results from that investigation are presented herein.