The Napa County Flood Control and Water Conservation District (District) conducts maintenance activities to reduce flooding along stream channels on public and private lands throughout Napa County. The District also responds to citizen and government alerts to potential flooding or erosion problems, and conducts annual creek and river surveys to assess and prioritize maintenance needs.

In 2011 and 2012, Horizon developed a Stream Maintenance Program Manual, prepared an IS/ND for CEQA compliance, and obtained long-term permits for the program from the Regional Water Quality Control Board (RWQCB) and California Department of Fish and Wildlife (CDFW). The manual includes maintenance approaches and methodologies for many natural instream conditions including non-native plant management, woody debris management, bank stabilization, and minor debris and sediment removal.

Horizon recently assisted the District in updating the manual to include additional District maintenance responsibilities, revised maintenance approaches, maintenance activities conducted by other agencies in partnership with the District, and maintenance of the Napa River/Napa Creek Flood Protection Project. Horizon developed and published an IS/MND for the updated manual in February 2019 and is assisting the District to obtain programmatic permits from RWQCB and the U.S. Army Corps of Engineers.