YCWA Flood Management for Relicensing 9/24/14 9/24/20141

Background of YCWA Flood Management YCWA was created as a primarily flood control agency A district hereinafter called an agency is hereby created for the purpose of accomplishing a function of statewide importance. Said agency shall be known as Yuba County Water Agency….” The agency shall have the power to control the flood and storm waters of the agency and the flood and storm waters of streams that have their sources outside of the agency, which streams and flood waters flow into the agency, and to conserve such waters for the beneficial and useful purposes of said agency ….” Major events in 1986 and 1997 resulted in damages within Yuba County (Feather River levee breaches) YCWA has limited ability to control floods – Levees – New Bullards Bar Dam (including USACE dedicated flood reservation) One major challenge is effect of Feather River, hence the Forecast – Coordinated Operations program with DWR – Uses forecasts to make pre-releases ahead of storm – Coordinated operations to avoid co-incident peaks 9/24/20142

Flood Management vs. Storage Management There are frequent releases from the New Bullards Bar Dam spillway, but rarely for flood management – Flood management releases are for flood damage reduction Major events Typically rainfall-driven (atmospheric rivers) rather than snow melt – Storage management releases from spillway typically occur to bypass inflows to avoid storage encroaching into USACE flood reservation New Colgate PH releases often inadequate to match inflow Encroachment into flood reservation results in different operational rules and control Existing capacity is more than adequate for storage management operation 9/24/20143

YCWA’s Current Flood Management Operations Operate according to 1972 USACE New Bullards Bar Reservoir Regulation for Flood Control – Specifies a flood reservation space (maximum of 170 TAF from 11/1 through 3/31) – Specifies maximum flows below New Bullards Bar Dam (50,000 cfs), in Marysville (120,000 cfs), in Feather below Yuba (300,000 cfs), and in Feather below Bear (320,000 cfs) YCWA uses forecasts, New Bullards Bar and watershed state information to make flood management release decisions – When large inflows forecasted, may make pre-releases from NBB to clear space ahead of peaks on South and Middle Yubas or on Feather – When encroached into flood reservation, YCWA considers flows on other tributaries when determining releases from NBB to evacuate NBB flood reservation space Spillway gate operations/rate of evacuation of flood reservation balances available information, communication with DWR operators 9/24/20144

Modeling Flood Operations for Relicensing Do not use spillway (or FCO) for storage management – Only operated once NBB storage is encroached into flood reservation – Use maximum release capacity (WSE limited) to evacuate water from flood reservation space as quickly as possible – Considers maximum allowable flows below NBB and in Marysville 9/24/20145

Operations of Proposed Flood Control Outlet for Flood Management NBB flood management release capacity are currently restricted. Need to be well into an event before substantial release capacity is available – Limits YCWA’s abilities to use forecasts and to make pre- releases – Limits YCWA’s abilities to coordinate releases with DWR Proposed FCO allows for greater releases, earlier in a storm Modeling of the FCO only allows for increased release capacity at a given elevation, reduces encroachment into flood reservation 9/24/20146