PROJECT ALERT NOTICE (CA) Flooding expected for CA this week as ARs bring more rain - Day 5

Date: Sat, 11 Feb 2017 14:20:42 EST

Summary: Flooding continues from multiple atmospheric rivers that brought rainfall and snow to parts of California.

Today, light showers are expected for southern and central California with precipitation tapering off later tonight. Although no rainfall is expectedfor northern California, many north central counties remain under flood warning today. Currently, 62 percent of USGS streamgages in CA are reporting streamflows more than 90 percent above normal flow for this time of year. The NOAA/NWS California Nevada River Forecast Center reports many California rivers remain above flood (14 sites) or monitor (30 sites) today.

The California Water Science Center (CAWSC) has 3 crews responding to this event today from the following service areas: Redding, CA (1); Sacramento, CA (1); and Santa Maria (1). Crews are performing high-water measurements, making repairs, flagging high water marks, and collecting sediment samples.

A USGS crew will be measuring streamflow, turbidity, and conducting suspended sediment sampling on the Feather River today. The USGS is conducting this work in emergency response to recent sedimentation concerns in the Feather River that result from dam releases made over a damaged and rapidly eroding spillway at Oroville Dam - a situation that has been developing since February 9. According to the California Department of Water Resources (DWR), Oroville Dam integrity is not a concern, but with the reservoir at 100 percent capacity, continued releases (55,000 cfs) over the damaged spillway have been necessary. With storm and snowmelt runoff continuing to flow into the lake, dam operators this morning were forced to also release water over an emergency spillway (unlined) that has not been used in the dam’s 48 year history. Releases over the emergency spillway will range between 5,000-10,000 cfs, an additional amount of flow in the Feather River that DWR officials say is still only half of the downstream flood system capacity. The USGS maintains a real-time continuous water-quality stations on the Sacramento River at Verona, CA (11425500). This station is located below the confluence of the Sacramento and the Feather Rivers and is more than 60 river miles downstream of Oroville Dam. Turbidity recorded at this site has increased substantially (by about 70 FNU) since noon yesterday. With more rain predicted for California beginning on Tuesday, the USGS will continue to monitor this situation as it develops and is prepared to provide emergency response as needed.

CAWSC managers remain in contact with water-resource managers and cooperative partners to coordinate USGS sampling or high-water measurements. No safety issues have occurred during this series of storms and all staff have followed USGS field reporting and safety protocols. No crews are expected to deploy tomorrow for recessional measurements. Updates will continue to be provided during the course of this event.