Floods
Dams, reservoirs, and high-water events
Photo of high water on Alameda Creek at Alameda Diversion Dam, near Sunol, California.
Monitoring rivers and streams during high-water events
The Consumes River, near Sacramento, experienced record streamflow over the 2022 New Year's holiday weekend as an atmospheric river moved through northern California.
Roads closed due to flooding
A flooded road in San Diego is a common scene throughout Southern California during El Niño-related storms.
The USGS maintains a network of nearly 500 streamgages in California that delivers a continuous source of streamflow data. When water levels change rapidly, or reach flood-stage levels, flood-warning alerts are issued help emergency managers assess potential hazardous conditions near the gage or for downstream locations.
California Streamgage Information

The USGS operates more than 7,500 streamgages in the U.S. and nearly 500 in California that collect data to determine the amount of water flowing in rivers and streams. Automatic alerts are transmitted when water levels change rapidly and/or reach flood stage. These alerts help emergency managers assess potential hazardous conditions.
California's Monthly Water Runoff

Water runoff occurs as the result of precipitation that is in excess of the demands of evaporation from land surfaces, transpiration from vegetation, and infiltration into soils. The water that remains available, or "runoff," is the water that makes its way to streams, rivers, and, possibly, to the ocean.