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For many Californians a wet and snowy winter means keeping dry inside and avoiding dangerous roads. For field crews at the U.S. Geological Survey California Water Science Center (CAWSC), however, wet weather means piling on safety gear and chasing storms to make real-time high-flow and flood measurements at swollen rivers, creeks, and waterways throughout the state.
CAWSC – in cooperation with agencies around the state – runs and maintains a network of more than 500 streamgages throughout California. This is part of a larger National Streamgage Network the USGS operates, which has more than 7,000 stations around the country. USGS streamgage data play a critical role in emergency preparedness and water resource management, providing accurate, reliable, real-time data to help officials keep communities safe during and after storms.
High-Flow and Flood Measurements
When rivers exceed or are expected to exceed flood stage, USGS crews travel to streamgage stations around the state to measure how fast water is moving at a cross-section of the river so that discharge can be accurately calculated. Streamflow or discharge is the amount of water flowing in a stream or river, expressed in cubic feet per second (roughly equivalent to the size of a basketball). USGS streamflow data helps water-managers time flood releases at dams and reservoirs during high-flow and flood conditions. Using accurate, real-time data to time flood releases – especially in flood-prone regions like the Sacramento and San Joaquin Valleys – is critical for protecting life, property, and infrastructure downstream.
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While conducting high-flow measurements, crews often deploy an acoustic Doppler current profiler (ADCP) – a device that uses sound waves to determine the cross-sectional area of the river and velocity of the water. The rate of streamflow will then be computed from the area and velocity plus the height of the water, which is measured by streamgages automatically. This data is sent every 15 minutes via satellite to the National Water Information System (NWIS), the national USGS water resources database.
ADCPs can be suspended from safe locations like a bridge or an overpass or towed using a boat or kayak. If conditions are safe, crews can also wade into moving waters to manually measure streamflow. Cableways (see photo in slideshow) also allow for the same data to be collected. Cableways are built to minimize potential hazards quickly moving water may cause for field crews.
In addition to ADCPs, USGS field crews use other tools and technologies to monitor water levels and movement. Most of the sites in the CAWSC streamgage network are Automated Local Evaluation in Read-Time (ALERT) streamgages, which are designed to send warnings when water levels reach a predetermined level or change rapidly. These data are used by the National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) to assess the need for emergency preparedness or early warning systems that help protect life and property. Local, regional, and state agencies also rely on USGS data for emergency planning.
USGS field crews throughout California deploy during rain, snow, and even dangerous flooding conditions year-round to ensure that streamflow data is accurate for use by emergency preparedness personnel, engineers, water managers, and the public. With support from local, state, and federal agencies, the USGS has monitored flow in streams and rivers across California for more than 100 years. USGS real-time maps of flood and high flow conditions for California are free and publicly available online, 24 hours a day, 7 days a week, 365 days a year through NWIS.
