The researchers examined 814 active gauges and modeled scenarios in which more gauges are installed across the state. They said adding 500 gauges to the network could more than double the length of streams monitored.

They acknowledged that this expansion would be expensive because each gauge can cost as much as $40,000 to install and then requires additional funds to maintain. Expanding the network, they said, will require substantial investments by state, federal and local agencies, as well as water districts.

“With appropriate investment, it’s possible to design and build better networks,” Grantham said. “Having more information about how much water is in our rivers and streams will help us to better manage rivers and streams.”

Many state and federal officials are working to address the deficiencies but lack resources, Andrews said, adding that she hopes the study can help inform efforts by the Legislature to prioritize funds.

A previous analysis led by the Nature Conservancy found that 89% of “significant streams” in California are poorly monitored.

Other water experts agree that California should be collecting more data on rivers and streams, as well as groundwater.

“Without accurate information about the amount and quality of water in our rivers and streams, and in our groundwater basins, it is extremely difficult to develop effective policies to more successfully and sustainably manage our water,” said Peter Gleick, senior fellow and co-founder of the Pacific Institute.

“A major expansion of gauges would permit us to more accurately monitor and enforce water-rights allocations, determine ecological conditions and needs for threatened and endangered fisheries, and improve California’s resilience to both floods and droughts,” Gleick said. Recent advances in technology, he said, can also allow for the deployment of more real-time “smart” gauges that measure not only streamflow but also water quality, temperature and other measures of waterways’ health.

Scientists have found similar gaps in streamflow monitoring in regions around the world. Studies have also shown there has been a long-term decline in the number of operating stream gauges in the United States due to lack of funding.

Inadequate streamflow data has long been recognized as a problem in California, and in 2019 the state Legislature passed SB 19, a law that directed state agencies to develop a plan to address the gaps and install more gauges.

In 2022, state water agencies released their plan for prioritizing the installation of more gauges.

“A robust and reliable stream gauge network can help state, federal, and local agencies manage water resources more effectively for multiple benefits and help avoid conflicts,” said Teresa Connor, northern region manager for the state Department of Water Resources.

Connor said in an email that about 1,000 stream gauges are currently operating and reporting data in the state. Many of them are maintained by the U.S. Geological Survey, while the Department of Water Resources operates nearly 300 gauges.

Connor said since the plan was completed, the state agency has started upgrading or reactivating about 50 gauges, and is working with USGS to bring online an additional 11 gauges with available funding.

“The USGS works closely with many partner agencies in California to identify needs for high quality streamflow monitoring for about 500 streamflow stations,” said Paul Laustsen, a USGS spokesperson. “This collaboration means we work together to avoid duplication, ensure critical sites have been prioritized for monitoring and provide reliable, impartial, and foundational data to address water issues facing California.”

In addition to the federal funds that have been appropriated for stream monitoring, USGS has received a four-year state contract totaling nearly $1.2 million to help address gaps in California’s network of gauges.

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