DWR and Napa County Partner to Bring More Stream Gages Online, Providing Critical Information for World-Renowned Wine Region

In a region known for its vineyards, scenic hills, and delicate ecosystems, accurate and timely data of Napa County’s streams is more than just a technical asset, it’s a lifeline. As part of DWR’s California Stream Gage Improvement Program (CalSIP), DWR and Napa County are collaborating to bring five stream gages online in the Napa River watershed, targeting data gaps in the watershed and key tributaries which will help water managers plan for dry periods and make faster emergency decisions during flooding events.

Napa County’s Five New Gages: Where and Why

Made possible with funding from the Budget Act of 2023, the CalSIP program is enabling the revival and deployment of gages at five critical sites in Napa County. These include the Calistoga reach of the Napa River, Conn Creek, Dry Creek, Milliken Creek, and Redwood Creek.

These sites were chosen to extend coverage into areas that have been largely unmonitored. The new network will enable water managers to focus on how each stream and creek contributes to the overall Napa River system. It also helps illuminate how smaller sub-watersheds respond to rainfall, seasonal pulses, and drought stress.

The new gages will work with the two existing Napa River gages to improve flow monitoring over the entire length of the river. Together, this enhanced monitoring network will provide what has long been missing: continuous, high-resolution flow data across the full watershed.

Key Benefits

• Low-flow detection and drought stress tracking: In late summer and fall, many smaller streams may approach zero discharge (meaning no measurable water flow is leaving the stream). The new stream gages will help detect precisely when and where flows drop, which is vital for ecosystem protection and water allocation decisions.  Additionally, after years of operation, improved understanding of watershed yield will help predict future drought responses.
• Tributary quantification: For the first time, Napa County will have continuous data on how much water each tributary contributes under different conditions. This insight is crucial for informing flood response such as providing advanced warning when high water may impact populations downstream.
• Restoration and salmonid support: Restoration planning will benefit from local flow data. Species such as steelhead and Chinook depend on small streams in the upper watershed for spawning or rearing refuge during dry periods.
• Improved hydrologic and watershed models: This new data will enhance the ability to simulate how rainfall runs off, the timing of flows, and interconnections between surface water and groundwater.
• Groundwater-surface water interactions: Napa Valley is designated as a high-priority groundwater basin under California’s Sustainable Groundwater Management Act (SGMA). Understanding how streams and groundwater exchange, especially during dry times, is essential for sustainable planning.

Napa County’s Watershed

Groundwater monitoring in the Napa Valley Subbasin shows that the aquifer system is increasingly vulnerable to seasonal stress, making improved understanding of recharge and discharge mechanisms even more critical. The addition of these five gages is more than a symbolic investment in instrumentation; it’s a decisive step toward closing information gaps that have limited adaptive water and ecosystem management in Napa County. Over time, the data will help managers move from reacting to problems as they happen to planning ahead and making decisions based on real data.

In addition to the new gages in Napa County, DWR has entered into funding agreements with 37 public agencies to add or improve approximately 150 stream gages statewide. More than $8 million in funding has been allocated to support these efforts. With this funding, agencies will be able to secure permits, acquire and install equipment, and calibrate stream gages through June 30, 2027.

Visit the DWR CalSIP Stream Gage Map to see where other stream gages are located and are coming online.