Napa Valley Groundwater and Surface Water Connections
Monitoring groundwater and surface water connections to inform sustainable groundwater management.
Introduction
A very important Sustainability Goal is being developed for the Napa Valley Groundwater Subbasin:
To protect and enhance groundwater quantity and quality for all beneficial uses and users of groundwater and interconnected surface water in the Napa Valley Subbasin both now and in the future. The Napa County GSA will implement sustainable management criteria and an adaptive management approach supported by the best available information and best available science, resulting in the absence of undesirable results within 20 years from GSP adoption.
What Has The Napa County Groundwater Sustainability Agency (GSA) Been Doing To Promote Groundwater And Surface Water Sustainability?
In response to the requirements of the State's Sustainable Groundwater Management Act (SGMA), the Napa County GSA along with the Napa County Groundwater Sustainability Plan Advisory Committee are working on a Groundwater Sustainability Plan for the Napa Valley Subbasin.
In order to better understand the connections between groundwater and the rivers and creeks in the Subbasin, Napa County installed a series of monitoring wells that record water level trends.
The network currently includes ten monitoring wells installed at five locations. Eight more monitoring wells at four additional locations are planned to be installed in the next year.
Groundwater And Surface Water 101
Groundwater is either hydraulically connected to surface water, or it is not (and therefore disconnected from surface water). The following images help describe these conditions.
Hydraulically Connected Streams
There are two different conditions where groundwater can be hydraulically connected to surface water. This can occur during "gaining stream conditions," when groundwater levels are higher than stream levels, and groundwater feeds water to the stream.
The other scenario is called "losing stream conditions," which occurs when groundwater levels are lower than stream levels, and streams feed water to the groundwater aquifer. This can sometimes occur due to natural conditions or can be influenced by nearby groundwater pumping through wells.
Hydraulically Disconnected Streams
Hydraulic disconnection happens when there is separation between the bottom of the streambed and the groundwater. This can occur during "losing stream conditions", when groundwater levels are lower than the stream's water level. In this case, the stream provides water to the groundwater aquifer through the "unsaturated zone." This can sometimes occur due to natural conditions or can be influenced by nearby groundwater pumping through wells.
The other type of hydraulic disconnect between streams and the groundwater happens during "dry stream conditions." In this case, there is no water flowing in the stream, so there is no connection between groundwater and surface water. This can occur naturally or be influenced by nearby groundwater pumping in wells.
Paired Groundwater And Surface Water Monitoring Sites
Monitoring wells are constructed at strategic locations, and at multiple depths, along the Napa River and its tributaries. The monitoring wells are outfitted with continuous monitoring equipment and also paired with surface water monitoring instruments. This allows us to observe both the surface water level and the adjacent groundwater level.
Shallow and deeper monitoring wells with continuous monitoring equipment installed
Monitoring wells are constructed at strategic locations, and at multiple depths, along the Napa River and its tributaries, shown here near First St in Napa.
What Are We Learning From These New Monitoring Wells?
Using water level data from these monitoring wells in Napa Valley, we can spot connections between shallow groundwater and surface water and understand how those conditions change over time and in wet and dry years, and at different locations.
Check out these monitoring locations for yourself....
Site 1: Napa River at First St
This site is located within the tidally influenced region of the lower Napa River. Groundwater levels here (in green and orange) are typically higher than the surface water level in Napa River (blue). This means that for most of the time, groundwater supplies water to the River (gaining stream conditions), discouraging brackish surface water from entering the aquifer system.
Site 2: Dry Creek at Washington St
This site is located on the west side of Napa Valley along the alluvial fan deposited by Dry Creek. Groundwater levels here (in green and orange) are typically lower than the surface water level in Dry Creek (blue). This means that for most of the time, the creek is supplying water to the groundwater (losing stream conditions), consistent with a characterization developed by the San Francisco Estuary Institute.
Site 3: Napa River at Oak Knoll Ave
This site is located upstream of the tidally influenced reaches of the lower Napa River and is at the downstream end of the Oakville to Oak Knoll Napa River restoration project. Groundwater levels here (in green and orange) are typically higher than the surface water level in Napa River (blue). This means that for most of the time, groundwater supplies water to the River (gaining stream conditions).
Site 4: Napa River at Yountville Cross Rd
This site is located at the Napa River Ecological Reserve. Groundwater levels here (in green and orange) show a direct connection between the Napa River (blue). In this case, groundwater levels are typically higher than the water level in Napa River. This means that groundwater flows to the River (gaining stream conditions). This condition is consistent with the site characterization developed by the San Francisco Estuary Institute as part of the Napa Valley Historical Ecology Atlas.
Site 5: Napa River at Pope St
This site, located near the Sulphur Creek confluence in St. Helena, shows that groundwater levels (green and orange) are typically below the water level in the Napa River (blue). This means that for most of the time, groundwater typically flows away from the Napa River (losing stream conditions).
Site 1: Napa River at First St
This site is located within the tidally influenced region of the lower Napa River. Groundwater levels here (in green and orange) are typically higher than the surface water level in Napa River (blue). This means that for most of the time, groundwater supplies water to the River (gaining stream conditions), discouraging brackish surface water from entering the aquifer system.
Site 2: Dry Creek at Washington St
This site is located on the west side of Napa Valley along the alluvial fan deposited by Dry Creek. Groundwater levels here (in green and orange) are typically lower than the surface water level in Dry Creek (blue). This means that for most of the time, the creek is supplying water to the groundwater (losing stream conditions), consistent with a characterization developed by the San Francisco Estuary Institute .
Site 3: Napa River at Oak Knoll Ave
This site is located upstream of the tidally influenced reaches of the lower Napa River and is at the downstream end of the Oakville to Oak Knoll Napa River restoration project. Groundwater levels here (in green and orange) are typically higher than the surface water level in Napa River (blue). This means that for most of the time, groundwater supplies water to the River (gaining stream conditions).
Site 4: Napa River at Yountville Cross Rd
This site is located at the Napa River Ecological Reserve. Groundwater levels here (in green and orange) show a direct connection between the Napa River (blue). In this case, groundwater levels are typically higher than the water level in Napa River. This means that groundwater flows to the River (gaining stream conditions). This condition is consistent with the site characterization developed by the San Francisco Estuary Institute as part of the Napa Valley Historical Ecology Atlas .
Site 5: Napa River at Pope St
This site, located near the Sulphur Creek confluence in St. Helena, shows that groundwater levels (green and orange) are typically below the water level in the Napa River (blue). This means that for most of the time, groundwater typically flows away from the Napa River (losing stream conditions).
What Do The Data Tell Us About The Connection Between Groundwater And Surface Water In Napa Valley?
In many places in the Napa Valley Subbasin, there is a hydraulic connection between groundwater and surface water. The data from the Monitoring Well sites shown above help us understand where gaining stream and losing stream conditions exist. The data helps support the idea that Napa River tributaries tend to lose water to seepage as they enter the Napa Valley floor.
The Napa County GSA continues to monitor and analyze data and apply management actions to support and maintain these connections.
How Can We Find Out More About Conditions In The Napa Valley Groundwater Subbasin?
The Napa County Resource Conservation District (Napa RCD ) in coordination with the Watershed Information & Conservation Council ( WICC ) have started a community science Stream Watch program to encourage public participation in the monitoring effort at 28 designated sites across Napa Valley.
The website: www.napawatersheds.org/streamwatch provides instructions and a guide for collecting standardized observations, including:
- a photo of the stream from a designated location,
- a description of whether the stream is dry, has isolated pools, or is flowing, and
- observations of trash in the stream.
Check out the video in the next slide for more information.
How to navigate the Stream Watch platform.
Stream Watch Is Expanding What We Know
Like much of California, Napa Valley has a limited number of stream gaging stations. Stream Watch observations contributed by the public and stakeholders broaden our common understanding of stream conditions across Napa Valley. Stream Watch observations can also help us all understand the relationships between surface water, groundwater, and climate at many more locations than would be possible through traditional stream gaging stations.
Take a tour of some of the Stream Watch locations on the following slide.
Stream Watch photo-point monitoring on Tulocay Creek
Stream Watch Site 1 - Napa River at Yountville Eco-Reserve
Stream Watch Site 2 - Napa River at Pope St
Stream Watch Site 3 - Napa River at Rutherford Rd
Stream Watch Site 4: Napa River at Larkmead Ln
Stream Watch Site 5: Redwood Creek at Dry Creek Rd
Stream Watch Site 6: Selby Creek at Larkmead Ln
Stream Watch Site 7: Soda Creek on Soda Canyon Rd
Stream Watch Site 8: Bear Creek near Hwy 29
Check out all of the other Stream Watch Sites here: www.napawatersheds.org/observations
Stream Watch Site 1 - Napa River at Yountville Eco-Reserve
This site has had a lot of observations since 2017, most of which indicate flowing conditions. The river at this location appears to flow year-round following average and above-average rain seasons, but can stop flowing in dry years. So far it has maintained isolated pools when not flowing, meaning groundwater is close to the bottom of the stream channel, and some aquatic species may survive the dry period.
Stream Watch Site 2 - Napa River at Pope St
This site has had a lot of observations since 2017, which show flowing conditions for most of the year, but also isolated pools, and dry conditions as well. The river at this location stops flowing every year regardless of rainfall amount; however, in average and dry years, it can go completely dry not even maintaining isolated pools.
Stream Watch Site 3 - Napa River at Rutherford Rd
This site has had a lot of observations since 2017, which show flowing conditions for most of the year, but also isolated pools, and sometimes dry conditions as well. The river at this location stops flowing in all years, but can have a long no-flow period or completely dry out following below-average rain seasons.
Stream Watch Site 4: Napa River at Larkmead Ln
This site has observations since 2017. These observations indicate flowing conditions averaging 42 weeks in recent years, with extended periods with isolated pools in dry years, and dry streambed for several weeks in very dry years. The river at this location maintains year-round flow in wet years, but can stop flowing in average rain years and even dry out completely following below-average rain seasons.
Stream Watch Site 5: Redwood Creek at Dry Creek Rd
This site has had many observations since 2017, which show flowing conditions typically between November to June, and then dry for most of the summer, with a small amount of isolated pools in between. The creek at this location dries out in all years. The length of the dry period is shorter following wet rain seasons and longer in dry years.
Stream Watch Site 6: Selby Creek at Larkmead Ln
This site has observations since 2017, most of which indicate dry stream conditions, with a small amount of isolated pools and only showing flowing conditions in January to March, 2019. The creek at this location remains dry almost all the time. It will flow for a few weeks or months in the winter in average and above-average rain years.
Stream Watch Site 7: Soda Creek on Soda Canyon Rd
This site has observations since 2017 that show mostly flowing conditions in Soda Creek, with some isolated pools and/or dry conditions over the summer. The creek at this location stops flowing during the dry season in all years, but can dry out completely following average and below-average rain seasons.
Stream Watch Site 8: Bear Creek near Hwy 29
This site has observations since 2017, which show that Bear Creek has flowing conditions averaging 27 weeks in recent years, except in recent very dry years when dry streambed conditions are more common. The creek at this location dries out during the dry season in all years. The length of the dry season is significantly longer following below-average rain seasons.
Check out all of the other Stream Watch Sites here: www.napawatersheds.org/observations
Want To Learn More And Get Involved?
Napa County SGMA Annual Reports: www.countyofnapa.org/3081/Documents-Resources
Stream Watch Website: www.napawatersheds.org/streamwatch
Napa County Groundwater Sustainability Agency: https://www.countyofnapa.org/3074/Groundwater-Sustainability
Napa County Resource Conservation District (Napa RCD): www.naparcd.org/
Napa County Watershed Information & Conservation Council (WICC): www.napawatersheds.org/
Contact:
Ashley Kvitek, Community Engagement Project Manager, (707) 690-3117, Ashley@NapaRCD.org
StoryMap Design by:
Barbara Dalgish, Luhdorff & Scalmanini Consulting Engineers, (530) 661-0109, www.lsce.com
