Climate Ready North Bay: Russian River Watershed

Historic climatic water deficit in the Russian River Basin

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Management Priorities

Sonoma County Water Agency’s Responsibilities and Jurisdictions

The Sonoma County Water Agency (SCWA) was created as a special district in 1949 by the California Legislature to provide flood protection and water supply services. Legislation enacted in 1995 added the treatment and disposal of wastewater to SCWA’s responsibilities. SCWA is not a county department but a special district of the state, having specific limited purposes and powers, and separate sources of funding. SCWA is recognized as a national leader among water utilities in bringing cutting-edge science to bear on it’s operations. It has been an active research partner of NBCAI’s and the USGS for over five years within the realm of climate adaptation, and was a key advocate for this North Bay Climate Ready project as a whole.

The mission of SCWA is to effectively manage water resources for the benefit of people and the environment through resource and environmental stewardship, technical innovation, and responsible fiscal management. SCWA’s key functions include: water supply to more than 600,000 residents in portions of Sonoma and Marin counties; sanitation services to over 22,000 residences and businesses; flood protection and stream maintenance for over 175 miles of creeks and waterways; environmental services related to compliance with environmental laws and regulations; production of highly treated recycled water; and ensuring transparency and communications with their community. SCWA environmental staff also works to improve the native fish resources of the Russian River and its tributaries by conducting and coordinating fishery enhancement projects. The Russian River is home to three fish that are threatened or endangered under the federal Endangered Species Act: coho salmon (endangered), Chinook salmon (threatened), and steelhead trout (threatened).

SCWA’s main water sources are the Russian River, Lake Sonoma, and Lake Mendocino. The U.S. Army Corps of Engineers (Corps) owns and maintains the Coyote Valley Dam in Lake Mendocino and Warm Springs Dam in Lake Sonoma, as well as facilities for the Central Sonoma Watershed Project, which includes Spring Lake Reservoir, Matanzas Creek Reservoir, Piner Creek Reservoir, Brush Creek Middle Fork Reservoir, and Spring Creek Reservoir. SCWA controls releases to meet downstream demands and minimum instream flow requirements when reservoir levels are within the conservation pool. SCWA is also dedicated to maintaining the Laguna de Santa Rosa, a natural tributary to the Russian River that stores approximately 80,000 acre-feet of water during peak floods. In addition, SCWA manages Occidental, Russian River, Sonoma Valley, and South Park Sanitation Districts, and Airport/Larkfield/Wikiup, Geyserville, Penngrove, and Sea Ranch sanitation zones (SCWA 2015).

Sonoma County Water Agency’s Climate-related Concerns and Management Priorities

Changes in climate impact SCWA operations on both short and long-term time scales. Short-term impacts include the immediate response necessary for acute demands of frost and heat events. The Corps is responsible for flood control, as well as resources needed for flood forecasting. Long-term impacts include a shift in priorities in planning that are now focused on building water supply reliability, largely as a result of the changes in transfer implemented via the 2004 amended Potter Valley Project (PVP) FERC license. Additionally, water supply in the Russian River basin is most sensitive to changes in springtime rainfall because the rule curve of Lake Mendocino prevents storing water needed for dry season demands until after March 1st of each year.

Currently SCWA does not have a drought definition based on climate indicators, but rather storage in Lake Mendocino is used as the indicator of available water, with drought severity evaluated relative to target reservoir levels. Due to the relatively small size and the seasonal rule curve of Lake Mendocino, it is the most sensitive component in the system to drought. SCWA has been required to seek emergency changes in operations of the Russian River System from the State Water Resources Control Board four times in the past five years due to low storage levels in Lake Mendocino. In addition, the hydrologic index determines the water supply condition of the Russian River System, but the current index is considered potentially outdated and not reflective of current available water. SCWA is actively working to update the hydrologic index, as storage and inflow thresholds defined in the Russian River System hydrologic index trigger changes in minimum in-stream flow requirements of the Russian River and Dry Creek.

Extreme events are of particular concern to SCWA, including strong atmospheric rivers, prolonged drought. Strong atmospheric rivers can cause extreme flooding to areas along the Russian River and its tributaries. Years with few or no atmospheric rivers have been linked to drought years. Due to the small size of Lake Mendocino and the amount of downstream demand, a two-year drought, such as experienced in1976 and 1977, can be very challenging to meet water needs. Frost events along the Russian River can cause sudden reductions in flow due to increased diversions from agriculture to protect crops from frost damage, but progress in recent years has been made on this issue via better coordination with upper Russian River landowners and the requirements to develop and implement Water Demand Management Plans. SCWA is also actively involved in the development of Basin Advisory Panels to create community-based plans for aquifer management in the Sonoma Valley and Santa Rosa Plain, and it is likely that SCWA will retain a meaningful groundwater management role with the advent of the recent statewide Sustainable Groundwater Management Act in concert with local water districts.

SCWA manages a number of resources and facilities that are particularly sensitive to climate during flood events or drought. Staff identified that Spring Lake and Matanzas Reservoirs, Wohler and Mirabel water diversion facilities, and the City of Santa Rosa downtown box culvert are all sensitive to flood events. In addition, flood control infrastructure is sensitive to increases in rainfall intensity.

Increased risk of fire associated with climate change is also a major concern because of potential impacts on water quality. In particular, the natural river bank filtration process that SCWA relies on to help ensure water quality could be compromised if inundated with high concentrations of ash and other post-fire erosion products.

Vulnerability Assessment Results

Key Vulnerability Assessment Findings for the North Bay Region

  • Rising temperatures across the region will generate unprecedented warm conditions for both summer and winter seasons
  • Rainfall is likely to be more variable in the future in term of both low and high annual extreme
  • The North Bay region is becoming more arid (subject to drier soil conditions) due to rising temperatures
  • Runoff may be increasingly flashy, with rates of groundwater recharge relatively less variable over time
  • Protecting available recharge areas will be critical to water supply sustainability
  • Water demand for agriculture may increase on the order of 10%
  • Fire frequencies are projected to increase on the order of 20%, requiring additional readiness planning and more aggressive fuels management
  • Vegetation may be in transition, meriting additional monitoring and consideration of a more drought-tolerant planting palette for restoration

See Climate Ready North Bay: Region-wide Findings and Applications for more about the vulnerability assessment findings for the Northbay Region.

Key Management Questions by Resource Area

The following management questions are addressed in the CRNB SCWA Technical Memo:

Management Question: How may climate change impact the inter-annual variability of the North Bay region’s rainfall?
Management Question: How will climate change impacts regional precipitation quantities for the Russian River Basin?

Management Question: How will climate change impact annual and spring precipitation variability in the Russian River Basin, and in turn, winter and dry season runoff?
Management Question: How will climate change impact the seasonality of annual rainfall in the Lake Mendocino basin?

Management Question: How might climate change increase the risk of flooding in the Russian River Basin?

Management Question: What is the relationship of annual recharge relative to annual runoff?
Management Question: What is the spatial variability of runoff and potential groundwater recharge and how might climate change impact these distributions?

Management Question: How will climate change influence the frequency and intensity of heat events that trigger big upticks in demand for irrigation?
Management Question: How might climate change influence the magnitude of landscape drought stress, estimated as climatic water deficit, across the Russian River basin? Where are the regions where this effect is mitigated by present day fog distributions?

Management Question: How might climate change affect the native vegetation distributions of Sonoma County?

Management Question: How might climate change affect fire frequency in Sonoma County and the Russian River?

Potential Climate Ready Russian River Watershed Data Applications

SCWA is actively engaged in a number of long-term planning processes where climate ready data can be used. These are summarized below.

  • SCWA Climate Adaptation Plan for Water Operations. A consultant has completed a climate adaptation work plan for the Water Agency to serve as the agency’s roadmap for climate adaptation planning. Climate Ready results completed as part of this study will be used to inform the climate adaptation planning process.
  • Forecast Informed Reservoir Operations (FIRO)-a collaborative effort with SCWA, Scripps, California Department of Water Resources, Bureau of Reclamation, USGS, NOAA, and the USACE.
  • NIDIS-National Integrated Drought Information System-a collaborative effort with federal agencies and Scripps Institute of Oceanography.
  • Fish Flow EIR. This project is being pursued as a requirement of the 2008 Biological Opinion issued by NMFS and entails modifying the Russian River hydrologic index and the minimum instream flow requirements to improve conditions for rearing salmonids and to improve water supply reliability of Lake Mendocino.
  • Lake Mendocino Reliability Study. Term 17 of the May 2013 order from the State Water Resources Control Board requires the Water Agency to work with water users in the Upper Russian River to assess the long term reliability of Lake Mendocino with predicted changes in system demands.
  • Groundwater aquifer planning in Sonoma Valley, Santa Rosa Plain and Petaluma Valley, including groundwater banking planning and site selection and compliance with the California Sustainable Groundwater Management Act.
  • Flood Protection Planning. SCWA is in the process of creating updated flood control design criteria, which entails setting standards for mitigating stormwater runoff in cities.
  • SCWA is partnering on a Climate Risk Dashboard project in concert with the Presidential Office of Science and Technology Policy that is evaluating the potential use of Climate Ready North Bay products for the Russian River as part of a “C-PREP” pilot.

Management Concerns for Future Analysis

What will the impact of climate change be on stream temperatures that in turn will impact fisheries habitat value?

While the BCM can provide downscaled temperature data relevant to this topic, responding to this management question requires a complementary stream temperature model be developed for the Russian River Basin. The Water Agency has been collaborating with NOAA to improve temperature modeling in the Russian River Basin. Currently an adaptation strategy has been to develop a notification system that alerts users of temperature forecasts that exceed 100 deg F.

How do reservoir operations potentially influence groundwater recharge, in particular during periods of sustained high flows during the dry season that exceed unimpaired flow estimates used in this study?

This study generated recharge estimates based on estimates of unimpaired flow conditions. If This might be a conservative estimate of actual recharge values for aquifers adjacent to the river due to sustained dry season flows provided by the reservoirs. A next step could be an analysis of recharge enhancement due to flow increases during the summer season due to reservoir releases.

How can we estimate impact of potentially variable groundwater recharge rates on actual aquifer levels?

To thoroughly assess the impacts to aquifer recharge requires the development of a coupled surface water groundwater model, as has been completed for the Santa Rosa Basin in an earlier study. This is an option to pursue for the other groundwater basins, once they have a groundwater model in place.

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