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Agricultural water use accounting provides path for surface water use solutions

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Authors

Glenn McGourty , UC Cooperative Extension
David J. Lewis, UC Cooperative Extension
Josh Metz
John M. Harper, UC Cooperative Extension
Rachel B. Elkins, UC Cooperative Extension
Juliet Christian-Smith, Water Foundation
Prahlada Papper, UC Berkeley
Lawrence J. Schwankl, UC Cooperative Extension
Terry Prichard, UC Cooperative Extension and UC Davis

Publication Information

California Agriculture 74(1):46-57. https://doi.org/10.3733/ca.2020a0003

Published online March 17, 2020

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Abstract

Agricultural water demands can conflict with habitat needs in many North Coast watersheds. Understanding different water use patterns can help reduce conflict over limited supplies. We measured on-farm crop water use and conducted grower interviews to estimate the agricultural water demand in the upper Russian River and Navarro River watersheds. Annual agricultural water demand was less than 11% in the Russian River, and 2% in Navarro River, of the total annual discharge in each watershed. However, because demands are concentrated in the dry season when instream flows are at a minimum, these relatively small amounts can represent a significant constraint to stream habitat conditions. We have shared our study results in broad basin and community water resource planning efforts, including flow management of the Russian and Navarro rivers and implementation of the Sustainable Groundwater Management Act in the Ukiah Basin. Findings and recommendations from this study have influenced on-the-ground solutions to meet water demand in these watersheds, including construction of off-stream wintertime storage capacity to replace summertime stream diversions, and use of a municipal recycled water conveyance system as a replacement for summer diversions.

Full text

Satisfying water demands for multiple uses in California is an increasingly acute and difficult issue. High interannual climate variation characterized by successive drought and flood years introduces extreme uncertainty into water allocation decisions. During drought, allocations for agricultural use have been curtailed and environmental flows reduced to perilous levels for endangered and threatened wildlife (NOAA 2005). The Russian River Basin exemplifies the challenges of managing water for agriculture and the environment and has become the focus of recent state regulations (2015–2016 Russian River Tributaries Emergency Regulation Information Order) to more accurately account for water demands within tributary streams that support critical habitat for coho and steelhead trout.

Another significant policy enacted to address competing demands in the Russian River is the 2013 California State Water Resources Control Board (SWRCB) Policy for Maintaining Instream Flows in Northern California Coastal Streams (SWRCB 2013; SWRCB 2014). The purpose of this policy is to develop a streamlined process for reviewing and approving pending water rights applications, which in some cases have been delayed for decades by the SWRCB Division of Water Rights. The policy requires water rights applicants to meet stringent minimum instream bypass flow requirements and to consider alternatives for meeting their respective water needs, including water conservation and use of alternative sources.

Results from a UC Cooperative Extension study of the upper Russian River and Navarro River watersheds indicate that, on an annual basis, the amount of water used for crop production in both watersheds is small relative to total annual discharge.

Results from a UC Cooperative Extension study of the upper Russian River and Navarro River watersheds indicate that, on an annual basis, the amount of water used for crop production in both watersheds is small relative to total annual discharge.

To avoid impacts to the environment, more research is needed to better understand and manage agricultural water demands. Completed and ongoing studies in the Russian River watershed are generating water budgets and insight into the relationships between water use and stream flows. There are differing indications that subsurface and groundwater stores have been impacted over the last two decades in both mainstem reaches of the Russian River (Constantz et al. 2003; Marquez et al. 2016) and tributary watersheds like Alexander Valley (Metzger et al. 2006). Deitch (2006) correlated changes in stream flow to daily agricultural water use patterns and found evidence of direct steam flow reductions during irrigation periods. These and other investigations point to knowledge gaps about the timing and volume for water uses like agriculture that can support development of solutions to reduce impacts to the environment and competition for limited water supplies.

Our premise is that the best opportunity to relieve competition for water involves working with local agriculture to generate an accurate accounting of current and future water demand, including location and timing of use, and evaluate existing and potential options for meeting this demand. To serve that purpose, the primary objective of this study was to calculate agricultural water demand in the Mendocino County portion of the Russian River and Anderson Valley portion of the Navarro River watersheds (fig. 1). This includes the volume and timing, or seasonality of use, that could then be compared to annual and seasonal fluctuations in stream flow volumes and environmental flow demands.

Study location including the upper portion of the Russian River watershed and the Anderson Valley portion of the Navarro River watershed.

FIG. 1. Study location including the upper portion of the Russian River watershed and the Anderson Valley portion of the Navarro River watershed.

Our second objective was to assess needs and opportunities for innovations, including grower motivations, in irrigation technology, practices and water sources. Findings from this research have already improved agricultural water demand knowledge and facilitated feasible and sustainable agricultural water use in the study area (see sidebar, next page). This on-the-ground and with-the-users approach to water use accounting and the application of the results for solutions to meeting multiple water demands provides a useful model for relieving competition for water use in other watersheds.

Site description

The Navarro River, flowing east to west, is the largest coastal watershed in Mendocino County, covering approximately 315 square miles. The portion of the Russian River within Mendocino County is approximately 362 square miles and flows north to south. The Navarro is a natural river with no dams or other obstructions on its mainstem, whereas the Russian River is regulated by the Coyote Valley Dam, which creates a maximum 110,000 acre-feet of storage in Lake Mendocino. Additionally, inter-basin transfers are made from the Eel River to the Russian River via the Potter Valley Project.

The climate of both watersheds is Mediterranean with most rainfall occurring in the winter months, followed by no rainfall from late May to late September. Because of the close proximity to the Pacific Ocean, there is a strong marine influence on the Navarro watershed, with fog occurring many late nights and mornings and cooling westerly winds during the day. This contrasts with the more inland position of the Russian River watershed in Mendocino County, which has relatively clearer skies and drier and warmer conditions. Rainfall in the Navarro River watershed averages 40.6 inches per year, whereas the city of Ukiah and the Russian River watershed average 36.6 inches per year (Bearden 1974). The Navarro is sparsely populated with approximately 3,200 people. The Russian River watershed in Mendocino County is also rural in comparison to other parts of California. However, Ukiah and other residential centers have a combined population of over 20,000 people. Both watersheds experience the economic activities of agriculture (vineyards, orchards, livestock, small-scale mixed horticultural enterprises and commercial softwood production), beverage production (wine and beer) and tourism.

Study design and methods

We completed this study in 2007 in the Russian River and in 2009 in the Navarro River watersheds, using the same study design and approach comprised of three elements for water use accounting.

  1. We quantified the current acreage and crop designations using available agricultural statistics, aerial photograph interpretations and field visits to validate crop type and extent determinations. This included comparisons with past irrigated agriculture acreage and estimation of potential additional irrigated acreage; field evaluations were conducted of irrigation systems to quantify applied water for irrigation, heat protection, frost protection, and postharvest needs and irrigation distribution uniformity.

  2. To estimate total annual agricultural water demand we summed the amounts of irrigation water, frost protection, heat protection, and postharvest volumes multiplied by the extent of existing and potential irrigated agriculture in the two watersheds. As part of this calculation, we compared the volume and timing of the total agricultural water demand to instream flow volumes. Instream flow volumes or daily discharge (cubic feet per second) were determined using stream flow measurements from U.S. Geological Survey (USGS) gauging stations.

  3. To assess the needs and opportunities in water use innovations, we conducted grower surveys on existing irrigation system infrastructure and irrigation management decisions. A 25-question survey (available as supplemental information online) was administered to further inform water amounts used, water conserving irrigation system technologies adopted, and other background information needed to explore options and drivers to meet water demand and conservation goals.

Mendocino County winegrowers and advocates find solutions for agricultural water use while protecting endangered species

This study was undertaken with the aspiration that it could lead to solutions relieving potential pressure on stream flows from agricultural diversions, including the feasibility for small-scale private winter flow storage and opportunities for water reuse. Our study quantifies the amount of water used by agriculture relative to the total flow of water in both watersheds. We noted while water diversions are a small percentage of total flow, agriculture diverts water at a time when flow rates are low, and the need of water for fisheries is critical. In our recommendations, we discussed the concept of off-stream water storage when water flow was more plentiful. We also discussed that growers were comfortable with using recycled water as a substitute for direct diversions from the Russian River.

Spring of 2008 was one of the most challenging frost protection seasons in the upper Russian River watershed in over 30 years. Many growers required up to 20 nights of frost protection in their vineyards and orchards. A combination of limited water releases from Lake Mendocino due to a very dry winter, and large diversion demands for sprinkler frost protection from vineyards and orchards, greatly reduced flow in the main stem of the Russian River. In a normal rainfall year, instream flows during frost season range from 200 to 600 cubic feet per second (cfs) as recorded at the USGS water gauge in Hopland. In 2008, instream flows averaged 175 cfs. On April 20, 2008, a very cold advective freeze event occurred, creating an instantaneous drawdown of 83 cfs when nearly every agricultural water diverter turned on their frost protection systems. This drawdown resulted in a 2-inch drop in river stage and caused the stranding and mortality of hundreds to thousands of juvenile coho and steelhead trout, endangered and threatened species, which the National Marine Fisheries Service (NMFS) considered a “take” under the Endangered Species Act. As a result, in April 2009, NMFS requested that the California State Water Resources Control Board place a moratorium on the use of river water for frost protection. Honoring this request would have made it impossible in many years to grow wine grapes in the region, resulting in large employment and economic losses (estimated at up to $235 million).

In response, the Upper Russian River Stewardship Alliance was formed by the Mendocino County Farm Bureau, the Mendocino Wine Grape Commission, the Upper Russian River Flood Control District, the California Land Stewardship Institute, the Redwood Valley County Water District and local NRCS and UCCE offices to work with resource agencies and to find more reasonable approaches to solving the problem of river drawdown that could potentially strand young salmonid fish.

The group met regularly and developed The Upper Russian River Frost Protection Pumping Coordination Protocol. This coordinated effort improved frost forecasting precision by making more private weather stations available to frost forecasters. When frost events are likely to happen, growers call the Sonoma County Water Agency, controller of water releases from Lake Mendocino, so that river flows can be increased during frost events. Additionally, a new USGS water gauge was installed closer to Lake Mendocino to more accurately measure flow.

The California Land Stewardship Institute and the NRCS worked together to apply for $5.7 million in grants for water management infrastructure to prevent another fish stranding like that on April 20, 2008. The grant funds focused on creating off-stream ponds to store water to be used during frost events so that instantaneous drawdown would be reduced. Twenty ponds were built, with a combined water storage of 435 acre-feet. These ponds are filled with water under appropriated water rights (water stored from behind the Coyote Dam at Lake Mendocino). Growers have the capacity to pump as much as 145 cfs during a frost event from their ponds, replacing Russian River diversions that could imperil juvenile salmonids. After frost events, ponds are scheduled for recharge at more gradual rates to maintain adequate flows and water levels for fish.

To further improve the water supply situation, the city of Ukiah received $45 million in grants and low interest loans and is constructing a pressurized “Purple Pipe” system for agricultural and landscape water use. The Ukiah Municipal Wastewater Treatment Plant treats wastewater to California's Title 22 water reuse standards, with capacity to provide almost 4,000 acre-feet of water for use on farmland, parks, cemeteries and school grounds in Ukiah environs. Previously, this water was returned to the Russian River after treatment. This will reduce the demand for Russian River diversions, increase water security for the upper Russian River watershed, and reduce the costs associated with wastewater discharge management.

In Anderson Valley, The Nature Conservancy (TNC), who partially funded the Navarro River watershed portion of this study, very quickly teamed with the UCCE Mendocino County Office, as well as the Anderson Valley Winegrowers Association and the Mendocino County Resource Conservation District, to address some of the issues raised in our study.

The first major initiative was to install 16 new stream gauges in various smaller tributaries to augment the single USGS gauge near Philo, as the single gauge in the Navarro River watershed was inadequate for real-time irrigation management and better understanding impacts of dry season diversions on stream flows. The new gauges also help to inform conservation planning and identify areas that would benefit from additional water storage. Some of the gauges funded and installed by TNC are connected to cell phone interfaces so that a grower can accurately monitor the effects of diversions as they occur.

TNC is working with growers and the California State Water Resources Control Board to change their water rights to forbear summer diversions when flow rates in the watershed are very low and to allow for off-stream storage earlier in the year when flow rates are high, above critical levels for fish migration, spawning and juvenile survival. TNC also identified cost share funding for pond construction for water storage, working with the local USDA NRCS office and Mendocino County Resource Conservation District.

These examples of solving environmental problems proactively and locally through cooperative, thoughtful planning and execution resulted in much more positive outcomes and responded to real concerns for the impacts on people, their property and community in proposed regulations from agencies external to the region. Compiling and analyzing on-the-ground water use data, and applying that science through local associations and organizations, demonstrates how public and private partnerships can be successful for all concerned stakeholders.

Estimated irrigated agriculture extent

We mapped irrigated agricultural acreage in the Russian River watershed (fig. 1) using aerial photographs taken between August and September 2004 (AirPhoto USA). Late summer and early fall images provided a stark contrast between green irrigated crops and golden-yellow dry grasses. We visually assigned acreage into five crop designations: grapes, orchards, row crops, pasture and unknown. We estimated potentially irrigable lands based upon slope and landscape position to evaluate potential future water demand. Crop acreage classifications were validated through systematic field visits.

We obtained agricultural acreage statistics for the Navarro River watershed from Mendocino County Department of Agriculture Annual Crop Reports (Linegar 2008), the California Department of Water Resources (CDWR 1964, 1979, 1989) and the California Department of Food and Agriculture (CDFA 1968, 1976, 2006, 2009). Additionally, we mapped irrigated agriculture spatial extent in a geographic information system (GIS) using U.S. Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP) photographs (NAIP 2009). Data were summarized to provide a picture of historical and current irrigated agriculture extent in the study area. While the Navarro River extends beyond the study area, our analysis was constrained to portions of the Navarro River watershed with active agricultural operations, namely Anderson Valley (fig. 1).

We estimated future irrigated agriculture in the Russian River watershed by visually determining potentially irrigable lands not currently in production based upon the slope and landscape position. In the Anderson Valley, we used aerial imagery from the 2009 USDA NAIP aerial mapping program to develop a land cover classification for the Anderson Valley watershed. Sample points from forest and non-forest land cover types were identified in the 2009 aerial images and used to inform an image classification procedure. Maximum Likelihood Classification (Nagi 2011) was used to generate the land cover classes with a 10-m pixel resolution.

National elevation data at 10-m resolution was used to derive topographic slope for the Anderson Valley. The National Elevation Dataset provides uniform topographic data across the United States and allows for explicit consideration of topography in geographic analysis and modeling (State Water Commission and USGS 2017). Slope classes of < 10% and < 20% were created to discriminate vineyard potential under different slope thresholds. In general, steeper slopes are more difficult and costly to farm. Vineyard land cover identified during air photo mapping was used to extract existing vineyard land cover from the model.

The Squawrock-Witherall soil complex, interspersed with Hopland and Yorkville soil series and known to be high in magnesium (Rittiman and Thorson 1993), was excluded from our final analysis due to its known impacts on vineyard performance including potassium deficiencies, potential toxicity from nickel, poor surface stability and high erosion potential. While there are some vineyards planted on these soils, low yields, soil instability when saturated, and high erosion make them difficult to manage. Generally, these sites are not recommended for agricultural enterprises.

Irrigation system evaluation

Our evaluation of existing irrigation systems and measurements of applied water volumes included field measurements and calculation of water used for irrigation, including distribution uniformity, frost protection, heat protection and postharvest applications.

Irrigation use and distribution uniformity

We conducted field evaluation and existing irrigation systems measurements on a subset of vineyards, apple and pear orchards, and irrigated pastures to understand irrigation use and system distribution uniformity (consistency in applied water volume and rate throughout an orchard or vineyard). Methods used to conduct these evaluations are described in Prichard et al. (2007), Schwankl (2007) and Schwankl and Smith (2004). Evaluations included field measurement of water application rates and irrigation system distribution uniformity on 33 vineyard blocks, seven orchard blocks and one irrigated pasture in the Russian River watershed, and 26 vineyard blocks and three orchard blocks in Anderson Valley.

Additionally, we conducted interviews with cooperating growers to document irrigation season duration and irrigation frequency. Measured application rate and grower interview information were combined to estimate total irrigation use. Reference evapotranspiration (ETo; reference rate at which water evaporates from the soil and transpires) data were obtained for 2007 from California Irrigation Management Information System (CIMIS) stations #106 Sanel Valley in Hopland, F90 4933-23 on the Light Ranch in Redwood Valley, and the U.S. Army Corps of Engineers Coyote Dam station in the Ukiah Valley. Anderson Valley values for ETo were obtained for the 2009 season from an AdCon (AdCon Telemetry, Austria) weather station at Roederer Estate in Philo. Russian River soils information and data were derived from the Mendocino County Soil Survey (Howard and Bowman 1991). Available water holding capacity data for dominant soil types within irrigated agricultural lands in Anderson Valley were obtained from Rittiman and Thorson (1993).

Grapevine water use and crop coefficient (Kc) are linear functions of shaded area beneath the canopy (Williams and Ayers 2005). To calculate specific crop coefficients for this study, we measured percent canopy area covering the vineyard floor. In the Russian River study area, site-specific crop coefficients were calculated in 19 wine grape blocks. Shaded area beneath the canopy at midday was assessed using photographs, digitizing dark and light areas beneath and between vine rows, and measuring actual shaded area (Prichard et al. 2007). In the Anderson Valley, we used the Paso Panel technique (Battany 2012) to directly measure canopy shaded area on representative sites and trellis designs. Field data were used to calculate grapevine crop coefficients according to methods outlined by Battany (2012). We took vine canopy field measurements at Roederer Estate Vineyards in Philo between 1200 and 1300 hours (solar noon) on September 28 and October 2, 2012. Vine canopies were healthy, green and fully expanded. A total of four sites planted to pinot noir and chardonnay were selected based on trellis type, vine vigor and row orientation; we recorded 40 observations from each site. Crop coefficients were calculated using the algorithm provided by Battany (2012). These values were used to produce an average Kc.

Frost protection calculations

Grower interviews, relevant production manuals (Snyder 2007), project team experience and study area knowledge were used to generate total frost protection water use estimates. The dominant frost protection method is overhead sprinkler water application, which maintains the plant material surface temperature above freezing. In general, frost protection is used on vineyards and orchards located below 700 feet elevation because radiant frost typically occurs below this elevation in the study area. Heavier cold air settles in lower parts of the landscape, which poses crop damage risk (when green tissue is present) under normal radiant frost conditions. The elevation break for frost damage in Redwood and Potter valleys is higher than in the Ukiah Valley, as the valley floors are 770 feet and 950 feet, respectively. It is important to note that infrequent advective frost events impact the entire study area regardless of elevation.

Frost protection application rate was assumed to be 50 gallons per minute per acre (gal/min/ac) for grapes, or 0.1 inches of water per hour. In orchards, one acre-inch is applied for each frost protection event (Elkins et al. 2006). If systems are not routinely maintained and repaired, these values can be as low as 35 to 40 gal/min/ac. Additional assumptions for frost protection duration (hours/frequency) and acreage for each sub-basin were made based upon grower interviews.

Heat protection calculations

Total water use for heat protection calculations relied on grower confirmation of heat protection methods, relevant production manuals, project team experience and study area knowledge. In general, the same sprinkler system used for frost protection in grapes is used for heat protection. Accordingly, we assumed the heat protection application rate was 50 gal/min/ac, keeping in mind variability can exist due to system maintenance and effectiveness. Not all farms have these systems or access to sufficient water for heat protection. Additional assumptions for duration (hours/frequency) and acreage in which heat protection were made also based upon cooperating grower responses.

Postharvest application

Total water use calculations for postharvest application in wine grapes relied on grower response data, project team experience and study area knowledge. In general, the same irrigation system used for frost and heat protection in grapes is used for postharvest irrigation. Accordingly, we assumed postharvest application rate was 50 gal/min/ac, keeping in mind variability can exist. Postharvest irrigation is used to germinate cover crop seed banks and enhance carbohydrate storage. The latter objective is most applicable for white varieties where growers strive for yields of 5 to 6 tons per acre. Postharvest application decisions also depend on water availability. Additional postharvest application assumptions for duration (hours/frequency) and acreage relied on grower responses.

In pear orchards, postharvest irrigation occurs in August and September while trees are actively growing. For this reason, postharvest irrigation was included in pear irrigation use calculations.

Total agricultural water demand

We calculated total agricultural water demand by summing water used for irrigation, frost protection, heat protection and postharvest application; volumes were informed by agricultural practice differences and access to water. Total (per acre) water use (and its ranges) were multiplied by both existing (mapped) and potential (modeled) irrigated agriculture to calculate total agricultural water demand. Total demand, including timing and volume, was then compared to annual stream discharge data. Data from the following USGS stream gauging stations were compiled and analyzed for the Russian River watershed: Russian River near Ukiah, station #11461000; east fork of Russian River near Ukiah, station #11462000; and Russian River near Hopland, station #11462500. Stream discharge measurements from USGS stream gauging station #11468000 near Navarro, Mendocino County, were compiled and analyzed for the Navarro River watershed.

Grower surveys

We administered surveys to wine grape and fruit tree growers in both watersheds through two focus groups; the surveys were designed to understand water use patterns and document water resource use and irrigation management practices. The 25 questions in the survey were developed to gather information on growers’ water resource management history, including frost and heat protection, irrigation system technology change, conservation program participation, and opinions on alternative water sources. All focus group participants and survey respondents (a total of 15 Russian River and 14 Anderson Valley grape, pear and apple growers) completed appropriate human subjects releases required by the Office of Research Institutional Review Board Administration for the University of California, Davis.

Transitions in irrigated acreage

Based upon our team's land use mapping and modeling, irrigated agriculture in the Mendocino County portion of the Russian River watershed consists of 75% wine grapes, 15% irrigated pasture, 9% pears and less than 1% in other vegetable and unconfirmed crops (table 1). CDFA crop acreage statistics identified 14,212 acres in wine grape vineyards and 1,867 acres in pear orchards within the study area (Bengston 2008). These values are 9% less for grapes and 1% more for pear orchards compared with our values.

Acreage of irrigated agriculture in the Mendocino County portion of the Russian River watershed by crop in 2007 and in 2009 in the Anderson Valley portion of the Navarro River watershed, Mendocino County

TABLE 1. Acreage of irrigated agriculture in the Mendocino County portion of the Russian River watershed by crop in 2007 and in 2009 in the Anderson Valley portion of the Navarro River watershed, Mendocino County

Irrigated agriculture acreage has increased in the Russian River area in the past 50 years. This resulted from conversion of dryland-farmed acreage to irrigated agriculture and the expansion of irrigated agriculture overall (fig. 2). Our 2007 estimate of irrigated acreage for Hopland and the Ukiah Valley area is 12,502 acres, roughly the same as the total agricultural acreage in 1957 (Carpenter 1958), but a 125% increase over 1957 irrigated acreage. Similarly, we estimated 16,661 acres of irrigated agriculture in the entire study area minus Potter Valley for 2007, or a 31% increase over the 1985 estimate (Sommarstrom 1986). And as of 2007, well over 95% of grape acreage was irrigated.

Comparison of total (top) and irrigated (bottom) crop acreage in the Hopland and Ukiah valleys from 1957 (Carpenter 1958) to 1985 (Sommarstrom 1986), to 2007. “Other” in 1957 includes truck farms, prunes and small grains, and in 1985 combines pasture with crops other than apples, pears and grapes.

FIG. 2. Comparison of total (top) and irrigated (bottom) crop acreage in the Hopland and Ukiah valleys from 1957 (Carpenter 1958) to 1985 (Sommarstrom 1986), to 2007. “Other” in 1957 includes truck farms, prunes and small grains, and in 1985 combines pasture with crops other than apples, pears and grapes.

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Author notes

We want to thank cooperating growers for their contribution of time and for granting farm access to evaluate irrigation systems. We also want to recognize the Mendocino County Water Agency and The Nature Conservancy for funding this research. Jim Nosera and Sarah Baker provided significant contributions in the collection and compilation of field data, including GIS roles.

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Agricultural water use accounting provides path for surface water use solutions

Glenn McGourty, David J. Lewis, Josh Metz, John M. Harper, Rachel B. Elkins, Juliet Christian-Smith, Prahlada Papper, Lawrence J. Schwankl, Terry Prichard
Webmaster Email: wsuckow@ucanr.edu

Agricultural water use accounting provides path for surface water use solutions

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Authors

Glenn McGourty , UC Cooperative Extension
David J. Lewis, UC Cooperative Extension
Josh Metz
John M. Harper, UC Cooperative Extension
Rachel B. Elkins, UC Cooperative Extension
Juliet Christian-Smith, Water Foundation
Prahlada Papper, UC Berkeley
Lawrence J. Schwankl, UC Cooperative Extension
Terry Prichard, UC Cooperative Extension and UC Davis

Publication Information

California Agriculture 74(1):46-57. https://doi.org/10.3733/ca.2020a0003

Published online March 17, 2020

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Abstract

Agricultural water demands can conflict with habitat needs in many North Coast watersheds. Understanding different water use patterns can help reduce conflict over limited supplies. We measured on-farm crop water use and conducted grower interviews to estimate the agricultural water demand in the upper Russian River and Navarro River watersheds. Annual agricultural water demand was less than 11% in the Russian River, and 2% in Navarro River, of the total annual discharge in each watershed. However, because demands are concentrated in the dry season when instream flows are at a minimum, these relatively small amounts can represent a significant constraint to stream habitat conditions. We have shared our study results in broad basin and community water resource planning efforts, including flow management of the Russian and Navarro rivers and implementation of the Sustainable Groundwater Management Act in the Ukiah Basin. Findings and recommendations from this study have influenced on-the-ground solutions to meet water demand in these watersheds, including construction of off-stream wintertime storage capacity to replace summertime stream diversions, and use of a municipal recycled water conveyance system as a replacement for summer diversions.

Full text

Satisfying water demands for multiple uses in California is an increasingly acute and difficult issue. High interannual climate variation characterized by successive drought and flood years introduces extreme uncertainty into water allocation decisions. During drought, allocations for agricultural use have been curtailed and environmental flows reduced to perilous levels for endangered and threatened wildlife (NOAA 2005). The Russian River Basin exemplifies the challenges of managing water for agriculture and the environment and has become the focus of recent state regulations (2015–2016 Russian River Tributaries Emergency Regulation Information Order) to more accurately account for water demands within tributary streams that support critical habitat for coho and steelhead trout.

Another significant policy enacted to address competing demands in the Russian River is the 2013 California State Water Resources Control Board (SWRCB) Policy for Maintaining Instream Flows in Northern California Coastal Streams (SWRCB 2013; SWRCB 2014). The purpose of this policy is to develop a streamlined process for reviewing and approving pending water rights applications, which in some cases have been delayed for decades by the SWRCB Division of Water Rights. The policy requires water rights applicants to meet stringent minimum instream bypass flow requirements and to consider alternatives for meeting their respective water needs, including water conservation and use of alternative sources.

Results from a UC Cooperative Extension study of the upper Russian River and Navarro River watersheds indicate that, on an annual basis, the amount of water used for crop production in both watersheds is small relative to total annual discharge.

Results from a UC Cooperative Extension study of the upper Russian River and Navarro River watersheds indicate that, on an annual basis, the amount of water used for crop production in both watersheds is small relative to total annual discharge.

To avoid impacts to the environment, more research is needed to better understand and manage agricultural water demands. Completed and ongoing studies in the Russian River watershed are generating water budgets and insight into the relationships between water use and stream flows. There are differing indications that subsurface and groundwater stores have been impacted over the last two decades in both mainstem reaches of the Russian River (Constantz et al. 2003; Marquez et al. 2016) and tributary watersheds like Alexander Valley (Metzger et al. 2006). Deitch (2006) correlated changes in stream flow to daily agricultural water use patterns and found evidence of direct steam flow reductions during irrigation periods. These and other investigations point to knowledge gaps about the timing and volume for water uses like agriculture that can support development of solutions to reduce impacts to the environment and competition for limited water supplies.

Our premise is that the best opportunity to relieve competition for water involves working with local agriculture to generate an accurate accounting of current and future water demand, including location and timing of use, and evaluate existing and potential options for meeting this demand. To serve that purpose, the primary objective of this study was to calculate agricultural water demand in the Mendocino County portion of the Russian River and Anderson Valley portion of the Navarro River watersheds (fig. 1). This includes the volume and timing, or seasonality of use, that could then be compared to annual and seasonal fluctuations in stream flow volumes and environmental flow demands.

Study location including the upper portion of the Russian River watershed and the Anderson Valley portion of the Navarro River watershed.

FIG. 1. Study location including the upper portion of the Russian River watershed and the Anderson Valley portion of the Navarro River watershed.

Our second objective was to assess needs and opportunities for innovations, including grower motivations, in irrigation technology, practices and water sources. Findings from this research have already improved agricultural water demand knowledge and facilitated feasible and sustainable agricultural water use in the study area (see sidebar, next page). This on-the-ground and with-the-users approach to water use accounting and the application of the results for solutions to meeting multiple water demands provides a useful model for relieving competition for water use in other watersheds.

Site description

The Navarro River, flowing east to west, is the largest coastal watershed in Mendocino County, covering approximately 315 square miles. The portion of the Russian River within Mendocino County is approximately 362 square miles and flows north to south. The Navarro is a natural river with no dams or other obstructions on its mainstem, whereas the Russian River is regulated by the Coyote Valley Dam, which creates a maximum 110,000 acre-feet of storage in Lake Mendocino. Additionally, inter-basin transfers are made from the Eel River to the Russian River via the Potter Valley Project.

The climate of both watersheds is Mediterranean with most rainfall occurring in the winter months, followed by no rainfall from late May to late September. Because of the close proximity to the Pacific Ocean, there is a strong marine influence on the Navarro watershed, with fog occurring many late nights and mornings and cooling westerly winds during the day. This contrasts with the more inland position of the Russian River watershed in Mendocino County, which has relatively clearer skies and drier and warmer conditions. Rainfall in the Navarro River watershed averages 40.6 inches per year, whereas the city of Ukiah and the Russian River watershed average 36.6 inches per year (Bearden 1974). The Navarro is sparsely populated with approximately 3,200 people. The Russian River watershed in Mendocino County is also rural in comparison to other parts of California. However, Ukiah and other residential centers have a combined population of over 20,000 people. Both watersheds experience the economic activities of agriculture (vineyards, orchards, livestock, small-scale mixed horticultural enterprises and commercial softwood production), beverage production (wine and beer) and tourism.

Study design and methods

We completed this study in 2007 in the Russian River and in 2009 in the Navarro River watersheds, using the same study design and approach comprised of three elements for water use accounting.

  1. We quantified the current acreage and crop designations using available agricultural statistics, aerial photograph interpretations and field visits to validate crop type and extent determinations. This included comparisons with past irrigated agriculture acreage and estimation of potential additional irrigated acreage; field evaluations were conducted of irrigation systems to quantify applied water for irrigation, heat protection, frost protection, and postharvest needs and irrigation distribution uniformity.

  2. To estimate total annual agricultural water demand we summed the amounts of irrigation water, frost protection, heat protection, and postharvest volumes multiplied by the extent of existing and potential irrigated agriculture in the two watersheds. As part of this calculation, we compared the volume and timing of the total agricultural water demand to instream flow volumes. Instream flow volumes or daily discharge (cubic feet per second) were determined using stream flow measurements from U.S. Geological Survey (USGS) gauging stations.

  3. To assess the needs and opportunities in water use innovations, we conducted grower surveys on existing irrigation system infrastructure and irrigation management decisions. A 25-question survey (available as supplemental information online) was administered to further inform water amounts used, water conserving irrigation system technologies adopted, and other background information needed to explore options and drivers to meet water demand and conservation goals.

Mendocino County winegrowers and advocates find solutions for agricultural water use while protecting endangered species

This study was undertaken with the aspiration that it could lead to solutions relieving potential pressure on stream flows from agricultural diversions, including the feasibility for small-scale private winter flow storage and opportunities for water reuse. Our study quantifies the amount of water used by agriculture relative to the total flow of water in both watersheds. We noted while water diversions are a small percentage of total flow, agriculture diverts water at a time when flow rates are low, and the need of water for fisheries is critical. In our recommendations, we discussed the concept of off-stream water storage when water flow was more plentiful. We also discussed that growers were comfortable with using recycled water as a substitute for direct diversions from the Russian River.

Spring of 2008 was one of the most challenging frost protection seasons in the upper Russian River watershed in over 30 years. Many growers required up to 20 nights of frost protection in their vineyards and orchards. A combination of limited water releases from Lake Mendocino due to a very dry winter, and large diversion demands for sprinkler frost protection from vineyards and orchards, greatly reduced flow in the main stem of the Russian River. In a normal rainfall year, instream flows during frost season range from 200 to 600 cubic feet per second (cfs) as recorded at the USGS water gauge in Hopland. In 2008, instream flows averaged 175 cfs. On April 20, 2008, a very cold advective freeze event occurred, creating an instantaneous drawdown of 83 cfs when nearly every agricultural water diverter turned on their frost protection systems. This drawdown resulted in a 2-inch drop in river stage and caused the stranding and mortality of hundreds to thousands of juvenile coho and steelhead trout, endangered and threatened species, which the National Marine Fisheries Service (NMFS) considered a “take” under the Endangered Species Act. As a result, in April 2009, NMFS requested that the California State Water Resources Control Board place a moratorium on the use of river water for frost protection. Honoring this request would have made it impossible in many years to grow wine grapes in the region, resulting in large employment and economic losses (estimated at up to $235 million).

In response, the Upper Russian River Stewardship Alliance was formed by the Mendocino County Farm Bureau, the Mendocino Wine Grape Commission, the Upper Russian River Flood Control District, the California Land Stewardship Institute, the Redwood Valley County Water District and local NRCS and UCCE offices to work with resource agencies and to find more reasonable approaches to solving the problem of river drawdown that could potentially strand young salmonid fish.

The group met regularly and developed The Upper Russian River Frost Protection Pumping Coordination Protocol. This coordinated effort improved frost forecasting precision by making more private weather stations available to frost forecasters. When frost events are likely to happen, growers call the Sonoma County Water Agency, controller of water releases from Lake Mendocino, so that river flows can be increased during frost events. Additionally, a new USGS water gauge was installed closer to Lake Mendocino to more accurately measure flow.

The California Land Stewardship Institute and the NRCS worked together to apply for $5.7 million in grants for water management infrastructure to prevent another fish stranding like that on April 20, 2008. The grant funds focused on creating off-stream ponds to store water to be used during frost events so that instantaneous drawdown would be reduced. Twenty ponds were built, with a combined water storage of 435 acre-feet. These ponds are filled with water under appropriated water rights (water stored from behind the Coyote Dam at Lake Mendocino). Growers have the capacity to pump as much as 145 cfs during a frost event from their ponds, replacing Russian River diversions that could imperil juvenile salmonids. After frost events, ponds are scheduled for recharge at more gradual rates to maintain adequate flows and water levels for fish.

To further improve the water supply situation, the city of Ukiah received $45 million in grants and low interest loans and is constructing a pressurized “Purple Pipe” system for agricultural and landscape water use. The Ukiah Municipal Wastewater Treatment Plant treats wastewater to California's Title 22 water reuse standards, with capacity to provide almost 4,000 acre-feet of water for use on farmland, parks, cemeteries and school grounds in Ukiah environs. Previously, this water was returned to the Russian River after treatment. This will reduce the demand for Russian River diversions, increase water security for the upper Russian River watershed, and reduce the costs associated with wastewater discharge management.

In Anderson Valley, The Nature Conservancy (TNC), who partially funded the Navarro River watershed portion of this study, very quickly teamed with the UCCE Mendocino County Office, as well as the Anderson Valley Winegrowers Association and the Mendocino County Resource Conservation District, to address some of the issues raised in our study.

The first major initiative was to install 16 new stream gauges in various smaller tributaries to augment the single USGS gauge near Philo, as the single gauge in the Navarro River watershed was inadequate for real-time irrigation management and better understanding impacts of dry season diversions on stream flows. The new gauges also help to inform conservation planning and identify areas that would benefit from additional water storage. Some of the gauges funded and installed by TNC are connected to cell phone interfaces so that a grower can accurately monitor the effects of diversions as they occur.

TNC is working with growers and the California State Water Resources Control Board to change their water rights to forbear summer diversions when flow rates in the watershed are very low and to allow for off-stream storage earlier in the year when flow rates are high, above critical levels for fish migration, spawning and juvenile survival. TNC also identified cost share funding for pond construction for water storage, working with the local USDA NRCS office and Mendocino County Resource Conservation District.

These examples of solving environmental problems proactively and locally through cooperative, thoughtful planning and execution resulted in much more positive outcomes and responded to real concerns for the impacts on people, their property and community in proposed regulations from agencies external to the region. Compiling and analyzing on-the-ground water use data, and applying that science through local associations and organizations, demonstrates how public and private partnerships can be successful for all concerned stakeholders.

Estimated irrigated agriculture extent

We mapped irrigated agricultural acreage in the Russian River watershed (fig. 1) using aerial photographs taken between August and September 2004 (AirPhoto USA). Late summer and early fall images provided a stark contrast between green irrigated crops and golden-yellow dry grasses. We visually assigned acreage into five crop designations: grapes, orchards, row crops, pasture and unknown. We estimated potentially irrigable lands based upon slope and landscape position to evaluate potential future water demand. Crop acreage classifications were validated through systematic field visits.

We obtained agricultural acreage statistics for the Navarro River watershed from Mendocino County Department of Agriculture Annual Crop Reports (Linegar 2008), the California Department of Water Resources (CDWR 1964, 1979, 1989) and the California Department of Food and Agriculture (CDFA 1968, 1976, 2006, 2009). Additionally, we mapped irrigated agriculture spatial extent in a geographic information system (GIS) using U.S. Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP) photographs (NAIP 2009). Data were summarized to provide a picture of historical and current irrigated agriculture extent in the study area. While the Navarro River extends beyond the study area, our analysis was constrained to portions of the Navarro River watershed with active agricultural operations, namely Anderson Valley (fig. 1).

We estimated future irrigated agriculture in the Russian River watershed by visually determining potentially irrigable lands not currently in production based upon the slope and landscape position. In the Anderson Valley, we used aerial imagery from the 2009 USDA NAIP aerial mapping program to develop a land cover classification for the Anderson Valley watershed. Sample points from forest and non-forest land cover types were identified in the 2009 aerial images and used to inform an image classification procedure. Maximum Likelihood Classification (Nagi 2011) was used to generate the land cover classes with a 10-m pixel resolution.

National elevation data at 10-m resolution was used to derive topographic slope for the Anderson Valley. The National Elevation Dataset provides uniform topographic data across the United States and allows for explicit consideration of topography in geographic analysis and modeling (State Water Commission and USGS 2017). Slope classes of < 10% and < 20% were created to discriminate vineyard potential under different slope thresholds. In general, steeper slopes are more difficult and costly to farm. Vineyard land cover identified during air photo mapping was used to extract existing vineyard land cover from the model.

The Squawrock-Witherall soil complex, interspersed with Hopland and Yorkville soil series and known to be high in magnesium (Rittiman and Thorson 1993), was excluded from our final analysis due to its known impacts on vineyard performance including potassium deficiencies, potential toxicity from nickel, poor surface stability and high erosion potential. While there are some vineyards planted on these soils, low yields, soil instability when saturated, and high erosion make them difficult to manage. Generally, these sites are not recommended for agricultural enterprises.

Irrigation system evaluation

Our evaluation of existing irrigation systems and measurements of applied water volumes included field measurements and calculation of water used for irrigation, including distribution uniformity, frost protection, heat protection and postharvest applications.

Irrigation use and distribution uniformity

We conducted field evaluation and existing irrigation systems measurements on a subset of vineyards, apple and pear orchards, and irrigated pastures to understand irrigation use and system distribution uniformity (consistency in applied water volume and rate throughout an orchard or vineyard). Methods used to conduct these evaluations are described in Prichard et al. (2007), Schwankl (2007) and Schwankl and Smith (2004). Evaluations included field measurement of water application rates and irrigation system distribution uniformity on 33 vineyard blocks, seven orchard blocks and one irrigated pasture in the Russian River watershed, and 26 vineyard blocks and three orchard blocks in Anderson Valley.

Additionally, we conducted interviews with cooperating growers to document irrigation season duration and irrigation frequency. Measured application rate and grower interview information were combined to estimate total irrigation use. Reference evapotranspiration (ETo; reference rate at which water evaporates from the soil and transpires) data were obtained for 2007 from California Irrigation Management Information System (CIMIS) stations #106 Sanel Valley in Hopland, F90 4933-23 on the Light Ranch in Redwood Valley, and the U.S. Army Corps of Engineers Coyote Dam station in the Ukiah Valley. Anderson Valley values for ETo were obtained for the 2009 season from an AdCon (AdCon Telemetry, Austria) weather station at Roederer Estate in Philo. Russian River soils information and data were derived from the Mendocino County Soil Survey (Howard and Bowman 1991). Available water holding capacity data for dominant soil types within irrigated agricultural lands in Anderson Valley were obtained from Rittiman and Thorson (1993).

Grapevine water use and crop coefficient (Kc) are linear functions of shaded area beneath the canopy (Williams and Ayers 2005). To calculate specific crop coefficients for this study, we measured percent canopy area covering the vineyard floor. In the Russian River study area, site-specific crop coefficients were calculated in 19 wine grape blocks. Shaded area beneath the canopy at midday was assessed using photographs, digitizing dark and light areas beneath and between vine rows, and measuring actual shaded area (Prichard et al. 2007). In the Anderson Valley, we used the Paso Panel technique (Battany 2012) to directly measure canopy shaded area on representative sites and trellis designs. Field data were used to calculate grapevine crop coefficients according to methods outlined by Battany (2012). We took vine canopy field measurements at Roederer Estate Vineyards in Philo between 1200 and 1300 hours (solar noon) on September 28 and October 2, 2012. Vine canopies were healthy, green and fully expanded. A total of four sites planted to pinot noir and chardonnay were selected based on trellis type, vine vigor and row orientation; we recorded 40 observations from each site. Crop coefficients were calculated using the algorithm provided by Battany (2012). These values were used to produce an average Kc.

Frost protection calculations

Grower interviews, relevant production manuals (Snyder 2007), project team experience and study area knowledge were used to generate total frost protection water use estimates. The dominant frost protection method is overhead sprinkler water application, which maintains the plant material surface temperature above freezing. In general, frost protection is used on vineyards and orchards located below 700 feet elevation because radiant frost typically occurs below this elevation in the study area. Heavier cold air settles in lower parts of the landscape, which poses crop damage risk (when green tissue is present) under normal radiant frost conditions. The elevation break for frost damage in Redwood and Potter valleys is higher than in the Ukiah Valley, as the valley floors are 770 feet and 950 feet, respectively. It is important to note that infrequent advective frost events impact the entire study area regardless of elevation.

Frost protection application rate was assumed to be 50 gallons per minute per acre (gal/min/ac) for grapes, or 0.1 inches of water per hour. In orchards, one acre-inch is applied for each frost protection event (Elkins et al. 2006). If systems are not routinely maintained and repaired, these values can be as low as 35 to 40 gal/min/ac. Additional assumptions for frost protection duration (hours/frequency) and acreage for each sub-basin were made based upon grower interviews.

Heat protection calculations

Total water use for heat protection calculations relied on grower confirmation of heat protection methods, relevant production manuals, project team experience and study area knowledge. In general, the same sprinkler system used for frost protection in grapes is used for heat protection. Accordingly, we assumed the heat protection application rate was 50 gal/min/ac, keeping in mind variability can exist due to system maintenance and effectiveness. Not all farms have these systems or access to sufficient water for heat protection. Additional assumptions for duration (hours/frequency) and acreage in which heat protection were made also based upon cooperating grower responses.

Postharvest application

Total water use calculations for postharvest application in wine grapes relied on grower response data, project team experience and study area knowledge. In general, the same irrigation system used for frost and heat protection in grapes is used for postharvest irrigation. Accordingly, we assumed postharvest application rate was 50 gal/min/ac, keeping in mind variability can exist. Postharvest irrigation is used to germinate cover crop seed banks and enhance carbohydrate storage. The latter objective is most applicable for white varieties where growers strive for yields of 5 to 6 tons per acre. Postharvest application decisions also depend on water availability. Additional postharvest application assumptions for duration (hours/frequency) and acreage relied on grower responses.

In pear orchards, postharvest irrigation occurs in August and September while trees are actively growing. For this reason, postharvest irrigation was included in pear irrigation use calculations.

Total agricultural water demand

We calculated total agricultural water demand by summing water used for irrigation, frost protection, heat protection and postharvest application; volumes were informed by agricultural practice differences and access to water. Total (per acre) water use (and its ranges) were multiplied by both existing (mapped) and potential (modeled) irrigated agriculture to calculate total agricultural water demand. Total demand, including timing and volume, was then compared to annual stream discharge data. Data from the following USGS stream gauging stations were compiled and analyzed for the Russian River watershed: Russian River near Ukiah, station #11461000; east fork of Russian River near Ukiah, station #11462000; and Russian River near Hopland, station #11462500. Stream discharge measurements from USGS stream gauging station #11468000 near Navarro, Mendocino County, were compiled and analyzed for the Navarro River watershed.

Grower surveys

We administered surveys to wine grape and fruit tree growers in both watersheds through two focus groups; the surveys were designed to understand water use patterns and document water resource use and irrigation management practices. The 25 questions in the survey were developed to gather information on growers’ water resource management history, including frost and heat protection, irrigation system technology change, conservation program participation, and opinions on alternative water sources. All focus group participants and survey respondents (a total of 15 Russian River and 14 Anderson Valley grape, pear and apple growers) completed appropriate human subjects releases required by the Office of Research Institutional Review Board Administration for the University of California, Davis.

Transitions in irrigated acreage

Based upon our team's land use mapping and modeling, irrigated agriculture in the Mendocino County portion of the Russian River watershed consists of 75% wine grapes, 15% irrigated pasture, 9% pears and less than 1% in other vegetable and unconfirmed crops (table 1). CDFA crop acreage statistics identified 14,212 acres in wine grape vineyards and 1,867 acres in pear orchards within the study area (Bengston 2008). These values are 9% less for grapes and 1% more for pear orchards compared with our values.

Acreage of irrigated agriculture in the Mendocino County portion of the Russian River watershed by crop in 2007 and in 2009 in the Anderson Valley portion of the Navarro River watershed, Mendocino County

TABLE 1. Acreage of irrigated agriculture in the Mendocino County portion of the Russian River watershed by crop in 2007 and in 2009 in the Anderson Valley portion of the Navarro River watershed, Mendocino County

Irrigated agriculture acreage has increased in the Russian River area in the past 50 years. This resulted from conversion of dryland-farmed acreage to irrigated agriculture and the expansion of irrigated agriculture overall (fig. 2). Our 2007 estimate of irrigated acreage for Hopland and the Ukiah Valley area is 12,502 acres, roughly the same as the total agricultural acreage in 1957 (Carpenter 1958), but a 125% increase over 1957 irrigated acreage. Similarly, we estimated 16,661 acres of irrigated agriculture in the entire study area minus Potter Valley for 2007, or a 31% increase over the 1985 estimate (Sommarstrom 1986). And as of 2007, well over 95% of grape acreage was irrigated.

Comparison of total (top) and irrigated (bottom) crop acreage in the Hopland and Ukiah valleys from 1957 (Carpenter 1958) to 1985 (Sommarstrom 1986), to 2007. “Other” in 1957 includes truck farms, prunes and small grains, and in 1985 combines pasture with crops other than apples, pears and grapes.

FIG. 2. Comparison of total (top) and irrigated (bottom) crop acreage in the Hopland and Ukiah valleys from 1957 (Carpenter 1958) to 1985 (Sommarstrom 1986), to 2007. “Other” in 1957 includes truck farms, prunes and small grains, and in 1985 combines pasture with crops other than apples, pears and grapes.

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Author notes

We want to thank cooperating growers for their contribution of time and for granting farm access to evaluate irrigation systems. We also want to recognize the Mendocino County Water Agency and The Nature Conservancy for funding this research. Jim Nosera and Sarah Baker provided significant contributions in the collection and compilation of field data, including GIS roles.

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