COMMITTEE AGENDA MEMORANDUM
Water Conservation and Demand Management Committee
SUBJECT:
title
Agricultural Water Use Baseline Study
End
RECOMMENDATION:
Recommendation
Receive and discuss the findings and recommendations of the Agricultural Water Use Baseline Study.
Body
SUMMARY:
Santa Clara Valley Water District (Valley Water) has completed an Agricultural Water Use Baseline Study (Study) at the request of the Water Conservation and Demand Management Committee and with the support of the Agricultural Water Advisory Committee. The goal of the Study is to better understand current agricultural water use practices, which account for about 8% of Santa Clara County’s water usage and identify opportunities for water use efficiency. Valley Water collaborated with researchers from the University of California-Merced (UCM). This Study found that the local agricultural sector in Valley Water’s service area was highly water efficient.
Approach
The Valley Water and UCM team collaborated to utilize remote sensing, well billing information, County of Santa Clara crop reports, and expert interviews to provide insights into the use of agricultural water in the Valley Water service area and potential areas of future investment or investigation. Since metered wells do not have associated crop details and specific metered wells often provide water to multiple parcels, parcel level water use estimates could not be developed. Instead, the team evaluated water use by the Agricultural Resource Areas (ARAs) defined in the County of Santa Clara’s 2018 Agricultural Plan (Attachment 1).
The assessment of Valley Water agricultural water use involved the development of both composite datasets of existing data, as well as ground truthing information on crops and irrigation systems. To ground truth, the team conducted a windshield survey to assess the present status of irrigation technology in the Valley Water service area. The team visually surveyed 675 parcels covering 10,330 acres. Field-collected data were used to validate geospatial data on crop type and any associated irrigation technology and to provide some ground truth comparison to the 2018 LandIQ crop distribution. The team also analyzed local reports, such as County of Santa Clara crop reports. Billing data was for both metered wells, which account for about 82% of agricultural water usage in the county and unmetered wells, which use Table of Averages to estimate water usage. The Table of Averages worksheet is used to estimate the amount of water being pumped by factoring the amount of land and the crops being grown. A mass balance approach was used to assess the sub-regional distribution of water use intensity in the Valley Water service area. The Mass Balance model is intended to reconcile sources and sinks of water (i.e., where water comes from, and where it goes). Mass balance for each ARA was calculated to identify over-irrigation or under-irrigation.
Well Production + Precipitation - Evapotranspiration = Mass Balance
Field-level measures of actual evapotranspiration or ETa from OpenET and precipitation from PRISM Climate Group (climate observations gathered from a wide range of monitoring networks to develop spatial climate datasets to reveal short- and long-term climate patterns) were compared with the sub-regional total groundwater well production.
Findings
This Study found that the local agricultural sector in Valley Water’s service area was highly water efficient. During dry years, less than 10% of water applied to crops is lost to infiltration or runoff. In comparison, Valley Water's Large Landscape Program, which provides water budgeting and irrigation surveys for commercial ornamental landscapes in Santa Clara County, found that on average in 2021, overwatering accounted for 30% of all water used.
In addition, discussions with local growers and farm suppliers conducted during the study have emphasized the appropriateness of current irrigation systems as based on grower needs (particularly for growers that are tenants). High-efficiency irrigation systems, for example, are inappropriate for certain crop types. Feedback also indicated water costs alone are insufficient to make a return-on-investment business case for large irrigation infrastructure and/or technology investments.
Recommendations
Since Santa Clara County agricultural users were found to be efficient, the main recommendation is to continue to look for opportunities to enhance Valley Water’s water existing conservation programs, such as the Mobile Irrigation Lab (MIL) and rebates for agriculture. To help prepare for the future, especially given the uncertainty in climate change, the study also recommends that Valley Water consider increasing our understanding of the types of crops each well supplies. Better understanding water usage per crop type will allow Valley Water to better plan for future agricultural water needs and design future conservation programs to help agricultural producers respond to climate change.
This topic is planned to be presented and discussed at the Agricultural Water Advisory Committee in early 2023.
ATTACHMENTS:
Attachment 1: Agricultural Resource Area map
Attachment 2: PowerPoint Presentation
UNCLASSIFIED MANAGER:
Manager
Kirsten Struve, 408-630-3138