Salinas Valley Seawater Intrusion

A watershed-related issue examined by the ENVS 560/L Watershed Systems class at CSUMB.

Summary

Seawater intrusioninto the Salinas Valley groundwater aquifers has advanced since it was first measured in 1944. Currently, elevated salinity levels have been recorded less than 1/2 mile from the City of Salinas at the 180 ft. aquifer and is beginning to encroach beyond the city limits of Castroville at the 400 ft aquifer. The saltwater intrusion has continued to move farther inland because continuing overdraft conditions for municipal and agricultural uses.

Location

The Salinas Valley watershed lies within the boundaries of Monterey County, California. Within the boundaries of the Salinas Valley Watershed lies it's groundwater aquifer system which is comprised of four major groundwater aquifers; the Upper Valley, Forebay, East Side, and Pressure 180. These aquifers create an interconnected underground water system that supplies the bulk of the irrigation and municipal water usage in the Salinas Valley.

Resources at stake

According to the Monterey County Water Resources Agency (MCWRA), the high dependence on groundwater for almost all of the water needs in the Salinas Valley have resulted in overdraft conditions in the Basin. As a result, numerous urban and agricultural supply wells have been abandoned or destroyed due to the degradation of groundwater supplies. Further overdraft of groundwater resources and seawater intrusion will continue without the development of additional water supplies to supplement existing groundwater supplies

Stakeholders

This problem involves a large group of stakeholders with a diverse set of interests. At the southern end of the Salinas Valley aquifer you have the businesses and communities surrounding Lake Nacimiento, which rely on the lakes recreational use economically. All the municipalities that lie within the Salinas Valley watershed, including the unincorporated area residents, rely on the aquifers for their drinking water. The Monterey County Water Resources Agency is the governmental agency closest to the actually monitoring and mitigating saltwater intrusion. Other stakeholders are the municipalities of Salinas, Castroville, Marina, which are directly affected. The agricultural community also has a strong vested interest for the aquifer is the primary supply for irrigation water.

Laws, policies, & regulations

Currently, groundwater resources are unregulated. The Monterey County Water Resource Agency monitors groundwater quality and levels but has little authority in regulating groundwater extraction. In 1961, Nacimiento Dam was completed to supply irrigation water to the Salinas Valley agricultural community and to recharge the aquifers. Attempts to change structural and operational practices at the dam have meet severe local opposition resulting in several lawsuits.

Systems

Once saltwater intrusion begins, it is irreversible. Our best hope is to stop its current progress and to modify our use of this resource so it will not continue in the future. Saltwater intrusion effects drinking and irrigation water quality, forcing some to search for alternative sources when the salinity of the water exceeds appropriate water quality standards. If salt levels are too high, the water becomes unpalatable for human consumption. Irrigation using water with high levels of salt will damage crops and soil health reducing future use of the land for agriculture.

Science

• The Watsonville Water Recycling Project, uses municipal recycled water in irrigation of crops near the front of the saltwater intrusion. This was the result of a large scale study to mitigate saltwater intrusion by creating a fresh water shield between the Monterey Bay Sanctuary and the 150 ft aquifer.
• Irrigation efficiency studies have been, and are continuing, to help reduce agricultural impact by reducing the quantity of water being extracted.

Scientific Tools

• Modeling has been used to help understand Salinas Valleys groundwater hydrological system. A model was used in a study of this system and described by April McMillian, for her Senior Thesis at California State University , Monterey Bay.
• Water Resources & Information Management Engineering, Inc. (WRIME) developed and calibrated a groundwater model and applied the criteria and IGSM to the analysis of alternatives.
• The three-dimensional, finite-element-based Integrated Groundwater and Surface-Water Model (IGSM) was originally developed by Dr. Young S. Yoon in 1976 at the University of California, Los Angeles. Designed to simulate confined ground water flow, IGSM later underwent major revisions and modifications including those made during application of IGSM to the Salinas Valley Groundwater Basin.
• The latest Water Use Summary Report developed by the Monterey County Water Resources Agency is also a good tool in understanding how groundwater is utilized in the Salinas Valley.

Future research

How this system works is understood fairly well. What is missing is the knowledge of exact quantity of water being extracted. If resources were not an issue, metering all agricultural wells to measure the exact quantity of water being extracted would be a good start. This information could be linked to the crop that was irrigated to provide information on specific crop water usage. Analysis of this information would assist agencies such as the University of California Co-Operative Extension, National Resource Conservation District, California Resource Conservation District and others to focus on educational outreach to growers on how to maximize their irrigation efficiency. Remote sensing images could be also be used to aid irrigation efficiency.

Hugo A. Loaiciga and Thomas J. Pingel from the Department of Geography at the University of Santa Barbara, conducted a poster presentation addressing the assessment of seawater intrusion potential from sea level rise in coastal aquifers of California. Considering the probable impacts of global climate change which includes the threat of sea level rise, future studies will have to directly address increases in level while examining sea water intrusion into coastal aquifers. The Oxnard Plain aquifer in Ventura County and the Salinas Valley coastal aquifer (Seaside Area) in Monterey County have been studied for the threat of sea-level rise. FEFLOW and ArcGIS were used as modeling and analytical tools. The image on the left from UNEP and WMO shows sea level rise due to global warming.

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The results of this study which began in September 2007 and ended in July of last year will impact future sea water intrusion studies to consider global climate change in their analysis. Click on the link to see the poster presentation File:Spatial poster presentation.pdf.

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Links

• Other Watershed Issues

Disclaimer

This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.