Water Table Elevations in the Salinas Valley, California: Animated Visualization using GIS

April McMillian

Senior Thesis

Earth Systems Science and Policy
California State University Monterey Bay

 

Data for this project were made available by the Monterey County Water Resources Agency. The content of the report does not necessarily reflect the opinions of the Water Agency.


 

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  Animations Animation #3 Animation #4

 

   



Synopsis

This report includes a PDF file and four animations illustrating changes in the Salinas Valley water table through time. The data are not real well data, but are instead the data from a numerical groundwater model supplied by the the Monterey County Water Resources Agency. Comparison of the model data with a few real wells indicates that the animations and analysis are largely accurate.

The report and animations can be accessed at a link near the top of this page.

As population around the world continues to increase dramatically, impacts on groundwater systems are likely to occur. Groundwater is the source of more than 50% of the world’s drinking water supplies, and many cities depend only on groundwater for municipal, industrial, and agricultural uses. With high demands on groundwater aquifers, the rates of pumping may surpass recharge, causing overdraft conditions in the aquifer. Problems with overdraft aquifers include declining water table levels, land subsidence and instability, water quality deterioration, seawater intrusion, and habitat loss.

The Salinas Valley in Monterey County, California is heavily dependent on its groundwater supplies for municipal and agricultural use, with agriculture using most of the resource. Population within Monterey County has increased by over 200% since 1950, and is expected to increase an additional 35% over the next 20 years. The rising population may have a large impact on the groundwater systems, causing water tables to decline, creating further problems.

One of the main problems within the Salinas Valley aquifer systems is seawater intrusion. Seawater intrusion was first noticed in the Salinas Valley in the mid- 1930’s, and has continued to spread inland with time. Two reservoirs were constructed on tributary rivers in 1956 and 1967 to allow river flow during summer months, thereby increasing recharge to the groundwater aquifers, and possibly slowing seawater intrusion. Though the reservoirs have been in operation for over 40 years, seawater intrusion is an increasing problem within the Salinas Valley.

As a part of the “Historical Benefits Analysis” by the Monterey County Water Resources Agency, the Salinas Valley Integrated Ground and Surface Water Model (SVIGSM) was developed to analyze the benefits of the reservoir operations to the Salinas Valley in terms of hydrologic, flood, and economic benefits. Though a groundwater budget was developed from the model output, no analysis of the changing water table level estimates was done graphically.

Animating contoured water table level maps is useful for the visualization of problems occurring within groundwater aquifers. Problems are better identified, and are clearer to understand by people who are not very familiar with watershed science. The maps can show what areas are increasing or decreasing, with respect to climate, land use, and other sources of recharge and discharge. Using these maps and animations will be beneficial for developing further projects for management of the Salinas Valley groundwater system to protect its supply, quality, and longevity.

 

ABSTRACT

Policies and water management plans are currently in development and practice for many groundwater systems throughout California to help identify, control, and predict problems with depleting groundwater systems. The Salinas Valley Integrated Ground and Surface Water Model (SVIGSM) was used to quantify the impacts that various management alternatives would have on the groundwater aquifers within the Salinas Valley groundwater basin. Water table elevations from the SVIGSM output were color contoured and mapped for consecutive years from 1949 through 1994. The animation shows the changes the Salinas Valley water table has undergone from the years 1949 through 1994. Four animations were created from these maps. Animation 1 includes the Monterey Bay to the Forebay sub-area, and is mapped from 1949 through 1994. Animation 2 shows the Upper Valley sub-area only, mapped from 1949 through 1994. Animation 3 is of the lower Salinas Valley and coastal areas, mapped from 1949 through 1957 with a contour line showing the location of sea level within the water table. Animation 4 shows the same area as in Animation 3, mapped from 1980 through 1994, showing a contour at 10 feet below sea level.


In Animation 1, water table elevations declined in the lower Salinas Valley and coastal areas during period of 1949 to 1957, and from 1983 to 1994. In the Upper Valley, water table elevation estimates remained relatively stable through time, with minor changes due to precipitation. Increases in the water table elevations are shown in all animations for the operation of the Nacimiento and San Antonio reservoirs. Water table elevations followed changes in precipitation during the period of 1957 through 1983. By understanding how groundwater elevations have changed over time, predictions and water management policies can be made to help the quality and longevity of groundwater systems in the Salinas Valley.



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