groundwater flow and transport model seaside groundwater basin ...

Seaside Model Report
October 26, 2007
Introduction
1.0 Introduction
1.1 Purpose and Scope of Report
The Seaside groundwater basin, which is located adjacent to and beneath
Monterey Bay (Figure 1.1), has been the subject of an ongoing adjudication.
Groundwater pumping exceeds the natural and secondary recharge, groundwater levels
have been declining, and the adjudication has focused on the corresponding threat of
seawater intrusion. While seawater intrusion has not been detected, except near Marina,
the parties to the adjudication recognized the inevitability of eventual seawater intrusion
were existing conditions to continue. However, the parties did dispute the best approach
to addressing the threat, with respect to both the institutional setting and the physical
solution.
A trial was held during late 2005 in the Monterey County Superior Court to
adjudicate the disputed issues. The outcome was that the Court ordered the creation of a
Watermaster, which was to be comprised of a collective of water users. The Watermaster
was directed to monitor groundwater conditions, develop a physical solution, and
implement the solution. The Court directed that the Watermaster report periodically to
the Court on progress toward meeting it obligations.
An obligation of the Watermaster is to develop a groundwater model. During the
trial, the testimony for the California-American Water Co. included the description of a
groundwater model, which was used to evaluate the threat of seawater intrusion. In its
post-trail decision, the Court ordered the creation of a groundwater model. Subsequently,
the Watermaster decided the groundwater model developed for California American
Water could meet the current basin-management needs. That model includes both
groundwater flow and solute transport components. The trial testimony did not include
written documentation of the model, which the Watermaster needs in order to use the
model.
This report represents the needed documentation. The objective of the report is to
describe the available data, the use of the data to develop the model, the predictive
simulations, and the structure of the model input files. The documented model is the
same as that presented to the court during the trial.
1.2 Description of Study Area
1.2.1 Physiographic Features
The Seaside groundwater basin underlies the hills and coastal plane at the
northern end of the Sierra de Salinas (Figure 1.2). The principal drainages are Arroyo del
Rey and El Toro Creek. Arroyo del Rey is a northwestward flowing tributary to
Monterey Bay. El Toro Creek is a northeastward flowing tributary to the Salinas River.
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