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Northern Utah Valley Ground-Water Optimization Simulations

Project Chief: Philip Gardner, USGS Salt Lake City, Utah
Cooperator: USGS Cooperative Water Program
Period of Project: June 2008 to September 2009

PROBLEM

Ground water is the primary source of drinking water in northern Utah Valley. Increased withdrawals coupled with recent drought have caused water levels in many wells to decline to their lowest recorded levels. In the summer of 2003, the U.S. Geological Survey (USGS), in cooperation with valley water users, began a study of the area’s ground-water resources and the effects of withdrawals on ground water conditions. One of the products of that study was a MODLFOW numerical ground-water flow model for northern Utah Valley. Recent development of post-MODFLOW ground-water modeling tools such as the USGS Ground-Water-Management (GWM) module for MODFLOW has facilitated model application in representing a range of specific management objectives and constraints within the modeling process. The GWM process incorporates simulation-optimization techniques which allow for the determination of optimal (best) management strategies from among many possible strategies. We are conducting an additional phase of the northern Utah Valley ground-water study to demonstrate the utility of this process in improving our understanding of the relationship between ground-water use and aquifer system response and in defining ground-water management strategies that meet the vision of valley water users for the protection of their water resources.

OBJECTIVES

The principal objective of this study is to continue to improve our understanding of the northern Utah Valley ground-water system and to aid in determining the effects of future water use on hydrologic conditions in the valley. Specifically, the study will apply mathematical management modeling techniques in conjunction with ground-water flow modeling to determine optimal ground-water management strategies, given a set of specific management objectives and a set of management constraints.

RELEVANCE AND BENEFITS

The USGS Cooperative Water Program has defined water availability as a program priority issue. More comprehensive water-use data and analysis are needed in northern Utah Valley to quantify the stress on existing supplies and to better model and evaluate possible water-resource management options to supplement traditional supply approaches. The result of the proposed study will be an improved understanding of the relationship between ground-water use and aquifer system response and a documented and tested approach to improved assessment of ground-water management strategies in the valley.

APPROACH

The study will apply recently developed USGS GWM process combined with the current USGS MODFLOW model of northern Utah Valley to the development of optimization models to solve ground-water management problems in the study area. USGS project staff will meet with valley water managers to gather water-resource management information and define management objectives and constraints. Once defined, management objectives and constraints will be formulated mathematically in the GWM optimization model. The calibrated ground-water flow model of northern Utah Valley will provide the basis by which the GWM process will develop specific functional relations between the simulated stresses in the model (wells, artificial recharge, etc.) and model-calculated response in heads and stream-flow. The GWM process will incorporate these response functions in matrix form and compute optimal values for decision variables (such as pumping rates) on the basis of the defined management objectives and constraints.

PRODUCTS

A USGS-series report will be written documenting the modeling process, results, and utility and limitations for future use in assessing ground-water management strategies. All model input files will be archived and made available to the public from the USGS Utah Water Science Center.

CURRENT UPDATE

Test models have been run, using the northern Utah Valley MODFLOW model coupled with the GWM process, that simulate hypothetical sets of management objectives and constraints. These runs were made to incorporate simplified versions of plausible future management scenarios for northern Utah Valley while testing GWM’s ability to yield optimal ground-water management solutions using a flow model that simulates a large (valley scale) and complicated area. The next step of this project is to work with water managers from northern Utah Valley to generate a realistic set of management goals and constraints based on projected ground-water demand and environmental, engineering, and economic constraints. Once these management scenarios are formulated, the simulation-optimization model will be used to determine optimal (best) management strategies from among many possibilities.

For more information on Management Optimization Modelling using the USGS Ground-Water Management Optimization Process visit http://water.usgs.gov/nrp/gwsoftware/gwm/gwm.html