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Scientific Investigations Report 2010–5117

National Water Availability and Use Pilot Program

Implementation of Local Grid Refinement (LGR) for the Lake Michigan Basin Regional Groundwater-Flow Model

By C.J. Hoard

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ABSTRACT

The U.S. Geological Survey is evaluating water availability and use within the Great Lakes Basin. This is a pilot effort to develop new techniques and methods to aid in the assessment of water availability. As part of the pilot program, a regional groundwater-flow model for the Lake Michigan Basin was developed using SEAWAT-2000. The regional model was used as a framework for assessing local-scale water availability through grid-refinement techniques. Two grid-refinement techniques, telescopic mesh refinement and local grid refinement, were used to illustrate the capability of the regional model to evaluate local-scale problems. An intermediate model was developed in central Michigan spanning an area of 454 square miles (mi2) using telescopic mesh refinement. Within the intermediate model, a smaller local model covering an area of 21.7 mi2 was developed and simulated using local grid refinement. Recharge was distributed in space and time using a daily output from a modified Thornthwaite-Mather soil-water-balance method. The soil-water-balance method derived recharge estimates from temperature and precipitation data output from an atmosphere-ocean coupled general-circulation model. The particular atmosphere-ocean coupled general-circulation model used, simulated climate change caused by high global greenhouse-gas emissions to the atmosphere. The surface-water network simulated in the regional model was refined and simulated using a streamflow-routing package for MODFLOW.

The refined models were used to demonstrate streamflow depletion and potential climate change using five scenarios. The streamflow-depletion scenarios include (1) natural conditions (no pumping), (2) a pumping well near a stream; the well is screened in surficial glacial deposits, (3) a pumping well near a stream; the well is screened in deeper glacial deposits, and (4) a pumping well near a stream; the well is open to a deep bedrock aquifer. Results indicated that a range of 59 to 50 percent of the water pumped originated from the stream for the shallow glacial and deep bedrock pumping scenarios, respectively. The difference in streamflow reduction between the shallow and deep pumping scenarios was compensated for in the deep well by deriving more water from regional sources. The climate-change scenario only simulated natural conditions from 1991–2044, so there was no pumping stress simulated. Streamflows were calculated for the simulated period and indicated that recharge over the period generally increased from the start of the simulation until approximately 2017, and decreased from then to the end of the simulation. Streamflow was highly correlated with recharge so that the lowest streamflows occurred in the later stress periods of the model when recharge was lowest.

Posted September 2010

For additional information contact:
Christopher J. Hoard
U.S. Geological Survey
6520 Mercantile Way
Lansing, MI 48911
Phone: 517-887-8949

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Suggested citation:

Hoard, C.J., 2010, Implementation of local grid refinement (LGR) for the Lake Michigan Basin regional groundwater-flow model: U.S. Geological Survey Scientific Investigations Report 2010–5117, 25 p.


Contents

Abbreviations and Acronyms

Acknowledgements

Abstract

Introduction

Purpose and Scope

Regional Groundwater-Flow Model

Model-Grid Refinement

Refined-Model Development

Construction of Intermediate and Local Model Grids

Boundary Conditions of the Refined Grids

Recharge

Surface-Water Network

Refined-Model Scenarios

Streamflow Depletion

Climate-Change Scenario

Assumptions and Limitations of the Models

Summary

References Cited

Appendix 1. Surface-Water Network



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