USGS

 

Comparison of Two Methods for Delineating Land Use Near Monitoring Wells Used for Assessing Quality of Shallow Ground Water

U.S. Department of the Interior
U.S. Geological Survey

Water-Resources Investigations Report  03-4067

 

By D.L. Lorenz, R.M. Goldstein, T.K. Cowdery, and J.D. Stoner

 

Contribution from the National Water-Quality Assessment Program

 

Mounds View, Minnesota

2003

 

This report is also available as a pdf.

 


ABSTRACT

Two methods were compared for delineating land use near shallow monitoring wells. These wells were used to assess the effects of agricultural cropland on the quality of recently recharged ground water in two sand and gravel aquifers located near land surface. The two methods for delineating land use near wells were (1) the sector method, which used potentiometric-surface maps to estimate average flow direction and a ground-water-flow model to estimate maximum length of contributing area to the monitoring well within an upgradient sector; and (2) the circle method, which used a 500-meter radius circle around the well based on a national empirical analysis. Land uses were compiled for 29 wells in each of two surficial aquifers in the Red River of the North Basin within the area defined by each method. Land use near each well was interpreted from orthorectified photographs and site inspection for both delineation methods. Land use near individual wells characterized by each method varied greatly, which can affect the results of statistical correlations between land use and water quality. Land use determined by the circle method related more closely to the land use for each entire study area. Land use determined by the sector method (within 200 meters from the wells) compared more favorably to ground-water quality based on nitrate concentrations. The maximum length of contributing areas to wells estimated in this study may be of value for other studies of unconsolidated sand and gravel aquifers with similar hydrogeological characteristics of permeability, water-table slopes, recharge, and depth to water. The additional effort required for estimating the model delineation of land use and land cover for the sector method must be weighed against the improved confidence in statistical correlation between land use and the quality of shallow ground water. Improved scientific confidence and understanding of relations between land use and quality of ground water may encourage more effective implementation of land and water management for protecting water quality.

CONTENTS

Abstract

Introduction

Land-use categorization

Land-use delineation methods

Methods of comparison

Comparison of land uses based on the sector and the circle methods

Implications for relating land use to ground-water quality

Summary

References


For additional information write to:

 

Chief, NAWQA Program

U.S. Geological Survey

12201 Sunrise Valley Drive,

MS 413

Reston, VA 201921

 

Copies of this report can be purchased from:

 

U.S. Geological Survey

Branch of Information Services

Box 25286, MS 517

Denver, CO 80225

 

Information regarding the National Water-Quality Assessment (NAWQA) Program is available on the Internet via the World Wide Web. Connect to the NAWQ Home Page at:

 

http://water.usgs.gov/nawqa/

 

Information about the Red River of the North River Basin Project of the NAWQA Program is available at:
http://mn.water.usgs.gov/redn/index.htm


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