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Estimating spatial variability of recharge in southern New Jersey from unsaturated-zone measurements

By Arthur L. Baehr, Leon J. Kauffman, Kimberlie Perkins, and Bernard T. Nolan

Water-Resources Investigations Report 02-4288

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Schematic illustrating the hydrologic cycle in a watershed with various land uses

ABSTRACT

Spatial variability of recharge in southern New Jersey was studied by sampling the unsat-urated zone at 48 sites distributed over approximately 930 square kilometers. Samples of unsaturated-zone sediment were collected during the summer and fall of 1996. Unsaturated flow was calculated using moisture-content data and estimates of conductivity and matric potential derived from sediment-size data. Matric forces were found to be important at about 70 percent of the sites despite the expectation that unsaturated flow in a humid climate is gravity driven. Upward water movement occurred at about 17 percent of the sites. The lower sediment layer at these sites consisted of sandy loam, indicating that upward movement can occur at depth only where the sediments are relatively fine-grained. At the other extreme, calculated flow at about 17 percent of the sites exceeded 250 centimeters per year. Because of the uncertainty inherent in unsaturated-flow calculations, the method provides only a scaling of recharge variability; however, the median calculated flow of 29.1 centimeters per year compares favorably with recharge estimates from previous water-budget studies. A map developed by spatial analysis of the recharge estimates identified an agricultural part of the study area where recharge was known to be low relative to recharge in other basins.


CONTENTS

Abstract

Introduction

Study area

Study methods

Unsaturated-zone sampling

Flow calculation

Recharge estimates

Uncertainty of calculations

Flow regime

Mapping spatial trends

Summary and conclusions

References cited


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