Soil Physical Methods for Estimating Recharge - Part 3

By W Bond

Measurements in and just below the plant root zone, using principles of soil physics, can be used to estimate recharge. This booklet describes the Zero Flux Plane Method, Methods Based on Darchy's law, and Lysimetry for making such estimates. The work presents the basic concepts of soil water physics that will be referred to in this and other booklets in the series. Another method, the Soil Water Flux Meter, is discussed briefly, but as this is not sufficiently well developed for routine use readers are referred elsewhere for full details. All these methods require that consideration be given to interpolation over time and spatial extrapolation or averaging. A brief discussion of this is given.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: Mar 1, 1998
• ISBN: 9780643106048

Book preview

Soil Physical Methods

for Estimating Recharge

W. Bond

Series Editor: Lu Zhang

Part 3 of THE BASICS OF RECHARGE AND DISCHARGE

National Library of Australia Cataloguing-in-Publication entry

Bond, WJ (Warren John).

Soil Physical Methods for Estimating Recharge.

Bibliography

ISBN 0 643 06297 1 (set)

ISBN 0 643 06283 1

1. Groundwater – Analysis. 2. Soils - Analysis.

I. Title. (Series: The Basics of Recharge and Discharge; Part III)

551.49

© CSIRO Australia 1998

This work is copyright and apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without the written permission from the publisher, CSIRO PUBLISHING, acting on behalf of CSIRO Australia. Requests and enquiries concerning reproduction and rights should be addressed to the Publisher, Academic and Reference:

This book is available from:

CSIRO PUBLISHING

PO Box 1139

Collingwood, Victoria 3066

AUSTRALIA

Ph:     +(61 3) 9662 7500

Fax:   +(61 3) 9662 7555

URL:  http://www.publish.csiro.au

email: [e-mail]

Cover Photograph: Bill van Aken, CSIRO Division of Land and Water

CONTENTS

1 Introduction and Scope

2 Basic Concepts of Soil Water Physics

Saturated soil water physics

Unsaturated soil water physics

Preferred Pathways, bypass Flow

Swelling Soils

3 Zero Flux Plane Method

Principles

Summary of assumptions

Advantages, disadvantages and when to choose

Worked example

Other examples of the application of the zero flux method

4 Methods based on Darcy’s Law

Unit gradient method

Measured gradient method

Summary of assumptions

Advantages, disadvantages and when to choose

Examples of the application of Darcy’s Law methods

5 Lysimetry

Lysimeter requirements

Weighing lysimeters

Non-weighing lysimeters

Use of lysimeters to measure recharge

Summary of assumptions

Advantages, disadvantages and when to choose

Examples of the use of lysimeters to measure deep drainage and recharge

6 Soil Water Flux Meters

7 General Discussion of Techniques

8 References

ABSTRACT

Measurements in and just below the plant root zone, using principles of soil physics, can be used to estimate recharge. This chapter describes several such methods. After defining groundwater recharge and its relationship to soil water flow below the root zone, the chapter presents the basic concepts of soil water physics that will be referred to in this and later chapters. These include an introduction to Darcy’s Law and the flow of water in saturated soils, water flow in unsaturated soils, and the important soil water (hydraulic) properties that are required to calculate soil water flows. A brief discussion is included of flow through preferred pathways (or bypass flow), when conventional soil water physics, based on Darcy’s Law, does not usually apply.

The methods discussed in detail in this chapter are the Zero Flux Plane Method, Methods Based on Darcy’s Law, and Lysimetry. For each of these methods, there is a presentation of the principles, summary of assumptions, a list of advantages and disadvantages, and a recommendation of when to select that method. In the case of the Zero Flux Plane method, which has not been well described previously, a worked example is also included. Another method, the Soil Water Flux Meter, is discussed briefly, but as this is not sufficiently well developed for routine use readers are referred elsewhere for full details.

The Zero Flux Plane Method is useful when accurate measurements at short time scales are required, and when frequent measurements are able to be made. It is a good method to use periodically as a check of other methods. Methods Based on Darcy’s Law are useful when a large number of measurements are required to characterise recharge behaviour in an area, and when a low-cost option is required. In this case, cost is traded against uncertainty because of the difficulty in precise estimation of the soil properties required for this method.