Soil Water Measurement E-Book

J. David Cooper

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 1235

Veröffentlichungsjahr: 2016

Beschreibung

This book is written for all those involved in measurement of soil water phenomena, whether they be environmental scientists, field technicians, agronomists, meteorologists, hydrogeologists, foresters, physical geographers, civil or water engineers or students in these subjects.  It contains a comprehensive description of all the major methods used for measurement of soil water content and potential, solute concentration, transport and balance of water and solutes, including recharge to groundwater aquifers.  The emphasis is firmly on techniques which can be applied in the field or on samples obtained from the field.
 
The theory and practice of the workings of the main instruments and methods available is described, along with practical tips on surmounting some of the main difficulties and explanations of many commonly encountered jargon words.

Leseprobe

Don’t think, try the experimentJohn Hunter, 1728–1793

I love deadlines. I love the whooshing noise they make as they go byDouglas Adams 1952–2001

Soil Water Measurement

A Practical Handbook

J. David Cooper

Former Head of Soil Physics Group and Instrument GroupCentre for Ecology and HydrologyWallingford, UK

Research FellowUniversity of BrightonBrighton, UK

With a contribution from Richard H. Cuenca

Professor EmeritusDepartment of Biological and Ecological EngineeringOregon State UniversityCorvallis, OR, USA

This edition first published 2016 © 2016 by John Wiley & Sons, Ltd

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Library of Congress Cataloging-in-Publication Data

Names: Cooper, David, 1946– author.Title: Soil water measurement : a practical handbook / David Cooper.Description: Hoboken, NJ : John Wiley & Sons, 2016. | Includes bibliographical references and index.Identifiers: LCCN 2015034625 | ISBN 9781405176767 (cloth)Subjects: LCSH: Soil moisture–Measurement–Handbooks, manuals, etc.Classification: LCC S594 .C67 2016 | DDC 631.4/32–dc23 LC record available at http://lccn.loc.gov/2015034625

A catalogue record for this book is available from the British Library.

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Cover image: © David Malan/GettyImages

Preface

The principal motivation for writing this book is that for over 35 years of measuring water in soil, I had not come across a book that brought together in one place the principles of operation of all the important methods and instruments available, together with their methods of use. This book aims to correct that.

The secondary motivation is that writing this book is a kind of penance for not having completed a PhD and written too few papers while I was working at the Institute of Hydrology/Centre for Ecology & Hydrology.

With a long career in the subject, I am indebted to many more people than there is space to identify here. It would be bordering on criminal, however, not to mention some of the more prominent ones. The late Jim McCulloch and John Bell must take pride of place for taking the chance on employing me over other, no doubt well-qualified, aspirants for a job in the Soil Physics Section of the rapidly expanding Institute of Hydrology and for guiding me towards a satisfying career in the underground. Other sometime colleagues at the Institute who both taught and helped me well beyond the call of duty include (in no particular order) the late Steve Wellings, the late Sam Boyle, Phil Holdsworth, Gareth Roberts, Richard Raynor, Paul Rosier, Cate Gardner, Alan Warwick, Ned Hewitt, Roger Wyatt, the late Pete Andrews, Jim Wallace, Atul Haria, Andy Dixon, the late Brian Smith, Tony Debney, the late Ian Calder, John Bromley, Ragab Ragab, Liz Morris, Keith Beven, Peter Germann, Jim Shuttleworth, the late John Stewart, Colin Lloyd, David Robinson, Brenda Burton, the late John Roberts, Jimmy Blackie, the late Tony Edwards, Tom Dean, Dave McNeil, Dave Harris, Richard Cross and Geoff Wicks. In the British Geological Survey, I enjoyed fruitful collaborations with David Kinniburgh, Helen Rutter, David Buckley, Brian Adams, Stephen Foster and Mike Edmunds. Outside these two organisations, David Fourt, Edward Youngs, Peter Leeds-Harrison, Declan Barraclough, Chris Young, Andree Carter, Tim Atkinson, Joseph Oisebe, Samson, Donald Laycock, Caleb Othieno, Val Mercer, John Smith, Georges Vachaud, Michel Vauclin and Tim Burt have been most helpful. Adrian Smith and Dee Galliford of the CEH library have been most helpful in providing access to both old and recent literature.

In writing this book, as well as several of those mentioned above, discussions with Gaylon Campbell, David Young and Mark Robinson have been fruitful. Aside from reviewing the early part of the manuscript, Richard Cuenca alerted me to and kindly contributed a section on COSMOS. Long-suffering staff at Wiley, particularly Kelvin Matthews, Ian Francis and Delia Sandford, have been immensely patient over my frequent missing of deadlines.

None of any of this would have been possible without the support and encouragement of my family, particularly my wife, Sue, who put up with my frequent absences working in various parts of the UK and abroad while being left to bring up six children and who has had to forego several years of my “retirement” while preparing this book.

To all of the above, my everlasting thanks.

J. David CooperEwelmeOxfordshire

Part IIntroduction

1Soil Water in Context

The interactions between water and soil are, arguably, the most fundamental relationships in the terrestrial environment. They control, in combination with other agents, such as the weather and plants, the fate of water after it falls as rain. This, in turn, determines aquifer recharge, river flow, water availability to crops and pasture for animals and the transport of nutrients and pollutants. These are critical in determining water resources, flooding, food production, the potability of water, ecology and public health. In view of these important roles, there has been and continues to be a great deal of scientific effort expended in understanding soil–water relationships. Nevertheless, many soil water specialists feel that the value of this work is not fully recognised and is underfunded by comparison with many other environmental topics. The reasons for this may include the fact that several aspects of the subject run counter to most people’s intuition, that work in the field is physically hard and frequently messy, that little spectacular equipment or results are involved and that the subject rarely offers good photo opportunities.

The applications of soil physics are principally in the fields of agriculture, environmental protection and water resources. Some of the more common uses are:

Measuring or estimating the soil bearing capacity to support agricultural operations

Characterising the soil water status at various stages of crop growth

Estimating irrigation requirements

Optimising the quantity and timing of fertiliser or pesticide applications

Estimating the water consumption of crops and other land covers

Estimating the recharge of water to aquifers

Estimating the rate at which pollutants travel through the unsaturated zone to groundwater bodies or watercourses

Forecasting and mitigating the hazards of floods

Serious study of the physics involved in the relations between water and soil started in the early 20th century in the United States, driven by the need to increase food production for a rapidly expanding population. Later, important centres of research developed in the Netherlands, Australia, Israel and the United Kingdom. The motivation was usually to increase agricultural yields, focussed either on irrigation in arid areas or land drainage in humid and low-lying ones. From the 1970s, environmental concerns have accounted for an increasing proportion of the research effort, focussing on flood generation, pollution of rivers and aquifers from both natural and artificial sources, water resources assessment and effects on biodiversity. This has taken the subject into the area between what would normally be regarded as ‘soil’ and the zone of saturated rock, which is the province of hydrogeologists. This is often referred to as the vadose zone, particularly in America, although many hydrologists prefer to define the unsaturated zone as a composite of the soil and vadose zone. In this book, the term unsaturated zone will be used, recognising that there is, in reality, no neat subdivision between the soil, the underlying porous material of weathered or unweathered rock and, indeed, the saturated zone.

The amount of work on soil physics has produced a steady stream of books on the subject (e.g. Marshall et al., 1996; Warrick, 2002, 2003; Hillel, 2004; Jury & Horton, 2004; Lal & Shukla, 2004; Rose, 2004). Some of these are highly mathematical and theoretical, while others attempt to explain the principles in relatively simple language. Few of them contain much detail explaining how it is actually done. There are also several books dealing with measurement methods and principles. Pride of place should probably go to the encyclopaedic work of Dane and Topp (2002), one of a series of books on all aspects of soil measurement. Over some 300 pages, it explains the principles behind most methods of soil water measurement, as well as having sections on all manner of other physical measurements in the soil. In similar mode is Mullins and Smith’s (2001) book, focussed more specifically on soil water. While giving comprehensive coverage of the principles of measurement, both books tend to lack information on the practicalities of making measurements in frequently imperfect conditions. The book closest in spirit to the present one is that of Dirksen (1999). This book is intended to update and extend the contents of Dirksen (1999); to explain without descent into hand-waving argument, but using no more mathematics than necessary, the principles of operation of the most common instruments and methods of water measurement in the unsaturated zone and to give as much practical guidance as possible on using the methods in real-life situations. The emphasis is firmly on techniques for use in the field. Much useful research has been conducted on real and artificial soils in the laboratory, and the discovery of some principles of soil water behaviour would not have been possible without laboratory measurements. The author is not, for instance, aware of any convincing demonstration of the applicability of Darcy’s law to unsaturated field soils. However, in almost all cases, laboratory measurements are intended to mimic field conditions and be applicable to that situation. It is the contention of this book that, for all the difficulties caused by distance, the weather, mud, stones, communications, power supply, spatial variability, animals and vandalism, field measurements are the final arbiter of research and monitoring work on soil–water interactions.

The limitations imposed by the nature of soil and the difficulties just mentioned mean that the accuracy achievable in any measurement is usually at best modest and in some cases extremely poor by most standards. It may come as a shock to some that, when we can measure the distance to the moon to a few cm and the value of some fundamental constants to 1 part in 1012, we often do well to achieve a measurement accuracy of soil water content better than 5% by volume. It is, however, also true that astrophysicists are often happy to get within a few orders of magnitude of the ‘true’ figure, so soil physicists are, at least, somewhere in between. The modest level of accuracy achievable usually makes it unnecessary to take into account quantities like the variation of density of water with temperature and small variations of the acceleration due to gravity from one place to another. These will be assumed equal to 1000 kg m−3 and 9.8 m s−2, respectively, throughout this text. The reader should, however, be aware that there are circumstances when such imprecision is not warranted, although such instances in soil physics are extremely rare.

With large increases in computer power and its availability over the last few decades, numerical modelling of ever more complex environmental systems has achieved great prominence. Additionally, many of the methods described in the later chapters of this book would not be practical without the availability of cheap computer power, whether for measurement of soil hydraulic properties by inverse methods, for statistical evaluation of data collected, for controlling the recording and storage of field data automatically or for incorporation into instruments to perform the calculations which turn an electrical signal into a meaningful quantity. The Internet is making large databases of soil properties and much other environmental information available to researchers and decision makers worldwide. So whether derived from the modeller’s own or their colleagues’ observations, or from elsewhere, a wealth of data is easily available, although its quality may be difficult to assess.

This book is not, however, about modelling, except in so far as it can be used to help interpret experiments, but the use of soil water measurements as input to a variety of models in environmental science, management of water resources, agriculture and ecology cannot be ignored. Measurements are important for modelling of environmental systems in several ways:

To provide a description of the properties of the various components of the system, such as soil water characteristics and hydraulic conductivity of the soil.

To supply data to drive the model, for instance, rainfall and other meteorological information.

To

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