Rainwater Harvesting for Agriculture in the Dry Areas

275 Pages·2012·12.97 MB·English

by  Theib Y. Oweis

Water Harvesting for Agriculture
in the Dry Areas
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Water Harvesting for
Agriculture in the Dry Areas
Theib Y. Oweis
International Center for Agricultural Research
in the Dry Areas (ICARDA), Aleppo, Syria
Dieter Prinz
Karlsruhe Institute of Technology/
Karlsruhe University, Karlsruhe, Germany
Ahmed Y. Hachum
College of Engineering, University of Mosul,
Mosul, Iraq
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Library of Congress Cataloging-in-Publication Data
Oweis, Theib Yousef.
Water harvesting for agriculture in the dry areas/Theib Y. Oweis, Dieter Prinz,
Ahmed Y. Hachum.
p. cm.
Includes bibliographical references and index.
ISBN 978-0-415-62114-4 (hbk. : alk. paper)—ISBN 978-0-203-10625-9
(ebook) 1. Water harvesting. 2. Rainwater. 3. Arid regions agriculture.
4. Water-supply, Agricultural. I. Prinz, Dieter. II. Hachum, Ahmed Yousif,
1945-III. Title.
S619.W38O94 2012
628.1–dc23
2012006874
ISBN: 978-0-415-62114-4 (Hbk)
ISBN: 978-0-203-10625-9 (eBook)
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Contents
Preface xi
Acknowledgements xv
About the authors xvii
Symbols xix
Abbreviations xxi
1 Principles and practices of water harvesting 1
1.1 Introduction 1
1.2 Concept and definition of water harvesting 2
1.3 History 3
1.4 Components of water harvesting systems 6
1.5 Importance and benefits of water harvesting 7
1.6 Impact of global climate change and adaptation measures 8
2 Hydrological aspects of water harvesting 11
2.1 Introduction 11
2.2 The hydrological cycle 11
2.3 Small hydrological watershed model 13
2.4 Hydrological characteristics 13
2.4.1 Evapotranspiration 14
2.4.2 Precipitation 14
2.5 Frequency analysis and design rainfall 16
2.6 Rainfall-runoff relationship 18
2.6.1 Factors affecting runoff 18
2.6.1.1 Soil type 18
2.6.1.2 Rainfall characteristics 18
2.6.1.3 Land cover 18
2.6.1.4 Slope of the micro-catchment 19
2.6.1.5 Size and shape of the micro-catchment 19
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2.6.2 Runoff models suitable for water harvesting 20
2.6.2.1 Runoff models for micro-catchment
water harvesting 21
2.6.2.2 Runoff models for macro-catchment
water harvesting 26
3 Methods and techniques in water harvesting 31
3.1 Introduction 31
3.2 Classifications of water harvesting methods 32
3.3 Micro-catchment water harvesting methods 33
3.3.1 Rooftop and courtyard systems 36
3.3.1.1 Suitable surfaces 36
3.3.1.2 Issues to be addressed 40
3.3.2 On-farm systems 41
3.3.2.1 Inter-row water harvesting 41
3.3.2.2 Negarim 43
3.3.2.3 Meskat 46
3.3.2.4 Contour bench terraces 46
3.3.2.5 Small pits 47
3.3.2.6 Contour bunds and ridges 48
3.3.2.7 Semicircular and trapezoidal bunds 51
3.3.2.8 Eyebrow terraces 53
3.3.2.9 Rectangular bunds 53
3.3.2.10 Vallerani-type micro-catchments 55
3.4 Macro-catchment water harvesting techniques 57
3.4.1 Introduction 57
3.4.2 Long-slope water harvesting 58
3.4.2.1 Hillside conduit systems 58
3.4.2.2 Limans 63
3.4.2.3 Large semicircular or trapezoidal bunds 64
3.4.2.4 Cultivated tanks/reservoirs and hafairs 64
3.4.3 Floodwater harvesting systems 65
3.4.3.1 Wadi-bed water harvesting systems 66
3.4.3.2 Off-wadi systems 69
3.5 Harvesting water for animal consumption 70
3.5.1 Traditional techniques 70
3.5.2 Modern techniques 71
3.6 Contamination concerns 71
4 Runoff inducement methods 73
4.1 Introduction 73
4.2 Methods of improving runoff 73
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Contents vii
4.2.1 Creating shallow channels 74
4.2.2 Clearing the catchment 74
4.2.3 Smoothing the soil surface 74
4.2.4 Compacting the soil surface 75
4.2.5 Surface sealing 77
4.2.6 Impermeable coverings 78
4.3 Advantages and disadvantages
of runoff-inducement methods 83
4.4 Further considerations 84
5 Identification of areas suitable for water harvesting 87
5.1 Introduction 87
5.2 Parameters for identifying suitable areas 87
5.2.1 Rainfall characteristics 87
5.2.2 Hydrology and water resources 89
5.2.3 Vegetation and land use 90
5.2.4 Topography, soil type and soil depth 90
5.2.5 Socioeconomics and infrastructure 92
5.3 Methods of data acquisition 93
5.3.1 Overview 93
5.3.2 Ground truthing 93
5.3.3 Aerial photography 94
5.3.4 Satellite and remote-sensing technology 94
5.4 Tools 98
5.4.1 Maps 98
5.4.1.1 Topographic maps 98
5.4.1.2 Thematic maps 98
5.4.2 Aerial photographs 98
5.4.3 Geographic information systems 98
5.5 Decision trees 103
6 Planning and design of water harvesting systems 105
6.1 Introduction 105
6.2 Soil–water–plant–climate relations 105
6.2.1 Soil 105
6.2.1.1 Texture and structure 106
6.2.1.2 Water-holding capacity and soil depth 106
6.2.1.3 Infiltration rate 108
6.2.2 Crop water requirements 108
6.2.2.1 Plant and drought 109
6.2.2.2 Estimating crop water needs 110
6.2.2.3 Field water budget 112
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viii Contents
6.3 Rainfall 117
6.3.1 Inter-seasonal distribution of rainfall 117
6.3.2 Design rainfall 117
6.3.3 Need for storage 119
6.3.4 Basic design procedure 119
6.3.5 Selection of site and method 121
6.3.6 Selection of crops 123
6.3.7 Runoff estimation 124
6.3.8 Catchment: Cropping area ratio (CCR) 124
6.3.9 Design examples 125
6.3.10 Optimization of system design 126
6.3.11 Further considerations in area ratio selection 126
6.4 Design considerations for trees 128
6.4.1 Design for trees 128
6.4.2 Life-saving harvested water 129
6.5 Dimensioning, materials and estimation of quantities 129
6.5.1 Dimensioning and system layout 129
6.5.2 Bund earthwork 133
6.5.3 Earthwork balance 135
7 Storage of harvested water 137
7.1 Introduction 137
7.2 Soil profile 138
7.3 Above ground storage 140
7.4 Surface/ground storage 143
7.4.1 Small storage ponds 144
7.4.2 Small farm reservoirs 144
7.4.3 Tanks 145
7.4.4 Hafairs 148
7.4.5 Large reservoirs 149
7.5 Subsurface/underground storage 149
7.5.1 Cisterns 149
7.5.2 Lining water storage structures 155
7.5.3 Groundwater dams 156
7.5.3.1 Sand-storage dams 156
7.5.3.2 Percolation dams 157
7.5.3.3 Subsurface dams 158
7.6 Selection of storage system 160
8 Implementation, operation, and maintenance
of water harvesting systems 163
8.1 Introduction 163
8.2 Implementing water harvesting systems 163
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Contents ix
8.3 Considerations in implementation 167
8.3.1 Over-design and under-design issues 168
8.3.2 Appropriate technology 169
8.4 Operating water harvesting systems 170
8.5 Maintaining water harvesting systems 172
8.6 Monitoring and evaluation 173
8.7 Extension and training 177
9 Socioeconomic issues 183
9.1 Introduction 183
9.2 Social feasibility studies 183
9.3 Land-tenure issues 184
9.4 Analyzing costs and benefits of water harvesting 184
9.4.1 Costs in water harvesting 185
9.4.2 Benefits of water harvesting 186
9.4.3 Economic feasibility analysis 187
9.4.3.1 Micro-catchments for field crops 188
9.4.3.2 Macro-catchments in sub-Saharan Africa 189
9.4.3.3 Examples from China and India 190
9.4.3.4 Some general recommendations 191
9.5 Integrated approach to planning and management 191
9.5.1 The role of government agencies 193
9.5.2 Community participation 193
9.5.3 Gender representation 195
9.5.4 Farmers as managers 195
9.5.5 The role of experts and donor agencies 196
9.5.6 Adoption or non-adoption of interventions 197
9.6 Water harvesting and sustainability in agriculture 198
9.6.1 Resource sustainability 199
9.6.2 Ecological sustainability 200
9.6.3 Social sustainability 200
9.6.4 Other sustainability aspects 201
9.6.4.1 Economic sustainability 201
9.6.4.2 Technological sustainability 201
9.6.4.3 Political sustainability 201
10 Water quality and environmental considerations 203
10.1 Introduction 203
10.2 Water harvested for human consumption 203
10.3 Water harvested for animal consumption 204
10.4 Water harvested for crop production 206
10.5 Water quality considerations 207
10.5.1 Rooftop and courtyard systems 207
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10.5.2 Runoff water from on-farm micro-catchment systems 211
10.5.3 Long-slope water harvesting 211
10.5.4 Floodwater harvesting 212
10.6 Impacts on downstream ecosystems and biodiversity 214
10.7 Water-borne diseases 215
References 217
Index 227
Color plates 237
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Preface
Water harvesting for agriculture is a term that means different things to different
people. Misconceptions and unclear definitions are common - water harvesting is
often confused with irrigation, soil and water conservation or other technologies;
while engineers and scientists may use different terminologies. This book tries to
clarify this confusion by developing a standard concept, and a framework that puts
the concept, the components and the different types of water harvesting in a universal
context. This will help design and implement systems to use scarce agricultural water
more efficiently.
There is growing awareness of the need to harvest rainwater. Many efforts have
been directed to collecting water from house roofs for domestic use. But water har-
vesting for agriculture is equally critical, particularly in dry areas. Water scarcity in
many countries is approaching critical levels. As more water is needed for domestic
use, industry and tourism, agricultural water is re-allocated to these sectors – while
food demand and food insecurity continue to grow. In many dry areas, a large pro-
portion of scarce rainwater is lost through evaporation. Water harvesting can reduce
these losses, and alleviate water-related stress in agriculture.
Another factor is climate change, which will lead to higher rainfall intensities in
many regions. This will increase runoff rates and associated soil erosion, reduce soil
water storage, and increase moisture stress on crops and vegetation. As this book
describes, water harvesting is a simple, low-cost method that can enable resource-
poor farming communities to adapt to climate change.
Despite the increased attention, and solid evidence of the benefits of water harvest-
ing, adoption by farmers is still low. The reasons (technical, socioeconomic, institu-
tional and policy issues) are many, complex, and differ from one situation to another.
We believe that understanding the reasons for slow adoption is an essential first step.
The book discusses factors that help or hinder the dissemination of water harvesting
technology, and suggests specific measures to accelerate adoption.
Most countries have indigenous water harvesting systems, some of which are
still functioning after centuries of use. There are many types of indigenous systems,
all based on the principle of collecting runoff water and channeling (concentrating) it
for beneficial use. Indigenous systems use traditional materials and tools which were
appropriate for earlier times, but these can be improved using modern materials and
tools. We show in this book how indigenous knowledge is still valid but modern tools,
materials and methods can help develop new practices that are more economic, dura-
ble and practical. The book emphasizes that new water harvesting systems must aim
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