Water harvesting for agriculture in the dry areas

Dry areas suffer not only from limited rainfall but also 'natural leakage'--90% of rainwater is lost directly or indirectly, and is unavailable for agriculture or domestic use. Water harvesting is a low-cost, easy-to-use, environmentally-friendly way to recover a large part of this lost water.

How does water harvesting work? Which sites or areas are best suited and how can these areas be identified? How to design, build and maintain a water harvesting system tailored to local needs? How can water harvesting contribute to combating land degradation, enhancing food security and adapting to climate change? This book provides the answers.

The book is based on many years of research, training and development by three of the world's leading experts in water management and agriculture. It is authoritative, comprehensive, and easy to read, containing practical examples, many illustrations and little jargon. This volume will be of great interest to researchers, development workers, farmers, policymakers, students of the natural sciences--in fact, anyone interested in efficient, sustainable management of water resources and agriculture.

Author Notes

T. Oweis is the director of the Integrated Water and Land Management Program (IWLMP) at the International Center for Agricultural Research in the Dry Areas (ICARDA) (CGIAR Future Harvest Center). He has carried out research into and published extensively on irrigation and water management since the 1980s, fulfilling numerous academic and institutional roles over time.

D. Prinz is an independent consultant in matters concerning irrigation, water management and harvesting, and water & soil conservation. During the course of his career, he has published and lectured extensively on many aspects of rural engineering, with a particular focus on water and land resources development; irrigation, water and soil conservation and water harvesting in agriculture.

A. Hachum is Professor in the Department of Water Resources Engineering, College of Engineering, Mosul University, Iraq and consultant for the Integrated Water and Land Management Program, ICARDA. He has published many articles as well as a number of monographs on the topics of irrigation and water harvesting.

Preface	p. xi
Acknowledgements	p. xv
About the authors	p. xvii
Symbols	p. xix
Abbreviations	p. xxi
1 Principles and practices of water harvesting	p. 1
1.1 Introduction	p. 1
1.2 Concept and definition of water harvesting	p. 2
1.3 History	p. 3
1.4 Components of water harvesting systems	p. 6
1.5 Importance and benefits of water harvesting	p. 7
1.6 Impact of global climate change and adaptation measures	p. 8
2 Hydrological aspects of water harvesting	p. 11
2.1 Introduction	p. 11
2.2 The hydrological cycle	p. 11
2.3 Small hydrological watershed model	p. 13
2.4 Hydrological characteristics	p. 13
2.4.1 Evapotranspiration	p. 14
2.4.2 Precipitation	p. 14
2.5 Frequency analysis and design rainfall	p. 16
2.6 Rainfall-runoff relationship	p. 18
2.6.1 Factors affecting runoff	p. 18
2.6.1.1 Soil type	p. 18
2.6.1.2 Rainfall characteristics	p. 18
2.6.1.3 Land cover	p. 18
2.6.1.4 Slope of the micro-catchment	p. 19
2.6.1.5 Size and shape of the micro-catchment	p. 19
2.6.2 Runoff models suitable for water harvesting	p. 20
2.6.2.1 Runoff models for micro-catchment water harvesting	p. 21
2.6.2.2 Runoff models for macro-catchment water harvesting	p. 26
3 Methods and techniques in water harvesting	p. 31
3.1 Introduction	p. 31
3.2 Classifications of water harvesting methods	p. 32
3.3 Micro-catchment water harvesting methods	p. 33
3.3.1 Rooftop and courtyard systems	p. 36
3.3.1.1 Suitable surfaces	p. 36
3.3.1.2 Issues to be addressed	p. 40
3.3.2 On-farm systems	p. 41
3.3.2.1 Inter-row water harvesting	p. 41
3.3.2.2 Negarim	p. 43
3.3.2.3 Meskat	p. 46
3.3.2.4 Contour bench terraces	p. 46
3.3.2.5 Small pits	p. 47
3.3.2.6 Contour bunds and ridges	p. 48
3.3.2.7 Semicircular and trapezoidal bunds	p. 51
3.3.2.8 Eyebrow terraces	p. 53
3.3.2.9 Rectangular bunds	p. 53
3.3.2.10 Vallerani-type micro-catchments	p. 55
3.4 Macro-catchment water harvesting techniques	p. 57
3.4.1 Introduction	p. 57
3.4.2 Long-slope water harvesting	p. 58
3.4.2.1 Hillside conduit systems	p. 58
3.4.2.2 Limans	p. 63
3.4.2.3 Large semicircular or trapezoidal bunds	p. 64
3.4.2.4 Cultivated tanks/reservoirs and hafairs	p. 64
3.4.3 Floodwater harvesting systems	p. 65
3.4.3.1 Wadi-bed water harvesting systems	p. 66
3.4.3.2 Off-wadi systems	p. 69
3.5 Harvesting water for animal consumption	p. 70
3.5.1 Traditional techniques	p. 70
3.5.2 Modern techniques	p. 71
3.6 Contamination concerns	p. 71
4 Runoff inducement methods	p. 73
4.1 Introduction	p. 73
4.2 Methods of improving runoff	p. 73
4.2.1 Creating shallow channels	p. 74
4.2.2 Clearing the catchment	p. 74
4.2.3 Smoothing the soil surface	p. 74
4.2.4 Compacting the soil surface	p. 75
4.2.5 Surface sealing	p. 77
4.2.6 Impermeable coverings	p. 78
4.3 Advantages and disadvantages of runoff-inducement methods	p. 83
4.4 Further considerations	p. 84
5 Identification of areas suitable for water harvesting	p. 87
5.1 Introduction	p. 87
5.2 Parameters for identifying suitable areas	p. 87
5.2.1 Rainfall characteristics	p. 87
5.2.2 Hydrology and water resources	p. 89
5.2.3 Vegetation and land use	p. 90
5.2.4 Topography, soil type and soil depth	p. 90
5.2.5 Socioeconomics and infrastructure	p. 92
5.3 Methods of data acquisition	p. 93
5.3.1 Overview	p. 93
5.3.2 Ground truthing	p. 93
5.3.3 Aerial photography	p. 94
5.3.4 Satellite and remote-sensing technology	p. 94
5.4 Tools	p. 98
5.4.1 Maps	p. 98
5.4.1.1 Topographic maps	p. 98
5.4.1.2 Thematic maps	p. 98
5.4.2 Aerial photographs	p. 98
5.4.3 Geographic information systems	p. 98
5.5 Decision trees	p. 103
6 Planning and design of water harvesting systems	p. 105
6.1 Introduction	p. 105
6.2 Soil-water-plant-climate relations	p. 105
6.2.1 Soil	p. 105
6.2.1.1 Texture and structure	p. 106
6.2.1.2 Water-holding capacity and soil depth	p. 106
6.2.1.3 Infiltration rate	p. 108
6.2.2 Crop water requirements	p. 108
6.2.2.1 Plant and drought	p. 109
6.2.2.2 Estimating crop water needs	p. 110
6.2.2.3 Field water budget	p. 112
6.3 Rainfall	p. 117
6.3.1 Inter-seasonal distribution of rainfall	p. 117
6.3.2 Design rainfall	p. 117
6.3.3 Need for storage	p. 119
6.3.4 Basic design procedure	p. 119
6.3.5 Selection of site and method	p. 121
6.3.6 Selection of crops	p. 123
6.3.7 Runoff estimation	p. 124
6.3.8 Catchment: Cropping area ratio (CCR)	p. 124
6.3.9 Design examples	p. 125
6.3.10 Optimization of system design	p. 126
6.3.11 Further considerations in area ratio selection	p. 126
6.4 Design considerations for trees	p. 128
6.4.1 Design for trees	p. 128
6.4.2 Life-saving harvested water	p. 129
6.5 Dimensioning, materials and estimation of quantities	p. 129
6.5.1 Dimensioning and system layout	p. 129
6.5.2 Bund earthwork	p. 133
6.5.3 Earthwork balance	p. 135
7 Storage of harvested water	p. 137
7.1 Introduction	p. 137
7.2 Soil profile	p. 138
7.3 Above ground storage	p. 140
7.4 Surface/ground storage	p. 143
7.4.1 Small storage ponds	p. 144
7.4.2 Small farm reservoirs	p. 144
7.4.3 Tanks	p. 145
7.4.4 Hafairs	p. 148
7.4.5 Large reservoirs	p. 149
7.5 Subsurface/underground storage	p. 149
7.5.1 Cisterns	p. 149
7.5.2 Lining water storage structures	p. 155
7.5.3 Groundwater dams	p. 156
7.5.3.1 Sand-storage dams	p. 156
7.5.3.2 Percolation dams	p. 157
7.5.3.3 Subsurface dams	p. 158
7.6 Selection of storage system	p. 160
8 Implementation, operation, and maintenance of water harvesting systems	p. 163
8.1 Introduction	p. 163
8.2 Implementing water harvesting systems	p. 163
8.3 Considerations in implementation	p. 167
8.3.1 Over-design and under-design issues	p. 168
8.3.2 Appropriate technology	p. 169
8.4 Operating water harvesting systems	p. 170
8.5 Maintaining water harvesting systems	p. 172
8.6 Monitoring and evaluation	p. 173
8.7 Extension and training	p. 177
9 Socioeconomic issues	p. 183
9.1 Introduction	p. 183
9.2 Social feasibility studies	p. 183
9.3 Land-tenure issues	p. 184
9.4 Analyzing costs and benefits of water harvesting	p. 184
9.4.1 Costs in water harvesting	p. 185
9.4.2 Benefits of water harvesting	p. 186
9.4.3 Economic feasibility analysis	p. 187
9.4.3.1 Micro-catchments for field crops	p. 188
9.4.3.2 Macro-catchments in sub-Saharan Africa	p. 189
9.4.3.3 Examples from China and India	p. 190
9.4.3.4 Some general recommendations	p. 191
9.5 Integrated approach to planning and management	p. 191
9.5.1 The role of government agencies	p. 193
9.5.2 Community participation	p. 193
9.5.3 Gender representation	p. 195
9.5.4 Farmers as managers	p. 195
9.5.5 The role of experts and donor agencies	p. 196
9.5.6 Adoption or non-adoption of interventions	p. 197
9.6 Water harvesting and sustainability in agriculture	p. 198
9.6.1 Resource sustainability	p. 199
9.6.2 Ecological sustainability	p. 200
9.6.3 Social sustainability	p. 200
9.6.4 Other sustainability aspects	p. 201
9.6.4.1 Economic sustainability	p. 201
9.6.4.2 Technological sustainability	p. 201
9.6.4.3 Political sustainability	p. 201
10 Water quality and environmental considerations	p. 203
10.1 Introduction	p. 203
10.2 Water harvested for human consumption	p. 203
10.3 Water harvested for animal consumption	p. 204
10.4 Water harvested for crop production	p. 206
10.5 Water quality considerations	p. 207
10.5.1 Rooftop and courtyard systems	p. 207
10.5.2 Runoff water from on-farm micro-catchment systems	p. 211
10.5.3 Long-slope water harvesting	p. 211
10.5.4 Floodwater harvesting	p. 212
10.6 Impacts on downstream ecosystems and biodiversity	p. 214
10.7 Water-borne diseases	p. 215
References	p. 217
Index	p. 227
Color plates	p. 237

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