2 nd Arab Water Forum Living With Water Scarcity Cairo, November 20-23, 2011 Dieter Prinz The Concept, Components and Methods of Rainwater Harvesting Cairo, 21 Nov. 2011 Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 1
The Concept, Components and Methods of Rainwater Harvesting Contents O The Concept of Rainwater Harvesting (WH) O The Components O Natural Framework Conditions O The Methods & Techniques of Water Harvesting O Water Storage O Ecological Aspects O Outlook O Summary Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 2
Rainwater Harvesting - Living with water scarcity but one source of water is underutilized... - Long tradition of Rainwater Harvesting (RWH) in MENA countries After a number of years of neglect, rainwater harvesting gained new interest in recent decades. Other terms under the umbrella of water harvesting: Runoff irrigation Runoff farming Spate irrigation (= Floodwater harvesting) Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 3
The Concept of Rainwater Harvesting (with special reference to agriculture) Definition of water harvesting: Collection and concentration of rainwater and runoff and its productive use for the irrigation of annual crops, pastures and trees domestic and livestock consumption and groundwater recharge. The basic principle of agricultural water harvesting: to capture precipitation falling on one part of the land and transfer it to another part ( target area ), thereby increasing the amount of water available to the latter part. Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 4
The Concept of Water Harvesting (with special reference to agriculture) II 4-ha land cultivated with annual rainfall of 150 mm Water not enough to produce any crop 2-ha land (not cropped) 2-ha land (cropped and productive) 3-ha land (not cropped) 1-ha land (cropped and more productive) Two important parameters: CCR = Catchment : Cropping Area Ratio RC = Runoff Coefficient (%) Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 5
The Goals of Water Harvesting in Dry Areas Recharge groundwater Reduce soil erosion risk Reduce risk, allow intensification The Goals Reduce flooding risk Improve living conditions Substitute groundwater Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 6
The Components Target Catchment Catchment Storage Runoff Microcatchment Water Harvesting Storage Target Target Storage Pond Catchment Macrocatchment Water Harvesting Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 7 Hill
Natural Framework Conditions Average rainfall per season Interannual variation Rainfall Distribution during rainy season Intensity of rainfall Number of rainfall events per season Floodwater Harvesting Long Slopes Water Harvesting Microcatchment Microcatchment Water Harvesting 100 200 300 400 mm/year Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 8
Further important parameters are: Soil Soil depth of cropping area (as deep as possible) Soil type of catchment area (for high runoff rates) Soil quality of cropping area (high water holding capacity) Soil Slope angle (inclination) Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 9
The Methods of Water Harvesting Overview Water Harvesting Methods s s s s Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 10
Techniques of Water Harvesting: (1a) Rooftop Microcatchments Rooftop WH Collecting areas (catchments): House tops, Roofs of commercial buildings Greenhouses Courtyards, roads High runoff coefficient (50 90 %) Storage of water in tanks, jars, cisterns Source: www.thecistern.com/storage/aquahouserain2.jpg. Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 11
Techniques of Water Harvesting: (1b) On-farm Microcatchments Size: 10 to 1000 m 2 CCR: 1:1 to 10:1 Simple in design May be constructed at low cost Techniques are easily replicable and adaptable They have higher runoff efficiency than macro-catchment systems No water conveyance system is needed. There are systems suitable to any slope and crop Treatment of catchment surface: Compacted, treated with chemicals or covered with plastic sheets Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 12
On-farm Microcatchments, cont. Semi-circular bunds for forage bushes Inter-row WH for grain, pulse and forage crops Contour bunds Catchments Photo: ICARDA Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 13
Techniques of Water Harvesting: (2a) Macrocatchments: Long-Slope Systems Size: 1 ha to 200 ha CCR: 10 : 1 to 100 : 1 Runoff coefficient: 10-50% of annual rainfall Cropping areas: Terraced or in flat terrain Hillside Runoff System Hafair (Photo: Oweis) Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 14
Techniques of Water Harvesting: (2b) Floodwater Systems: Floodwater Spreading Size: 200 ha to 50 km 2 CCR: 100 : 1 to 10,000 : 1 or more Engineering skills needed Upstream downstream problems on water resources use likely Tree Plantation Diversion Structures Wadi Main Barrier Spillway 50 150 m Source: GTZ, redrawn Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 15
Floodwater Systems: Jessour Photo: Oweis Jessour system as applied in Tunisia Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 16
Water Storage Storage Media Soil Storage of runoff is a precondition for Supplemental Irrigation (if other water sources are not at hand) Reservoir Pond Tank Cistern 17 Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 17
Water Storage in Ponds Problems: No data on rain intensities No data on event duration No water infiltration data No soil storage data Dry reservoir in a watershed in NE Libya Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 18
Ecological Aspects Wetlands may dry up, if runoff is alienated for agricultural purposes When catchments are cleared, compacted or otherwise treated, this has got an impact on biodiversity and very often on the extent of soil erosion, too. Water harvesting makes to a large extent use of water, which otherwise would have been lost to atmosphere without any benefit Water harvesting can reduce the quantities of water which otherwise would have been extracted from renwable or unrenewable groundwater or from permanent rivers. The water harvested should be utilized in an effective way, using suitable crops (which can tolerate some days of inundation as well as dry periods), cropping techniques and irrigation modes. Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 19
Outlook In the past, water harvesting has been not only a source of drinking water, but the backbone of agriculture in dry MENA areas. After a decline, it gained new interest during past decades. To make full use of the potential of water harvesting, suitable areas have to be identified (by using remote sensing data, GIS, field visits) the farmers have to be convinced and trained; their participation in the decisionmaking process is essential, demonstration and (on-farm or on-station) research activities have to be started. For larger projects it will be necessary, to supply skilled personel for the hydrological & engineering planning and execution, to offer microcredits and/or subsidies to farmers by the government. Water Harvesting project in Kayes Province, Mali Suitable laws and regulations related to land and water (runoff) use should be available. Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 20
Outlook, cont. The future role of water harvesting will be as a linking element between rainfed agriculture and irrigated agriculture. Rainfed Agriculture When planning water harvesting projects, the principles of IWRM shall be applied. Water Harvesting Soil- and Water Conservation Supplemental Irrigation The WH design should reflect the future impact of Global Climate Change. Irrigated Agriculture Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 21
Summary Water harvesting = The collection of runoff and its use for the irrigation of annual crops, pastures and trees, and for human and livestock consumption. Main components: The runoff area, the target and the storage medium. The water is stored in the soil, in tanks, in cisterns, ponds or reservoirs. Methods & techniques: Two different groups of techniques are distinguished, defined by the ratio between collecting and receiving area: Micro- and Macrocatchment Water Harvesting. Catchment Runoff Storage Target Each group comprises a wide variety of different techniques, serving the different natural and socio-economic conditions. Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 22
The future role of water harvesting will be as a linking element between rainfed and irrigated agriculture, using untapped water resources and alleviating the stress of drought-ridden rural societies. شكرا THANK YOU! Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 23
prof.prinz@t-online.de Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 24
Water Harvesting Methods s s s s Prof. Dr. Dieter Prinz, Karlsruhe, Germany: The Concept, Components and Methods of Rainwater Harvesting 25