Assessment of Best Practises and Experience in Water Harvesting Rainwater Harvesting Handbook African Development Bank TABLE OF CONTENTS 1. General description......................................................................................................................1 1.1 Introduction ..................................................................................................................................... 1 1.2 Definition.......................................................................................................................................... 1 1.3 Overview of RWH concepts............................................................................................................ 1 1.4 Current use....................................................................................................................................... 4 1.5 Main reasons and scenarios to utilize of RWH............................................................................. 5 2. Implementation approaches and strategies ................................................................................7 2.1 AfDB strategic approach to RWH ................................................................................................. 7 2.2 Current practices and experiences................................................................................................. 9 2.3 Participation, gender issues, demand driven, partnership ........................................................ 11 2.4 RWH as project activities ............................................................................................................. 12 3. Topologies and check list...........................................................................................................13 3.1 Proposed standard design procedures (AfDB) related to RWH, .............................................. 13 3.2 Decision tree on RWH................................................................................................................... 15 3.3 Check list for necessary information, studies and data.............................................................. 15 4. RWH monitoring indicators and schedules..............................................................................21 4.1 State of the art monitoring indicators..........................................................................................21 5. References ..................................................................................................................................22 Annex A: Suggested ToR regarding RWH for CSP, Sector and Project Missions........................27 Annex B: Decision tree on RWH in domestic water supply............................................................28 Annex C: Decision tree on RWH in agriculture..............................................................................29 Annex D: Summery data sheets........................................................................................................30 1. Domestic Rainwater Harvesting (DRWH) .......................................................................................... 31 2. Rock and other surface catchment systems ........................................................................................ 35 3. Sub-surface Dams, Small Dams, and Sand Dams............................................................................... 38 4. Earth dams and water ponds/pans....................................................................................................... 40 5. Recharge Structure ............................................................................................................................... 42 6. Conservation Tillage ............................................................................................................................. 45 7. Planting Pits (Zai, Zay, Chololo, Matengo, Ngoro) ............................................................................48 8. Katumani Pitting ................................................................................................................................... 50 9. Semi-circular bunds or hoops, Demi-lunes, or half moons................................................................ 52 10. Negarims............................................................................................................................................... 56 11. Tied Contour Ridges (furrows or bunds) .......................................................................................... 59 12. Fanya-juu Terracing ........................................................................................................................... 62 13. Contour Stone Bunds .......................................................................................................................... 64 14. Earth Bunds with external catchment (Teras).................................................................................. 67 15. Contour Ridges with external catchments ........................................................................................ 69 ANNEX E: Key actors.......................................................................................................................71 Disclaimer : The authors of this handbook assume no responsibility whatsoever for the use of this handbook and any recommendations made. All information and data is intended to be guiding principle only and detailed information is advised to be obtained during actual programming of rainwater harvesting projects. 1. General description 1.1 Introduction Rain Water Harvesting (RWH) techniques have been utilized throughout time as some irrigation methods have been used by the people of Ur (present Iraq) around 4500 BC and are at present used in India (Khadin structures). Today rainwater harvesting is being used worldwide for drinking (human and livestock) and agricultural purposes. Previously, the concept of rainwater harvesting has received very little consideration (especially for drinking purposes) in larger donor financed projects, but recently, with the increasing pressure on available water resources, renewed interest has emerged. The main objective of this handbook on rainwater harvesting is to provide AfDB with an effective reference tool for including various rain water harvesting approaches and techniques in the programming and design of projects. The data and recommendations in the handbook are based on available literature and findings made during field trip in March 2006 to three African countries. 1.2 Definition Water harvesting in its broadest sense can be defined as the "collection of runoff for its productive use". Runoff may be harvested from roofs and ground surfaces as well as from intermittent or ephemeral watercourses. Water harvesting techniques, which harvest runoff from roofs or ground surfaces fall under the term ‘Rainwater Harvesting’ while all systems which collect discharges from watercourses are grouped under the term ‘Floodwater Harvesting’1. 1.3 Overview of RWH concepts It has been chosen to summarize the concepts of rainwater harvesting as seen below: Micro catchment Domestic Small scale dams In situ RWH RWH Surface catchment External catchment Check dams, sand (conservation Individual (HH) Rock, concrete, plastic Run-off diverted into dams (sub-surface tillage)/on the field or institution sheets, treated ground field (contour stone dam), water pans, water conservation (schools etc.) surfaces or other bunds, trapezoidal ponds or pits (zai, negarim, roof catchment suitable surfaces bunds etc.) (charco), earth dams contour bunds, fanja systems juu, demi-lunes etc.) ↓ ↓ ↓ ↓ ↓ ↓ Productive purposes Productive purposes Domestic and livestock Domestic (consumption, personal and food security, and food security, consumption, nurseries, hygiene, cooking, cloths washing) water and soil water and soil small-scale irrigation conservation conservation In-situ RWH is also called water conservation and is basically a prevention of net runoff from a given cropped area by holding rain water and prolonging the time for infiltration. In-situ RWH is achieved mainly by conservation tillage and has in this handbook been merged with micro catchment. 1 Pilot Project On Water Harvesting In The IGAD Region, P.6 1 Construction of larger dams with storage capacity normally above 100.000 m3 could be categorized as rainwater harvesting. Nevertheless these multi purposes structures will not be treated in detail further in this handbook.2 Domestic rainwater harvesting (DRWH) • Harvesting of rainwater on roofs at individual, community or institutional level • Consists of roof, gutters, first flush device and storage tank. • Rain pattern, catchment area and storage capacity determines the quantity. • Collected water normally has a high acceptability to user both in term of taste and appearance. • The quality of water (avoidance of contaminants like faecal coliforms, turbidity and insect larvae) can be controlled by proper operation and simple disinfections techniques if needed. • Useful in areas with rainfall between 200 and 1000 mm. Especially favourable in areas with two separated rainy seasons • Areas with more or less rainfall also potential depending upon available water resources and water quality. • Mainly used for domestic purposes Individual household domestic RWH, Ruiri, Community domestic RWH, Losimingori village, Meru district, Kenya Monduli district, Tanzania Surface catchment