(Photos: Erik Nissen-Petersen)
On the positive side Rural communities prefer rock catchments over other water supply types because: Even small rain showers produce large quantities of run-off that collects into reservoirs. Construction and maintenance is simple and inexpensive. Rock catchments do not occupy productive agricultural land and rocks usually are nobody’s property.
On the negative side Losses through evaporation are high, and roofing of storage structures requires good design and workmanship. Water quality may be below World Health Organisation (WHO) standards, but the communities concerned can work on this. The sun’s UV rays do sterilise water to a certain degree. Water put in transparent plastic bottles and subject to the full sun for at least five hours will be completely free of germs and bacteria. This method is obviously cheaper and more environment-friendly than using firewood or charcoal to boil water for drinking.2 Mosquitoes breed in the water of open reservoirs, spreading malaria. This can be prevented by roofing or by raising tilapia fish in the reservoirs or by pouring a few litres of clean vegetable oil onto the water. Tanks and masonry dams provide domestic water, but not the quantities required for livestock or irrigation. The large quantities of Should water contain dust or dirt particles, these can be made to settle by applying a few drops of seed oil of the horseradish or drumstick tree (Moringa oleifera) that grows well in dryland. It acts like a natural flocculant.
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Miti October-December 2011
water required for the latter can only be stored in earth dams situated at the foot or near the rock.
Community participation Experience has shown that where only a narrow technical focus is adopted, many projects have failed. It has been noted that follow-up and maintenance grow feeble once external funds for a project have dried up. Usually, rock catchments are built and used by communities. To ensure success of a project, it is crucial to involve the community at every stage, from inception to long-term maintenance. It is labour-intensive to construct catchments large enough to supply water to many households throughout the dry season. Most rock catchments are constructed during droughts when demand for water is highest and work in the fields lowest, which is the best combination for communal labour-intensive activities. Food-for-work programmes are also suited to construction of rock catchments. At its simplest, maintenance consists only of cleaning the catchment area and its storage reservoir before the rains start, and sometimes to replace the water taps.
Cost/benefits The cost and benefit analysis of rural water supplies comprises three components, namely: Construction cost of the project Annual (recurrent) cost of maintenance and repairs, and Comparison of construction and recurrent costs of rock catchments with conventional methods of water supply like boreholes, large earth dams or water sold by vendors. The economic viability of a rock catchment depends on the cost of alternative water sources. The local inhabitants can usually evaluate whether a rock
catchment is their best option. However, a community also needs to decide on the type of storage facility, which is the most expensive part of the undertaking. Communities have a choice of the following storage facilities: Earth dams: These are the cheapest type of storage facilities to construct, using manual labour or draught animals. However, earth dams experience loss of water through seepage and evaporation. In addition, maintenance costs for earth dams are high due to erosion of the spillway by overflowing surplus water; dam walls that get damaged by grazing livestock; and siltation because of non-cleaning or absence of silt traps. Rubble-stone masonry dams: These make use of present rock configurations like gorges and natural rock pools, are easy to construct and cheap to maintain. Such dams have no seepage losses but are still subject to losses through evaporation. Water tanks: These provide the most expensive storage facility. They have no seepage or evaporation losses, but their main disadvantage is their limited storage capacity. So, as one can see, rocks in drylands can be worth gold, or to say in Swahili “Mawe ni pesa” (rocks are money/wealth). Erik Nissen-Petersen is a consultant on water in ASAL Email: asalconsultants@yahoo.com and asal@ wananchi.com Jan Vandenabeele is the Executive Director of Better Globe Forestry Email: jan@betterglobeforestry.com
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