__NOTOC__<small-title />[[Image:ground ctch icon.png|right|80px]]
[[Image:BareRockCatchment.jpg|thumb|right|200px|Natural rock catchment on Sullivan Rock, USA. <br> Photo: [http://bibbulmuntrack1000.blogspot.com/2010/09/5th-training-324-km-5-days-walk.html Paul Madden.]]]
[[Image:RockCatchment.jpg|thumb|right|200px|Rock catchment project in Kitui, Kenya. <br> Photo: [http://www.friendsofkitui.com/rockcatch.htm Friends of Kitui.]]]
The Kitui district in Kenya has over 400 rock catchment tanks and dams.
===Suitable conditions===
* The rock that makes up the catchment should be bare and free of vegetation/soil. It should have no fractures or cracks that would result in a loss of water through seepage.
* Site the dams for rock catchments to maximize the natural topography – to get the best storage volume, build on gorges between rocks, rock pools, and rock shelves. Make dams on the lower side of existing rock pools.
===Resilience to changes in the environment===
====Drought====
'''Effects of drought''': Tend to dry up quickly.<br>
More information on managing drought: [[Resilient WASH systems in drought-prone areas]].
===Construction, operations and maintenance===
'''General advice on cement''': A common cause of cracks in structures and linings (e.g. in tanks, dams, waterways, wells) is errors in mixing and applying the cement. First of all, it is important that only pure ingredients are used: clean water, clean sand, clean rocks. The materials have to be mixed very thoroughly. Secondly, the amount of water during mixing needs to be minimal: the concrete or cement needs to be just workable, on the dry side even, and not fluid. Thirdly, it is essential that during curing the cement or concrete is kept moist at all times, for at least a week. Structures should be covered with plastic, large leaves or other materials during the curing period, and kept wet regularly.
* Fish can be introduced to eat mosquito larvae, while at the same time providing a source of nutrition.
===Costs===
* '''Range of scale:''' a range from 20 Ksh per m3 (USD 0.27), for a reservoir volume of 5000 m3 (a valley dam constructed by oxen), to 100 Ksh per m3 (1.37 USD), for a reservoir storage volume of 100 m3
# Water tanks are the most expensive to build (but have no seepage or evaporation losses, only limited amount of water by the size of the tank).
===Field Experiences===
In Kenya, the tradition of Harambee (to pull together) on communal self-help projects has greatly assisted many villages with the affordable implementation of rock catchment dams. In the semi-arid Machakos and Kitui in Kenya, the Wakamba communities have organized themselves into self-help groups, called Mwethya, many decades ago. They know that by working together they can cope with the harsh climatic conditions. This self-help spirit, combined with lack of fresh groundwater, has been the main drive in the construction of the hundreds of rock catchments built in that region for the last 50 years.
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===Manuals, videos, and links===
* [http://www.ehow.com/how_6713156_calculate-runoff-coefficient.html How to Calculate Runoff Coefficient]. Rain is a normal phenomenon for many mid-latitude areas. It creates runoff, a term for water movement. A runoff coefficient is a number that relates the rainfall rate and runoff rate. Using the runoff coefficient, scientists and hydrologists can calculate how much water passes over a given area per second. There are two ways you can find the runoff coefficient. One is by using the Rational Method, and the other is by using a runoff coefficient table.
* [http://www.waterforaridland.com/Books/Book4water%20from%20small%20damspdf.pdf Water from Small Dams: A handbook for technicians, farmers and others on site investigations, designs, cost estimates, construction and maintenance of small earth dams]. Erik Nissen-Petersen for Danish International Development Assistance (Danida), 2006.
===Acknowledgments===
* CARE Nederland, Desk Study: [[Resilient WASH systems in drought-prone areas]]. October 2010.