Rock water catchment and open reservoirsPosted by Francis McBride on Jan 4, 2016 in Permaculture | Comments Off on Rock water catchment and open reservoirs
Rock water catchment is carved out of the rock outcrop to capture and store the rainwater runoff for use in homesteads and adjacent lands. Arid and semi-arid regions of the world have very large rock outcrops that slope down large chunks of land. Water is not leached into these rocks and just flows down the slope. This water can be stored and not left to drain away.
The naturally occurring bare rock catchments have a high runoff and can store the water in an open reservoir with a capacity of 20 cubic meters to about 4,000 cubic meters. The water can then be siphoned and stored in storage tanks away from the catchment. A rock of about a hectare can provide a million liters of water for every hundred millimeters of rain.
Best conditions for a rock catchment
The rock outcrop should not be having any vegetation or soil. It should also not have any large cracks where water can get lost through seepage. Water can seep through cracks and pockets of soil on the rock.
The dam should at a site that has a high depth to surface ratio. A deep and a narrow dam minimize water loss through evaporation. The wider the surface of the dam, the more the surface that is hit by the sun rays causing evaporation.
The dam should be set in an area that the catchment maximizes the natural topography. It should be a place where the water naturally flows down and lower than the natural gorges of the rock surface.
A stone wall enclosure can be built around the rock dam to protect the water from pollution or the risk of people or animals falling into the water. All vegetation around the rock catchment should be cleared and any loose soil covered with concrete.
If there is no proper location for the building of the natural rock dam, a masonry dam can also be built. Even in areas where there is a proper location for a natural dam, a masonry dam can be built to take care of the excess amount of water that may flow out of the natural dam. Gutters or some form of walls may be needed to slow down the flow of the water down so that it does not flow from the reservoir.
Learn more about rock catchment water harvesting
Rock catchments are innovative ways of capturing water that flows down the rock outcrops in arid and semi-arid areas. In some cases, these dams are large enough to serve the community around them until the next rain. You can learn much more about rock catchment techniques and practical guides at Open permaculture school and regenerative leadership institute.