Changes

Natural rock catchment and Open water reservoir

2,334 bytes added, 15:57, 1 October 2015

no edit summary

{{Language-box|english_link= Natural rock catchment and Open water reservoir | french_link= Coming soon | spanish_link= Coming soon | hindi_link= Coming soon | malayalam_link= Coming soon | tamil_link= Coming soon | korean_link= Coming soon | chinese_link=岩石集水区及开放式水库 | indonesian_link= Coming soon | japanese_link= Coming soon }}__NOTOC__[[Image:ground ctch icon.png|right|80px]][[Image:BareRockCatchment.jpg|thumb|right|300px200px|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|300px200px|Rock catchment project in Kitui, Kenya. <br> Photo: [http://www.friendsofkitui.com/rockcatchWater_Issues.htm html Friends of Kitui.]]]The technique applied Rock catchment dams are developed from a rock outcrop to catch and concentrate rainwater runoff into a storage structure for utilizing rocks for water supply productive use. In arid and semi-arid lands with large rock outcrops, a lot of runoff is called rainwater harvesting generated after rains. Through development of rock surface into a catchment, the runoff can be harvested and the structures built stored for harvesting rainwater from rocks are called rock catchmentsdomestic and livestock use to alleviate water shortages.  These are naturally occurring catchments of bare rock that have high runoff coefficients (around 0.9). Water can be stored as an open reservoir behind a retaining structure, with storage capacities ranging from 20 – 4,000 m3, or can be stored directly in a covered storage tank that collects water directly from the catchment. The capacity of rocks to supply water is significant, because a rock surface of 1 hectare (10,000 square metres = 2.47 acres) can provide 1,000 cubic metres (1 million litres) from every 100 millimetre of rain. Even low and erratic showers can supply large volumes of water provided the rock area is sufficiently large enough to compensate for the low rainfall.

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 , cracks, or cracks soil pockets that would result in a loss of water through seepage.* The dam should be built in a site that has a high depth to surface ratio (it is more deep than it is wide) so as to minimize evaporation losses.

* 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.

* Catchment may be enclosed by stone gutters (a stone wall built with rough stone/hardcore, joined with mortar)* There should be no severe soil erosion in the catchment area* Masonry dams (gravity or pumped) are more site-specific than tanks and earth dams because:<br>#Gorges between two rocks can be closed with a straight dam wall.#Rock pools and rock shelves, the latter being nearly flat areas on rock outcrops, can be surrounded with two-winged or three-winged dam walls.* Other requirements: availability of materials such as sand, hardcore, and ballast locally; skilled person/mason; labour; a means of transporting materials

|-

! width="50%" style="background:#efefef;" | Advantages

! style="background:#ffdeadf0f8ff;" | Disadvantages

|-

| valign="top" | - High runoff coefficient is similar to roof catchments, even small showers produce water <br>

|}

 ===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=== ====Design and construction tips====* Build the dam in stages if it means it will be more solid* An out-take, gravity pipe and water tap point should be constructed to abstract water downstream from the dam* The downstream side of the dam should be protected against erosion in case the dam overflows* The size of the dam and catchment area should be consistent with the available labour force* The shape of the reservoir created by the dam should minimize evaporation losses* Local construction materials should be used and relied on* The catchment area should be protected against pollution  '''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.

'''Specific advice''':

[[Image:RockCatchmentRoof.jpg|thumb|right|300px200px|Building a roof for the rock catchment dam to keep it clean and minimise evaporation losses.<br> Photo: [http://www.googlesamsamwater.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDcQFjAC&url=http%3A%2F%2Fwww.samsamwater.com%2Flibrary%2FBook1_Water_from_Rock_Outcropslibrary/Book1_Water_from_Rock_Outcrops.pdf&ei=Ys59T4_iLanM2gXA4NTlDA&usg=AFQjCNFY-XFDfUONAlG7HCp0p7Q4YDDOhw&sig2=UKAZc-rFHN-M4tfVsNOZGQ Water from Rock Outcrops.] DANIDA.]][[Image:RockPool.jpg|thumb|right|300px200px|A rock pool in near Taveta, Kenya.<br> Photo: [http://www.googlesamsamwater.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDcQFjAC&url=http%3A%2F%2Fwww.samsamwater.com%2Flibrary%2FBook1_Water_from_Rock_Outcropslibrary/Book1_Water_from_Rock_Outcrops.pdf&ei=Ys59T4_iLanM2gXA4NTlDA&usg=AFQjCNFY-XFDfUONAlG7HCp0p7Q4YDDOhw&sig2=UKAZc-rFHN-M4tfVsNOZGQ Water from Rock Outcrops.] DANIDA.]][[Image:MeasureRockGradient.jpg|thumb|right|300px200px|To measure the rock gradient, a spirit-level horizontal on a 100cm length of timber is used. This rock is determined to be too steep. <br> Photo: [http://www.googlesamsamwater.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDcQFjAC&url=http%3A%2F%2Fwww.samsamwater.com%2Flibrary%2FBook1_Water_from_Rock_Outcropslibrary/Book1_Water_from_Rock_Outcrops.pdf&ei=Ys59T4_iLanM2gXA4NTlDA&usg=AFQjCNFY-XFDfUONAlG7HCp0p7Q4YDDOhw&sig2=UKAZc-rFHN-M4tfVsNOZGQ Water from Rock Outcrops.] DANIDA.]]

In general, it seems that smaller scale dams owned privately might have more chance of success in terms of participation in the construction

and maintenance processes. However, using a self-help method of community organising, larger projects can also be successful.

* 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 [[Image:RubbleStones.jpg|thumb|right|300px200px|Rubble stones save about 50% of the cost of cement, sand, and ballast. <br> Photo: [http://www.googlesamsamwater.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDcQFjAC&url=http%3A%2F%2Fwww.samsamwater.com%2Flibrary%2FBook1_Water_from_Rock_Outcropslibrary/Book1_Water_from_Rock_Outcrops.pdf&ei=Ys59T4_iLanM2gXA4NTlDA&usg=AFQjCNFY-XFDfUONAlG7HCp0p7Q4YDDOhw&sig2=UKAZc-rFHN-M4tfVsNOZGQ Water from Rock Outcrops.] DANIDA.]]

There are 3 types of rock catchment costs to compare:

# Earthen dams are the easiest and cheapest to construct using manual labor or animal draught (yet vulnerable to seepage, erosion, and evaporation).

# 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.

====Akvo RSR projects====The following RSR project(s) include rock catchment or other open water reservoirs.<br>{|style="border: 2px solid #e0e0e0; width: 20%; text-align: justify; background-color: #e9f5fd;" cellpadding="2"|- style="vertical-align: top"|[[Image:akvorsr logo_lite.png|center|60px|link=http://akvo.org/products/rsr/]]|- style="vertical-align: bottom"|[[Image:project 440.jpg |thumb|center|140px|<font size="2"><center>[http://rsr.akvo.org/project/440/ RSR Project 440]<br>Raising awareness on rainwater harvesting</center></font>|link=http://rsr.akvo.org/project/440/ ]] |} <br> ===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.friendsofkitui.com/waterissuesWater_Issues.htm html Friends of Kitui] - Water Open reservoir, water projects.

* [http://www.googlewaterforaridland.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDcQFjAC&url=http%3ABooks/book%2F201water%2Fwww.samsamwater.com20from%2Flibrary20rock%2FBook1_Water_from_Rock_Outcrops20outcrops.pdf&ei=Ys59T4_iLanM2gXA4NTlDA&usg=AFQjCNFY-XFDfUONAlG7HCp0p7Q4YDDOhw&sig2=UKAZc-rFHN-M4tfVsNOZGQ Water from Rock Outcrops: A handbook for engineers and technicians on site investigations, designs, construction and maintenance of rock catchment tanks and dams]or ([http://www.washdoc.info/docsearch/title/156042 alternative link]). A full project guide from start to finish, on building a dam in a natural rock catchment. Includes building options, how to measure and calculate, how to organise the community, how to fund raise and make a proposal, costs, and more.

* [http://www.waterforaridland.com/ Water for Arid Land]. Lots of manuals for technical methods.

* [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. * Nissen-Petersen, Erik, [http://www.googlewaterforaridland.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDcQFjAC&url=http%3ABooks/book%2F201water%2Fwww.samsamwater.com20from%2Flibrary20rock%2FBook1_Water_from_Rock_Outcrops20outcrops.pdf&ei=Ys59T4_iLanM2gXA4NTlDA&usg=AFQjCNFY-XFDfUONAlG7HCp0p7Q4YDDOhw&sig2=UKAZc-rFHN-M4tfVsNOZGQ Water from Rock Outcrops: A handbook for engineers and technicians on site investigations, designs, construction and maintenance of rock catchment tanks and dams] or ([http://www.washdoc.info/docsearch/title/156042 alternative link]). Danish International Development Agency (DANIDA), 2006. * [http://www.bebuffered.com/downloads/profit-from-storage-reprint-2013_digitalvs.pdf Profit from Storage: the value of 3R]. RAIN, et al. * [http://www.rippleethiopia.org/index.php RiPPLE] (Research-inspired Policy and Practice Learning in Ethiopia). Rock Catchment Dams.

• ← Older edit

Winona

Akvopedia-spade, akvouser, bureaucrat, emailconfirmed, staff, susana-working-group-1, susana-working-group-10, susana-working-group-11, susana-working-group-12, susana-working-group-2, susana-working-group-3, susana-working-group-4, susana-working-group-5, susana-working-group-6, susana-working-group-7, susana-working-group-8, susana-working-group-9, susana-working-group-susana-member, administrator, widget editor

30,949

edits