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Natural ground catchment and Open water reservoir

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→‎Size the pond

{{Language-box|english_link= Natural ground 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=天然地面集水區與開闊水域之水庫 | indonesian_link= Coming soon | japanese_link= Coming soon }}__NOTOC__[[Image:ground ctch icon.png|right|80px]][[Image:LinedPond.JPG|thumb|right|350px200px|Natural pond with lining, Ethiopia. Photo: [http://www.ideorg.org/GetInvolved/Media.aspx iDE.]]] 

Large open water ponds are useful in storing rainwater. Natural depressions (pans) also hold rainwater in a similar way but are not modified or designed. Ponds described in this section include those that are either excavated and/or which might make use of the natural topography, and which in most cases involve an embankment around part of the pond to retain the water (the material for which may have come from excavation works). They come by different names in different countries, but names include johads and “hafirs”. These reservoirs can also be formed in existing seasonal water courses or valleys, in which case they may also be called valley dams, which are essentially the same as gully plugs (check dams). They can have limited to high aquifer recharge capacity – for ponds purposely built to increase groundwater recharge. Ponds are excellent in storing surface water for various uses (e.g. irrigation, livestock), although they may also recharge groundwater. Ponds can be lined as well as unlined.

===Suitable conditions===

* Base of the pond should be impermeable, e.g. unfissured rock or clay, to save costs and prevent having to find a form of lining.

* Minimize excavation – use natural or man-made topographical features, e.g. borrow pits from road construction, or sloping ground.

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

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

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| valign="top" | - Even if using a pond for direct water use, ponds nevertheless recharge into surrounding ground and can recharge wells around the pond so there is continued water after pond dries up. <br>

===Resilience to changes in the environment===

====Drought====

'''Effects of drought''': Tend to dry up quickly, especially if unlined; Conflict over water for animals.<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 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.

====Size the pond====

[[Image:SmallNaturalPond.JPG|thumb|right|350px200px|Small, natural pond for rainwater harvesting.<br> Photo: [http://ruralradiowww.ctacomminit.intcom/RainwaterHarvesting.htm community-radio-africa/content/cta-rural-radio-packs CTA Rural Radio Packs.]]]

Pond size (and therefore dam height) can be decided according to water demand, evaporation & seepage losses, length of critical period and average stream flow according to the following:

* Determine water requirement (R litres/day)

* Experience from South Africa indicates that access to finance seems to be important in allowing farmers to implement ponds.

===Costs===* '''High cost of construction – in Sudan, :''' a hafir 80m x 60m x 3m deep (14,400m3) for 400 beneficiaries cost US$8,000. The hafir was completed in 3 months with 190 diggers, did not use food for work but spent the money on tools and installation of inlet/outlet. * '''Range of scale - Kenya:''' 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

===Field experiences===

'''Private ownership and Desilting'''<br>

The oxen worked in pairs for five hours a day. Two pairs were used in two shifts every day. They were fed two kgs daily of a mixture of bran and oilseed cake (noug) and grazed for seven hours. The feeding of concentrates was considered necessary because drought had reduced grass cover to a minimum. All oxen were watered every three days, which is a common practice. Seven ponds were excavated in 81 days. The amount of silt taken away totaled 3,254 cubic metres. The average volume of silt excavated per ox-pair per day was 13 cubic metres in 62 loads. The cost of excavation by scoop totaled US$ 0.30/0.40 per cubic metre. Excavation costs using heavy earth moving machinery were about US$2.00 to US$3.00 per cubic metre.

===Manuals, videos, and links===

* [http://www.smallreservoirs.org/ Small reservoirs tool kit] Edited by Marc Andreini, Tonya Schuetz, and Larry Harrington. Small Reservoirs Project. Topics include: intervention planning, storage and hydrology, ecosystems and human health, institutions and economics.

* [http://ruralradiowww.cta.int/RainwaterHarvestingen/article/2014-07-07/rural-radio-resource-programme-packs-a-punch.htm html CTA: Rural Radio Packs]. Interviews in mp3 and transcript format about rainwater harvesting techniques.

* [http://www.ideorg.org/OurTechnologies/WaterStorageSystems.aspx IDE]. Provides materials like plastic liners and drums for various rainwater harvesting methods. Serves Africa, Asia, and Latin America.

* [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. ===Acknowledgements===* CARE Nederland, ''Desk Study : [[Resilient WASH systems in drought -prone areas]].'' October 2010. * [http://www.bebuffered.com/downloads/profit-from-storage-reprint-2013_digitalvs.pdf Profit from Storage: the value of 3R]. RAIN, et al.

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