Changes

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.

* 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.

* In pastoralist areas, it might be good to site ponds in areas where traditionally pasture is used first after the rains. In this way, as much water as possible can be used to cover water demand before it is taken by seepage and evaporation, leaving other sources with less seepage and evaporation, e.g. sand dams, to be used later on in pasture accessed during the dry season.

- Maintaining dams requires communal effort and communal institutions might not be strong enough <br>

- High combination of evaporation and seepage rates means that water in ponds does not last very long, e.g. 4-6 months in India. <br>

- Microbiological and chemical water quality is likely to not be acceptable for direct consumption <br>

- High cost of construction

====Drought====

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

'''To increase resiliency of WASH system''': Reduce evaporation & seepage; Follow proper construction methods; Reduce siltation so there can be more volume capacity; Promote private ownership of ponds, so that de-silting process more likely; Improve access to low-cost loans with long-time repayment conditions so that farmers can replicate technology; Phased construction until capacity is sufficient for water demand.

'''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====

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.

'''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.

* [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.