Difference between revisions of "Natural ground catchment and Open water reservoir"

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(Suitable conditions)
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[[Image:BareRockCatchment.jpg|thumb|right|400px|Water catchment area on Sullivan Rock, USA.]]
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This category covers a range of large open water ponds that store 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 (see relevant section). They can have limited to high aquifer recharge capacity for ponds purposely built to increase groundwater recharge, see section on infiltration ponds under Managed Aquifer Recharge (MAR). This section discusses ponds constructed with the primary goal of storing surface water for various water uses (e.g. irrigation, livestock), although they may well also recharge groundwater. Ponds can be lined as well as unlined.
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.
 
 
 
==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 volume, make dams on the lower side of existing rock pools.
 
 
 
{{procontable | pro=
 
- High runoff coefficient = similar to roof catchments in that even small showers produce water <br>
 
- Minimal seepage <br>
 
- Maintenance is simple and cheap <br>
 
- Rock catchments do not occupy farmland and often no one owns the land, so it easy to implement<br>
 
| con=
 
- Not many sites suitable <br>
 
- If building tanks that store water directly, storage capacity is limited compared to an open reservoir<br>
 
- Cost is high – experience from Kenya shows that a 56 m3 dam cost $4,000 including labour (= $71 per m3 of storage) <br>
 
- Vectors can breed in open water<br>
 
- Microbiological and chemical water quality is likely to not be acceptable for direct consumption (see “Natural ground catchment & open water reservoir”)
 
}}
 
 
 
==Construction, operations and maintenance==
 
 
 
==Costs==
 
 
 
==Field Experiences==
 
 
 
==Reference manuals, videos, and links==
 
* [http://www.ehow.com/how_6713156_calculate-runoff-coefficient.html How to Calculate Runoff Coefficient].
 

Revision as of 07:41, 5 April 2012

This category covers a range of large open water ponds that store 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 (see relevant section). They can have limited to high aquifer recharge capacity – for ponds purposely built to increase groundwater recharge, see section on infiltration ponds under Managed Aquifer Recharge (MAR). This section discusses ponds constructed with the primary goal of storing surface water for various water uses (e.g. irrigation, livestock), although they may well also recharge groundwater. Ponds can be lined as well as unlined.