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Water Portal / Rainwater Harvesting / Surface water / River-bottom intake

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{{Language-box|english_link=Water Portal / Rainwater Harvesting / Surface water / River-bottom intake | french_link= Prise d'eau en lit de rivière | spanish_link= Toma de Fondo | hindi_link=वाटर पोर्टल / वर्षाजल संचयन / सतही जल / नदी-तल से जल-संग्रहण | malayalam_link= Coming soon | tamil_link= Coming soon | korean_link= 워터 포탈/빗물 수집/지표수/강 바닥 흡입구 | chinese_link=河底引水口 | indonesian_link= Asupan Dasar Sungai | japanese_link= 川底取水口 }} [[Image:River-bottomIntakeintake icon.JPG|thumbpng|right|300px|River-bottom intake mechanics. <br> Click image to zoom.80px]]

'''River-bottom or Tyrolean intakes ''' (different than a [[Tyrolean weir]]) for drinking-water systems are usually used in small rivers and streams where the sediment content and bed load transport are low. The water is abstracted through a screen over a canal (usually made of concrete and built into the river bed). The bars of the screen are laid in the direction of the current and sloping downwards, so that coarse material can- not cannot enter. From the canal, water enters a sand trap and then may pass a valve and flow by gravity, or be pumped into the rest of the system.

Intake designs aim to avoid clogging and scouring and to ensure the stability of the structure even under flood conditions. Where the river transports no boulders or rolling stones, an unprotected intake may be adequate.

===Suitable conditions===

* Rivers with little sediment and bed load.

* Where there is adequate flow.

* Upstream of bridges (to reduce velocity/turbulence).

===Resilience to changes in the environment=== ====Drought effects on concrete===='''Effects of drought:''' Badly made concrete or cracked linings (e.g. in tanks, dams, waterways, wells, and other structures). <br>'''Underlying causes of effects:''' Less water used for curing; Impure water used for mixing. <br>'''To increase resiliency of WASH system:''' Ensure adequate mixing, ratios, purity of ingredients; Minimize water content in mixture; Ensure adequate curing.  More information on managing drought: [[Resilient WASH systems in drought-prone areas]]. ===Construction, operations and maintenance===[[Image:River-bottomIntake.JPG|thumb|right|300px|River-bottom intake mechanics. <br> Click image to zoom.]]

For small community water supplies only small quantities of water are needed and often very simple intake structures can be used. With a per capita water use of 30 litres/day and the peak intake 4 times the average water demand, 1000 people would require an intake capacity of only 1.4 l/s. A 150 mm diameter intake pipe would be sufficient to keep the entrance velocity 0.1 m/s. If an entrance velocity of 0.5 m/s were allowed, a pipe as small as 60 mm would be adequate.

Screening is done by passing the water through closely spaced bars, gratings or perforated plates. It does not change the chemical or bacteriological quality of the water. It serves to retain coarse material and suspended matter larger than the screen openings. Even when screened-out material forms a filtering mat of deposits, the screening still is purely of a mechanical nature. Bar screens usually consist of steel strips or bars spaced at 0.5-5 cm. If the amount of material expected to be screened out is small, the bars are set quite steeply, at an angle of 60-75° to the horizontal, and cleaning is done by hand using rakes. If larger amounts will be retained, cleaning by hand should still be feasible; to facilitate the cleaning work, the bars should be placed at an angle of 30-45° to the horizontal.

 

The water should flow towards the bar screen at quite a low velocity, 0.1-0.2 m/s. Once the water has passed the screen, the flow velocity should be at least 0.3-0.5 m/s in order to prevent the settling out of suspended matter.

 

In the openings between the bars the velocity of flow should be limited to a maximum of 0.7 m/s; otherwise soft, deformable matter will be forced through the screen openings. A clean screen will allow the water to pass with a head loss of only a few centimetres. However, the head loss rises sharply when the clogging of the screen builds up. Regular cleaning should keep the head loss limited to 0.1-0.2 m head of water. Allowing for delayed cleaning and mechanical failures, it is good practice to design a barscreen for a head loss of 0.5-1.0 m.

====Maintenance====

* During the dry season, there may not be enough water in the river or stream to supply all users.

==Costs=Manuals, videos and links= ==Field experiences==* [http://www.lifewater.org/resources/rws1/rws1p4.pdf Choosing Where to Place Intakes.] Water for the World.

==Reference manuals, videos, * [http://www.ircwash.org/sites/default/files/Smet-2002-Small_TP40.pdf Surface water intake and links==small dams]. Chapter 11. Revised by Nhamo Masanganise.

===Acknowledgements===* Masanganise, Nhamo. [http://www.samsamwater.com/library/TP40_11_Surface_water.pdf ''Surface water intake and small dams''].* Brikke, François, and Bredero, Maarten. ''[http://www.googlewashdoc.cominfo/docsearch/title/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CC0QFjAB&url=http%3A%2F%2Fwww.who.int%2Fwater_sanitation_health%2Fhygiene%2Fom%2Flinkingintro.pdf&ei=cwJpT-zaO-OiiQKCst2rBw&usg=AFQjCNEWOQhTgF3a7lzhuw5OA2KmbVGxcA&sig2=Rt2EURUyGVqDcwFg6p0xAw 117705 Linking technology choice with operation and maintenance in the context of community water supply and sanitation: A reference document for planners and project staff]''. World Health Organization and IRC Water and Sanitation Centre. Geneva, Switzerland 2003.

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