__NOTOC__{{Language-box|english_link= Water Portal / Rainwater Harvesting / Groundwater recharge / Sand dam | french_link= Coming soon | spanish_link= Coming soon | hindi_link= वाटर पोर्टल / वर्षाजल संचयन / भूजल पुनर्भरण / रेत बांध - सैंडडैम | malayalam_link= Coming soon | tamil_link= Coming soon | korean_link= Coming soon | chinese_link=沙坝 | indonesian_link= Bendungan pasir | japanese_link= Coming soon }} [[Image:94px-Icon_sanddam.png|right|80px]][[Image:Sand dam.JPG|thumb|right|250px200px|Sand dam construction in Kitui, Kenya. Photo: M. Hoogmoed.]] '''Sand dams''' are a simple, low cost and low maintenance, replicable rainwater harvesting technology. They provide a clean, local water supply for domestic and farming use and are suited to semi-arid areas of the world.
Regions with highly erratic rainfall often have rivers with temporary seasonal sandy bed streams. They only experience heavy water run-off for short periods of time after rain. During such periods of high flows, large quantities of sand are transported downstream. Some sand can get trapped on the upstream sides of rock outcroppings along the stream. The sand traps form natural water storing aquifers. Sand dam technology provides a means to reproduce this water collecting mechanism and to increase the size of existing aquifers.
Sand dam projects here have not only improved water availability, but benefited the community socially and economically. Locals are trained to participate in construction of the dam, maintenance, financial management, and also in natural resource management.
===Suitable conditions ===[[Image:Sand dam flood.JPG|thumb|right|250px200px|Sand dam during flooding. Photo: [http://www.rainfoundation.org/index.php?id=151 RAIN Foundation.]]]
Sand dams can be constructed and used for household, community and even municipal uses. There are examples of sand dams which are connected via infiltration galleries, off-take wells and pump stations into municipal piped water systems. Expert input , however, is required to determine the best site for the dam and to make sure the project is adapted to the physical conditions as well as social circumstances of the local community. Having a lead artisan per catchment area to decide on siting seems to help success rates. Physically, the site must be suitable for construction of a dam, provide safe drinking water, and be able to use sand sedimentation to increase water availability. Firstly it must be decided if the river is appropriate, secondly the best section of riverbed must be chosen, and then the optimum location for extraction.
Generally, the dam requires a sandy riverbed in a hilly area. Preferably the riverbed consists of coarse sands laid on impermeable bedrock. The river should be seasonal but must have a base flow. Whether this is the case can be determined by the type of vegetation growing around the river. The river shouldn’t be too wide (max. 25m) and should have two high riverbanks.
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<br> ===Resilience to changes in the environment===
====Drought====
'''Effects of drought''': Can dry up; Water yields low. <br>
Sand dams require careful maintenance, and immediate repair, as flooding causes hundreds of tons of water to fall over the dam wall and onto the spill-over apron. Flood water may also spill over and erode the wing walls and, perhaps, even over the riverbanks during heavy rains. When determining the dam and spillway height at the selected location, it is very important that the water level and flood line remain below the riverbanks after construction of the dam, or that flooding will not lead to problems up or downstream of the dam. If the flood level is higher than the riverbanks, construction of a dam is not advisable.
===Construction, operations and maintenance===[[Image:Sand dam diagram.JPG|thumb|right|250px200px|Cross section of a sand dam.<br> Diagram: Netherlands Water Project. <br>Click image to see details.]][[Image:Sand dam trench.JPG|thumb|right|250px200px|People excavating a trench. Source: [http://www.sswm.info/category/implementation-tools/water-sources/hardware/precipitation-harvesting/sand-dams RAIN (n.y.)]]]First a trench needs to be dug. Its position is marked out using pegs. Then it is excavated and the soil placed downstream. It can also be dug out into bedrock. It should then be checked for weathering zones and cracks. Round bars are placed vertically along the trench to reinforce it. Then a foundation is laid consisting of 2 layers of cement with barbed wire in between. Once this has set, the trench is filled with masonry of or mortar and hardcore. The wing walls and final dam wall can then be constructed. Finally any exposed parts of the construction are plastered.
====Building the sand dam (and wing wall)====
'''Specific advice'''
[[Image:SandDamConstruction.JPG|thumb|right|250px200px|Sand dam under construction. Somaliland. Eric Fewster, BushProof / Caritas]][[Image:CompletedSandDam.JPG|thumb|right|250px200px|Completed sand dam. Somaliland. Eric Fewster, BushProof / Caritas]]
* Timing is important: dams should be built during the dry season, but don’t build dams too close to the rains in order to avoid the trench filling up with water or the dam being washed away.
* The method depends on the type of dam and the type of ground. The construction of sand dams in cascades improves total storage and efficiency and minimizes seepage losses. Dams made of concrete, stone-masonry (cheapest and easiest) and brickwork require skilled labour for construction, but are stronger and have a longer lifespan.
After the dam is built, an outlet for water extraction must be constructed for drinking, agriculture, etc. Hand dug scoop holes are the simplest possibility, however the water can easily be contaminated. Covered shallow wells, either with or without [[Handpumps]] or a [[Rope pump]] protect the water much better. It is also possible to construct an outlet pipe with a tap. In certain designs for sand dams, a pipe is shown that takes water by gravity ''through'' the dam wall. These are said to not work well due to either a blocked intake, a broken tap on outlet side and the possibility of weakening the dam wall. Where water is abstracted directly, risk of contamination increases. In such a case, household water treatment should be advocated (e.g. [[Sodis]]). <br>
[[Image:Sand dam scoop hole.JPG|thumb|right|250px200px|Groundwater abstraction from the riverbed by means of a scoop hole. Kitui District, Kenya. Source: [http://www.sswm.info/category/implementation-tools/water-sources/hardware/precipitation-harvesting/sand-dams HOOGMOED (2007).]]] [[Image:Sand dam well.JPG|thumb|right|250px200px|Men fetching water using a hand pump from a closed well near a sand dam in Kituï, Kenya. Source: [http://www.sswm.info/category/implementation-tools/water-sources/hardware/precipitation-harvesting/sand-dams RAIN (Editor) (n.y.)]]]
====Maintenance====
Brikke and Bredero, in their publication ''[http://http://www.googlewashdoc.cominfo/docsearch/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 title/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]'', recommend the following O&M activities in the chart below:
[[File:SandDam_OM.jpg|none|600px|]]
====Estimated Lifespan====
The lifespan depends on the materials used and expertise with which it is constructed and maintained. The dams in Kitui Kenya were built at a cost of US$7,500 and have a minimum lifespan of 50 years.
===Costs===
The construction of dams is largely carried out by the local community. Costs mainly relate to local availability of cement, masonry and professional supervision.
The cost of a sand dam in Kenya was very low, yielding 2,844 m3 of water was US$3,260 = US$1.15 per m3 storage.
The cost to benefit ratio for the sand dam's first year of operation is 1:12. ===Field experiences===
In Kenya, it has been used with good outcome in the Kitui, Machakos and Samburu districts. Other countries with similar dry environments such as the U.S.A, Thailand, Ethiopia and Namibia also have used it in numerous and diverse forms.
Communities in this area depend on agriculture and livestock farming, which is very limited due to the unstable water supply. In 2007 several NGOs implemented 7 sand dams and 10 surface runoff tanks. This combination should provide a reliable source of water for 10 communities in the area. The project will in the future expand to other parts of the country also.
====Akvo RSR Projects====The following project utilize sand dams.<br>{|style="border: 2px solid #e0e0e0; width: 60%; text-align: justify; background-color: #e9f5fd;" cellpadding="2"<!--rsr logo here-->|- style="vertical-align: top"|[[Image:akvorsr logo_lite.png|center|60px|link=http://akvo.org/products/rsr/]]<!--project blocks here-->|- style="vertical-align: bottom"|[[Image:project 393.jpg|thumb|center|140px|<font size="2"><center>[http://rsr.akvo.org/project/393/ RSR Project 393]<br>Dawa Eresa Subsurface and Sand Dam project</center></font>|link=http://rsr.akvo.org/project/393/ ]] |[[Image:project 404.jpg|thumb|center|140px|<font size="2"><center>[http://rsr.akvo.org/project/404/ RSR Project 404]<br>Feasibility Study for Rainwater Harvesting</center></font>|link=http://rsr.akvo.org/project/404/ ]] |[[Image:project 674.png|thumb|center|140px|<font size="2"><center>[http://rsr.akvo.org/project/674/ RSR Project 674]<br>Wateroogst: <br> Konso Woreda/Eshimale</center></font>|link=http://rsr.akvo.org/project/674/ ]] |} <br> ===Manuals, videos, and links===* MANUAL: [http://www.rainfoundationsamsamwater.org/fileadmin/PublicSitecom/Manualslibrary/Sand_dam_manual_FINAL.pdf A practical guide to sand dam implementation]. Rainwater Harvesting Implementation Network (RAIN).
* MANUAL: [http://www.samsamwater.com/library/Manual_on_SAND_DAMS_in_Ethiopia.pdf Manual on sand dams in Ethiopia]: A practical approach on sand dam site selection, design and construction. A tool for combining sand dams with other rainwater harvesting structures. ERHA (Ethiopian Rainwater Harvesting Association) and RAIN Foundation.
* MANUAL: [http://www.internationalrivers.org/resources/before-the-deluge-coping-with-floods-in-a-changing-climate-3987 Before the Deluge: Coping with Floods in a Changing Climate]. How to adapt to floods caused by climate change. International Rivers Network.
* MANUAL: [http://practicalaction.org/docs/technical_information_service/sand_dams.pdf Sand Dams: Feasible Rainwater Harvesting Technology for Arid and Semi-arid Lands]. Practical action.
* DOC: [http://wescoord.or.ke/documents/SandDams/FAQsonSandDams.doc FAQs on Sand Dams]. Provided by Excellent/ASDF with input from Dabane Trust.
* VIDEO: [http://www.thewaterchannel.tv/index.php?option=com_hwdvideoshare&task=viewvideo&Itemid=53&video_id=63 Videos===={|style="font-size: 125%"|-|{{#ev:youtube|r-FqlHQxvGk|200|auto|<center>Kitui Sand Dams - CPWC]</center>}}* VIDEO|{{#ev: [http://www.youtube.com/watch?v=|aOH7ar274S4 |200|auto|<center>RAIN sand dam workshop <br>& field visit in Ethiopia, 2009], by RAIN foundation and EHRA.</center>}}* VIDEO|{{#ev: [httpyoutube|YjzcfPax4As|200|auto|<center>Excellent - Sand Dams in Kenya</center>}}|{{#ev:youtube|2Vz2kaL2bs4|200|auto|<center>Scott Wilson Millennium <br>Project - Kenya, 2010<//tv.oneworld.net/mediamanage/play/3820//148271/ Sand dam movie - Excellent Development.com]center>}}|}
====Links====* [http://www.sanddamexcellentdevelopment.org www.sanddamcom/home Excellent: Pioneers of Sand Dams].org - All information on sand dams]* [http://acaciawateracaciawateruk.comstandaardsite.nl/site/pagespg-29143-7-89562/engpagina/homewelcome.php html ACACIA Water]. The strength of Acacia Water is the specialization in the field of groundwater, while at the same time being able to place issues in a broader perspective and to link up with other fields of action. As a result we often work in a multidisciplinary environment with a broad variety of expertise.* [http://www.iah.org/recharge IAH]* [http://www.waterforaridland.com Water IAH-MAR is a forum for Arid Land]* [http://practicalactioninformation on the work within the international groundwater community on the management and enhancement of aquifer recharge, a vital tool in the sustainable management of the world's underground water resources.org/docs/technical_information_service/sand_dams.pdf Practical action]* [http://www.excellentdevelopment.com/dams.php Excellent Development]
===Acknowledgements===* CARE Nederland, ''Desk Study : [[Resilient WASH systems in drought -prone areas'']]. October 2010.* Brikke, François, and Bredero, Maarten. [http://www.whowashdoc.intinfo/water_sanitation_healthdocsearch/hygienetitle/om/wsh9241562153/en ''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'']or ([http://www.who.int/water_sanitation_health/hygiene/om/wsh9241562153/en/ alternative link]). World Health Organization and IRC Water and Sanitation Centre. Geneva, Switzerland 2003.* Maddrell S and Neal I, [http://www.samsamwater.com/library/Maddrell_and_Neal_2012_Sand_Dams_a_Practical_Guide_LR.pdf Sand dams: a Practical Guide], Excellent Development, London. 2012.* Jacob H. Stern, Ph.D and Alvera Stern, Ed.D, et al. [http://c.ymcdn.com/sites/www.echocommunity.org/resource/collection/E66CDFDB-0A0D-4DDE-8AB1-74D9D8C3EDD4/Sand_Dams.pdf Water Harvesting Through Sand Dams]. ECHO Technical Note. 2011