__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|200px|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|200px|Sand dam during flooding. Photo: [http://www.rainfoundation.org/ 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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- Year-round source of good quality water and groundwater recharge <br>
- Environmentally friendly <br>
- Erosion control <br>
- Good for coping with drought, especially when accompanying riverbank storage replenishes sand dam in dry seasons <br>
- Silt management within river basins <br>
- Added soil moisture infiltration <br>
- Long lifespan if maintained correctly.
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- Site-specific technology – not suitable everywhere. <br>
- External expert knowledge needed <br>
- Labour intensive construction <br>
- Capital intensive Although cost per volume is cheap, the actual structure that needs to be made is expensive. <br>- The site must fit very specific conditions If dam is built in stages, it can be difficult for the community to show up next season for the sand next stage of work.<br>- Must rebuild if the river changes course <br>- The possible dam construction sites may be too far from the water users <br>- In Kenya, experience shows that up to 80% of dams might not be successful functioning as they should due to poor design. <br>
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<br> ===Resilience to changes in the environment=======Drought===='''Effects of drought''': Can dry up; Water yields low. <br>'''Underlying causes of effects''': Less recharge of aquifer due to less rainfall. Increasing population & water demand; Size of aquifers – e.g. limited sand volume; Too much silt accumulates behind dam; Wells not sunk deep enough into water table; Incorrect siting creates leaking dams.<br>'''To increase resiliency of WASH system''': Competent siting & construction; Build sand dam in stages to reduce silt; Soil & water conservation techniques in upper part of catchment; Dig abstraction wells/pipes deeper. More information on managing drought: [[Resilient WASH systems in drought-prone areas]]. ====Floods====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|200px|Cross section of a sand dam.<br> (Diagram: Netherlands Water Project. <br>Click image to see details).]][[Image:Sand dam trench.JPG|thumb|right|200px|Excavation of People excavating a trench for . Source: [http://www.sswm.info/category/implementation-tools/water-sources/hardware/precipitation-harvesting/sand dam construction-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)====
'''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.
'''Specific advice'''
[[Image:SandDamConstruction.JPG|thumb|right|200px|Sand dam under construction. Somaliland. Eric Fewster, BushProof / Caritas]]
[[Image:CompletedSandDam.JPG|thumb|right|200px|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.
* Usually sand dams are built onto a rock layer, but where there is no rock and only clay, it can still work but as long as the foundation is keyed into the clay layer and where the wall does not protrude more than 0.5m above original sand level, otherwise there is a risk the structure overturns during a flood event.
* Key into banks or construct wing walls to avoid erosion around edges of the sand dam. Where wing walls are built, a good technique is to start with the wing walls and work inwards to the centre, since community enthusiasm lags by the time wing walls are constructed (if not built first), yet they are essential to proper functioning. Length of the wing wall varies according to bank characteristic: loose riverbanks, 7 metres; hard soils, 5 metres; hard & impermeable soils or rocks, wing wall is not needed. Planting napier grass along upstream riverbanks controls erosion and fixes the course of the river in a flood.
* The height of wall built before each flood event should not exceed accumulation rate of coarse to medium sand during that flood event, otherwise ponding & silt deposition will occur, which can lower specific yield and higher capillarity, then lead to limited extraction rates in wells upstream and more water lost to evaporation. Dams at 1.3m depth showed that where finer material content (0.063 mm or less) is increased, specific yield is known to decrease remarkably. Accumulation rate and therefore height varies according to location and should be adjusted at each site after the first flood event demonstrates the rate of accumulation. Height per stage will probably be between 0.3 metre and 1 metre per stage according to experience from past projects. Some silt deposition will always occur as velocities decrease toward the end of the flood event; the idea is to limit its quantity in final sand volume.
* In upstream parts of a catchment it is recommended that sand dams are always built in stages, since the availability of coarse material is generally limited and base flow is small or absent (base flow = sub-surface flow which aids surface flow so that silt/clay can still be flushed away once rainfall stops, rather than sinking directly into the sand bed). It has also been suggested that to build in stages over several years is also more beneficial for functioning of dam committees. Build them within a spillway, which was part of the first stage & wing wall construction.
====Water extraction====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 hand or rope pumps without [[Handpumps]] or a [[Rope pump]] protect the water much better. It is also possible to construct an outlet pipe with a tap. This however In certain designs for sand dams, a pipe is difficult to maintain, and can weaken shown that takes water by gravity ''through'' the damwall. Meanwhile the local community needs These are said to be trained not work well due to manage either a blocked intake, a broken tap on outlet side and maintain the possibility of weakening the damwall.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|200px|Women fetching water Groundwater abstraction from the riverbed by means of a local aquifer through 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|200px|Closed Men fetching water using a hand pump from a closed well near a sand damin Kituï, Kenya. Source: [http://www.sswm.info/category/implementation-tools/water-sources/hardware/precipitation-harvesting/sand-dams RAIN (Editor) (n.y.)]]]
====Maintenance====
If done timely, the maintenance required is not costly. Small malfunctions in the dam however can lead to destruction of the entire dam. Therefore, the dam should be regularly checked for cracks and damage. Particularly after floods, and extreme temperature changes cracks are likely. These need to be repaired as soon as possible by a trained mason. During the dry season, raised-sand dams should be raised by a maximum of 50 cm if the reservoir has filled up.
Further, the outlet and upstream riverbed should be cleaned regularly to make sure the dam does not get blocked. Silt, rocks, dead animals, etc. should be removed regularly. This can also help prevent contamination of the water. The quality of the water in the well should be checked, once in a while, by an expert.
Maintenance can normally be carried out by the users of the system or by a caretaker or watchman. Larger repairs may require skilled labour, which can usually be provided by local craftsmen. In some cases, unskilled labour may be required on a large scale (e.g. for repairing a broken raised-sand dam, or a leaking subsurface dam). The labour may be provided by the users (with or without pay), or by other people who are hired for the purpose.Users may need to establish a local committee to manage issues, such as controlling or supervising water use, preventing water contamination, carrying out O&M activities, financing O&M, and monitoring how much stored water is still available (a piezometer or auger hole may be installed to allow a caretaker or watchman to estimate how much water is left and decide if rationing has to be introduced). Proper management may also help to prevent social conflict. For O&M tasks at the dam site, a person who lives or farms near this site could be appointed. This person could also be responsible for water allocation and be involved in monitoring activities, if users obtain the water near to, or at, the site. His or her authority should be clear and accepted by all users. In order to insure success at all stages of construction, operations and maintenance, the local community needs to be trained as well to manage and maintain the dam. Promote catchment-level planning & management so that varying groups have a vested interest in the same source. They can start to addressimprovements in soil/water conservation, food production & health. Previous dam committees have shown that they tend to stop functioning effectively after the construction phase. By taking longer to build the dam, e.g. 3 stages over 3 years, it may give enough time for a catchment-based dam association to form & start functioning. Brikke and Bredero, in their publication ''[http://www.washdoc.info/docsearch/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 7500 USD 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.
* Operation and maintenance: 5 days per year
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=Case studies==
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.
==Reference manuals==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===* ManualMANUAL: [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://sasol@kenyawebacaciawateruk.standaardsite.com Sasol Project Kenya]* [http:nl/pg-29143-7-89562/pagina/wwwwelcome.acaciawater.com html ACACIA Water]* [http://www.unepThe 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.orAs a result we often work in a multidisciplinary environment with a broad variety of expertise.jp UNEP]* [http://www.iah.org/recharge IAH]* [http://www.waterforaridland.com Water IAH-MAR is a forum for Arid Land]* [http://practicalaction.org/docs/technical_information_service/sand_dams.pdf Practical action]* [http://wwwinformation 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.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.washdoc.info/docsearch/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] 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