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Column: Ever heard of sand dams?- by Rasha Azrag & Guy Reeves

September 30, 2014 - 13:12 -- Ingeborg van Schayk

The column below was contributed by by Rasha Azrag & Guy Reeves.

"I am always wary of ‘technology-led’ solutions. The under-developed world is littered with rusting tractors and broken water pumps." [1]

Surprisingly, this quote is from a document that promotes a technology; which is pictured below. While it might at first glance look like a dried-up reservoir it is in fact a fully functioning sand dam that provides year-round clean water in a water scarce environment.

 

Below the surface of the sand held behind the wall 20-40% of its volume is in fact water. This can be readily retrieved providing a year-round supply of water. The video below provides a clear explanation of how sand dams work (see 1:30 to 2:02) and the manner they have been implemented by local communities in SE Kenya.

 

This video was made by the Aljazeera ‘Earth Rise’ program. Alternatively, for a concise diagrammatic explanation of how sand dams work see [1]. 

Clearly, where the conditions necessary for successful construction and implementation are met, sand dams represent a sustainable solution to the critical requirement for water for domestic and agricultural uses.

But why mention sand dams to malaria professionals?
Well, it struck me when I recently first heard of sand dams on BBC radio that this is a technology that has the potential to positively integrate with mosquito control. While many mosquitos rarely utilise river or marsh habitats, as we have discussed in our earlier column "No more broken waterpipes and water containers" [2], provision of any reliable water supply has the potential to have immense indirect benefits on larval control (e.g. through reducing water storage in containers). Unsurprisingly, the possible synergies between mosquito control and sand dams have not escaped the notice of organisations involved in their development.

So, we contacted Excellent Development (a UK based NGO [3] to ask a few questions about their work.

First of all what countries are sand dams currently used in?
Most sand dams are found in southeast Kenya, where Excellent Development has supported the construction of 413 with 126 community self-help groups. This has brought an improved source of water close to home for over 460,000 people. Excellent Development has also enabled the construction of sand dams in the following countries: Swaziland, Mozambique, Chad, South Sudan, India, Zimbabwe and Uganda.

Is there any data on the impact of sand dams on mosquito control?
None that Excellent Development is aware of. However, the principle is sound – as it is well known that reducing open water sources suitable for mosquito breeding is an effective way to control malaria. This is commonly referred to as an added benefit of sand dam technology in the literature. But, it seems there have been no quantitative studies of this hypotheses. This is an opportunity for further research.

Does water seeping under the dam wall generate mosquito-breeding pools?
In our experience this is incredibly uncommon. But, there are very rare occasions when there are water seepages through small fissures in the rock.
It should also be noted that a sand dam takes two to three rainy seasons to fill with sand. Until then, it can hold open water that would be suitable for mosquitoes to breed. However, once mature, the dam will protect water within sand for at least 50 years.

Can sand dams be built anywhere?
Sand dams must be built in a seasonal sandy riverbed, which are common throughout semi-arid dryland regions.

How long can they last?
Sand dams can last at least 50 years. They have virtually zero operation and maintenance costs – making them ideally suited to poorly served rural areas.

Approximately how much does it cost to build a sand dam with a community?
Excellent Development’s sand dams cost between £9,699 and £34,802 – depending on the size of the river catchment. This includes a 25% contribution from the community, which provides labour and locally available construction materials, such as sand and stones.

It appears that sand dams are a sustainable technology that has the potential to integrate well with mosquito control efforts, yet as the responses above detail there is currently no data on this. --Anybody feel inspired to think about doing something on this?--

On a very positive note, reading through the literature [1, 3, 4] of some of the organizations involved it is very clear that they have not been seduced by the technical strengths of their approach to the exclusion of recognising the importance of the manner of its implementation. This is exemplified in the completed partial quote which started this column:-

"I am always wary of ‘technology-led’ solutions. The under-developed world is littered with rusting tractors and broken water pumps. Yet, sand dams are a technology. Their success lies in the method of implementation." [1]

If you have comments, ideas or experience on the relationship between sand dams and vectored disease please post them below.

Equally if you have any questions about technical details or on their holistic implementation approach the Excellent Development team will endeavour to respond to them.

We would like to thank the Excellent Development team for their help in writing of this column.

References
[1] Excellent Development Sand dams brochure, quote on page 1, diagrams of how sand dams work page 4.

 


Rasha is a medical entomologist working in the department of Zoology/ University of Khartoum, Sudan and used to teach basic entomology courses to undergraduate students and molecular entomology to master students in the Medical Entomology and Vector Control program. She has experience from working in different vector control programmes, from basic classic control methods to the use of genetic methods.

Guy is a research scientist at the Max Planck Institute for Evolutionary Biology in Plön, Germany. Part of his research involves the exploration of genetic methods to control vectored diseases.
 

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Comments

Submitted by Bill Jobin (not verified) on

Mabruk. Storing water in sand dams is an excellent idea, another way that engineering can help suppress malaria. It has obvious benefits for also eliminating the snails which transmit schistosomes. In the Blue Nile Health Project in the Gezira irrigated area and the Rahad irrigated area, we constructed and rehabbed slow sand filters to provide safe drinking water. Your sand dam already does that. Congratulations.

Bill, always looking for more engineering solutions

Guy Reeves's picture
Submitted by Guy Reeves on

In the absence of mythic approaches which are effective in all possible circumstances, realistically there likely to be some environments where sand dams could be expected to have their greatest impact on mosquitos while in others they may have limited or no positive impact.
In thinking about how to start systematically examining the relationship between mosquito control and sand dams it might be helpful to speculate on what environments this link could best be explored in.
Any Ideas?

MPI, Plön (Germany)