Low cost water storage tanks and ponds
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CTA. 2007. Low cost water storage tanks and ponds. Rural Radio Resource Pack 07/1. Wageningen, The Netherlands: CTA.
Permanent link to this item: http://hdl.handle.net/10568/57235
Ponds and underground water tanks can store large quantities of water for domestic or agricultural purposes.
Cue: When rain only falls for a few months each year, it is very tempting for farming families to try to store some of that rainfall for use during the dry months. Water storage tanks, both above ground and under ground, are one answer. Some collect water from roof tops, while others collect run off from the ground. Man made ponds, sometimes called charco dams, are another option. Depending on the soil type these may need to be lined with a plastic sheet, to prevent the water being lost. But how affordable are these technologies for smallholder farmers? Can they afford to build them individually or is it best to work as a group? And what technical support will farmers need to build them? In general these structures are a more expensive system of rainwater harvesting, and most farmers will need some technical help in building them, or else they may quickly crack and leak and become useless. Simon Mkwinda is the Chief Land Resources Conservation Officer in the Malawian Department of Land Resources. He spoke to Excello Zidana about how families can use tanks and ponds to harvest rainwater, and began by explaining that there are two types of water storage tanks. IN: ?Basically there are two types of tanks ?? OUT: ??change the materials to make them low cost.? DUR?N: 7?48? BACK ANNOUNCEMENT: Simon Mkwinda of the Department of Land Resources in Malawi, explaining that structures for storing rainwater, such as tanks and ponds, do not have to be very expensive. The interview comes from a radio resource pack produced by CTA. Transcript Mkwinda Basically there are two types of tanks. The first one is what we call ?above ground tanks?. They are constructed of course using different materials but mostly bricks with cement. And in most cases we advocate construction of this type of tank for domestic uses. Then the second type is what we call ?underground water tanks?. This involves digging a pit in different shapes, but in most cases we advocate what they call hemispherical shape because these are proved to be strong enough to store large quantities of water. Now in terms of catchments that we use for collecting water from on the ground, mostly they could be rock outcrops or even any cultivated area where it is a source of runoff. Now instead of this runoff just flowing uncontrolled on the ground, we advocate that the runoff should be channelled to these tanks to store the water for usage later on. But by doing so, the construction of these tanks, it means they are assisting in reducing the amount of runoff that would otherwise would be flowing on the ground uncontrolled thereby causing erosion, soil erosion. So by constructing these tanks in a way we are also trying to help in controlling soil erosion which is rampant in the country. Zidana How would you look at the materials used for constructing tanks. You talked of cement. Is it feasible for a local farmer to construct these things? Mkwinda Yes at face value you may say these technologies are expensive and farmers may not be able to afford. But there are different methods of constructing these structures. For example if you are talking of an underground tank, depending on the condition of the soils you are dealing with, instead of using materials like cement and bricks or reinforcement wires, chicken wires and the like, you may do just with a plastic sheet. Because the idea is to keep water and you want to prevent seepage of water that has collected in the tank. At the same time, some of the rooftops you may construct using iron sheets. Iron sheets are very expensive. But then you can modify that. You can just provide a plastic sheet or even just grass. Because the idea is that you want to reduce evaporation of that water that you have stored in that tank. So there are those modifications which can make the whole thing cheaper and manageable by smallholder farmers. But most important of all, let?s not look at rainwater harvesting single-handedly, or in isolation. We have to empower farming communities with other initiatives that would assist them in generating income, so that some of these technologies they can adopt them quite easily. For example, World vision in Chingale. They are integrating in their programme issues that would bring a lot of income to the communities, like getting them involved in seed multiplication. The income they get from the seed multiplication programme is enabling the communities to source some of the materials on their own, as individuals or groups. Zidana What do you encourage farmers to do when they are thinking of constructing or having ponds? Mkwinda Pond construction is another technology that we are promoting among smallholder farmers, and you construct it in a strategic place, particularly near low-lying areas. The idea being that once you dig out a pond you should be able to let water, run off, to settle in that one, and the farmers should be able to utilise that water for different uses. If it is in low land it would be more ideal for irrigation, it may be ideal for fish farming. But then like I said, it depends on the conditions of the area where you are constructing these ponds. Sometimes it may be necessary for you to line the pond with plastic sheets to reduce seepage of the water. Zidana Do you see this technology to be good for farmers or worth promoting? Mkwinda It is worthwhile to promote it. In Malawi we have adequate rain for a limited number of months in a year, or in a season. We are talking of maybe at most 4 months of receiving rain. The other months are dry months. If we don?t develop a culture of storing the water we receive in that short period, then year after year we will be crying that we are unable to do A, B, C, D, because we don?t have water. This technology is coming into fill that gap. Let farmers harvest the rainwater as much as we can so that the stored water can be utilised for different purposes, domestic, livestock watering, irrigation, you name it. But then I should also mention that, yes, in our discussion here we have just looked at the structures. Those are the ones that we normally say are very expensive, because they require farmers to spend a lot of money. But there are other technologies we call in situ rainwater harvesting technologies which can be done right in the field, which are low cost, very simple, farmers can do them on their own, of course with guidance from extension workers. Zidana Can you cite some examples? Mkwinda Examples of these include pit planting, where you dig pits in the field, then you apply manure in those pits. The idea being after the rains have fallen most of the rains collect in those pits, and then you come and plant your crop in those pits. In this way you are assisting the crop to grow up so well because you have stored water in those pits. Another example is what we call swales. Swales are nothing other than small trenches that you dig on a contour in a field at a pre-determined interval. The idea is instead of runoff just flowing overland you store the runoff in those trenches, with the idea of recharging the soil profile, so that whatever crop you grow in that field should not suffer from moisture stress, especially in periods of dry spell. There are so many other technologies like water infiltration pits, rainwater harvesting from roadsides, whereby instead of just losing the water into drains, you channel the water into a field where you can grow a crop. Those are some of the techniques which are low cost, which we are already promoting. But like I said earlier, even the structures, you can try to modify them to suit the socio-economic status of the communities that you are dealing with, by modifying their design. You can change the materials to make them low cost. End of track.