Issue Pack: Water harvesting

April 30, 2012 | Backgrounder from Resource Pack 89
Environment and climate changeWater management

Backgrounder

True stories about water harvesting

 
Farmer Abadi Redehey lives in the Central Zone of Tigray Region, a semi-arid highland area in northern Ethiopia. Here, the wet season lasts from July to September or October and is followed by a long dry season. Even in the wet season, rains can be irregular. The farmer has less than half a hectare of cropland to sustain his family. Because he farms on sloping lands, he has to be creative to solve drainage problems and get good yields.

On a visit to the town of Axum, Abadi noticed the town’s sewer system. The sewers drain water in open canals. On his farm, water remains on the soil surface. The farmer was inspired to dig canals to help water drain, and to capture runoff water and groundwater.

Abadi dug long, deep canals diagonally across the slope. He set long, flat stones on both sides of the canal to help the water flow easily. He covered the canals with more flat stones, then with a layer of soil. The canals, now from half a metre to almost two metres under the surface, lead water to dug pits with earth walls. During the rainy season, these pits fill in 8-12 hours, and excess water drains to a nearby river. Abadi uses water from the pits for irrigation during the dry season, with the help of a treadle pump.

He gets up to three harvests per year from his plots: a cereal crop during the wet season and one or two harvests of irrigated vegetables during the dry season. He grows fruit trees and sells onions at the market. By diversifying his cropland and livelihood, he can now ensure food security for his family. Abadi made his innovation entirely with his own resources and at his own expense.

Alex Ole-Pere lives in a semi-arid area in southern Kenya. Rainfall is highly erratic and unpredictable, and the risk of crop failure from drought is high. It is becoming harder to support large cattle herds on grazing land that is gradually shrinking, so more and more people in the area are turning to crop production.

Alex saw that every rainy season a lot of water from the nearby mountains was wasted as it raced towards the rivers. So he came up with the idea of building a dam to collect this rainwater. He built a reservoir close to his homestead and constructed a diversion from a local waterway. The diversion directed the water from the stream into the reservoir. He built a dam, about 20 by 30 metres wide, by digging out the earth and putting it on the side of the reservoir. He uses the water he collects to irrigate vegetables and tree seedlings. Apart from sustaining the crops and trees on Alex’s farm, the reservoir also serves the larger community. “My neighbours normally come to fetch water from my dam in bad times. They can take both for their families and for their livestock. I have enough,” he says proudly.

Peter Olochoki Letoya had a realization when he moved to a very dry area in East Mau, Kenya. He saw that he needed to do something about the water shortages that were distressing his crops and threatening his family. He decided to collect rainwater from his rooftop and store it in underground reservoirs. Since then, his reservoirs have been full. In the beginning he was afraid his idea would not work. “When I first started to dig the holes for the reservoirs, I was hiding behind the house so that the neighbours would not see me. I did not want people to think I was crazy,” he recalls. But now some of his neighbours have adopted his methods.

To build the tank, the farmer dug a pit and lined the sides with plastic sheets to avoid seepage. The top of the tank is covered with cedar posts. He chose cedar because it does not rot easily and is not damaged by insects. Peter’s tanks have attracted attention because, compared to the concrete tanks recommended by district engineers, they are very cheap to construct. “My tank is about 10 percent of the price of the normal tanks found in this area,” he says. Peter Olochoki Letoya now has three underground rainwater reservoirs. These range in capacity from 1000 to 2500 litres. His family uses one for drinking water and the other two for watering trees and bushes. He is thinking about collecting rainwater in an elevated tank so that he can use drip irrigation.

Background information on water harvesting

 
Rainwater harvesting

A home rainwater harvesting system usually includes the following three components: a collection surface (usually a clean roof or ground area), a storage tank, and a device which transports the water from the roof to the storage tank, often a gutter. Other equipment is sometimes added. For example, first-flush systems divert water which contains dirt and debris from the roof surface from entering the storage tanks with the first rain after a prolonged dry period (see resource document #12 at end of this issue pack for further explanation and diagrams). A home system may also have filtration equipment and settling chambers to remove debris and contaminants before water enters the tank.

A roof is the most common collection surface, but water can also be collected from courtyards, threshing areas, paved walking areas, plastic sheets, and trees. Even the surfaces of large rocks can be used to collect water (see Farm Radio International script 83:9). Corrugated iron sheet roofs work well for collecting water. So do tile and slate roofs, and most types of thatch. The leaves of some types of grasses, such as coconut and anahaw palm, are good for rainwater collection when thatched tightly. Gutters can be made of many materials, including polyvinyl chloride (PVC), bamboo and folded metal. Plastic pipes can be cut in half to make gutters.

Storage tanks (above-ground) or cisterns (below-ground) are often the biggest financial investment in a home rainwater harvesting system. If the volume of water to be stored is very small, household containers like plastic bowls and buckets, jerry cans, and clay jars can be used. Larger amounts of water are stored in tanks or cisterns that vary in capacity from one cubic metre (which holds 1,000 litres) to hundreds of cubic metres. A typical maximum size for a home system is 20 or 30 cubic metres. The size of the storage container will depend on the cost of buying or constructing materials, the length of the dry period, the amount of space available, the soil conditions, and whether the stored water is expected to meet all or just part of domestic needs. (See resource document #11 for instructions on how to make an underground water storage tank with locally available materials. Also, see resource document #13 for details on how to calculate the best size of a storage container and on water treatment options.)

It’s very important that the cover or lid to the tank or cistern fit tightly. Then, it will exclude mosquitoes and other insects, prevent evaporation, and keep out animals and children.

Surface water harvesting

Harvesting surface water involves collecting runoff water after a rainstorm, or obtaining water from intermittent streams, rivers or wetlands in open ponds or reservoirs. This stored surface water is typically used for irrigation, livestock and aquaculture. For domestic use, this kind of water would require treatment. Water in rivers or streams can be directly collected through a “Tyrolean weir” (see resource document #9 for an explanation) or by using a fingerpond system (see resource document #9 as well).

Surface water can be collected indirectly by diverting it to ponds and / or spreading it over a large surface area. This type of surface water spreading increases soil moisture and crop yields, and is called spate irrigation. Surface water harvesting – at a small or large scale – revives and improves the productivity of the soil and allows for crop cultivation, tree planting and raising livestock.

Typical surface water harvesting techniques include:

  • stone or earth embankments used as contour bunds,
  • terracing,
  • traditional systems such as the Sudan trus system (see feature below),
  • semi-circular bunds such as demi-lunes, and
  • pits, including zai and tassa in West Africa or chololo and ngoro in East Africa.

Trus – indigenous water harvesting in Central Darfur

In Central Darfur, Sudan, a traditional way of harvesting run-off surface water involves the construction of low earth bunds on clay soils. The bunds are called trus (tera is the singular form). Trus probably began in women’s home gardens, while the large family farm in sandy soil provided the staple crops. Recently, the trus system has been extended to grow staple crops.

Here’s how the trus system works. A U-shaped earth bund is constructed with the top of the “U” facing upslope towards the catchment. The bund traps runoff after rainstorms from catchments which are usually two or three times the size of the cultivated land area. The most complicated part of building a tera is achieving the right “fit” between the slope, the catchment, the directional orientation and the size of the tera. Farmers spend a great deal of time fine-tuning their designs. Because of the labour required to build such embankments, the cropping area tends to be small – perhaps one hectare in size.

The trus method is useful in areas which have low and poorly distributed rainfall. In these areas, it can bring higher yields than rainfed agriculture on sandy soils. In Central Darfur, a major constraint on farming is labour availability. On sandy soils, weeding must be done very soon after the rains so that crops can make the best use of moisture in the soil. The clay soils in the trus are much heavier to work than the sandy soils and thus demand more labour. But they also retain moisture and fertility much longer. Trus have extended the growing season to include the winter months. This enables farmers to plant crops such as tomatoes, watermelons and cucumbers which are harvested in the off-season, allowing farmers to benefit from higher prices.

Groundwater harvesting

Groundwater can be used either for domestic purposes or for irrigation, livestock or aquaculture. Recharging groundwater in the sub-soil and in aquifers is vital in order to maintain groundwater at levels close enough to the surface to be easily accessible, and to ensure the flow of water towards wells. Groundwater is retrieved through sources such as wells, springs and boreholes. Groundwater recharge can be assisted with the following methods:

  • Ponds and reservoirs with permeable bottoms, promoting infiltration into the sub-soil or aquifers;
  • (Sand) storage dams: behind these dams a new body of sand is deposited, creating additional groundwater storage capacity.
  • Sub-surface dams in highly permeable riverbeds: preventing groundwater from being drained away.

For more information on these methods, consult the resources listed below in section D.

Water treatment and use

Because water plays a role in the transmission of many diseases, health is always a concern when using a rainwater collection system. Storage tanks and surface water reservoirs can host disease vectors: mosquitoes for malaria and dengue, snails for bilharzias, and larvae for guinea worm. Hookworm spreads easily in muddy areas. Algae grow in nutrient-rich, still and shallow water exposed to sunlight. Excess standing water can lead to health hazards and be contaminated by livestock.

Thus, it is important to take steps to ensure water safety. Rainwater collection surfaces must always be kept clean. Tanks should be designed to protect them from infestation by leaves, dust, insects, vermin such as rats, and other pollutants. Because algae grow with access to sunlight, it’s a good idea to keep storage tanks in a dark place, which also keeps the water cool.

All tanks should be carefully sealed, and all openings fitted with mosquito-proof screens. Some experts recommend that one or two teaspoons of household kerosene be added to the tank. This creates a film which prevents mosquitoes from settling on the water. Water can be treated before drinking with a variety of methods, including chlorine, boiling, and slow sand filtration.

If collected water is to be used for drinking and cooking, it is essential to monitor water quality, and water treatment is advised. It is recommended that a basic water quality test be carried out on collected rainwater during the first year following the completion of a harvesting system. Further testing, including for the presence of mosquito larvae, is necessary whenever the quality of the water is in doubt.

Other important preventive measures include:

  • fencing off catchment areas (e.g. by thorn bushes) to prevent animals from contaminating harvesting areas;
  • marking water protection zones;
  • hygiene awareness and practice; and
  • removing breeding places for mosquitoes, snails and larvae.

Production ideas

Publicize success stories by interviewing:

  • farmers who successfully harvest water on their farms, or in their homes,
  • NGO project managers or government managers who are working on successful water harvesting projects.

Convene a roundtablein which local politicians, traditional leaders, ordinary citizens, leaders of women’s groups, NGOs and others discuss water scarcity in your area, and the possibilities for the community to work together to harvest water.

Write and produce a five-minute dramaabout a village that uses community-level water harvesting  and a neighbouring village that does not. Here’s one idea: A village has installed many domestic rooftop rainwater harvesting systems, as well as a community-level project such as a sand dam. This village has enough water for agriculture, livestock, and clean drinking water. During a drought, they are able to find enough water to keep livestock alive and crop yields reasonable. A neighbouring village without such infrastructure experiences hard times – livestock are dying and young and elderly people are in jeopardy. People from the 2nd village are discovered stealing water from the first village.

Interview individual farmers or members in a farmers’ groupabout how their farms, their households, their small businesses, or their food processing could be improved by harvesting water. Questions to ask include:

  • Are there possibilities for harvesting water in your area? Is the community taking advantage of them? If not, what are the barriers? What are some possible ways in which these barriers could be addressed?
  • Do you know of NGOs, government programs, tax incentives, progressive farmers, who/that are promoting or using water harvesting?
  • What are the barriers to water harvesting – technical knowledge, cost, policy / legal barriers? Can you think of some solutions to those challenges?

Interview an expert on water harvestingfrom a national or international research institute, university, or NGO. Questions to ask include:

  • Which approaches to water harvesting have proven successful in this country or region?
  • Are these approaches affordable and practical for small-scale farmers and their communities? If not, what barriers might prevent small-scale farmers from using water harvesting methods? How can these barriers be overcome?
  • How is information about water harvesting being communicated to farmers and other rural householders?
  • Are there successful indigenous or traditional methods of harvesting water?

Produce a call-in or text-in program.Invite a water harvesting expert to the studio, and invite callers to call or text questions about water harvesting and ways to use it in their community or family.

Produce 4-6 radio spotswhich explain the importance and benefits of water harvesting. Each spot could start with the same “punchy” lead line and discuss one method of water harvesting, including:

  • rooftop systems
  • planting pits
  • terracing
  • sand dams
  • any traditional methods known in the area

Produce a jingle or song on water harvesting and its benefits.

Have a poetry contest: Invite listeners to submit poems about water harvesting and offer a prize to the “best poem.” Read all the good submissions on the air.

Further resources

Radio programs

Documents

Videos

 Organizations

Acknowledgements

  • Contributed by: Vijay Cuddeford, managing editor, Farm Radio International
  • Reviewed by: Neil Noble, Practical Answers Technical Adviser, Practical Actio

Related Scripts

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  3. Interview Farmer uses a water pump to triple his maize yields May 30, 2013