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Radio Scripts

Radio Scripts

Package 89, Script 3
December 2009

Water harvesting: An issue pack

Notes to Broadcaster

Water scarcity already affects more than a third of the world’s population. With climate change, this number will undoubtedly increase. But there are many practical solutions to water shortages. One solution is water harvesting. Rainwater harvesting – often with a roof to catch water and a storage tank – is used extensively, while there are many traditional and modern systems for harvesting surface water and ground water.

Though they are not discussed in this issue sheet, other strategies to adapt to water scarcity include recycling water, enacting and enforcing laws to protect streams and rivers, and using drought-tolerant crops and crop varieties.  

This issue sheet starts with three stories about farmer water harvesting. It then offers some background information on the different types of water harvesting. Next, it suggests some starting points for creating locally relevant radio programs on water harvesting. Finally, it points to various resources on water harvesting – radio programs, documents, organizations. 

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.

 

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:

 

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:

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. Information about water treatment techniques can be found in the booklet Smart Water Solutions (downloadable at http://www.irc.nl/page/28654). 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:

 

 

 

 

 

 

Radio programs

 

Documents

 

Organizations

Acknowledgements

Special thanks to the Climate Change Adaptation in Africa (CCAA) program, a joint initiative of Canada’s International Development Research Centre (IDRC) and the United Kingdom’s Department for International Development (DFID), for supporting this script package on climate change adaptation.

Canadian Flag Program undertaken with the financial support of the Government of Canada provided through the Canadian International Development Agency (CIDA)