Rainwater from large rock surfaces can be used to irrigate crops

    | March 17, 2008

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    DCFRN script Package 83 – which focuses on the work of farming and also includes some scripts on maternal health and a script on rainwater harvesting – will be mailed to our partners and posted online in just a few weeks. But we wanted to provide you with a “sneak preview” of this script, about a new technology for collecting rainwater, in time for World Water Day. We are also pleased to tell you that Package 85, which is scheduled to be mailed later this year, will feature a number of scripts on the subject of water and sanitation.

    Notes to Broadcaster

    Farmers in the Kibaale District of western Uganda face a number of challenges. One of the chief is crop irrigation. Weather patterns have become unpredictable and unreliable. Traditionally, rains fell from March to May and from August to November. The midpoint of these rainy seasons usually marked the peak rainfall intensity.

    Farmers time their farming activities to coincide with the expected weather. For example, during dry months, farmers prepare land, harvest and dry crops. In wet months, they plant seed and apply fertilizer.

    But for the last several years, the weather patterns have changed. Rains can come during any month, including those which used to be relatively dry – December, January, February, and June.

    One solution to this unpredictability is to harvest as much water as possible, store it safely, and apply it to crops during dry periods or even droughts. But individual farmers cannot afford to purchase conventional irrigation equipment such as treadle pumps and sprinkler kits. Fortunately, in many parts of Kibaale, there are wide rock outcroppings with flat surfaces. Much water can be collected from these rocks during rainfalls, and stored for future irrigation.

    This script shows how an agricultural officer has devised a method to capture rainwater from a large rock outcropping and channel it into a cement underground tank. So far, the method has been used only to provide water for domestic animals. However, the water could also be used to irrigate vegetables, bananas and other crops during dry spells. In Kibaale, it is thought that the district would finance the construction of the underground tank, which is the most costly part of the system.

    Do farmers in your area irrigate their crops? If so, find out whether they use innovative methods to capture and store rainwater for irrigation? If they do not irrigate their crops, why not? Is there a lack of technical knowledge, or a lack of funds? If there are large rock outcroppings in your listening area, would your district government be interested in experimenting with capturing irrigation water from rock surfaces? Perhaps the scheme could also be financed by farmers’ groups.

    Programme signature tune.

    Host: Good day, dear farmers, and welcome to our farming programme. Today we will talk about tapping water from the surface of large rocks to use in irrigation. We are privileged to have Mr. Bahindura John with us. Mr. John is an agricultural officer who specializes in irrigation practices and extension of technology to farmers. Please stay tuned.

    A short piece of music.

    Host: Welcome back after the break. Now we shall ask the extension officer to share his experience on this subject.

    Mr. Bahindura John: Thank you and good day to listeners. It is a big privilege to share my experience with the technology for tapping rainwater from rock outcroppings, and storing and using it to irrigate crops.

    Host: To start, could you give us a simple explanation of this technology?

    Mr. Bahindura John: In brief, this technology involves using rock surfaces, water channels and underground tanks to store water. It is similar to rainwater harvesting methods which harvest water from rooftops and store it in water jars or cement tanks. The difference with this method is that the water can be used not only by the household, but to provide water for domestic animals, and to irrigate crops in the field. Let’s talk about the rock surfaces first. We are looking for rock outcroppings that are relatively large and flat, and where there is a steep incline, so that water can easily run off to a collection point. Some changes have to be made to the rock surface. Remove any dirt and debris, including algae, and then build lines of bricks or stones to direct the water downwards. This directs the rainwater runoff into the tank and helps to speed up the water collection.

    Host: Can you explain to us what algae are?

    Mr. Bahindura John: These are tiny organisms which cling to the rock surfaces. Usually, algae look like clusters of little green threads.

    Host: What materials should be used to build the tank?

    Mr. Bahindura John: The tanks are made of chicken wire mesh and cement, and are oval in shape. They are about two and a half metres long, two and a half metres wide, and from four and one half to six metres deep. They should be either lined with plastic sheets or their floor and walls should be cemented.

    Host: And how is the water channel constructed?

    Mr. Bahindura John: The channel walls can be made of bricks with cement applied to them to protect them from wearing out from contact with water. The width of the channel should be determined by the size and quality of the rock surface from which the water is harvested. Two or more pieces of netting should be placed at intervals along the channel to ensure that any debris in the water is caught before it enters the tank. The debris should be manually removed from the netting from time to time in order to ensure a steady flow of water downstream to the tank. It is important to cover the top of the channel completely with wood, iron sheets or another solid material. This protects the water from contamination by foreign matter such as soil and leaves.

    Host: Thank you for your thorough explanation. It seems that, after all, it is not such a complex technology. I hope that many farmers can try it. Could you tell us how the storage tank is managed?

    Mr. Bahindura John: The walls and floor of the tank should be scrubbed from time to time. This should be done when there is only a little water in the tank. Contaminants, whether solid or liquid, should be physically removed. The top of the tank must always be covered to prevent any contamination from outside. This covering also helps stops water from evaporating and minimizes any cracking of the tank surface due to expansion and contraction caused by direct sunlight. If any leakages arise, they should be sealed by a technician.

    Host: Thank you, Mr. Bahindura. Can you tell us a little more about the costs and benefits of the system?

    Mr. Bahindura John: The cost of the tank is 850,000 Ugandan shillings (500 US dollars). In Kibaale, it is anticipated that the district production office would fund the construction of the tank. There are many benefits from bringing rock-channelled water to crops. The first is that water will be more readily available for irrigation throughout the dry season. Secondly, minerals from the rocks will be captured in the water. These minerals can then be taken up and used by plants. Water from rock outcroppings will also improve soil conditions, since more rock particles will be broken down and made available for plant growth. The water would be used mainly to irrigate annual crops and vegetables, for example, cabbages, tomatoes, spinach, carrots, and green peppers.

    Host: What acreage of land could be irrigated by the water stored in this size of tank?

    Mr. Bahindura John: The water should be sufficient to cover at least an acre, and should last for three months.

    Host: What would be the impact on yields and on yield security?

    Mr. Bahindura John: Because we have not tried this technology yet for crops, we do not have any figures or estimates. But, it is reasonable to say that, if the crops have an ensured source of irrigation water, yields would increase and the harvest would be more secure.

    Host: Do you think that the investment in the tank will pay off?

    Mr. Bahindura John: We believe that the investment will pay off. Demand for food has grown, but farmers are still dependent on rainfed agriculture, so irrigation water is valuable and much needed.

    Host: Thank you very much, Mr. Bahindura, for enlightening us so thoroughly on this new technology.

    Mr. Bahindura John: Thank you for hosting the programme. Thank you for listening. Bye for now.

    Host: Listeners, this marks the end of our programme. If you have any questions about this technology, please get in touch with us here at the station, and we will forward your questions to Mr. Bahindura. And don’t forget to tune in next week, same day and time, for yet another useful programme.

    Contributed by: Anthony Lwanga, Kagadi Kibaale Community Radio, Kagadi, Uganda.
    Reviewed by: Chris Reij, Center for International Cooperation, VU University, Amsterdam.