Water Supply
Figure 13. Proportion of infrastructure in poor condition % 0 by scheme utilization.
Research Program on Water, Land and Ecosystems( WLE), which the Institute leads with support from the
CGIAR Fund, the new study complements other recent research that used remote sensing to fill major gaps in our knowledge about the actual extent of smallholder irrigation. Findings from that research were recently published in IWMI Working Paper 172, Mapping Irrigated Areas in the Limpopo Province, South Africa.
One of the findings is that the area under informal irrigation is three to four times larger than that of public schemes. Comparative analysis of the two approaches is needed to generate new insights that further inform government organizations about the effectiveness of different measures for revitalizing smallholder irrigation.
Source: IWMI
Irrigation Water Use: Surface irrigation
Probably one of the oldest methods of irrigating fields is surface irrigation( also known as flood or furrow irrigation), where farmers flow water down small trenches running through their crops.
Humans’ first invention after learning how to grow plants from seeds was probably a bucket. Ancient people must have been strong from having to haul buckets full of water to pour on their first plants. For most of human history, people did not have mechanized spray irrigation systems to apply water to crop fields. It was more like,“ Hey, Big Guy, take this reed bucket and go down to the river and fill‘ er up.”
Surface irrigation is still used today throughout the world, especially in lessdeveloped areas where mechanical
techniques are not available. In fact, in the United States in 2000, about 29.4 million acres were irrigated by flood irrigation as compared to about 28.3 million acres irrigated by spray irrigation. Flood irrigation is not the most efficient irrigation method, but it is cheap and lowtech. On the one hand, less water is lost to evaporation than in spray irrigation, but on the other hand, more water can be lost from runoff at the edges of the fields.
Here are some more-efficient surface-irrigation techniques that farmers use:
1. Leveling of fields: Flood irrigation uses gravity to transport water, and, since water flows downhill, it will miss a part of the field that is on a hill, even a small hill. Farmers are using leveling equipment, some of which is guided by a laser beam, to scrape a field flat before planting. That allows water to flow evenly throughout the fields.( Actually, this method of levelling a field is also used to build flat tennis courts).
2. Surge flooding: Traditional flooding involved just releasing water onto a field. In using surge flooding, water is released at prearranged intervals, which reduces unwanted runoff.
3. Capture and reuse of runoff: A large amount of flood-irrigation water is wasted because it runs off the edges and back of the fields. Farmers can capture the runoff in ponds and pump it back up to the front of the field where it is reused for the next cycle of irrigation.
Africa Water, Sanitation & Hygiene • July- August 2017 33