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Water Portal / Rainwater Harvesting / Surface water / Road runoff harvesting

3 bytes removed, 03:34, 15 November 2012

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This technology is categorized under WOCAT as a combined structural/ vegetative measure. [[Bunds]] and channels are stabilized with perennial grass. Its purpose is primarily to increase soil moisture for crop production, and it achieves impact through water harvesting. In soil conservation terms it reduces land degradation and soil erosion by water.

Runoff is led to the farm from the tar road in a main excavated channel of about 300 metres length, which cuts through a neighbour’s farm. There are also supplementary channels which lead runoff from a hillside. The estimated catchment area is (at least)10 hectares in size. This supplies water to a cultivated area of about 5 ha. The main channel leads runoff into the farm through an initial fanya chini structure (a channel with the earth thrown downslope). When the runoff reaches the end of the channel , it is diverted round into a similar structure, which leads the water in the opposite direction. To make a simplification, runoff water is conveyed in a zigzag fashion, or ‘reticulated’‘reticulated', through the farm. At certain points the farmer has put water control gates in specific channels, to select the direction of the flow.

The structures that transport the water within field are mainly fanya chini but some are fanya juu (embankment above the channel). In all cases the embankment is made of earth, excavated from the channel. The channel’s dimensions are (approx) 1.0 m deep and 1.0 – 2.0 m wide; with embankments that are 1.5 m high and spaced at 18 m apart. These dimensions are well above those recommended for standard fanya juu/ fanya chini design (Thomas, 1997). The structures are on a slight grade (sited by eye) to allow the water to flow. The average field slope is 3°. The approximate vertical interval between structures is thus 0.9 m. The embankments are stabilized with grass or perennial crops such as banana or sugar cane.

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