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Art of water harvesting to farm all-year-round

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PIUS MAUNDU

By PIUS MAUNDU
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As the rains become scarce turning once arable lands into semi-arid areas, it is time farmers intensify water harvesting activities if they are to farm without hitches.

There are several technologies to help you harvest water, from the rains and rivers, among other sources, and use it to farm during rainy days. Seeds of Gold talked to several water experts and unveils the technologies you can readily employ on the farm

The dam stretches across but under the surface of sandy riverbeds. The dyke erected across the riverbed blocks the flow of water in the sand, thereby, creating an underground water reservoir upstream.

They are built of soil in dry riverbeds and this should be done preferably on underground dykes that exist naturally under the sand. Water trapped in the resulting dams lasts long because it cannot evaporate. Sub surface dams are the most reliable and low cost water reservoirs that can be built with little expert knowledge.

The dams allow floodwater to pass over the underground dam walls without affecting the flow of water to people living downstream.

Water is extracted from the dams by sinking a shallow well in the riverbed. Alternatively, the dam is connected to a pipe which extracts the water into a well sunk on the riverbank. In Kitui county, a subsurface dam has been built in Kisasi across Nzeeu River and has served residents for the last 16 years. It costs about Sh70,000 to build the dam.

Harvesting rainwater from the rooftop is an easy way to tap it for farming. The aim is to get the water before it flows to riverbeds. One sets up a gutter system and tanks.

Water harvested from the roof of houses using gutters is stored in tanks and used for drinking after it is treated. It is also suitable for watering livestock and farming. A 10,000-litre water tank goes for about Sh70,000. One can, however, build a concrete water tank to save costs.

Harvesting water from roads

Roads are a major source of surface runoff when it rains. This water sometimes ends up destroying roads thus should be harvested and channelled to reservoirs and farmlands.

Harvesting water from roads entails creating shallow channels which offload the runoff into terraces installed in farmlands. More regular channels down the road ensure that as much water as possible is channelled from the roads into farmlands. Climate-smart road designers recommend that those building roads should provide channels to offload surface runoff ensuring that roads not only last longer but are also huge sources of water. Creating the channels can cost Sh1,000 each but one needs additional cash for reservoir.

Sand dams are concrete structures installed across a riverbed to check the downward flow of sand.

When it rains, the concrete barrier stops water and sand from flowing downwards resulting in a pool of water and sand to make the dam. Most of the water in the resulting reservoir percolates into the grains of sand in the dam over time.

The water is extracted directly from the dam or it is accessed from a well sunk on the riverbank downstream of the sand dam. Sand dams are a big source of water for irrigation in arid and semi-arid regions. It costs about Sh1 million to build a sand dam, with the bulk of the cost going on materials and labour which entails excavation and building of concrete wall.

These are shallow bowl-shaped water reservoirs that are sunk at homesteads and farms to collect surface runoff. The ponds can be used to rear fish and to hold water for crop and livestock farming.

Farm ponds sunk in highly porous soils have to be lined with polythene material or clay soil to reduce water seepage. It is recommended that the ponds are fenced off to prevent accidents. Surface runoff is directed into the ponds through the inlets and to prevent evaporation, a windbreak of useful trees is planted on the windward side of the pond.

A farm pond should be situated near the lowest part of a catchment (roads, fields or compounds) so that rainwater runs into the reservoir by gravity. It costs some Sh200,000 to make a pond measuring 40m in diameter and 4m deep, with the bulk of money going to labour.

Sprawling rocks are a major source of water, with the rock surface acting as a roof where rainwater hits and spreads.

Special gutters are installed on the rock surface to funnel the water to a tank installed on the lower side.

The water is suitable for watering livestock, farming or for domestic use. There are more than 100 rock catchment water sources in Kitui County, most of them installed in the 1970s.

In Makueni County, residents of Maseu village rely on rocks to tap water that is used at homes and at a secondary school. It costs some Sh400,000 to build a rock catchment area with the reservoir, with the bulk of the money going to materials and labour.

These are sunk in places with a shallow groundwater table. There are certain trees that indicate that an area has a higher groundwater table. They include Cyperus rotundus, Cangueria tomentosa, Delonix elata, Hypaene thebacia, Ficus natalensis, Ficus sycamore and Kigelia aenthiopia.
One can also sink a shallow well on seepage lines downstream of earth dams, in land depressions, near underground springs or swampy areas.
The well shaft is sunk until the water table is reached and extracted using a pulley system. According to experts, sinking an 8m deep shallow well costs about Sh142,000, with the money going to buying materials like cement, iron bars and galvanised wire and labour.