Water harvesting techniques for smallholder and large-scale farmers

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Sand-dams dug by Kitui people and Sahelian Solutions (SASOL), a Non-Governmental Organization.

Kenya Meteorological Department recently warned of heavy rains between September 19 and 25, unfortunately many farmers may miss utilizing the opportunity to harvest enough of this rain water and store it for future use due to lack of even simple ways of harvesting water.


According to the Agroforestry world, Kenya is a water scarce country with less than 600 cubic meters per capita below the global 1000 cubic meters per capita. Water scarcity is a critical constraint to the country’s socio-economic development and its achievement of Kenya’s Vision 2030 as well as the global development agenda detailed in the Sustainable Development Goals. The situation is exacerbated by climate change and increasing water demand due to population growth and urbanization.


To respond to the water scarcity and inadequate distribution, new techniques need to be explored and old techniques revisited. Small – scale water harvesting techniques provide a direct solution, especially in rural and drought prone areas hence the use of water harvesting techniques.

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In urban areas dam construction, long distance conveyance of water or desalinization may provide options for ensuring water availability. These solutions are generally too costly and complicated for rural water security. Rural population require low cost systems that can be constructed, operated and maintained with the highest level of community involvement and autonomy.


Fog harvesting is another techniques. It is captured with the help of polypropylene mesh net or ridges to capture water loaded fog that forms in humid months in mountainous or coastal areas. The mesh normally collects small water droplets which trickle into collection troughs, gutters and drains into a series of tanks. Fog harvesting is cheap and the level of technology and maintenance is simple, furthermore the technique is easy to replicate.


Another example is sand dams made by Kitui people and Sahelian Solutions (SASOL) a Non-Governmental Organization. They constructed 500 sand dams serving more than 150,000 people. The dams are placed across a bed of intermittent small rivers, consisting of a 1.5 to 2 meter high impermeable barrier from stone or concrete placed on a firm impermeable layer of rock or clay. This rocks prevent water from going back to the ocean. Runoff water is stopped from flowing and will create an artificial aquifer which can store up to 35% of its total volume as ground water.

READ ALSO: Trench water harvesting sustains farm two months after long rains


Contour Trenching. This involves digging trenches along contour lines. Water flowing down the hill is retained by the trench, and it infiltrates the soil below. A good example is in Amboseli dug by Westerveld Conservation Trust. When they dug the trenches they chose deep and closely spaced trenches 4 meters and a meter deep at 25 meter intervals down the slope high enough to capture rain of up to 150mm per day.


In between two dug up trenches, crops can be grown and benefit when there’s less rain from the subsoil water reserve gathered after the rainy season.


Finger ponds is an innovative technique that is used to enhance the natural productivity of wetlands and floodplains. The ponds may consist of stretched artificial ponds 5 to 12 meters long, extending to the wetlands like fingers hence the name.
These ponds normally fill up during the flood cycle and trap fish within them as the floods recede. Some of the advantages are that the environmental impact of finger ponds in terms of habitat destruction, nutrient leaching and disease vectors was established to be generally low.

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Grey water shoud be another rich target. Grey water is the waste water from baths, showers, washing machines, dishwashers and sinks and this water normally makes up 50-80% of households waste. (the greenage UK). If properly recycled properly, greywater can save approximately 70 liters of portable water per person per day in domestic households. Greywater cannot be used for drinking but can be used for flushing toilets, wash clothes and even water your garden.

 

Advantages of rainwater harvesting

  • RWH is a quick solution, to increase the availability of water, in areas that have inadequate resources.
  • It increases ground water levels and mitigates the effects of drought.
  • It reduces rain water run-off, which may otherwise, flood storm water drains.
  • It serves as a cost-effective method to reduce soil erosion.