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Saturday,October 31,2020 16:39 PM

Harvest rainwater using trenches

By Vision Reporter

Added 1st December 2003 03:00 AM

Water is one of the world’s most precious resources. Humans cannot survive much beyond three days without it. Birds, plants and animals too suffer in the absence of water.

Water is one of the world’s most precious resources. Humans cannot survive much beyond three days without it. Birds, plants and animals too suffer in the absence of water.

Water is one of the world’s most precious resources. Humans cannot survive much beyond three days without it. Birds, plants and animals too suffer in the absence of water.

But as the population in Uganda surpasses 24million people with the world population put at about 6billion, underground water levels are falling on every continent. Most people on earth are not getting enough water for the basic necessities of life and rivers are drying up before they reach the sea.

The importance of water for both domestic and industrial use is becoming an important issue as a result.

This has called in several modes of water collection, among them rainwater harvesting. Rainwater harvesting is just the principle of collecting rainwater for use.

This method is one of the oldest technologies that is gaining popularity in a new way. The practice started about 4000 years ago in Palestine and Greece.

The techniques of harvesting rainwater are simple and easy to follow.

Among them is the storage of rainwater on surface for future use. This method is one of the oldest and structures like underground tanks, ponds and check dams are used to store the water.

The other method is rooftop rainwater harvesting. This is a common method in both the villages and towns. The technique involves collecting rainwater that falls on sloping house roofs by the aid of gutters, which water is then directed into a tank or any other container, meant for the purpose of storing water.

Dr Moses K. Musaazi a lecturer in the Faculty of Technology, Makerere University says the rooftop technique is the cheapest method for harvesting rainwater.

“Basically the method involves the use of gutters and a tank which may be placed under the ground or above the ground so that rainwater dropping on the roof is tapped and guided into the tank with the aid of the gutters,” he explains.

Dr Musaazi however says tapping water collected in an underground tank is more difficult as compared to that in an overhead tank.

“While you need gravity to tap water in an overhead tank, you will need a manual or an electric pump to tap water from an underground tank,” he says.

He says the underground tank does not occupy so much space and also holds more water as compared to an overhead tank. He however says cleaning an underground tank is very difficult.

According to Musaazi, up to 30,000 litters of water can be tapped from a three-bedroom house in just one season, which is enough to take one household into another season.

Present estimates indicate that prices for an underground tank vary accordingly and often range from sh250,000 to sh1.5m.

According to Musaazi, water harvested after rain can be used for all domestic purposes including drinking washing and irrigation.

“This water does not require treatment. It has been tested a number of times and found safe for drinking,” he says.

Harvesting rainwater can also be done by use of trenches. These are constructed when the permeable stream is available at shallow depth. Trenches may be 0.5 to 1metres wide, 1 to 1.5metres deep and 10 to 20metres. long depending up the availability of water.

The other methods are diversion of run off into existing surface water bodies and the nearest tanks or depressions.

According to the United Nations, it is estimated that as the world population surpasses 6billion and as the planet warms up, the water tables around the world are falling at an average of three meters (9.8feet) a year.

World Watch magazine based in the United States predicts that water shortfalls may soon lead “not only to hunger but also to civil unrest and war.”

To suit this view participants at a forum tackling on the world water crisis in Japan early this year proclaimed that the third world war could happen due to water-- or, rather, the lack of it.

The statistics said the same thing: as the share of fresh water per person decreases globally, and the population demanding it increases, there are bound to be conflicts which, as history dictates, can lead to military action and, ultimately, even a world war.

The UN believes that rainwater harvesting could have a major role to play in easing the worldwide shortage of fresh water. UN global water statistics show that global water-use has more than doubled since 1950.

Today it is estimated that one person in six has no regular access to safe supplies and contaminated water gives 200m people a year water-related disease.

UN statistics also show that oil-rich but water-poor Saudi Arabia purchase half of its water abroad while Israel imports 87% of its water and Jordan imports 91%.

Harvest rainwater using trenches

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