Water 1 Any land anywhere can be used to harvest rainwater
The fundamental reason: extend the fruits of the monsoon
The basic principle: Catch water where it falls
Water 2 Water Harvesting   watertop_06.jpg (1999 bytes)
Description
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TRADITIONAL

Indigenous systems

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MODERN

Contemporary systems

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HARVESTERS

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Ferrocement Tanks
Ferrocement Fundamentals
Ferrocement consists of a thin sheet of cement mortar which is reinforced with a cage made of wire mesh and steel bars.  Because ferrocement is structurally more effectient than masonry, the thickness of the walls of the container are as low as 10 to 15 mm.   Ferrocement components can be casted in any shape using suitable mouolds.  The technology is extremely simple to implement, and even semi-skilled workpersons can learn it with ease.  Ferrocement requires only a few easily available materials - cement, sand, galvanized iron (GI) wire mesh, and mild steel (MS) bars - in small amounts compared to masonry and RCC.

One of the primary requirements of a water harvesting system is that of containers to store the harvested water in a hygienic condition. This need is more pronounced in high-rainfall areas, where it is more feasible to store water in containers for direct use, rather than for recharging the groundwater. Generally, in small domestic systems, the cost of constructing tanks with conventional materials like masonry or RCC is far more than that of the rainwater collection and piping component. Ferrocement can provide a low-cost and easy-to-build solution to the need for low-cost containers. This technology is particularly relevant for regions like Meghalaya, Arunachal Pradesh and Kerala, which have high frequency of rainfall.

The Structural Engineering Research Centre (SERC), Ghaziabad, has done research and development on a large number of low-cost structures and implements like water/grain storage containers, irrigation channels, biogas digesters and septic tanks, primarily using ferrocement. SERC scientists are imparting training in ferrocement technology to rural artisans under the National Drinking Water Mission.

Ferrocement containers can be used to store grain and seed, apart from water. Tanks of 1000-2000 litre capacity can be constructed with ease, which are much cheaper than masonry, RCC or plastic tanks. These are easy to repair, and can be easily transported because of their sturdy nature. Such containers have been used on a wide scale since about the past 25 years in Thailand, Malaysia and some African countries. Ferrocement containers with capacity as much as 5000 litres have been constructed in Thailand.

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The process of building a ferrocement container is very simple which users can do themselves, with some training. For a typical circular pot-shaped container, the only materials required are hessian cloth, chaff (waste from agricultural produce), GI wire mesh, MS bars, cement and sand.

To prepare the mould, the hessian cloth, stitched into a sack resembling the shape of the container, is filled with chaff that is compacted in layers. Dry leaves or dry grass can be used in place of chaff. Once the sack is filled with the filler material, it is beaten into the required shape by a wooden bat. A GI wire mesh (22-26 guage - see Table 1) is tied around the mould leaving sockets at suitable locations for inlet, overflow and cleaning pipes. Tying 6 mm diameter mild steel (MS) bars at wide intervals both horizontally and vertically strengthens the reinforcement cage.

Table 1: Parameters for various capacities of ferrocement containers
Capacity (ltrs) Thickness of walls (mm) Ratio cement:sand Thickness of GI wire (guage)
400 10 1:3 26
600 10 1:3 24
900 12 1:2.5 24
1500 15 1:2.5 22

Once the reinforcement cage is tied, cement mortar having cement-sand proportion of 1:2.5 or 1:3 (see Table 1) is prepared, having water content equal to 0.45 times the volume of cement. The mortar is plastered in two layers along the wall thickness, the second layer being applied 24 hours after the first. The ferrocement wall normally has a thickness of 10 to 15 mm, depending on the volume of the container (see Table 1). The cement mortar is applied ensuring a minimum clearance (cover) of 3 mm between the reinforcement mesh and the outer surfaces of the wall. The mould of the container is removed 24 hours after casting of the walls is completed, by removing the filler material, and the container can be brought into use after 10 days of wet curing.

SERC has developed large capacity ferrocement rooftop water collectors of upto 10,000 litres.

Source: Sharma, P, "Ferrocement Bhandaran Patra (Ferrocement Storage Tanks) - National Drinking Water Mission", SERC, Ghaziabad, 1990

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