TANK BASED Roof Top Rain Water Harvesting

STAGE I: Collection & Carrying (same as other Roof top systems)

STAGE 2 Filteration (same as other Roof top Systems)

STAGE 3: Storage in Surface Ponds/Wells

a) THROUGH: RECHARGE PITS

b) THROUGH RECHARGE TRENCHES

RWHS THROUGH RECHARGE PITS

Recharge pits are simple, economical and eco-friendly way to use the rooftop rainwater to charge the groundwater. This method is best suited for houses with a rooftop area of 50-150 sq.mts. It can also be used to catch water from a small catchment like water tap standposts etc. and is ideal for recharging shallow aquifers.

This works best when done in alluvial areas where permeable rocks are exposed on the land surface or at very shallow depth.

The basic technique involves collecting the rainwater and directing it into a pit. A pit of 2-3 meters and filled with simple materials that will filter the water that is being directed into it, can work wonders to charge the ground water.

There are 3 components:

harvesting (collecting) the rainwater from the rooftop

Directing the collected water through pipes to the recharge pit

the recharge pit to charge the groundwater

The method involves collection of rainwater from rooftops, designing down pipes for rain, separating the first 2mm through a first flush system, filtering the rainwater through a gravel-and-sand filter charging the ground water wherever feasible like wells, handpumps, recharge pits, trenches or shafts etc.

The first 2 steps of harvesting the roof-top rainwater are similar to the previous section. So the same steps can be followed.

Step by step construction of Recharge Pit

Dig a pit 4m wide near your house till you reach the water level.

Go one more metre deep and put a layer of charcoal and 11/2 metres of river sand which acts as a strainer. If required, use an iron sheet all around the pit to keep the pit from collapsing. Remove the sheet after you put charcoal and one and half metres of river sand.

Insert two 2-inch PVC pipes, perforated at the lower ends 25 cm apart. Cover the perforated ends with net to prevent stones and other particles from coming up.

Connect one pipe to the DOWNPIPE that comes from the roof.

A strainer at the top will keep leaves and other wastes from going down along with the rainwater.

Rainwater displaces the dense hard water underground. If water comes up to the surface, put half a metre of ordinary sand on top of river sand. This will prevent the water from overflowing. Once a week, pour bleaching powder solution through the pipe on the roof. This will keep the water pure underground.

Take Care :

That the water that flows down does not move through any harmful chemicals, oils, petrol, or pesticides etc. If these are stored on the roof, do not use the rain-water from this roof. Otherwise the groundwater being recharged will get contaminated with harmful products.

Make sure that you clean the recharge pit once a year. Dig out the filler material. And fill it once again with clean materials. This also ensures that the filler material does not get clogged with run-off sand, mud etc.

Maintenance of Recharge Pits

The Recharge Pits have to be cleaned regularly as it would have clogged with run-off sand, mud, leaves etc. Clean the recharge pit once a year. Dig out the filler material. And fill it once again with clean materials.

RTRWHS through Recharge Trenches

Recharge trenches are similar to recharge pits.

This method is suitable for buildings having a rooftop area of 200-300 sq. m. Ideally the trench is constructed across the land slope along the boundary walls. The trench may be 0.5 to 1 m wide, 1 to 1.5 m deep and 10 to 20 m long, depending upon the availability of land and rooftop area. The trench is filled with boulders at the bottom followed by pebbles and by sand on the top. The collected water from the roof is diverted through the drain pipe to the trench. The trench should be periodically cleaned.

How it works:

Ideally the trench is constructed across the land slope along the boundary walls of the house. The trench may be 0.5 to 1 m wide, 1 to 1.5 m deep and 10 to 20 m long, depending upon the availability of land and rooftop area. The trench is filled with boulders at the bottom followed by pebbles and by sand on the top (filler material).

The collected water from the roof is diverted through the drain pipe to the trench.

Recharge trenches, by their nature of larger area, charge larger amount of water compared to recharge pits. Hence it is better used in rooftop areas that collect large amount of water.

Step by step construction of Recharge Trenches

Dig a trench about 0.5 to 1 m wide, 1 to 1.5m. deep and 10 to 20 m. long depending upon availability of water to be recharged

Fill the trench with boulders (5-20cm), gravel (5-10 mm) and coarse sand (1.5-2 mm) - the boulders at the bottom (bottom most layer), gravel in between and coarse sand at the top.

Provide a mesh around the outlet at the roof so that leaves or any other solid waste debris is prevented from entering the trenches. A desilting/ collection chamber may also be provided on ground to arrest the flow of finer particles to the trench.

Provide a by-pass arrangement before the collection chamber to reject the first showers.

Maintenance:

The Recharge Trenches should be cleaned regularly as it would have clogged with run-off sand, mud, leaves etc.

Clean the recharge pit once a year. Dig out the top layer of sand and replace with fresh sand.

Take Care:

Make sure that you clean the recharge trench is cleaned once a year. The top layer of sand should be cleaned or replaced (if possible) so that the trench continues to work.

Advantages

This is an ideal method of rainwater harvesting where there is inadequate ground water supply or the surface resources are either lacking or insignificant.

It also helps in reducing flood hazards

It also improves the quality of ground water through dilution since rainwater is bacteriologically free from organic matters and is soft in nature.

"Step into my trench," said the tank to the drop