Water is the basis of life! The rapid growth of population in recent years and the uncontrolled utilization of our natural resources have put a question mark on our ways of using water. Do you know that the average availability of usable water has correspondingly reduced from 6000 cubic meter per capita per day to 1500 to 1800 meter per capita per day?
In the last 4-5 decades, owing to our negligence and the increased greed, fresh water resources witnessed a sharp decline in their water quality and quantity. This makes it essential to conserve the ground water as it takes years to replenish. In areas where ground water is used, care must be taken to minimize the quantity of water withdrawn and bring it on per with quantity of water being replenished. And the best option emerges out in this case is Rainwater Harvesting. In our last post, we discussed about rainwater harvesting; this time we will get to know the modern methods of rainwater harvesting.
There are primarily two ways of harvesting rainwater – Surface runoff rainwater harvesting and roof top rainwater harvesting.
In simple words, it is a method of collecting rainwater and storing it for reuse, rather than allowing it to run off. This stored water can be utilized for various purposes such as gardening, irrigation etc. Let’s take a look at various way of harvesting rainwater.
- Surface runoff harvesting – This kind of rainwater harvesting is meant for urban areas where rainwater flows away as surface runoff. This runoff could be caught and used for recharging aquifers by choosing appropriate methods.
- Roof Top rainwater harvesting – In this type of harvesting, rainwater is collected from the roof of the house/building. It can either be stored in a tank or diverted to artificial recharge system. This method is cost effective and if implemented carefully helps in increasing the ground water level of the area.
There are various methods of using roof top rainwater harvesting.
- Storage of direct use – In this method rain water collected from the roof of the building is diverted to a storage tank. The storage tank has to be designed according to the water requirements, rainfall and catchment availability. Each drainpipe should have mesh filter at mouth and first flush device followed by filtration system before connecting to the storage tank.
This is the most cost effective way of rainwater harvesting. The primary benefit of collecting and using the rainwater during rainy season is not only to save water from conventional sources, but also to save energy incurred on transportation and distribution of water at the doorstep. This also conserves groundwater, if it is being extracted to meet the demand when rains are on.
- Recharging ground water aquifers – Ground water aquifers can be recharged by different kinds of structures to ensure percolation of rainwater in the ground instead of running off from the surface. The most widely used recharging methods are:
- Recharging of bore wells – Rainwater collected from rooftop of the building is diverted through drainpipes to settlement or filtration tank. After settlement filtered water is diverted to bore wells to recharge deep aquifers. Abandoned bore wells can also be used for recharge.
- Recharging of dug wells – In this method, rainwater from the rooftop is diverted to dug wells after filtering it. Cleaning and desalting of dug well is done on a regular basis to increase the recharge rate.
- Recharge pits – These are actually small pits of any shape rectangular, square or circular, contracted with brick or stone masonry wall. The bottom of these pits is filled with filter materials.
- Recharge Trenches – This option is used where upper impermeable layer of soil is shallow. A trench is excavated on the ground and refilled with porous media such as pebbles, boulder or brickbats. Bore wells can also be provided inside the trench as recharge shafts to enhance percolation.
- Soak ways or Recharge Shafts – This option is feasible for conditions where the upper layer of soil is alluvial or less pervious. At the top of soak away required size sump is built to contain runoff before the filters through soak away.
- Percolation Tanks – These are actually artificially created water bodies with appropriate permeability to enable adequate percolation for ground water recharging. These tanks are built in big areas where land is easily available and topography is appropriate.