Rainwater Harvesting (RWH)
RWH is the technique of collecting,
storing and distributing rainwater for multiple uses. The collected water can
be stored for direct use or diverted for borewell/groundwater recharge.
In simple terms it is a way to capture
the rainwater when it rains, for later use.
RWH
can be traced back to thousands of years in India. Our ancestors traditionally harvested
rainwater through
tankas, johads, madakas and many such local innovative
structures that can be seen even today, across the country.
Rainwater
is the ultimate source of all the fresh water that we use. In India, rainfall
occurs in short periods of high intensity, allowing the rain falling on the
surface to flow away fast. This leaves little scope for recharging the
groundwater, which results in water scarcity in most parts of the country.
Through RWH, this erratic rainfall can be conserved, stored & used as per
convenience, either directly or for recharging groundwater.
RWH can be done in homes, apartments,
societies, schools, institutions, commercial premises and any other space as
long as there is a catchment area in the form of a roof or open space to
capture the rain.
Domestic rainwater
harvesting is a
relatively simpler affair, where even a rain barrel can serve as a storage unit
for rooftop RWH. Individual homes have successfully implemented this
easy and eco-friendly method of augmenting household-level water availability.
Farmers also have implemented RWH to transform a barren piece of land into a self
sustainable, lush green farm.
The rainwater harvested depends upon the
catchment area, the rainfall pattern in the area and the drianage/ collection
system used.
To understand the potential for
rainwater harvesting, lets take the example of a house in Delhi with a terrace
area of 100 sqm. Taking the average annual rainfall in Delhi as 600 mm, and
assuming 70% harvesting efficiency (as some rainwater will be lost due to
evaporation, collection etc.), we can calculate the amount of water harvested
thus:
Volume of water harvested = 100 x 0.6 x
0.7
= 42,000 litres
This volume is more than twice the
annual drinking water requirement of a 5-member family, whose average daily
drinking water requirement is 10 lpcd.
Rainwater harvesting can broadly be
divided into 3 categories based on the types of usage, the area in which
harvesting is carried out and the people involved.
- Storage
or recharge: Based on the type of usage, structures can either be used to
store the collected water for direct use or to recharge groundwater.
- Urban-rural
difference: Urbanization has resulted in the shrinking of open spaces as
well as unpaved areas. This has resulted not only in flooding of cities
but has also caused water scarcity due to groundwater depletion in general
and saline water intrusion in coastal cities. While rural harvesting is
mostly traditional and is carried out in surface storage bodies like
rivers, tanks, ponds, lakes etc., urban harvesting, due to lack of open
space for capturing the runoff, is mostly in sub-soil storage as
groundwater recharge.
- Rooftop
& driveway harvesting: When we say rainwater harvesting, the first
thing that comes to our mind is the terrace. This greatly restricts the
scope of rainwater harvesting as a considerable amount of water that falls
around the built-up area is let out of the building as run-off. Driveway
run-off water should not be led into a sump for immediate use or to a
source well, but it can very well be directed into recharge wells.
The RWH system must ensure that not a
drop of rainwater falling within the premises is let into the sewerage or
wasted as runoff. This can be achieved only if the method adopted within the
premises satisfies the following criteria:
- Completeness:
Both rooftop and driveway runoff water must be harvested.
- Apportioning
of water: To avoid overload of any one system, leading to overflow and
loss.
- Proper
design: Volume of water likely to flow through and the nature of the soil
in the area should be considered.
- Maintainability:
Design should incorporate features allowing for periodic maintenance of
the structure.
It is a process by which the groundwater
is augmented at a rate exceeding that obtained under natural conditions of
replenishment. Any man made scheme or facility that adds water to an aquifer
may be considered to be an artificial recharge system.
Recharge structures are
constructed to allow rainwater to replenish groundwater. The various ways
in which recharge can be done is through:
- Abandoned
dugwell
- Handpump
- Recharge
pit
- Recharge
trench
- Gravity
head recharge tubewell
- Recharge
shaft
- Flood
mitigation: Appropriately designed recharge structures in open public
spaces, will help keep the roads from flooding. When water is not allowed
to leave the premises, the chances of it choking up the roads are minimal.
- Increasing
groundwater levels: Marked improvement of both the quantity as well as the
quality of the groundwater in areas which have implemented rainwater
harvesting
- Greater
water availablity: Rainwater collected in storage tanks is available as
and when needed
- Prevents
soil erosion and flooding especially in urban areas
In compliance to CGWA (Central Ground
Water Authority) directions, steps have been taken by
states/UTs to promote
and to make rainwater harvesting mandatory. Andhra Pradesh, Gujarat, Haryana,
Himachal Pradesh, Kerala, Madhya Pradesh, Maharashtra, Tamil Nadu, Ranchi
Regional Development Authority, Bombay Municipal Corporation and Pimpri –
Chinchwad Municipal Corporation, Municipal Corporation of Ludhiana, Improvement
Trust, Jalandhar, Jaipur Municipal Corporation, Mussorie Dehradun Development
Authority, and Union Territories of Delhi, Daman & Diu and Puducherry have
made necessary provisions in their building bye-laws to make installation of
rain water harvesting systems mandatory.
hi! I would like to use some of your rainwater harvesting diagrams for a project on climate resiliency. Who/how can I go about getting permission? I'm not sure if your images are copyrighted. Thank you!
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