Essential Benefits of Rainwater Harvesting
Fresh water is essential for everyday life. We need it in all aspects of life from drinking to cooking to bathing to cleaning.
One of the biggest city of opportunities and new innovative business is dying because itâ€™s neglecting its water bodies. It was said in a study that the IT capital is likely to follow South Africaâ€™s Cape Town and run out of water. A recent study also found out that the city has lost 79% of its water bodies to encroachment and poor urban planning. Studies show that the water table of the city has has shrunk by 12m in the past two decades alone. The growing population is also putting increasing pressure on the water table to supply to homes and offices every day.
Before Bengaluru gained fame for being the garden city, it was known as the city of a thousand lakes for the sheer number of big and small water bodies that used to pepper the landscape of the city. The man-made tanks around the city used to meet the water demands of the city and the oldest proof is from a stone carving at the Agara lake that dates back to 870AD. While this was the mindset of the old city dwellers, the fast urbanization of the city saw a sacrifice of the lake areas and tank areas to grow concrete structures.
As the city expanded its size and added to its population, water became a precious resource. A city that previously had communities built around the lake is now struggling to meet the daily water demands of its citizens. Piped water was another major factor that killed lakes. Citizens stopped understanding the importance of preserving the freshwater lakes as the convenience of piped water dominated. The lakes slowly became polluted with untreated sewage and bad maintenance.
The social influence of lakes also reduced as people were not dependent on them to get water into their homes. Losing this connect was one of the biggest contributors to people not being active participants in the preservation of lakes. This reduced citizen participation made it easy for developers to claim lake beds and create homes and offices to meet the growing demands of the city.
While there is a bill being proposed to revive the old lakes and recharge the existing ones, there is also a responsibility that needs to be shouldered by the citizens of Bengaluru. While Bengaluru receives ample rainfall, it has not used methods to store this precious resource. There are several actions that need to be taken in order to revive the water bodies of Bengaluru. A few suggestions for solutions that can be implemented are
It takes will to revive the lost lakes of Bengaluru. A will that has to be driven both by the citizens and the government. It is important to ensure that freshwater is available in order for a city to thrive both environmentally and economically.
This is an excerpt from the book Catch the Rain where it falls by A R Shivakumar
Can our footpaths be porous?Wouldnâ€™t it be an amazing idea if we could harvest rain through our walk paths.
In Bengaluru, a kilometer of walk-path with porous pavements has a potential to harvest 30 lakh litres of rainwater per year. With moderate percolation efficiency of 75%, around 15 families of Bengaluru can depend entirely on recharged groundwater all through the year.
Porous footpaths are cheaper to build and easy to maintain compared to conventional footpaths. Rainwater from the road or even nearby houses can flow into these porous footpaths and percolate into the ground. This is a very effective and low cost option to harvest rainwater for groundwater recharge. Imagine if every road had these porous footpaths around Bengaluru.
These type of porous footpaths can be paid out in parks as well. Bruhat Bangalore Mahanagara Palike (BBMP) has an area of around 825 sq.km. in the city limits. The civic amenity open areas include bus stops, playgrounds, educational institutions, recreational parks, footpaths, etc. There are around 1060 parks in Bengaluru. The total land cover dedicated for 1060 parks is 770 hectares. Total water requirement of these parks at the rate of 2 litre per sq.m. for around 253 non-rainy days is 154 lakh litres.
The rainwater harvesting proposed for parks and footpaths in Bengaluru is mainly planned to harvest water from open area including the paved walk-paths and the structures inside the park.It is planned to allow the rainwater to percolate mainly in the green areas which are not paved and cemented. During heavy rains, the excess flow from the saturated soil of the green area will flow into the walk-path which is paved. The rainwater which is flowing in this paved area is guided to go out to the nearest storm water drain (following the natural gradient).
The rainwater harvesting interventions will intercept the outlet of rainwater channel which is carrying the storm water from the park (at the exit point of the park). A silt trap is designed to collect the debris and the silt flowing along with the rainwater. The relatively clean water flowing out of the silt trap is systematically diverted into the infiltration gallery. The accelerated infiltration galleries are the structures which are open wells created using pre-cast cement rings.
The accelerated recharge wells are dug wells inside the park at the lowest level (gradient). These wells are typically 1.5m, 2m and 3m in diameter with a depth of 3 to 6m. Precast cement rings which are of appropriate diameter and height of around 0.3 to 0.5m are placed one above the other without cement mortar in between joints. Loose aggregate (stones) are packed in the annular space between the cement rings and the excavated well. The entire well inside the cement rings is kept empty without any filler material. These cement ring wells will have a safety metal grill at the ground level. The last cement ring of the well is placed over the safety grill to prevent easy access into the well. These accelerated infiltration galleries - cement ring wells, are closed at the top with a cement slab. The silt traps which are harvesting the surface flow of rainwater from the parks will discharge rainwater through a pipe into these wells. Most of the water percolates into the soil and joins the groundwater underneath.
A shallow borewell/tube well is drilled closer to these accelerated infiltration galleries to collect the harvested water underground. These borewells will supply water for plants in the parks during the non-rainy days.
Some of the parks which have large paved areas, playgrounds or structures are provided with underground sumps to harvest rainwater directly. The harvested rainwater is used in toilet blocks and also for watering plants.
It is inexpensive and needs our will to address and bring about the change.
This is an excerpt from the book Catch the Rain where it falls by A R Shivakumar
Namma Metro has the potential to harvest around 300 million litres of rainwater every year. Metro rail infrastructure in Bengaluru has created rapid mass transport and also created one of the largest roofs in public space.
As the metro rail viaducts are elevated and not in reach of public or other animals the surface is relatively clean. Also the trains are electric and will have no diesel or oil spills. The passenger cars are air-conditioned with fixed windows, which will prevent littering. This logically will bring in the ideas of Rainwater Harvesting from the largest roof of Bengaluru - around 50,000 sq.m.
Bengaluru Metro Rail Corporation (BMRC) is one of the urban utilities to have adopted rainwater harvesting in a massive and practical way. The Metro made simple arrangements to catch all the rainwater that falls on its station areas and use the same for non-potable uses.
Then metro reach 1 to reach 4 has 44 stations and 33 of them are over the ground.The roofs are available in this type of infrastructure can be of two types:
The stations form a roof area at high-density traffic flow and commercial activities centres. The Viaduct runs all along the motor roads and is elevated. Every raindrop that falls on Bengaluru roads will only go down the drain. But every drop that falls on the Metro corridor can be harvested. Each of the stations on the Metroâ€™s operational stretch between MG Road and Byappanahalli have water tanks of over one lakh litre capacity each, to store rainwater.
The rainwater from the Viaduct flows in the direction of the natural gradient as of the ground/road beneath. The flow of this water on top of the viaduct is directed to the centre and finally reaches the grating at the centre of the pillar.
It is proposed to harvest rooftop rainwater from stations and viaducts. The rooftop rainwater from stations is a high volume flow at a busy junction and is proposed to channelize this water through underground pipes either under the road/footpath to inside storm water drain sidewall. The rainwater pipes through this underground system is discharged into a system of first flush lock and filtration system underground at the nearest open space/park/playground/parking area.The filtered rainwater is temporarily stored in an underground sump. The stored water will be pumped up and taken for final processing. Similarly, the water collected from the stockyards and rising staircase and roof of the stations are also trapped/harvested.
The stored rainwater can be treated at storing or treated on line while pumping. The rainwater being a pure form of water does not have salt and minerals or chemicals which are undesirable. Treating filtered rainwater is only by chlorination to remove bacterial contamination.
The rainwater flowing on the viaduct can be handled in two-ways:
The metro rail rainwater harvesting has a potential of around 300 million litres of clean water per annum. The above proposal is only a suggestion from KSCST, IISc Bengaluru.
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