Tuesday, 29 April 2014

Bangalore Parks are more ‘GREENER’

Bangalore Parks are more ‘GREENER’

Paradise found!

Now the lush green parks are self sufficient when it comes to meeting their water requirements in Bangalore… read on….

Bruhat Bangalore Mahanagara Palike has on area of around 825 sq.km. in the city limits. The civic amenity open area includes bus-stops, play grounds, educational institutions, recreation parks etc. There are around 1060 parks in Bangalore. The total land cover dedicated for 1060 park 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 3896 Million Liters.
The rainwater harvesting proposed for parks in Bangalore is mainly planned to harvest water from the 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 the 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 the dug wells inside the park at the lowest level (gradient). These wells are typically 1.5m, 2m and 3m in diameter with depth of around 3 to 6m. Pre-cast cement rings which are of appropriate diameter and height of around 0.3 to 0.5m. These rings are placed one above the other without any cement mortar in between joints. Loose aggregates (stones) are packed in the annular place 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 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 ground water underneath.

A shallow bore well / tube well is drilled closer to these accelerated infiltration galleries to collect the harvested water underground. These bore wells will supply water for the plants in the parks during the non-rainy days.
Some of the parks which have larger paved areas, playgrounds or structures are provided with underground sumps to harvest rainwater directly. The harvested rainwater is used for the toilet blocks and also for watering the plants.

Total area of parks in Bangalore (770 hectares)
Number of Parks
Daily water requirement @ 2 lt per Sqm #
Yearly water requirement for 253 days (less rainy days 56*2)
Average area of each park
Annual potential of Rainwater from each park with collection efficiency of 75%
Water requirement of each park per year
Cost of rainwater harvesting per park (@ Rs 125000=00 for 2500 Sqm)
# BBMP Bangalore is promoting tree based parks (less of lawn) and organic manure for plants