http://deccanherald.com/deccanherald/feb222005/spt2.asp
It's time to park the rain
Rainwater harvesting wherever hydro-geologically possible will be the key to water sustainability of our parks so that they remain beautiful forever, feels S VISHWANATH.
Garden City. The title is a pleasing one and in the recent years, thanks to the efforts of the Bangalore Mahanagara Palike and the Horticulture Department of the Government of Karnataka, parks have seen a magnificent revival. Attracting the fitness freaks for their brisk morning and evening walks or just to sit and be with nature, parks have truly become the socialising centres. The green thumbed gardeners of Bangalore deserve applause for their beautiful nurseries of exotic and local flora.
A green island
There is however a small cause for concern. Parks demand water right through the year and especially in summer.
About 10 litres of water per square metre is the norm used to calculate water demand. Many parks however do not have adequate water to meet this demand. Though some do get water from the BWSSB and some from their own bore-well it has to be brought in tankers for many. One possible solution being discussed is to harvest rainwater to at least meet partially the water requirement of the park.
How to harvest water
This park in question has a 2,500 square metre area. The landscaped or planted area is about 2,000 square metres. The water demand is therefore about 20,000 litres per day. In a year the water requirement is about 6,000 kilolitres considering water requirement for 300 non-rainy days.
Rainwater harvesting is simply the process of collecting and storing water for later productive use. There are two basic ways of rain harvesting, storage of rainwater or its recharge into the ground. Storage may be a limited option in open ponds because of the large evaporation losses and the possibility of mosquito breeding in open water bodies. With an average rainfall of 970 mm, rainwater falling on the park in a year is about 2,425 kilolitres of which about 60 per cent can be harvested. This means 1,455 kilolitres or about 25 per cent of the yearly requirement for watering the park can be met through rainwater harvesting.
Digging the well
The harvesting in this particular case was done through four recharge and
withdrawal wells based on the infiltration capacity during a heavy downpour of 50 mm per hour. For each quadrant of the park a 3 feet diameter and 22 feet deep well was dug and lined with concrete rings. Water was struck at 12 feet depth in the month of January and the well was continued further by about 10 feet.
The well will be observed for its behaviour in the summer months and if need be deepened.
Rainwater from a quadrant of about 25 x 25 metre will be led into this well through swales and a silt trap in the rains to recharge and replenish the aquifer. The well water will be drawn in the non-rainy days through a portable half-HP pump with a mist sprayer for watering. It is expected that open well water will be sufficient for the park right through the year.
Surprising as it may sound in many places in the city, water tables are actually rising. This is thanks to the BWSSB which gives piped water to each house and therefore there is no withdrawal from wells. It also helps that 40 per cent of this piped water leaks and recharges the groundwater.
Further augmentation comes from sewage but that is not welcome. Well diggers out of a job for some time are back in business this time digging recharge wells for rainwater harvesting.
Sustainability
Parks will become sustainable for their water requirement only if the
landscaping changes to less water intensive ones. Further requirements would be the installation of drip irrigation systems and a switch from water intensive grass based parks to more a shrub, bush and tree based model with xeri-scaping.
Efficient ways to water plants without water wastage and evaporation losses will need to be found.
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