JAIPUR: For managing urban water reservoirs in future, architects and town planners would have to incorporate rainwater harvesting techniques. Though water harvesting has become mandatory in all buildings, a lot of surface run off water from roads and parking lots can be effectively used to re-charge ground water.

According to Jaipur-based Prof Prithvi Singh Kandhal, associate director emeritus, National Center for Asphalt Technology based at Auburn University Alabama, US: “In Rajasthan, the groundwater is plunging at an alarming rate. Jaipur is a very good example. According to the Central Underground Water Board of India, all underground water will disappear in about 10 years. Hence architects and town planners must be proactive to integrate rainwater harvesting techniques in the design of all buildings, including parking lots and streets. This would significantly recharge the ground water in overexploited/critical urban areas.”

Rajasthan receives a scant 16 inches of rain annually. Most of it is during June to September, leaving the soil to parch the rest of the year. “The porous asphalt pavement which can be used for parking lot or low-volume traffic streets works like this. The top 75 mm asphalt layer is specially designed to make it porous. Rainwater goes through it rapidly,” said Kandhal.

The water is then stored in an underlying open-graded stone bed, which is about 225 mm thick. From there, water percolates slowly into the underlying soil. There is hardly any evaporation loss. The porous parking lot or street can be integrated with rainwater harvesting techniques into the design of buildings and parking lots. Give me a 10 ft wide street and I can demonstrate it for JDA,” said Khandhal.

“Porous asphalt pavement is one of the responses to plunging ground water table in Jaipur and elsewhere in India. It can be integrated with the roof rainwater harvesting system effectively and economically. Properly designed and constructed porous asphalt pavement can last more than 20 years. Such a pavement can be used for parking lots, recreational areas, and low-volume-traffic roads and streets. Government should encourage (and mandate in critical areas) construction of porous asphalt pavements in urban spaces,” said Khandhal.

Based on Prof Khandhal’s expertise, The Franklin Institute of Philadelphia, Pennsylvania has developed porous asphalt pavement technology for the parking lots.