Dwarka Underpass has been in the news for the sheer visual shock of seeing 6m (20ft) high column of water on a road after a more than average rainfall in a single day.
Actually, the water was standing not just in the underpass but also on the road leading into the underpass from both sides. Approximately, 1.5 km stretch of road including the underpass had water logging. The water logging was so bad that, even today, 4 days after the downpour, and hectic efforts to pump out the water, the road is still blocked for traffic.
As per our calculations, the total volume of water that was standing in this entire area was between 10-12.5 crore (100 -125 Million) liters. If we take Delhi’s average rainfall, then over the year, this area alone would hold approx 40-50 crore (400-500 Million) liters of water!
To put this figure in perspective,
10 crore liters = 7,50,000 people’s requirement for one day or more than 2000 people’s total water requirement for one whole year!
WHY THIS HAPPENS:
1) Faulty drainage planning – An underpass is an artificial depression dug out from the ground. Drainage in an underpass is always a problem because it’s almost always impossible to align the slope of the underpass drainage with that of the main drain outside the underpass (whose level will be higher than the underpass). The problem becomes worse when the underpass is located at a site which is topographically also a naturally depressed zone. In such an area the tendency of water from all the surrounding catchment area is to flow towards that depression with no escape route in sight.
It is important therefore to ensure that the drainage for surrounding catchments is planned in such a way that all water gets diverted away from the underpass BEFORE it enters the depressed zone.
2) Poorly designed / constructed rainwater harvesting systems. As per court orders all flyovers are supposed to do rainwater harvesting. It does not seem like the Dwarka Underpass has done it. Even if it has,
a) The system is obviously insufficient because its recharge capacities have not been designed after taking into consideration the runoff generated by the entire CATCHMENT of the underpass area.
b) Poor intake of the system because of faulty design / construction.
c) The system is poorly maintained. Rainwater Harvesting (RWH) system needs regular cleaning to maximize its intake capacity. If this is not done, the system gets choked and becomes defunct. Its cleaning is especially necessary where the RWH system takes (water from road / open surfaces etc where the silt load is high.
1) Proper Drainage planning. The Problem can be corrected even now. However, planners will need to look beyond the underpass and plan for catching run-off from the catchment area for the underpass itself.
2) Rain water Harvesting – All along the 1.5 km stretch, maybe perhaps more (analysis of exact site conditions needs to be made) an extensive rainwater harvesting system needs to be made. This will ensure that the runoff gets recharged to groundwater and there is no surplus flow left to “water-log” the underpass.
POLICY CHANGE NEEDED
The Dwarka Underpass is just a stark reminder of the urgent need to change policies to reflect urban water conditions:
1) WATER PLANNING SHOULD BE AN INTEGRAL PART OF THE DESIGNING WITH INTEGRATED EFFORT FROM ALL AGENCIES: Drainage and Water Harvesting planning to be done by agencies in co-ordination. When the underpass would have been constructed, PWD would have been given jurisdiction only over the immediate stretch of land over which the underpass is to be constructed. Hence, their designing and implementation would have to be a closed loop with minimal co-operation / interface with authorities managing that catchment area roads and drainage. So even if PWD wanted to plan an extensive drainage system, it would not have been able to do so. By the same logic, they might have been aware of / might have been advised by experts to do RWH for the entire catchment but since their intervention area was limited, they might not have been able to implement those suggestions.
2) RAINWATER HARVESTING SYSTEMS SHOULD BE MADE PART OF THE STORM WATER DRAINAGE SYSTEM. Currently, since RWH is seen as an ad-hoc activity, it is largely unplanned and adequate provisions for maintenance – BOTH OF STRUCTURES AND CATCHMENTS – are not made. RWH systems should be integrated with Storm Water Drainage systems. This will at least ensure that an annual schedule and provision for maintenance will be made by government. It should also be ensured that the catchment conduits for runoff and the RWH systems are maintained simultaneously. This will help ensure efficient working of the systems.
Unless we plan for these now, such fiasco will increasingly occur over time. And why not turn a fiasco into an opportunity – harvest water from all such areas!