HYDERABAD: With India Meteorological Department (IMD) predicting heavy to very heavy rainfall in the next few days, the civic authorities are still racking their brains over how to tackle a probable flood, despite having several recommendations by experts to prevent any such disasters.
After turning its back on Kirloskar and Voyants Consultancy recommendations on how to prevent urban flooding, the Greater Hyderabad Municipal Corporation (GHMC) authorities seem to be paying no heed to key suggestions made by Dr Kapil Gupta, professor, civil engineering department, IIT Bombay on urban flooding in 2018.
The expert said days of non-stop rains in the past exposed Hyderabad's inability to deal with urban flooding. If the recommendations were implemented in a span of three years, the city might have protected several areas from submergence and could avoid huge property loss, especially during flash floods in October last year and floods during the current month.
In the current situation, flooding is caused as the development of the sewer system is very slow and due to indiscriminate constructions along natural drainage.
There are some other bottlenecks that are becoming obstacles for smooth flow flood water. However, removal of bottlenecks can stop 70 per cent of flooding in Hyderabad. One of the key observations was to increase the number of automatic weather stations (AWS) to prepare for the flood situation. There should be an AWS for every 4 sq kms. However, there are only 33 AWS against the 207 AWS to cover the entire GHMC area, that too, 50 percent are defunct which proved costly during the recent floods.
Officials said Kapil Gupta, in his recommendations, said unplanned construction in low-lying areas, solid waste in urban drainage channels and increased rainfall due to changing climatic patterns were some of the identified common causes of urban flooding in Hyderabad. A few of his observations and recommendations include, land use changes, surface sealing due to urbanisation (which increases run-off), occupation of flood plains and obstruction of flood flows, urban heat island effect (which has increased the rainfall in and around urban areas), sudden release of water from dams located upstream and the failure to release water from dams resulting in backwater effect.
The indiscriminate disposal of solid waste into urban water drains and channels is a major impediment to water flow during the monsoon season. He also emphasised that it was important to understand the watershed and the vulnerability of each area. The vulnerable area should be identified and a method for mobilisation of resources should be known. Hyderabad is home to three main water bodies namely Hussain Sagar, Osman Sagar and Himayat Sagar.
Unregulated urbanisation, land encroachment, building of wrong structures in wrong places were the main reasons for urban flooding, he said, adding that we saw it in many states now and none of the states had started demarcation of flood zones.
The flood management expert also suggested to avoid urban flooding in Hyderabad, several infrastructural improvements were required. First, the existing drainage path should be well demarcated. There should be no encroachments on the natural drainage channels of the city. Storage of rainwater in tanks at the rooftop, intermediate, ground or underground levels can reduce the overflows and help in reducing urban flood volumes. Storage or holding ponds should also be provided at judiciously selected locations to store water during heavy rainfall so that it does not cause downstream flooding. Once the rain subsides, the water can be released gradually.
Gupta also observed that roads were surfaced and resurfaced several times, thus increasing their level above the plinth-level. Various cities, across the world, have constructed porous pavements. These allow the water to gradually infiltrate into the underlying soil thereby maintaining the pre-development sub-soil water conditions. Porous pavements are presently being used for parking lots, driveways and sidewalks. With reasonable safeguards, they offer an elegant engineering alternative for streets and highway surfaces.
Thus, porous pavements are an exciting example of sustainable building practice. Gupta also suggested constructing detention or retention ponds along urban drainage systems to provide temporary storage for stormwater peak flows and controlled pond outlets. Construction of a retention pond will also help reduce floods. In the low-lying areas, flood water has to be diverted to nearby parks and stored in ponds, for immediate results.
A senior GHMC official, requesting anonymity, said if these basic recommendations were followed properly, the city could avoid inundation to a great extent. He said some of the recommendations could be implemented swiftly due to their cost effectiveness, unlike Voyants, Kirloskar committee and JNTU expert Prof K Lakshman Rao's recommendations. A proposal has been sent to the government and is awaiting its approval.
