Year after yr, flash floods have performed havoc with Bengalureans, notably these in and round low-lying pockets. Erratic rains fuelled by local weather change issues give them no time to organize, as a month’s rainfall pours down in just a few hours. The frequency of those high-intensity occasions has elevated dramatically, demanding pressing however sensible options.
So why not construct large underground tanks in low-lying areas to let flood waters rush in? Why not let the forces of nature, the push of gravity and human ingenuity mix to let the surplus water settle safely, minimizing human struggling? Could this saved water be used later to handle the problems linked to a dry season?
Successful fashions overseas
Globally, such methods have labored though they demand an enormous preliminary funding. In the German metropolis of Munich, for example, 13 underground tanks have been constructed to arrest the recurring floods. The tanks have been constructed in massive vacant plots comparable to Bengaluru’s civic amenity websites. Each tank had two tiers of 8-metre depth. Flood waters would circulate into the tanks to be pumped out later when required.
Flood-prone Tokyo and Pittsburgh too had constructed such tanks. The one in Tokyo, arguably the world’s largest underground water tank, is bigger than a soccer discipline. Fifty-nine pillars, every 18m tall, help the tank’s ceiling.
The fashions look promising. But not many are satisfied. Their competition: Why spend money on such costly tasks when you’ll be able to clear up the town’s present tanks and lakes – lots of that are in low-lying areas -, and use them for rainwater storage? This is a mammoth job but possible, however the stormwater drains that result in these water our bodies are horribly polluted with sewage and stable waste.
A giant storage downside
“Bengaluru has a storage problem, not a water problem,” notes architect Naresh Narasimhan, who had conceptualised Okay-100, a joint undertaking by the Bruhat Bengaluru Mahanagara Palike (BBMP) and Bangalore Water Supply and Sewerage Board (BWSSB) to rework the Rajakaluves into clear waterways flanked by aesthetic city areas. The Okay-100 results in Bellandur lake, one of many metropolis’s largest.
For years, the BBMP has been attempting to resolve the drain capability downside via a grand reworking train. But even after years, practically 175km of drain community are at present with none flood safety buildings. The Palike has now put aside ₹1,200 crore to construct concrete partitions on both aspect of the drain. So far, about 686km of the town’s 859km of major and secondary stormwater drains (Rajakaluves) have been transformed.
Giant watersheds
Beyond the Rajakaluves, the main target must also be on changing the massive water our bodies on the town’s outskirts into rainwater storage tanks. Explains Naresh: “There are eight giant watersheds around Bengaluru. We have to pass a law to create a string of pearls around the city. And these have to be protected and water stored there. In times of crisis, this water can be used.”
The watersheds with the lakes exist already: Hoskote lake, Byramangala kere, Bellandur and Varthur lakes, Yele Mallappa Chetty kere, Hesaraghatta lake. “Besides, we should bring back the Arkavathy river and revive the Dakshina Pinakini. There is a mega plan and a micro plan, and it has to be ruthlessly mandated that rainwater is stored, delayed and not released so that the aquifers are not depleted,” says Naresh.
Decadal failures to scale up the town’s rainwater harvesting potential, storage capacities and to streamline its storm water administration have left Bengaluru on the mercy of an exterior water supply. Faced with depleting water ranges on the Krishna Raja Sagar (KRS) reservoir, BWSSB has now urged the Cauvery Neeravari Nigam Limited (CNNL) to put aside Bengaluru metropolis’s share for the remainder of 2023. To cater to the town’s potable wants, it needs adequate water in each KRS and Kabini reservoirs.
Did Bengaluru not see this coming? The warning indicators have been loud and clear for many years, and but the town’s file of retaining and reusing its treasured rainwater has been poor. This is why, former BWSSB Chief Engineer Thippeswamy has been articulating the necessity to undertake the confirmed ‘Sponge City’ idea perfected by the Chinese.
Sponge City advantages
The goal is straightforward: Retain water at its supply, decelerate the circulate, clear water naturally and adapt it on the sink the place it accumulates. In this mannequin, rainwater will get soaked in some ways: Rooftop gardens, roads that permit water permeate down, ponds, filtration swimming pools, wetlands and public areas that permit the water to seep underground. In Bengaluru, just a few stretches of the sensible metropolis roads have earmarked areas for water to seep down. But this wants pressing scaling up.
BBMP, says Thippeswamy, ought to assume past flood management and discover methods to retain the water. This clearly mandates a coordinated effort with the BWSSB. The ongoing white-topping of roads throughout the town has already raised critical issues about concretisation stopping pure infiltration of rainwater to feed the groundwater desk.
A file photograph of sponge parks being developed by Greater Chennai Corporation.
| Photo Credit:
PRINCE FREDERICK
Chennai expertise
Chennai has taken the lead amongst Indian cities in adopting the sponge metropolis mannequin. Thippeswamy is satisfied that Bengaluru ought to comply with the system, which is now being adopted by cities internationally. The Greater Chennai Corporation has launched into a grand plan to rework your entire metropolis right into a sponge, arresting each floods and groundwater depletion.
Fifty-seven ponds are to be developed as mannequin Sponge City Parks, scaling up throughout Chennai. Equipped with recharge wells, inlet and outlet pipes, the parks will act as short-term storage factors throughout heavy rains. Permeable pavements in all newly constructed parks, real-time flood forecasting and spatial determination help system to develop lake and reservoir operation steering are additionally a part of the plan. Several such parks have already sprung up with walkways, timber and fencing throughout.
Efficacy of flood alerts
Bengaluru has all the explanations to rework itself as a sponge metropolis. But it might not occur in a rush, like all slow-moving tasks within the metropolis. Can well timed flood warnings provide some respite to the residents? Based on telemetric climate stations and rain gauges positioned at key areas, the Karnataka State Disaster Management Authority (KSDMA) has a system in place to alert the BBMP, in addition to BWSSB, the police, Bescom and the catastrophe administration groups.
However, the Palike insists that no alert will help throughout flash floods. The civic company, as an alternative, identifies flood-prone areas upfront and focuses its consideration there. In June 2020, the Karnataka State Natural Disaster Management Centre (KSNDMC) had launched the ‘Bengaluru Megha Sandesha’ cell app to offer real-time data and alerts on climate, rainfall and flooding within the BBMP jurisdiction. But the app is but to make a lot of an impression with poor public consciousness ranges.