Urban News

Contour maps detailing the city’s topography, a key factor in the BMC’s flood modelling plans, were finally prepared last month but cannot be used immediately. They are awaiting the Ministry of Defence’s clearance, since they will involve high-security areas.

Mumbai’s 437 sq km includes defence establishments in the island city and western suburbs, nuclear reactor at BARC in Trombay, BMC’s vital installations including lakes and water reservoirs, the Mumbai Port Trust and the airport, which the MoD will edit out of the maps. The MoD had initially denied permission for aerial photography, relenting after the BMC agreed the high-risk areas wouldn’t be on the final maps.

“We submitted the maps last month but are now awaiting the MoD’s approval. They will edit the maps and block the high-risk areas. We don’t know how long this will take,” said an official of the storm water department.

MWH, Mumbai, and ORG Informatics, Gurgaon, were assigned the task of preparing the maps. An MWH official said once the MoD okays the base map, it would be superimposed on the contour maps and these would be edited again. “Areas surrounding the blocked places will be blurred on the final map. We will take another one-and-a-half months following the clearance to publish the final maps,” he said.

The aerial photographs have been taken from 1,000 metres, at a resolution of 1:20. They capture all objects of length 20 cm and more; the maps will show even minor storm water drains, river tributaries and manholes. 

The contours will indicate elevation and depth, the steepness of slopes and runoff data, which have undergone large changes due to large-scale development and reclamation of land. In 1993, when the BRIMSTOWAD study for the storm water drains and nullahs was first undertaken, there were 150 catchment areas.

The spate of construction has blocked many nullahs and river tributaries and cut down part of the hills. All this will have an effect on the catchment areas where the maximum rain water accumulates. The contour maps will help us identify the high and low areas in catchments. There will be individual maps for each of them to predict floods,” said the official.

The contour maps were first recommended by the Chitale Committee following the 2005 deluge. The GIS-based flood-modelling system will include digitised maps showing the precise carrying capacity of drains, and geological factors like hill slopes and riverbeds. It will have columns for areas, rainfall, drains and flood points and will predict how much rain can flood which areas.

Last year, the BMC had promised the maps would be ready this monsoon. Aseem Gupta, additional municipal commissioner in-charge of storm water drains, said the administration is trying to get clearance as soon as possible. “We hope to use them in the next monsoon and have asked the MoD to clear them with priority,” he said.

DISRUPTIONS

FLIGHTS

* 3 diverted to Ahmedabad in the morning: Spice Jet flight SG 131 from Delhi (8 am), Indian Airlines flight IC971 from Chennai (9 am), Go Air flight G8229 from Delhi  One-hour delays all day, after morning’s low visibility (400 m around 8 am) slowed operations

* Strong winds (15 to 25 knots) prevented simultaneous use of the two runways

TRAINS

* Services on Central Railway and Western Railway, delayed 20-30 minutes due to water on tracks and low visibility

* A tree fell on WR overhead equipment between Dadar and Matunga Road at 10.55 am, cleared by 11.25 am. Slow trains diverted to fast tracks

* 27 services, 18 of CR and 9 of WR, cancelled