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Brace for record tide without promised flooding forecast May 18, 2009

Posted by Bahadir Sahin in English, Haber (News).
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It will be the highest in 100 years but prediction mechanism won’t be ready till next year
When the Mumbai coast braves its highest tide in 100 years in July, as experts have predicted, a promised flood modelling system won’t be in place. The system that can be used to forecast which low-lying areas will be inundated and to what extent, so that the civic administration can take early preventive measures, will be ready in another six months or so.

They will come in handy only during next year’s monsoon.

The system based on contour maps had been on the anvil for two years. To prepare the digitised maps, the civic administration had last year started taking aerial photographs of the city from low-flying aircraft. The process is yet to be completed. “We have taken 120 air rounds and will require another three to complete the digital photographs of Mumbai. The photographs will be superimposed with the GIS base maps to transform them into contour maps. It will take four more months for the maps to be ready. More time will be needed for the flood model software to be in place,” said an official from the Storm Water Drains department.

On July 24, at 2.03 pm, the city will record a tide 5.05 metre high, not seen in the last 100 years, experts have predicted. The high tide a day earlier will be 5.01 metre high.

The topography of the coastal city, coupled with the improper drainage system, usually results in flooding if a high tide coincides with heavy rainfall. The civic administration had suggested the flood modelling system to develop an online real-time system, with the help of geographical integrated system for low-lying and steep areas for sustained and effective flood forecasts.

The model will give out details of places that have the possibility of flooding, depending on factors like rainfall intensity, high tide and topography. Civic officials had last year assured that the maps and the system will be ready before the 2009 monsoon.

MWH India and ORG Informatics have been appointed to set up the system as part of “upgradation of the master plan for BRIMSTOWAD’ conceived first in 1993. The overhaul includes digitised maps depicting contours to predict floods depending on drainage capacity of various areas. Based on the maps, civic officials said they will be able to re-design and calculate the size of catchments areas. As per BRIMSTOWAD there are 125 now.

“Contour maps will show elevation of valleys and hills, and steepness of slopes by using curve connecting points. Elevation points will determine catchment boundaries. Due to largescale development in the last two decades in the western and eastern suburbs, the original catchment boundaries have been changing drastically leading to new flooding areas every year.”

The catchments will be re-designed and the width and depth of nullahs increased or decreased to control flow of rainwater.

Officials blame the civil aviation department and the Ministry of Defence for the delay in making the contour maps. “We had permission for only three hours of flying and that was only if the air traffic was low and the defence personnel were available to fly with us,” said a senior civic official.

The MoD had initially rejected the contour mapping plan for “security reasons” but later gave the nod on the condition that high-security zones like Mumbai Port Trust, the Bhabha Atomic Research Centre and the international airport be not included in the final maps.

The mapping requires aerial photographs taken from a height below 1,000 metre. The distance between two points on each curve will be 20 cm, which means the maps will be adequately detailed to enable the plotting of minor storm water drains, river tributaries and every manhole.

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