GUWAHATI, March 26 - Experts from the Columbia University engaged by the Assam State Disaster Management Authority (ASDMA) to study and suggest measures for checking flooding in Guwahati have laid emphasis in their report on undertaking preventive measures to reduce the risk of flooding rather than the actions during flood emergencies or immediately after such disasters towards offering relief.
They proposed establishment of an urban flood management cell within the ASDMA that will include representatives from various agencies and departments such as GMC, GMDA, Water Resources, etc., along with some experts. This would provide both the required coordination and expert inputs.
They have identified five key areas of intervention � urban planning and development; hills and water bodies; data, information and decisions; natural and artificial drainage and community and institutions.
Flooding in Guwahati has been described by these experts as the result of high rainfall intensity and duration, besides the unsystematic land use planning, the bowl-like topography of the city and limitations in the natural and artificial systems of drainage of Guwahati metropolitan area (GMA) watershed, poor urban infrastructure planning, design and maintenance, and lack of institutional coordination, among other things.
They maintain that MIROC and CNRM simulations project increase in warm nights. RegCM4.3 simulations project that heavy rainfall events may significantly increase in Guwahati, in Assam and the homogenous North East zone. The trends in June, July, August and September mean and annual specific humidity based on simulations may increase significantly.
Moreover, they said a clear and comprehensive topographic understanding of Guwahati�s current situation is necessary to ensure that the flows of water are properly directed without needless and ineffective pumping to higher ground.
Given the frequency of flooding experienced by Guwahati now and the likely increase in flooding risks due to a projected rise in high rainfall events from climate change, the city�s Master Plan should pay close attention to reducing vulnerability to urban flooding, they said.
Moreover, they said at present, no single map represents the entire drainage system of the GMA and the collective responsibility of various agencies. Some underground drains are not accessible because the manholes have been completely sealed up by road asphalt, while in others business and households have covered the drains completely.
In recent years Guwahati has experienced an increasing number of extreme rainfall events, even as the average seasonal total rainfall for the monsoon has decreased, said the experts.
The robust signals of climate change and their projections out to 2044 from their investigations are � various model simulations project a robust signal of increase in the annual minimum and mean temperatures over the next 30 years. Simulations also project decrease in cold days and a decrease in cold temperature events.
However, urban flooding risk and their mitigation do not appear as important considerations in the 2009 or in the draft 2014 Comprehensive Master Plan (CMP). Detailed analyses of flood hazards that are available (such as the ASDMA commissioned �Hazard Risk and Vulnerability Assessment�) do not appear to have been considered.
As a city gets more built up through land use changes in the periphery and more dense development in the wards, there is a rising trend in the volume of run-off water. For Guwahati this would mean that in the coming years, the city would need to direct and manage the draining and or absorption of more surface run-off volumes.
Demographic pressures and lack of planning low-income housing have led people to settle in hill and forest areas. Marshy lands and the low-lying areas of seasonal ponds too have been built up over the years.
Change in land use from natural vegetation to impermeable artificial cover, poorly designed roads, cutting of trees and clearing vegetation, replacing absorptive surface with non-permeable surfacing have all resulted in increased run-off from hills. Regulating urban expansion in the hills around Guwahati would be a valuable step in reducing rainfall run-off and siltation, and significantly reducing the risk for landslides, they said.
Occupation, income, housing and access to basic infrastructure all play a part in determining the exposure to and intensity of flooding impacts, they said.
Residential and commercial construction across the city has increased surface run-off, and limited the area of the wetlands and water bodies as well as their absorptive and carrying capacities as the city�s natural sinks, they said.
Significantly, for the Guwahati metro area only five rainfall gauges are currently available, spread across three agencies � two gauges each with NESAC and WRD, and one with IMD.
