Waterlogging has become a severe problem in most cities in India. In recent years, there has been a growing trend of urban flood disasters in India, in which major cities across the country have been severely affected. It has been observed in most cities like Mumbai, Kolkata, Chennai, Bengaluru and Guwahati that the intensity of floods has a certain relation with unplanned growth of urban areas that are under tremendous demographic pressure.
Frequent extreme weather events have led to dramatic waterlogging and flash floods in recent years that have resulted in heavy casualties and serious economic losses.
Several factors contribute to flash floods. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and duration is how long the rain lasts. Topography, soil conditions and ground cover also play important roles.
The growth of cities also contributes to urban flood risk. The increased construction of hard, sealed surfaces hinders rain from getting soaked into the soil and thereby causes runoff.
When urban population grows at an exceptionally rapid rate, most cities and towns are unable to cope with the changing situations due to their resource constraints and management limitations. Waterlogging, solid waste disposal, and black smoke from vehicular and industrial emissions, air and noise pollution, pollution of water bodies by industrial discharge are the regular problems of cities.
Waterlogging or rain-fed flood is now being considered a natural calamity. This hazard affects cities economically leaving a prolonged and wide-range negative impact.
Flash flood inundation and waterlogging has been a major problem in several parts of Guwahati city in the last few years. After every medium to heavy shower, several localities face the problem of artificial waterlogging. Rapid development of watershed areas decreases filtration capacity of the land, thus giving rise to runoffs, which expands to a flash flood situation.
Indiscriminate unplanned urbanisation leading to expansion of the city limit has added new dimensions to the calamity.
The drainage system of Guwahati depends heavily on the existing natural drains.However, the drains are always full of garbage, waste materials and sewage. The feeder drains to the main channels overflow due to siltation problems, and the water carrying capacity is reduced significantly. During monsoon season, when the river Brahmaputra flows above the danger level, most low-lying areas of Guwahati face water-logging and flash floods.
The city also lacks a comprehensive drainage system at present, except in some areas. The small drains along the streets cannot provide relief from flash floods. Due to their inadequate depth and width, these drains are not capable of carrying storm water. The problem is compounded by the fact that there is severe encroachment near the drains, leading to dumping of solid waste in the drains that hampers the normal flow of water and which results in flooding.
Largescale hill-cutting activities, and destruction of forests in the hills surrounding Guwahati city have led to loss in water-retaining capacity of the soil that leads to landslides and soil erosion. During heavy rain, landslides and soil erosion cause heavy siltation and reduce the drainage discharge capacity. This leads to accumulation of rain water in areas having no outlet and results in massive water-logging.
The unabated cutting of earth and green cover in the hills of Meghalaya bordering Assam has also caused considerable siltation problems in rivers, rivulets and drains of Guwahati, besides creating runoff problems which causes flash floods.
A major reason of flash floods in Guwahati is water coming down from the hills. Urban planning schemes of watershed management in the hills should be implemented using modern technology.
For the movement of storm water during monsoon season, the existing natural drain channels need to be cleared of garbage. The rivulet channels should be kept clear of any waste. The interconnectivity of these natural drains can be handy in directing the flood water from the city quickly. Encroachments over drain channels should also be removed. Also, the government needs to plan a systematic storm water drainage system.