Guwahati is situated on the banks of the Brahmaputra and several of its tributaries pass through the city. There has been rapid urban growth in the city over the years with uncontrolled development activities. These activities have had a detrimental impact on the ecology and environment of the city, which is surrounded by wetlands that are presently under threat due to encroachment and unplanned urban development.
Further, the city is prone to landslides and is located on quake-prone (Zone-V) belt too. In addition to being vulnerable to these natural hazards, the city is frequently affected by seasonal flash floods, which are not entirely caused by natural factors alone.
Let us discuss the primary factors responsible for this major irritant to the city dwellers one by one. Guwahati city has a typical situation of man-made hazard as it does not experience normal flooding events, but is characterised by urban flooding owing to a number of issues highlighted below.
Deforestation: The most serious environmental problem we face now is deforestation. Its effects, if unchecked, are most certain to bring about permanent ecological harm with a dramatic increase in flash flood problem in Guwahati. Deforestation on hill slopes leads to loosening of soil and it creates massive erosion along the hill edges. Excessive rains, too, add to the woes and it carries this loose soil into the drain channels leading to siltation. Guwahati faces a severe problem of landslides during the monsoons, for which rains are considered the primary factor, but the triggering cause is excessive cutting along the hills and encroachment on them. Uncontrolled deforestation on the hills around Guwahati has resulted in more exposed slopes which are more prone to soil erosion as compared to the vegetation covered slopes. Increased soil erosion not only results in loss of soil fertility, but also causes problems of waterlogging and flash flood.
Unplanned urban development: Guwahati is sitting in the midst of natural wetlands, forests, hillocks and the river edge of one of the mightiest rivers in the world. These collectively form an interlinked ecological system, which is under threat due to rapid and unplanned development. Environmental degradation is fast becoming a major threat to this sensitive arrangement of natural entities and the population which relies on it.
Encroachment: Encroachment on a large number of wetlands that serve as natural reservoirs has also reduced the retention capacity of the drainage system, thus causing the flood level to rise. The desire to enjoy a better life and to earn handsomely lures migrants from villages and towns towards the cities. Guwahati is facing a major threat as a big portion of migrant population illegally occupies hillocks to build their shacks. They exert pressure on the already tottering infrastructure of the city and thereby make the flood mitigation process an arduous task.
Road building: Unplanned road building has wrought havoc in eco-sensitive zones comprising hillocks, forests and wetlands. Because of the unprecedented population growth in the city, the construction of roads for transportation has become inevitable. Little concern is shown for the natural environment in the process, the severe effect of which shows up in the form of frequent flash floods and landslides in and around Guwahati.
Migration: Migration has been a continuous phenomenon for Guwahati city for the past several decades. Economic opportunities along with many other social and political reasons lure people to migrate to the city. Better urban services as compared to rural areas such as education, medical facilities, better transportation, etc., also encourage migration. During the past few years, with an increase in employment opportunities due to growth of industries and other secondary and tertiary sectors, migration has taken place from various rural areas of the State, and even from outside, into Guwahati. As in most cases, these people are poor or from economically backward background who tend to settle in illegal settlements, thereby encroaching on hills or fragile lands.
Ecosystem and land use: Guwahati city is located in a valley surrounded by hills on three sides. The city boundaries also have a large area under hillocks and water-bodies. These natural elements are under threat due to rapid urbanisation, and as they also form part of the natural drainage system of the city, their preservation is utmost necessary. Unplanned expansion of the city has led to deforestation and encroachment on the hillocks. Such expansions are open invitation to disasters like landslides and floods.
Waste discharge into rivers: One of the important tributaries of the Brahmaputra, the Bharalu river which flows through the city, is an important channel for the drainage of the city. Due to siltation, the Bharalu river bed has considerably risen. A major chunk of the waster discharged from the city is directly released into this river. Waste water from households, commercial and business establishments, small and medium industries also ends up in the Bharalu river and gets discharged into the Brahmaputra. Even in the upper reaches, refinery waste water from the Indian Oil Corporation�s refinery at Noonmati flows directly into the river. With choking of the natural drainage, the city has become more prone to waterlogging and urban flooding.
Transport: Guwahati is the largest city of the Northeast, and hence the transport system of the city plays a vital role in connecting other parts of the country with the region. Many of the roads do not have footpaths, roadside drains and streetlighting. The overall condition of roads is important for a city to fight flood-like situations as inadequate storm drains and broken patches of roads only compound the problem. Despite all this, the density of vehicles is one of the highest in the entire country.
Recurring floods hamper the infrastructure of the city every year and the frequency of such events is increasing. During floods, basic amenities like drinking water, power supply and medical services are impacted and it adds to the vulnerability of the people. Besides, the overall lack of drainage, the absence of a solid waste management system, and pollution of surface water bodies and groundwater resources have created an interlinked situation that leads to flooding and waterlogging in the city every year. Flash floods have thus become a major threat to the city and its residents. The natural drainage channels and wetlands have been insensibly encroached upon, and their rejuvenation is very much necessary to find out a long-term solution to urban flash floods.