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Creating a smart flash flood-free Guwahati

By Dipanjon Konwar

Guwahati city is today a favourite destination for the denizens of North East India and elsewhere. The city has a peculiar topography; it is bowl shaped with hill ranges � Nilachal, Chitrasal, Narakasur on three sides and many beels/water bodies � Silsako, Bor-Sola, Saru-Sola, Deepor in the plains. The city also has a network of rivers flowing across it � Basistha, Bahini, Bharalu, Mora-Bharalu for natural drainage of the rain water. But, the pressure of the population seeking jobs and fortune in this city, building houses on hills and plains, has led to a gradual shrinkage and disappearance of the retention basins and water bodies. This has affected the natural runoff of the rainwater, thus leading to flash flood and submergence of the city after a smart shower lasting an hour or so. And, more than 50 mm rainfall in less than six hours means disaster, with flooding of the city and landslides.

The problem of rainwater runoff from the hills combined with tonnes of silt carried down has blocked the drainage system, creating artificial flood � a man-made disaster � with increasing death toll each year. Although the rainfall pattern varies with respect to different locations of Guwahati city, it is revealed from a study by the Indian Meteorological Department, Borjhar and analysis of the rainfall characteristics of more than five decades that the quantum of the yearly rainfall has almost remained the same, though there is some variation in distribution in its duration and intensity in some years.

This author was the convener of a 2-day seminar in 2004 on rainwater flood in Guwahati organised at The Institution of Engineers (India) by an international NGO. Two experts from Canada shared their experience of how they handled the problem of siltation and artificial flooding in their country. The findings of the seminar�s technical sessions were submitted to the GMDA in form of a report.

The root causes of the rainwater flood mentioned in the report were:

Increased rainwater runoff mixed with sediment arising out of unscientific hill cutting, with no proper sediment and silt control plan and conservation measures, due to construction of houses on hill slopes;

Shrinking of water retention basins and local water bodies (beels), due to human activities and encroachment;

Inadequacy of the existing drainage channels. Capacity has been narrowed either by encroachment or disposal of domestic and industrial wastes in the open drains and natural channels;

Since that seminar nothing has changed; in fact, the situation has only worsened. Recently there was news of the soil conservation department proposing to sign an MoU with the IIT Guwahati regarding preparation of a report for watershed management for Guwahati hills to check erosion and siltation. But, more than suggestions, we need coordination among various departments and strong leadership at all levels for implementations of such ideas.

Some of the suggestions that evolved at the 2004 seminar are listed below:

Government should include in the building bye-laws, in addition to the map and zoning of development intensity zones, the micro or macro zoning of the city depending on topography and demarcating the catchment area of each drainage system. This should be done to determine the retention capacity of the water bodies as well as the carrying capacity of the drainage system. Inputs can be taken from the Assam Remote Sensing Application Centre (ARSAC) of various maps such as land use map, urban sprawl map, flood-prone area, forest, wetland map, etc. Inputs can also be taken from the National Institute of Hydrology (NIH), Guwahati regarding flood studies, watershed development, groundwater assessment and drainage data from the hydrological information system. The Central Ground Water Board can also assist in providing field data of water bodies, ground water resource, natural runoff, etc;

To evolve proper means to salvage all the existing water bodies and to make them attractive for recreational purposes by proper development and at the same time creating public vigil to stop any illegal encroachment;

The same approach may be adopted for the hills and instead of declaring these as �Green Zone� or �Reserved Forest� in the Guwahati City Master Plan, these may be allocated for sustainable development for recreational facilities and social forestry programmes with private and public sector participation instead of leaving them wide open for uncontrolled encroachment by squatters and allowing disturbance of the topography by unscientific cutting of the hills. Low income group housing could be constructed with funds under the Atal Awas Yojna to attract these illegal hill dwellers and transfer them to the plains;

New wet ponds (pukhuris) may be developed, as was done by our ancestors in Assam, in suitable places, in vacant government land to act as reservoirs during the monsoon;

To create silt traps and use locally available materials like bamboo, straw, logs to build barriers like rock-check, straw-bale, log-check dams and brush barriers on the hill sides for low cost sustainable conservation of soil and sediment control. Many international sediment control standards are available, which may be adopted taking into consideration the local soil characteristics. Efforts must be made to regularly clear and clean existing and proposed silt/sediment traps;

Adopting best management practice of sediment and erosion control will ease the problem of the congested drainage system. For the bare hill sides, cheap and quick maturing measures such as hydro-seeding and dry seeding are available along with chemical soil stabilisers to prevent landslides and to remedy the erosion of the soil. Also, along the Bharalu, Bahini, Basistha river-sides, a vegetative buffer strip with shrubs and trees must be created to reduce runoff and act as silt trap too;

Rainwater harvesting on the rooftops of apartments and commercial buildings should be made mandatory. This will in turn control the sediment flowing to nearby drains or to others� compounds. It will also decrease runoff, the amount of water flowing out to the drains;

It should be ensured that the level of road profile is maintained at a fixed level and depending on that, the elevation of the plot should be maintained by each plot owner according its location. The corner levels of the plots should be fixed with respect to the road level.

An effective master drainage plan as per the City Master Plan and with proper stormwater study for Greater Guwahati is required. Inclusion and amendment of necessary building bye-laws to implement the master drainage plan are also required.

In the present context it will be the responsibility of the Guwahati Smart City Development Agency Limited (GSCDAL) to coordinate with the other two urban local bodies � GMC and GMDA � and various departments like PWD, soil conservation department, water resources department, forest department, SDRF, etc. It should be remembered that unless the implementing authority applies necessary statutory instruments for implementation, best results of the solutions cannot be expected. Rainwater harvesting, erosion and sediment control plan for big construction, fixed building grades and approach road grade are to be covered by necessary bye-laws. In addition to restoration of beels and riverfront development, other components such as affordable housing, rainwater harvesting, hills rejuvenation and soil conservation may be included in the area-based development proposal of Smart City Guwahati. As part of smart solution components we must include emergency response and a centralised command and control centre to handle any man-made or natural disaster that threatens this burgeoning city.

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