In Bhubaneswar, Ekamara Kanan, Jayadev Vihar, Gajapati Nagar, Sainik School, Vani Vihar, west of Mancheshwar, Acharya Vihar, Iskcon temple area, Aiginia, Jagamara and Pokhariput are the areas through which the natural drains pass. Most of the city’s existing drains are in dilapidated conditions and, so, not working properly.
A number of drainage channels are also encroached by unauthorised constructions. The widening of the highway near the Iskcon temple created urban flooding as there is no channel for storm water discharge. In the absence of this, the storm water accumulated on both sides of the highway.
The general topography of the Bhubaneswar municipal area has a gentle slope from west to east. The level difference is about 80 metres between the west end (Kalinga Nagar near Chandaka Road) and the east end (near Jharpada and Baragada). Thus, the overall topography slopes from western highlands to eastern plains, rendering a natural advantage of drainage. Buildings are often constructed without flood inundation in mind. A large number of multistoried apartments have been constructed without considering the drainage pattern of the area. Also, in many areas, the widths of the nala have been reduced. Another reason is that the entire city has not been covered with surface water drain.
There are 10 major natural drains running west to east. Bhubaneswar’s storm water flows into these 10 drain channels. The city’s drain No1 opens to river Kuakhai and the other nine drain channels (No2 toNo10) flow into the Gangua Nala. Gangua Nala is a natural stream. length of the Nala is 35.7 km. The bed width is 30 mts and the bed level at the mouth level at the mouth is 2.62 m. Its independent catchment area is 75.6 km in the city.
As the Gangua Nala is filled with silt, the water discharge by the city drainage system is not becoming effective. The existing width of the Gangua Nala, varies from 40 to 120 feet. Now it is reduced to 12 to 35 feet delaying the final discharge through the nala and causing waterlogging in the existing drainage channels.
In a number of areas, rainwater causes flooding on the road despite the existence of the drainage system. It is seen that the inlets to drain water from the roads into the roadside drains are either not properly aligned or nonexistent leading to severe waterlogging on roads. Natural streams and watercourses have formed over thousands of years due to the forces of flowing water in the respective watersheds. Ideally, the natural drains should have been widened (similar to road widening for increased traffic) to accommodate the higher flows of storm water.
Besides, due to upcoming structures in these areas, the floodwater cannot drain properly and creates water logging. Another reason is that the entire city has not been covered with storm water drains. During the initial planning of neighbourhoods in Bhubaneswar, the area even for the smallest housing street has been fixed at a minimum of 30 feet. Only about nine feet out of these 30 feet actually carry traffic.
The remainder used for storm water drainage and avenue trees. These trees and the surrounding green areas help to reduce urban flooding in the city. The overall widths of the land earmarked for roads and streets is not determined by traffic alone, but by the requirements for storm water drainage and services (overhead electric lines, water, etc.). But in today’s planning, there are narrow roads. These roads do not allow to accommodate storm water drainage and other facilities.
There is also no space for avenue trees. For storm water drainage purpose, 30 feet is commonly accepted as a minimum width of the road. There is a need to increase road width in different neighbourhoods of the city.
A master plan for drainage is highly needed for Bhubaneswar. Provision of a simple connecting element, namely, drainage inlet through which the water can flow from roadside drain into the underground drain can significantly reduce waterlogging on the roads. The natural widths of all major drainage channels in the city should be protected, and there should not be any encroachment at least four to five meters on either side of the channel. The exact bed width, land width and the land requirement for drainage channel can be calculated after preparation of a drainage master plan of the various zones of the city.
A proper storm water design means a proper knowledge of a collection of data like intensity of rainfall, runoff details and location of the catchment area, etc.
The peak rate, volume, and timing of runoff are important characteristics in the planning and design of storm water management practice. It appears most of the time that many of the data may not be correct and thus the design of the storm water drains with these data results urban flooding. It is imperative to plan and design surface water drains appropriately so as to dispose of surplus rain water within minimum time. Storm water drainage network should be designed with proper hierarchy. The drainage and slope map can also help in the planning and design of storm water drainage and urban flood management.
Keeping in view the projected rate of urbanisation, it is imperative to consider a 50-year planning horizon. Because the development is bound to take place during this period and it will be difficult to upgrade the drains once they are laid. Ideally, the natural drains should have been widened (similar to road widening for increased traffic) to accommodate the higher flows of storm water. 50 to 60 per cent of roads in the city lack storm water drains. There is a need to construct more drains for the city roads affecting urban flooding and these drains should connect with the existing drainage channel of the city, so that the storm water can be channelized properly. There is a need to prepare storm water drainage manual for urban drainage design. The manual should provide policy and design requirements for storm water management throughout the city.
With the rising population, new residential areas are bound to come up, but first priority should be given to water discharge system. The present day urban planning practices neglect the effect of the change of land use on surface runoff volume. Storm water drainage is a necessity for city planning. During city planning, it is important to understand where the water needs to be drained from the streets. There is a need to prepare drainage master plan to identify the existing drainage deficiencies and develop solutions to address the the problem of urban flooding. There should be provision in the master plan for widening of existing storm water drains as well as for construction of future drains for newly developed areas.
(Dr Praharaj teaches at the Department of Architecture, College of Engineering and Technology, Bhubaneswar)
