Improvement of drainage congested areas through Drainage Development Schemes (DDS):
Drainage problem stems from the fact that the water that accumulates from rainfall or spills from streams do not drain out quickly and stagnates. Thus, this brings more area under floods. In many cases, the submergence of the countryside continues long after the rainy season. Inadequate waterways and slope to drain out the accumulated water in time is the main culprit. Congestion leads to the non-availability of land in time and missing out on the cultivation season in such areas.
Natural causes of drainage congestion: The drainage problem in the Brahmaputra basin is primarily due to the high stage of the Brahmaputra for a prolonged period during monsoon. The tributaries are not able to discharge freely into the Brahmaputra during such periods leading to drainage congestion.
The problem is aided by the morphological changes brought by the river itself. When the silt-laden water of Brahmaputra overspills its banks during the rainy season, the heavier silt particles settle down near the banks, thus progressively raising the banks above the immediate countryside. For this reason, natural levees or highlands are often observed along the banks of Brahmaputra with the low lying areas between these levees and higher ground in the countryside.
Similarly, the tributaries also form levees along their banks which are prominent near their confluence with the Brahmaputra. Over a long period, a depression is formed between levees of two adjacent tributaries and that of the Brahmaputra. These areas suffer from drainage congestions. Geographically, the main drainage congested area in the valley lies between Brahmaputra river and the two national highways which run parallel to it on the north and south.
Manmade causes: To get relief from the problem as well as from floods, 934 km length of embankments on the Brahmaputra and 2486 km length of embankments on tributaries were constructed by Assam government between 1954 and 1985. As the free flow of water from the countryside to the rivers was stopped by these embankments, they created drainage congestion in turn. To overcome this, a number of sluices were constructed on these embankments to drain out rainwater and control back flow from the river during the high stage of the river. However, these were insufficient in numbers, and inadequate in capacity in many cases.
Other man-made causes are – construction of railways and roads, private bunds, obstruction put in natural drains, encroachment on the waterways and drains, etc. In the case of roads and railways, inadequate numbers of culverts are a major cause. Also, many of the bridges constructed over tributaries are found to have inadequate waterways. This leads to drainage congestion and afflux in the upstream areas of many bridges in the valley. The ‘Rastriya Barh Ayug’ or National Flood Commission of India has mentioned several such Railway bridges in Brahmaputra valley as inadequate. The WRD, Assam has also identified such road bridges with inadequate waterways on some of the North bank tributaries of Brahmaputra.
Action taken so far: To get rid of the drainage congestion in different areas, the Assam government constructed 494 drainage channels and 60 major sluices up to the year 1985. In the meantime, the Master Plan for the mainstream of the Brahmaputra river was finalized by Brahmaputra Board in 1986 where 20 drainage congested areas remaining unattended till then were identified. Later, nine additional congested areas were identified while finalizing various sub-basin (tributary) Master plans of the Brahmaputra. Schemes were prepared by the government through the Brahmaputra Board for drainage development of these identified areas. Schemes for 15 of these congested areas for a total area of 1552 sq km are found techno-economically viable whereas the remaining 14 areas for a total area of 528 sq km have been found either not required or not possible/ desirable. So far, three such schemes have been implemented by Brahmaputra Board and one scheme is under execution in the valley.
Raised Platforms: Raised platforms are constructed in chronically flood-affected areas. These are very useful in providing shelter to flood-affected people and livestock. They are also effective as centers for the distribution of relief during floods. It is sometimes categorized under non-structural measures since the structure itself is not meant to resist floods directly.
Large numbers of platforms have been constructed so far in Brahmaputra valley by Assam Govt under various schemes including MNREGA, MLA/MP fund and under the general fund for flood control. Brahmaputra Board has also constructed 18 Raised Platforms so far in the valley with funding from the Central Govt.
Non-Structural Measures
Flood plain zoning: Flood plain is an area of land adjacent to a river that experiences flooding during periods of high flow. In flood plain zoning, the flood plain is demarcated into different zones as per their vulnerability from flooding. Developments are allowed accordingly to the vulnerability of different zones.
Essentially, it is an administrative measure where regulations are brought through the enactment of a law. Since water is a state subject as per the Indian constitution, enactment of such law is the responsibility of the State Governments. Although a model bill has been provided to all states by Central Government, only Uttarakhand, Rajasthan and Manipur have so far enacted legislation for Flood Plain Zoning. None of the seriously flood affected states including Assam has implemented it so far for various reasons.
The Brahmaputra valley is very flat. Therefore, most part of the valley is within the flood plains of the Brahmaputra or its tributaries. For this reason, vast areas of the valley would come under high-risk zone under such an act, leaving a very little area free for development. Further, the entire Brahmaputra valley is densely populated. People have already settled in most areas of the flood plains and necessary infrastructures already built in such areas. Therefore, at present, it is difficult to implement flood plain zoning in the conventional sense. However, the state should ensure that remaining un-encroached flood plains of the valley be left to the river and new development restricted in encroached flood plains.
This will reduce expensive flood control measures and the cost of recurrent reliefs to the people. The measure will also ensure space for the river to carry its floods. The concept of zoning may also be modified with the concept of ‘Living with Floods’. This is already prevalent to a great extent among Mising community of the valley. The traditional stilt houses (Chang ghar) of the community need to be redesigned to accommodate the modern lifestyle and acceptability of all. Govt may encourage such houses in flood-prone areas by financing it under ‘Pradhan Mantri Gramin Awaas Yojna’.
Planners also need to come up with suitable changes in the cropping pattern to avoid crop damages during monsoon periods. Fruitful engagement of people in such areas during flood periods may be planned for overall socio-economic development. Thus, the Government may modify the concept to suit the requirement of the valley and make necessary enactment accordingly.
Flood forecasting:
Timely forecasting of floods, their intensity, etc can save life and property. The Central Water Commission (CWC)- a Central Govt organization started flood forecasting in Brahmaputra river since 1971. The model of forecasting has been progressively improved with time by the use of developing technologies. The CWC claims more than 2000 forecasts issued every year with an accuracy of more than 98%. Rainfall/storm specific flood advisories with a lead time of 3 days are issued at present. The forecast facilitates pre-deployment of Disaster Response Forces in the Brahmaputra basin.
The lead-time of the advisory forecast is needed to be increased further to allow advance warning. In addition, forecasting for all major tributaries is needed to be covered in flood plains of these tributaries. The huge loss of human life in Balbala area of Goalpara District due flash flood of Jinari river in 2004 could have been avoided had there been good flood forecastingsystems in such tributaries.
NESAC, a branch of NRSA, has been engaged in this direction on the behest of the Assam Government and has made substantial progress. A Committee has been recently formed by Govt of India for upscaling flood forecasting activities including inundation forecast in Brahmaputra Basin where all concerned organizations are involved. The Committee aims to converge all flood forecasting activities by various agencies under a single platform. The committee is mandated to develop a comprehensive model and provide necessary services to cover the entire Brahmaputra valley within 2020. Hopefully, the Committee achieves its goal and Govt is able to provide meaningful and timely warning to the entire Brahmaputra valley.
Dhruba Jyoti Borgohain is a retired chief engineer of the Brahmaputra Board. He can be reached at: [email protected]