Opinion (Spotlight Weekly)

Kosi Canal And Hooghly River Navigability

By Dr. AB Thapa

Nepal and India have agreed to conduct jointly the feasibility study to construct the Kosi navigation canal linking Nepal with the Ganges. Both the countries have already signed an agreement to conduct the feasibility study in 1997. The total length of the proposed Kosi navigation canal would be 165 km, out of it a 120 km long section of such canal would be in the Indian territory. The proposed navigation canal would be linking Nepal with the seaport through Ganges, Bhagirathi and Hoogly rivers India has not only already endorsed our proposal to build the Kosi navigation canal linking Nepal with the seaport through Ganges, but it has even gone one step further. Government of India has agreed to bear the entire cost of the feasibility study of the Kosi Navigation Canal Project

It need not be explained that Nepal’s aspiration to get an access to the seaport through the Kosi canal waterway would not be fulfilled until it is assured that further downstream the conditions of the Ganges and the Hooghly waterways are good for navigation. As a result, it has been clearly stated in the .1997 Kosi study agreement that the economic study of the India’s Waterway No 1 linking Allahabad with the Haldia port would also form the part of the detailed study of the Kosi canal waterway.

Impediment to Ganges Navigation

The major part of Bengal has been formed by mud and sand washed down by the Ganges, Brahmaputra and their tributaries. The south of the Gangetic Delta is still a land of swamps, creeks and forests. In the flat land, the rivers meander, swelling in the monsoon, shrinking in the dry season, often changing their courses and debouching into the Bay of Bengal through several channels.

In the past, the Bhagirathi known as the Hooghly further downstream was the main stream of the Ganges River. The Ganges runoff found its way into the sea by flushing out the silt and sand keeping the waterway through Calcutta region in good condition. It is said that less than three hundred years ago the Ganges showed a tendency to flow more and more through its eastern channel, the Padma. Ultimately the Bhagirathi turned into a relegated spill channel receiving water from the Ganges only for 3 to 4 months during the flood season. Now, after the completion of the construction of the Farakka barrage, a good proportion of the Ganges flow is diverted into the Bhagirathi throughout the year. Despite all these efforts, the problem to develop the Bhagirathi into a deep waterway might not be completely resolved without further engineering interventions..

The Hooghly River is formed by the confluence of the two rivers about 130 kilometres upstream of the Port of Calcutta. These two rivers are the Bhagirathi and the Jalangi. It is reported that the Jalangi, like the Bhagirathi, was also once very active navigable waterway forming perennial navigation link between the port of Calcutta and its vast hinterland of Assam and Upper India but has now become a spill channel receiving upland water for only about 3 to 4 months in a year.

Important Tributaries

There are few important tributaries which also join the Bhagirathi/Hooghly. The first among them, the Dwarka, rises in the Birbhum hills and joins the Bhagirathi in Murshidabad district. The river has a length of 134 km and has a drainage area of 8,850 sq.km.

The Ajoy rises in the Santhal Pragana Hills and joins the Bhagirathi near Katwa. It's length is 276 km and it drains 6,050 sq.km.

The biggest tributary is the Damodar which is 541 km long and has a catchment area of 25,820 sq.km. It joins the Hooghly near Fulta point.

The tributaries Rupnarayan and Haldi joining the Hooghly have a catchment area of 8,530 sq.km and 10,210 sq.km. respectively. The total drainage area of all the tributaries joining the Bhagirathi-Hooghly is 60,000 sq.km.

Now Bhagirathi Can Be Easily Controlled

The upland discharge entering into the Bhagirathi / Hooghly should be increased to the extent possible to arrest the process of deterioration of the Calcutta Port. The importance of such flow augmentation would be equally vital for the improvement of the Bhagirathi / Hooghly Waterway. The objective to enhance the navigability of the Bhagirathi / Hooghly could also be achieved to a great extent by providing structures to control the flow and water level. The schemes to control the flow and levels could be taken up as a multipurpose project.

The engineering option to control the flow and levels should not be regarded as a complete substitute for the augmentation of the Bhagirathi / Hooghly flows. Such option could, however, be far more attractive if the dry season flow of the Bhagirathi / Hooghly would also be at the same time increased. For planning this type of structures to control the flows and levels, the past experience gained by the countries in Europe and America could be very much valuable.

In recent years the Bhagirathi / Hooghly waterway has been completely cut off from the Ganges and thus it is under total control, as a result it has virtually become a canal. The unpredictable Ganges high flows carrying enormous sediment load is not any more a threat as in past to the Bhagirathi / Hooghly waterway due to the following reasons.

The upland discharge from the Ganges is fully controlled by the Farakka and Jangipur

Barrages The total drainage area of all the tributaries of the Bhagirathi / Hooghly is quite small. It is only about 60,000 sq. km. Among the tributaries the biggest with a drainage area of 25,820 sq. km is the Damodar. This river is already fully controlled by 4 storage dams. Two other tributaries Rupanarayan and Haldi with a total drainage area of 18,740 sq. km meet the Bhagirathi / Hooghly far away in the south near the sea.

Now the Bhagirathi / Hooghly is not any more a big river, as a result it would not be too expensive to adopt various appropriate engineering measures to control the flow and water depths of this waterway..

Engineering Interventions

Fundamentally, waterways fall into three categories: natural rivers, canalized rivers, and artificial canals. On natural rivers navigation requires continued efforts to retaining the channel in predetermined course by stabilization of banks and bed, by elimination of side channels, and by easing major bends to obtain a channel of uniform cross section. On canalized rivers navigation is facilitated by constructing locks that create a series of steps, the length of which depends on the natural gradient of the valley and on the rise at each lock. On artificial canals navigation can depart from natural river valleys and pass through hills and watersheds, crossing over valleys and streams along an artificial channel, the banks and sometimes the bed of which need protection against erosion. The route of an artificial canal can be selected to provide faster travel on long level pounds ( stretch between locks), with necessary locks grouped either as a staircase with one chamber leading directly to another or as a flight with short intervening pounds

Upper Reach Bhagirathi / Hooghly Waterway

The total length of the Bharigathi / Hooghly waterway from the Ganges to Saugor on the Bay of Bengal is about 540 kilometres. Out of it abut 240 kilometres of the upper reach that extends from the Ganges off-take point to Nabadwip is either completely beyond the tidal range or is moderately affected by the tides. The total drop in topographical elevation of the river bed in this stretch could be about 10 metres.

A series of low height dams (barrages) could be provided to fully control the water levels to maintain certain predetermined minimum water depth for navigation all the year round.. Perhaps two dams with proper side embankments might be adequate to improve the upper reach Bhagirathi / Hooghly waterway to the desired extent without causing serious drainage problems to the adjoining areas. However, the number of such dams might have to be increased to 3 if serious submersion and drainage problems are expected to encounter.

Fortunately it might not be too expensive to build few low height dams in the upper reach of the Bhagirathi / Hooghly waterway. Now the Bhagirathi no more looks like a wild river as in the past. It resembles a canal in appearance. The flows entering into the Bhagirathi / Hooghly is fully controlled by the Farakka and Jangipur Barrages.

Adequate navigation locks should also be provided for the passage of vessels across the dam. The size of the locks should be decided considering the present as well as the future needs.

Other Uses of Bhagirathi Dams

The proposed Bhagirathi / Hooghly dams for raising the water depths for navigation could also be used for the following other purposes.

Power Generation: The water head created by the dams can be used for the generation of power. It could be a peaking station if it is possible to have an adequate storage volume for diurnal regulation. The total installed capacity of all three power stations could be about 300 MW to supply power to meet 3 hours' peak energy demand even when the upper reach Bhagirathi discharge is only about 500 cumecs.

As a bridge: The dams to regulate the flow of the Bhagirathi / Hooghly waterway could be used as bridge for highway and railway.

The Illinois Waterway

Several technical characteristics of the Bhagirathi / Hooghly waterway in its upper reach bear close resemblance to similar characteristics of the Illinois Waterway of the USA. . These characteristics are the flow pattern, very gentle bed slope of the river, and the need to have very low height dams to raise the water levels.

The Illinois Waterway extends from Chicago Harbour at Lake Michigan to Grafton, Illinois and its confluence with the Mississippi River. In the Chicago area it includes the Calumet-Sag Channel and the Chicago Sanitary and Ship Canal.

Basic Parameters: Waterway length – 527 km; Minimum waterway depth – 2.7 m; Minimum waterway width - 70 m.

Dams to Raise Water Levels: Seven dams have been built on Illinois waterway to raise the water level by 48.85 metres. Among those dams the La Grange Dam raising water level by 3.05 m extends the backwater 125 km upstream. Similarly the Peoria Dam raising water level by 3. 4 m extends the backwater 118 km upstream.

(Dr. Thapa writes on water resources)