Three mighty rivers dying

Heavy siltation hinders navigability

by Shamima Rahman Khan


Bangladesh is a deltaic country located at lower part of the basins of the three mighty rivers of the world. The huge amount of discharge and heavy sediment load cause the rivers to be unstable and the channels are constantly migrating laterally. The history of development of Bangladesh river is a history of gradual channel migration. As a result there are active bank erosion all over the country at different researches of rivers and along coast line.

This paper is therefore meant to highlight on this problem, the causes of the problem, the background history for generation of the problem and the activities of Bangladesh Water Development (BWDB) to face the problem.

Bangladesh a land of an area of 144,000 sq. km comprises one of the largest deltaic plains in the world, formed by confluence of the Brahmaputra-Jamuna, the Ganges and the Meghna. The main rivers of Bangladesh comprising two major eastern Himalayan rivers, the Ganges and the Brahmaputra and anon-Himalayan river, the Meghna, together with their numerous tributaries and distributors, from a dense network of the river systems in Bangladesh. Jointly, draining to the Bay of Bengal they represent the lowermost alluvial deltaic reach of the alluvial system with about 93% of the upper reaches lying outside the territorial boundary of Bangladesh. The total catchment area of these rivers stands at 1.72 million sq. km convering areas of China, India, Nepal, Bhutan and Bangladesh of which originate outside the boundary of Bangladesh. The annual volume of flow just below the confluence of the Brahmaputra and the Ganges is 795,00 million m3. The systems of the three major rivers discharge into the Bay of Bengal through a single outlet in Bangladesh which is the lower meghna (BANCID -1997).

The extensive floodplain of the major rivers and their tributaries and distributaries is the main physiographic feature of the country. The country is criss-crossed by around 230 rivers most of which are either tributary of distributary of the three major rivers. The total length of the river corses is approximately 24,000 km and cover 9770 sq. km of 7% of the country. The entire land of Bangladesh is almost low and extremely flat with the exceptions of a few hills in the north, northeast and south-east part of the country (BANCID - 1997).

The floodplain of these rivers and their tributaries and distributaries covers about 80% of the country. As a result of flat topography of the floodplain, one-fifth to one-third of the country is annually flooded by overflowing rivers during monsoon. Rainfall and river floods are annual phenomena causing untold miseries to the people and damages to crops, properties and infrastructure.

The history of developments Bangladesh rivers is history of channel switching and gradual migration. Sedimentological aspects of Bangladesh rivers are characterised by a fine sedimentary environment. The consequence is that the threshold velocity for sediment mobility is very low approximately about 0.2m/s. Due to low threshold velocity, the rivers are highly mobile with continuous reworking and deformation of their beds and banks transporting huge quantities of sediments.

The large discharge and heavy sediment load cause the rivers to be unstable and the channels are constantly migrating laterally. This instability of the river regime coupled with huge discharge and sediment load cause erosion, scouring and deposition and a chain action proceeds.

The Brahmaputra-Jamuna is a generally anabranched, wandering braided river. The present course of the river is only about 200 years old. The number of major channels varies from three in the upstream reaches to two in the lower reaches. During low river stage, a braided plan form is obvious with the emergence of numerous large sand bars. Several years map compilation by ISPAN (1993) indicates that in about 158 years (1834-1992), the entire Bangladesh reach of the river migrated westward by bank-erosion, with an average are of some 50m per year. Apart from the this secular westward migration, erosion occurs at different rates in different hierarchies of channels (Bristow, 1987; HALCROW, 1993a. Thorne et at, 1993 RRI-LP-CNR-DELFT, 19993).

The Ganges is a wandering river irregular point bars. The river on its northeastward migration built and abandoned several deltas before course (Niyogi, 1972).

The Padma Rivers has roughly a straight course in the upper reaches and a double-thread braided lower arch. ISPAN (1993c) studies indicate that the river windened considerably. In the lower reaches some 46% widening took place between 1984 and 1993, the middle reach widened by 21% during the same period. The upper reach remained relatively stable. The right bank of the middle and the lower reaches, on the other hand, is experiencing considerable erosion with some 200m/year in the lower reach to some 110m/year in the middle reach (ISPAN 1993).

Bangladesh has enormous wetland areas, out of which the principal ones are rivers and streams, freshwater lakes and marshes including haors, baors and beel, water storage reservoirs, fish ponds, flooded cultivated fields and estuarine system with extensive mangrove swamps.

The total area of the wetlands in the country has been estimated at seven to eight million hectares, or about 50 percent of the total land surface. The important coastal and inland wetlands encompass the vast floodplains and delta system of the Ganges, Meghna, Jamuna and Brahmaputra rivers.

The major wetlands of Bangladesh including Ramsagar, Medabeel, Tanguar haor, Arla beel, Dekhar haor, Kuribell, Eralibeel, Chandabeel, Dubriar haor, Hakaluki haor, Kawadighi haor, Hail haor, Bell Bhatia, Chalan bell, Ata Danga haor, Kaptai lake, Bogakine lake, Sundarban West, Sundarban South, Sundarban East, Chakaria Sundarban, Naf estuary and St Martin's island and reef.

In the recent decades, wetlands are being decreased due to many human interventions, In the Ganges, Brahmaputra floodplains alone, an estimated 2.1 (two point one) millionha of wetlands have been lost due to flood control, drainage and irrigation development projects. Severe erosion in the catchment areas caused increase siltation and have major impacts on the wetland areas. Each year about 2.5 billion metrictones of sediment are being transported by the major rivers of the country having a profound effect on the geomorphology of the floodplains and the coastal region. The continuous loss of the land maintain life resulting in the reduction of wildlife habitat and displacing the wetland based socio-economic activities.

The people's participation is central to all development activities and particularly for sustainable management of wetlands in Bangladesh. Participation means people are closely involved in the economics, social, cultural and political process that affect their live and livelihood. The objective is to ensure people's constant access to decision making and implementation of programmes activities at all levels. Participation in this sense is an essential element of sustainable development and resources management.

The Ministry of Environment and forest (MoEF), of the government of Bangladesh, with the cooperation of NGOs, professional groups and academics and researchers have prepared the National Environment Management Action Plan (NEMAP). The NEMAP process involved a series of workshops with people from all walks of life including local officials, local people's representatives, academics, farmers, fisherfolk, women and the poor.

During the NEMAP consultation process, degradation of wetland as a major environmental concern was expressed. The deterioration of wetlands in different parts of the country and the need to bring these wetlands under proper management was highlighted in the NEMAP report. NEMAP also recommended that grassroots level efforts will be fruitful for preserving environment and wetlands.

Chanda Beel is an important wetland in the Gopalganj district, with an area of 10,890 hectares. The wetland was rich in flora and fauna which is going to be threatened due to human activities, overfishing, unplanned development activities, increased siltation, pollution from pesticides and fertilizers etc. Participatory wetland management through grassroots participation became an essential elements to overcome the identified problems and conserve the natural resources of the wetland. In this connection, BCAS has undertaken a project entitled "Promoting grassroots Participation through Advocacy on Environment and Natural Resources of Chanda Beel" recently.

According to concerned sources, The main objectives of the project are: to give the local communities, particularly the women and poor greater say about how local natural resources are used and managed, to built upon the existing experience of identification of local environmental problems involving people, Government, NGOs and carry out awareness campaign in a selected locality to tackle the identified environmental problems, to improve access and control of environment and natural resources by the local communities and to prepare a Participatory wetland Management Plan for Chanda Beel.

Meanwhile, The water level has been marking a drastic fall in all major rivers in the country including Padma (Ganges), Meghna, Kirtonkhola this year causing frequent disruption in all reverine including the ferry service.

As the several thousands of char land has been emerging on about 3.8 thousand kilometres river routes as the amount of siltation this year is higher than other years, serious obstacle has been created in the movement of riverine vehicles including ferries in all rivers of our country including the Padma, Jamuna and Meghna, Kirtonkhola, prior to the onset of the dry season.

Though the cost of transport by road is about three times higher than the river routes, no effective steps are being taken for keeping the river routes operative, sources added.

Sources in the Bangladesh Water Development Board (WDB) said every year the water of the rivers of Padma an Jamuna carries about three billion metrictonnes of silt in the 500 kilometre river routes but this year the amount of siltation is about four (4) billion metric tonnes. As a result, huge shoals have emerged in the rivers this year causing the problem.

Ferry and others river transport between 137 Km of Barishal-Mongla port, 79 KM of Dhaka-Chandpur, 52 Km of Chandpur-Narayanganj, 235 Km of Chatagonj-Barishal, 169 Km of Dhaka-Barishal, 241 Km of Chatagonj-Chandpur, 48 Km of Mongla port-Khulna, 15 Km of Mawya-Charjanajat, 44 Km of Aricha-Baghabari, 74 Km of Mawya-Aricha, 18 Km of Aricha-Nagarbari, 10 Km of Aricha-Daulatdia routes-might be suspended at any time, officials said.

Sources in Bangladesh Inland Water Transport Authority (BIWTA) told this writer that the depth of the rivers Padma and Jamuna is now at 1.5 to 2 mitres at different place. It said, at least 2.5 to 3.00 mitres depth of water has necessary for normal movement of river transports. It said water level was decreasing by 20 centimetres everyday.

The sources said, About 4,000 km riverine routes, dredging is usually done on a total of 1200 km riverine routes comprising over 1000 km for coaster route and nearly 200 km for ferry services, particularly in dry season. About 34 lakh cubic metre dredging is done every year against the necessity of 70 lakh cubic metre. As a result, operation of riverine transports on the remaining routes of about 3,000 km become difficult in the dry season.

Water Development Board sources said that the two mighty rivers-Padma and Jamuna together carries over three billion metrictones of silts in their 500 kilometres waterways per year.

Road communications between seventeen districts of the country's southern areas and some districts of northern zone may disrupt any moment as the navigability in the rivers Padma and Jamuna have now became seriously reduced due to the huge deposition of silt with the recession of floods.

Bangladesh Inland Water Transport Authority (BIWTA) has been removing silt from the waterways through dredging at Daulatdia from September 20 on an urgent basis.

"four dredgers are in operation round the clock and removed over lakh cubic metres of sands (silts) during the last two month Daulatdia," a source said, adding that they would soon start dredging at Pratapur on Aricha-Nagarbari route by another dreger.

Besides, Over 15,600 kilometres of river routes across the country have lost navigability due to siltation in the past 29 years, while another 3,300 kms routes have become risky on operation of riverine vessels. A total length of the river routes was 24,000 kilometres in 1971, but it was reduced to 8400 KM in 1984 during the rainy season and again declined to only 5200 KM during the dry season. The route has now been reduced to 6,000 KM in rainy season and 3,800 KM in dry season, the sources added.

Menwhile, BIWTA dredging unit sources said 1.2 core cubic metre have been dredged in last eight years on ferry service routes. The BIWTA fixed a target of dredging 22 lakh cubic metres this year compared to 16 lakh cubic metres last year. The sources said the dredging of rivers by the dredgers have become almost impossible as the dredgers are in dilapidated condition. The dredgers are often gong out of order due to lack in replacement of spares. On an average, two dredgers remain out of order round the year for want of spares, which usually require to be imported from abroad, they added.

Source: The Independent , December 8, 2000