Ganges-Padma River System
Ganges-Padma River System one of the three major river systems of Bangladesh. The bengal delta occupies a unique position among the larger deltas of the world for its varied and complex river and drainage system. The whole delta is criss-crossed by innumerable large and small channels of which some are decaying, some are active, while some others are being drained only by the tidal flow. In the northeastern part of the delta there are some abandoned or partially abandoned courses of decaying rivers while the eastern and southeastern delta is characterised by the flow of active rivers with heavy discharges. The southwestern portion of the Ganges delta, which includes the world's largest mangrove forest, the sundarbans, is completely a maze of tidal creeks and channels. The river system's channels however carry a substantial amount of water through its various distributaries which join these tidal channels and estuarine creeks. Almost the whole delta is dotted with numerous lakes, marshes and low-lying swamps. In recent years, the area of these marshes and swamps has gradually shrunk owing to the encroachment of human habitations and reclamation of land for agriculture.
Another significant feature of the delta-rivers is their continual shifting of courses. Most of the major streams of the delta including its premier channel, the Ganges-Padma, have been ceaselessly changing their courses or migrating laterally and occupying new sites. Even the minor channels of the delta show the same tendency. The general flow or direction of these deltaic rivers is north-south. Most of the rivers of the western part of the delta such as the ichamati and Kuttiganga, follow a rather south-easterly direction while some of the eastern rivers show a marked south-westerly tendency (viz, the arial khan, bishkhali, etc). These flow-tendencies of the deltaic rivers have a linkage to the geo-tectonic situation of the region. The main channel of the Ganges-Padma has long been maintaining a southeasterly direction. At the same time, numerous deltaic spill-channels, particularly those of the Sundarbans, clearly exhibit some abnormal and haphazard tendency of flow-direction, which has given rise to the existing complex maze of the drainage system in the region. Most of the deltaic rivers and all of the Sundarbans channels experience a marked tidal influence.
The Ganges delta shows a mixed drainage pattern. The stem-stream of the delta, the Ganges-Padma, is a braided channel with a meandering course. Most of the other major distributaries also follow a sinuous course. A number of major streams, however, follow straight courses which can presumably be identified as tectonically controlled channels, viz, those of the southeastern creeks. At places the pattern of the streams is parallel, while at other places the pattern is trellis or rectangular.
The ganges and the padma are the main channels of this river system. The Bhagirathi-Hugli, gorai-madhumati and Arial Khan are three second-order rivers of the system. The Jalangi, bhairab, Mathabhanga, kobadak, bhadra, Ichamati, kumar, nabaganga are some other important streams of the delta. Among the tidal or coastal creeks, the Matla, Hariabhanga, Saptamukhi, Malancha, pasur, Haringhata, Rabanabad channel, Tentulia and Hatiya channels are worth mentioning. The Sundarbans, which occupies the southwestern deltaic coast, is also famous for its complex network of tidal creeks.
A combination of two tributaries the Bhagirathi and the Alakananda forms the Ganges. Although the Alakananda is the larger river, the Bhagirathi is traditionally accepted as the original Ganges. The Bhagirathi originates from the Gangoutri glacier north of Kedarnath at a point called Gaumukh. Beyond the outfall of the Kosi, the Ganges turns into the plains of Bengal round the outcrops of the rajmahal hills receiving only a few local drainage channels on the left bank. A few kilometres below farakka barrage in West Bengal (India) the river starts throwing off distributaries that join the right hand channel of the Bhagirathi, which once formed the main arm of the Ganges. Usually, through this channel all the low water discharge of the river flowed into the bay of bengal, whereas during the flood stages the overflow used to take place through the left-arm main channel, the Ganges of Bangladesh. After throwing off distributaries like the Jalangi, Mathabhanga, Ichamati, Bhairab, Nabaganga and Gorai-Madhumati, it takes the mighty jamuna on its left bank at goalandaghat and from this point the river is designated as the Padma. Later on it flows into the Bay of Bengal as the meghna through a number of estuarine channels.
The Ganges has a total length of about 2,600 km and a catchment area of approximately 907,000 sq km. Within Bangladesh, the Ganges is divided into two sections - first, the Ganges (258 km long) starting from the western border with India to its confluence with the Jamuna at Goalandaghat, some 72 km west of Dhaka. Second one is the Padma, about 120 km long, running from the Goalandaghat confluence to chandpur where it joins the Meghna. The total drainage area of the Ganges is about 1,087,400 sq km, of which about 46,300 sq km lies within Bangladesh.
The recorded highest flow of the Ganges was 76,000 cumec in 1981, and the maximum velocity ranging from 4-5 m/sec, with depth varying from 20m to 21m. The average discharge of the river is about 11,500 cumec, with an annual silt load of 492 ton/sq km. The average gradient for a reach between Allahabad and Benaras is 1:10,500; from Farakka (India) to Rampur-Boalia in rajshahi is 1:18,700, from Rampur-Boalia through hardinge bridge to Goalandaghat is 1:28,000. The slope flattens to 1:37,700 for a distance of 120 km from Goalandaghat to Chandpur. Within Bangladesh, the mahananda tributary meets the Ganges at godagari upazila of Rajshahi district and the distributary baral taking off at charghat on the left bank. The important distributaries taking off on the right bank are the Mathabhanga, Gorai, Kumar and Arial Khan.
In the deltaic part of the bengal basin the Ganges is 1.6 to 8.0 km wide and despite having broad meanders shows a braided character. In the western part of the Ganges delta most of the rivers show a rather decaying tendency. The pattern of the drainage system however maintains a typical complex picture. The northern rivers of this part of the delta are generally fed with spillage from the main channel of the Ganges and runoff water of the monsoon rains. A small quantity of underground seepage-water is also added to the flow. The southern channels are obviously affluently drained with the tidal saline water of the Bay of Bengal.
The Bhagirathi-Hugli, Bhairab, Sialmari, Mathabhanga, Ichamati, kalindi-jamuna are the important channels of the northern part of the western Ganges delta. These streams, except the lower Hugli, are the decaying channels of the old delta. The Bhagirathi-Hugli, the westernmost major distributary and a former main course of the Ganges, is the principal stream of the region. The Biddyadhari, Bidya, Kuttiganga, Baratata, Saptamukhi and Hariabhanga are some of the southern deltaic rivers in the western part of the delta. The rivers Kalindi and raymangal form the boundary between India (West Bengal) and Bangladesh in the southern deltaic region. The main flow of the Mathabhanga falls into the Bay of Bengal as the Ichamati.
The Bhairab is another important distributary of the Ganges flowing through the western part of the delta. It distributes in both West Bengal and Bangladesh and changes its name according to its location. It takes off from the Ganges about 16 km west of Akherganj in murshidabad district after traversing a tortuous course across the district and then loses itself in the Jalangi. During the greater part of the nineteenth century there was very little flow in the Bhairab, as its intake from the Ganges was closed. At present it has become the main feeder of the Jalangi and the joint flow of these two are known as the Bhairab-Jalangi in West Bengal.
The Sialmari is also an offshoot of the Ganges. It takes off opposite Rampur-Boalia in Bangladesh. After travelling through a meandering course, it empties itself into the Jalangi below Kopila. It is also heavily silted up and receives a small flow from the Ganges during the monsoon. The Kalindi-Jamuna of the western part of the Ganges delta bifurcates from the Hugli opposite Triveni and passing through Jessore and 24-Parganas of West Bengal, it enters khulna district along with the Ichamati to fall into the Kalindi which demarcates the boundary between India and Bangladesh for a long distance.
The Mathabhanga is another west Gangetic river. It originates in Bangladesh territory by leaving the main channel of the Ganges about 16 km below the point where the Jalangi diverges forming the boundary between Karimpur PS (India) and daulatpur upazila (Bangladesh). This river bifurcates into two after re-entering Krishnaganj PS of Nadia district (West Bengal) and the original name of the channel is lost. The western branch called the Churni flows west and ultimately falls into the Hugli at Chakdaha. The eastern branch, the Ichamati, forms the eastern boundary of nadia district and finally joins the Jamuna at Tibi in the North 24-Parganas and flows through the Sundarbans to discharge into the Kalindi.
Like the drainage network of the western part, the eastern network is also very complex and interrelated. The Padma-Meghna, through which the combined discharge of the Ganges, Brahmaputra and Meghna flows into the Bay of Bengal, is the major river of this part of the delta. The Ganges receives the combined flow of some North Bengal rivers near Godagari in Rajshahi district. The Brahmaputra joins the Ganges at Goalandaghat of faridpur district and in Chandpur district the Meghna falls into the Padma and as a huge and wide river the combined flow of these three river systems falls into the Bay of Bengal as the Meghna.
The rivers like Kumar, Chitra, Madhumati, Nabaganga, Kobadak, Arial Khan, Pasur, Rupsa, Bhadra, atharobanki, Bishkhali and Araibanki are some of the numerous streams of the eastern part of the Ganges delta fed by the Ganges-Padma spillage. The easternmost channels like the Arial Khan and mid-central streams like the Bhadra and rupsa-pasur are very active and carry sufficient water while some of the northern and northwestern rivers of this part suffer from acute drainage failure in the lean period. The main grid of the drainage system in Bangladesh is based upon the Raymangal, Hariabhanga, Kobadak-Arpangachhia-Malancha, Shibsa-Pasur-Marjhata and Madhumati-Haringhata rivers, all of which flow from north to south. The Khulna-Jamuna, Galghasia and Dholpetua rivers flow between the Raymangal and Kobadak rivers. The Galghasia joins the Dholpetua river and the two join the Kobadak to form the arpangachhia.
In the maze of the deltaic channels, cross-channels like the Sakbaria, Bajbata and Koyra connect the Kobadak-Arpangachhia with the shibsa. The Shibsa is formed of the Bhadra, Dhaki and Deluti rivers, which drain the Boira swamps and bring some of the Pasur flow. The Shibsa joins the Pasur near the sea to form the Morzal river, which flows into the Marjatta estuary. The Hansraj-Kaga, a branch of the Shibsa, bifurcates and joins the latter again a little downstream.
The Kobadak, once a mighty river, has become a seasonal river in its upper reaches. It meets the Dholpetua to form the large estuarine creek the Arpangachhia at the northern edge of the Sundarbans. This river runs south to southeast to reach Khulna city where it joins the Khulna-Atrai channel and is known as the Rupsa. Just south of Khulna city the Rupsa splits into two, the eastern arm resumes as Bhairab and flowing south joins the estuarine creeks Keora and Bhola.
The Gorai and Mathabhanga are two important streams of the northern delta. The Mathabhanga, meaning 'broken head', might have had this name from the fact that just below the off-take point the flow of the channel is disconnected from the Ganges. The Mathabhanga splits into four major channels the Churni, Chitra, Nabaganga and Kumar in the Kushtia region. The Churni falls into the Bhairab. The Chitra flows south to southeast and splits into the Khulna-Atrai and Chitra at Uzirhat. Both channels join the Bhairab, maintaining a distance of a few kilometres from each other. The upper reaches of the Nabaganga stream has turned into a lean channel, while its lower course still carries much of the Gorai flow to the Pusur in the south. In the monsoon this river becomes lively with an affluent flow from the spillage of the other rivers. About 16 km down from alamdanga town, the Kumar or Pangasi splits off the Mathabhanga and continues to flow south-east and bifurcates about 8 km north of Magura town. One channel falls into the Gorai and the other joins the Nabaganga.
The Gorai, another important river of the Ganges-Padma river system, has developed from the combined flow of the three large offshoots of the Ganges north of Kushtia town. The Kaliganga, its first split-channel, takes off south of kushtia and joins the Kumar near shailkupa. The lower reaches of the Gorai have almost dried up due to the damming effect of construction of one of the main canals of the The ganges-kobadak irrigation project (G-K Project). On its southeasterly course it has changed its name several times, viz, Madhumati, Baleshwar and Haringhata. It receives flows from the Kumar, Nabaganga and Chitra through different channels. At present the Rupsa-Pasur receives much of its flow from the Gorai through its spill-channel, the Nabaganga. The Rupsa-Pasur receives the Mongla channel and the Mirgamari cross-channel, a spill from the Bhola on the left bank on its downward flow to the Sundarbans at Mongla Port and Chandpai forest outpost respectively. On the right bank it receives the flows of the Dhaki, Manki and Bhadra, three affluent spill-channels of the Shibsa system. About 32 km north of the sea, the Rupsa-Pasur joins the Shibsa system and results in the formation of a 7.5 km wide Morzal river and debouches into the Bay of Bengal through the estuary of the Marjhata and Pasur.
The Arial Khan, one of the most active and huge channels of the eastern part of the delta, was a major outlet of the Padma during the second half of the nineteenth century. The Faridpur Khal and the Kumar, two distributaries of the Padma in the eastern part, fall into the Arial Khan at shibchar. Although its upper reaches are to some extent disturbed by a siltation problem, the lower reaches are enriched with the contribution of the Meghna through its tributary, the Shafipur channel near muladi. The Arial Khan joins the Meghna about 11.5 km northeast of Barisal town. In the northern part of barisal district, The Arial Khan receives the flows of the Darika Don, Swarupkati Khal, and Kaliganj rivers. The Madhumati also falls into it. The Barisal river, Kalijira river, Gabkhan Khal, Rajapur Don, Bukhianagar Don, Bakerganj and Punjab rivers, Burishwar, etc are some of the numerous rivers and streams of the eastern part of the Ganges delta under the Ganges-Padma river system.
The coastal drainage system of the Ganges delta includes the Sundarbans tidal channels and creeks as well as the estuarine channels of the eastern coast of the delta up to the Meghna mouth. The Sundarbans river system represents a complex network of drainage where the great trunk channels enter the tide-dominated southwestern part from the north, and are connected by innumerable distributaries, which after numerous bifurcations and interlacings unite into large estuaries falling into the Bay of Bengal. These larger estuarine channels may be regarded as arms of the sea, which have penetrated the coastal land of the delta. The principal estuarine channels, proceeding from west to east are the Raymangal, Malancha, Bara Panga, Marjhata, Bangara, Haringhata or Baleswar, Rabanabad-Tentulia, Shahbazpur (Lower Meghna). The other noteworthy rivers of the coastal areas are the Pasur, Bishkhali, Thakuran, Kabadak, Hariabhanga, Dholpetua, Shibsa, Bhadra, Bhola, Buriswar, Andharmanik and Bahadur. Most of these streams belong to the Sundarbans area. The minor rivers and streams are innumerable in this coastal area.
For almost all of the Sundarbans rivers, there is a sloping bank with very little water on it near the land. However, the bank is cut through by the channel between two islands or the mid-channel bars. Here channels are variously situated, each having a different course, but all have a considerably soft bottom with an increasing depth of water towards the land. In places, the depth of water ranges from 20 m to 30 m in the Sundarbans channels. Scarcely any change is perceptible in the course of these coastal rivers as they approach the sea. However, the processes of erosion and deposition go on rapidly among the off-shore islands (mostly newly-formed) and sand-banks at their mouths, especially at the Meghna mouth, where tracts of land or chars, are eroded away from one area and deposited at another area almost every year. The banks of the rivers are abruptly steep, according to the strength of the currents. Where the current is weak the slope is moderate. All rivers of the Sundarbans area (ie, the southwest coastal area of the delta) have a clayey bed and all are much influenced by tides. The depth in these channels is considerable and the pattern of drainage is complex. Almost all larger estuarine channels are fairly wide (10 to 25/30 km) and sufficiently active. They enjoy profuse tidal flow of waters with the inland run-off from the deltaic tributaries. [Md Abdur Rob]
Bibliography JHE Garrett, Bengal District Gazetteers: Nadia, Calcutta, 1910; MA Islam, 'The Ganges-Brahmaputra River Delta', Journal of University of Sheffield Geological Society (l), 1978; BWDB, Morphological Features of the Major Rivers of Bangladesh - Part 1, Bangladesh Water Development Board, Dhaka, 1988; Haroun Er Rashid, Geography of Bangladesh, University Press Ltd., Dhaka, 1991.