River Systems of West Bengal

Inhaltsverzeichnis

1. Frontmatter

2. Chapter 1. River Systems of West Bengal: Water Quality and Environment

   Gautam Kumar Das

   Abstract

   Numerous rivers flow across the state of West Bengal forming a river network with the tributaries and distributaries of these rivers across the state. The principal river basins in the state are Ganga, Brahmaputra, and Subarnarekha which form a number of subbasins in the land of Bengal. Rivers in majority change their courses in all directions and such shifting of river courses cause the changing scenario of the direction of flow with space and time. Interbasin transfer of river water helps in irrigation and flood control and was introduced in the state of West Bengal in the British era. River commons happen to be a social contract which is closely related with the common properties’ resources of the riverside people. Among these rivers, which have water throughout the year, problems like water pollution are relatively less. During the dry season, pollution levels are high for factories or municipalities located along rivers with knee-dip water. Recently, thirteen river stretches in West Bengal have reached such levels of water pollution that they are not even suitable for outdoor bathing. Using the physicochemical parameters obtained from these stretches of the rivers, water quality indices were computed and after that the water quality rating was determined. From the obtained values of water quality rating, it is observed that the water quality of most of the river stretches in West Bengal is quite poor and often below the permissible limit.

3. Chapter 2. Shilabati River and Its Environments

   Gautam Kumar Das

   Abstract

   The mixing of huge quantities of eroded materials from the upstream and middle stretches deteriorates the water quality of Shilabati River downstream. Along with such huge sediment load, discharge of untreated wastewater from both point and nonpoint sources results in the water of Shilabati River being unusable. Though water quality rating shows water in good conditions after calculation of water quality index still the river water is not to be prescribed for drinking, outdoor bathing, or other domestic purposes as the faecal coliform bacterial count shows their number higher than the permissible limit as standardized by the Central Pollution Control Board. Apart from the water conditions, Shilabati River is known for its geographical diversity and historical importance.

4. Chapter 3. Environmental Deterioration of Churni River

   Gautam Kumar Das

   Abstract

   Churni, a distributary of Mathabhanga River and about 56 km in length, is presently in dying state due to periodical release of industrial water effluents in the Mathabhanga River from a sugar manufacturing plant and distillery unit of Bangladesh. Dissolved Oxygen in the river water becomes nil when the sugar producing plant releases untreated industrial sewage sludge and water effluents. The Water Quality Index revealed the poor quality of river water for use by the riverside inhabitants. The black dolphins have gradually been decreasing in the river water of Churni, their natural habitat, due to such aquatic pollution.

5. Chapter 4. Mayurakshi River—Water Resources and Environments

   Gautam Kumar Das

   Abstract

   Mayurakshi flows through Birbhum district, and this river can be called the lifeline of this district. Birbhum district is known as one of the driest districts of West Bengal due to low annual rainfall. In such a situation, the Mayurakshi River provides much of the water for supplying irrigation water to people’s day-to-day use, to a dry district like Birbhum. For the purpose of water supply, the state government has constructed reservoirs and irrigation canals with dams and barrages on the Mayurakshi and its tributaries. But since the volume of water carried by these rivers and their tributaries is not very high, no reservoirs have been constructed to control the floods. As a result, if the concerned department of the government is forced to release a lot of water at once from the reservoir of the dams and barrages due to excess rainfall during monsoon in a year, flooding occurs across the Mayurakshi River basin. Water quality of the Mayurakshi River is good and it was recently excluded from the list of polluted rivers in India by the Central Pollution Control Board.

6. Chapter 5. Water Quality Rating of Damodar River

   Gautam Kumar Das

   Abstract

   The Damodar River was once known as the sorrow of Bengal due to the loss of life and property caused by the floods in almost every monsoon. Since the middle of the twentieth century, the Damodar River has been blocked by dams and barrages, and after then the river course has not been changed. The water available from the reservoir of the dam has improved the scenario of agricultural advancement in several districts of the Damodar Valley. Around Damodar, the river basin has a lot of badlands where there is no cultivation. The government forest department is succeeding in planting eucalyptus on such badlands. Natural forests in Damodar valley have gradually been encroached upon by humans. Among a few scattered forest patches, the forest covering the entire Susunia Hills in Damodar basin is important for its species diversity of floral assemblages. Along the river course of Damodar, the main industrial area of West Bengal has developed. Though the sewage effluent from such industries empties into the Damodar River after treatment, the water of Damodar River is unfit for use even for outdoor bathing due to the presence of innumerable faecal coliform bacteria and higher values of biochemical oxygen demand in the river water exceeding the permissible limit. Of late Damodar river water is probably polluted by the mixing of the surface runoffs from the non-point sources.

7. Chapter 6. Changing Water Quality of Jalangi River

   Gautam Kumar Das

   Abstract

   The river waters of Jalangi got polluted at its downstream stretch at Krishnanagar due to municipal waste discharge as well as mixing of industrial effluent. Jalangi river water has now been upgraded to usable condition for outdoor bathing after drastic sewage treatment by chlorination for disinfection of faecal coliform bacteria as well as using screen and sedimentation tank for the precipitation of different solids remained in the domestic sewage at the outlets of eight drains of Krishnanagar municipality. The water quality rating applying the values of water quality index shows 60% good and 40% fair conditions of surface water of Jalangi River for the months from January to May 2020 which was almost poor during 2013–14 and 2014–15 respectively. Application of modified standard values of individual parameters for the computation of WQI results in the appropriate WQI values reflecting the proper concentrations of physicochemical parameters of river waters of Jalangi.

8. Chapter 7. Environmental Morphodynamics of Rupnarayan River

   Gautam Kumar Das

   Abstract

   The confluence of the Rupnarayan River is located in between the other two river estuaries at a distance of only a few kilometers. The other two river estuaries Damodar and Haldi lie to the north and south respectively of the Rupnarayan which outfall into the Hooghly River. The water of these river estuaries enters and mixes with the water of Rupnarayan River at high tide. Effluents released from Kolaghat thermal power plant and wastewater released from Haldia industrial area mixes with the tidal water of Rupnarayan River which pollutes the river water. Sewage discharges from Haldia, Tamluk and Kolaghat municipalities mixed with the waters of Rupnarayan and became unusable most part of the year. Apart from such pollution, the water of Rupnarayan is now slightly saline for increasing water salinity in the lower reaches of Hooghly River due to sea level rise. Consequent upon the existence of low salinity in estuarine water, abundant occurrence of giant prawn broods in the confluence has changed the socioeconomic pattern in the localities of three districts surrounding the Rupnarayan River.

9. Chapter 8. Water and Environments of Kangsabati River

   Gautam Kumar Das

   Abstract

   The Kangsabati River, famous for the Kangsabati Reservoir in Mukutmanipur, flows across Purulia, Bankura, and Paschim Medinipur districts and joins the Keleghai River in Purba Medinipur district to form the Haldi River. For various reasons including transport and communications across the course of this river upstream the normal flow has practically been stopped. Due to damming on a temporary basis particularly in middle and downstream stretches the river is in dying condition particularly during the lean time. Although there are no significant cities other than Midnapore town, the Kangsabati water pollution is caused by mixing of waste materials in the river water from the non-point sources. The pollution level of this river is determined and categorized as priority IV because the value of BOD concentration shows 6.4 mg/l of the surface water samples of Kangsabati River near the Midnapore town.

10. Chapter 9. Water Quality Determinants of Mathabhanga, Churni and Jalangi Rivers

    Gautam Kumar Das

    Abstract

    Industrial manufacturers like sugar mills and distillery plants, and milk units drain waste effluents into the waters of Mathabhanga, Churni and Jalangi rivers of Nadia district in West Bengal. Apart from industrial effluent discharge, Mathabhanga, Churni and Jalangi rivers receive domestic sewage on a regular basis through drainage systems from Majdia town, Ranaghat and Krishnanagar municipalities respectively. The wastewater effluent and domestic sewage affect the aquatic environment resulting in drastic changes in the river water quality of Mathabhanga, Churni and Jalangi rivers which are deleterious to both aquatic flora and fauna and this is how most of the river stretches of Mathabhanga, Churni and Jalangi got polluted. For the determination of the magnitude of pollution, the water quality index of river water is computed. The obtained result reveals that the present condition of surface water of Mathabhanga and Churni is in worse condition where the situation of Jalangi River at its downstream is comparatively better.

11. Chapter 10. River Environments of North Bengal

    Gautam Kumar Das

    Abstract

    The rivers of North Bengal are perennial and generally carry rain and snow water from the upland hilly region that flow to the downstream plains. This natural flow of the rivers of mountainous origin with a more or less stable state of equilibrium is considered as natural waterways. But the flows of such natural waterways are interrupted by the gradual reduction of carrying capacity that accommodates the river discharge from the upland areas due to human encroachment of the part of the riversides and floodplains. Apart from the reduction of the accommodation capability, the increase of rainfall including the snow-melt water for current issues like global warming due to climate change causes huge discharge into the rivers of North Bengal by which the state of equilibrium is not maintained. Destruction of riverside forests and conversion of forest lands into tea estates, agricultural lands, human habitation etc. is another problem that is accelerating soil erosion and spilling over the banks resulting in flooding. Changing river courses into new fluvial inlets sometimes causes avulsion of rivers where the main river channel becomes abandoned. Concrete bridges for roadways including railway bridges over the rivers contract the river course, a narrow one for its natural flow that sometimes causes flooding in the area. Apart from these, there are several towns and municipalities along the banks of rivers in North Bengal that discharge sewage from municipalities. The sewage along with wastewater enters the river water causing it unusable even for outdoor bathing. For this reason, Paharpur to Siliguri is the polluted stretch of Teesta in 2018 and along Sevoke during 2022 in the category of Priority-V as demarcated by the Central Pollution Control Board.

12. Chapter 11. Bidyadhari—A Sewage-Fed Tidal River

    Gautam Kumar Das

    Abstract

    Small streamlets like Nona Gung, Noai, Sunti and Yamuna rivers form the river systems of Bidyadhari. Originating from the district of Nadia and outfalls in the Jhilla River of the Sunderbans, Bidyadhari has been carrying wastewater effluent of the megacity Kolkata since the British period by which the river got polluted all along its tidal stretch from Haroa upstream to Malancha Downstream. The point sources of mixing of domestic wastewater and industrial effluent from Kolkata metropolis are the places of union of canals. The concentrations of determinants of declined water quality like dissolved oxygen of the river water are very low and even sometimes are below detectable limit. The water quality rating in the context of the values of computed water quality indices is extremely low in conditions that indicate its extremely poor usability in all aspects for agriculture, aquaculture and domestic uses.

13. Chapter 12. Water Quality Rating of Kolkata Waterbodies

    Gautam Kumar Das

    Abstract

    Kolkata’s wetlands not only provide breathing oxygen or keep the surrounding environment cool, but these wetlands also provide huge fish produce by which the fishing community sustains its livelihood by fish farming in the wetlands. But the serious polluting substances cause a decrease of water quality in Kolkata wetlands principally by human interference. Kolkata water bodies are polluted mainly by the inorganic and organic solid wastes, toxic chemicals, and organic compounds etc. which are generally found in the wastewater coming from the domestic discharges. The analytical results of the surface water samples collected from the different water bodies in and around Kolkata metropolis show the extreme deterioration of water quality of the waterbodies which are even unusable for outdoor bathing.