Amsterdam, capital of the Netherlands, is 166 sq km in area having a population of 8.72 lakhs. Amstel, 31 km in length, is the only river of Amsterdam. Two small streams Drecht and Kromme Mijdrecht united to create the Amstel river. The river after combining with several canals, confluences with the North Sea at a place, which is two metres below the sea level. To save the city from flood or entry of sea water, the Netherlands has innovative structures with dykes, canals and dams, flood gates made of state-of-the-art technology. One hundred and sixty canals totalling 100 kms in length in various elevations in Amsterdam primarily discharge the water of the city to the sea and serve as waterways. The water of the river and canals is clean because the city wastewater is treated before discharge to the canals. The average elevation of the city is two metres below sea level. To prevent floods, the water levels of the river and canals are continuously monitored and maintained by pumping to canals of higher elevation to discharge into the sea. To encounter the rising sea levels due to climate change, Amsterdam has already started renovation of the dykes and dams with advanced technology.
Guwahati, the prime city in Northeast India, is situated between the Brahmaputra river on the north and Shillong plateau on the south. With Narengi on the east and Lokapriya Gopinath Bordoloi International Airport on its west, Guwahati covers an area of 219 sq km with 11.2 lakh population. Elevation of the riverbank of the Brahmaputra is 51.3 m from sea level, while the average elevation of the city is 49 m. The danger level of the Brahmaputra in Guwahati is 49.68 m. The Bharalu river, which discharges the wastewater of the city, including stormwater, originates from South Khasi Hills of Meghalaya as Basistha river, one section of the river traverses a distance of 9.29 km towards north as the Bahini. The Bharalu nullah coming from Geetanagar in south-west direction meets the Bahini river at Jonali and flowing northwest as the Bharalu river, traverses a distance of 6.2 km to discharge into Brahmaputra river at Bharalumukh. In the past, the Bharalu nullah was a pollution-free rivulet with some streams from Narengi joining it but there is no such streams seen now. This author recollects the beauty of the Bharalu river flowing in rhythm with clear water along the RG Baruah Road while bicycling to the State Zoo area during 1963-64. At that time there were almost no human habitations from Chandmari to the State Zoo.
The average elevation of the Bharalu river is 48.8 m and minimum elevation of both the banks is 49.5 m. As the difference of elevation of bank and river is very small, the discharge capacity is very low and as a result, even medium intensity rains cause overflow of the banks, creating artificial flood. At present, the sluice gates at Bharalumukh are closed when the water level of the Brahmaputra reaches 45.1 m to prevent a back flow. In the rainy season, the gates have to be closed several times and the Bharalu water has to be pumped out into the Brahmaputra. The Bahini river carries an excess amount of sediment from the hills of Meghalaya, for which the carrying capacity of the Bharalu is decreasing. Every year the government extracts the sediment and solid waste from the Bharalu, before monsoon starts. This has to be repeated several times to enhance the carrying capacity of the Bharalu. The catchment area of the Bharalu river is about 11 sq km. The water carrying capacity of the Bharalu is 5 cubic meter/sec; 50 mm of rain in an hour generates 5.5 lakh cubic metre of runoff and the Bharalu needs about 30 hours to carry the water to the Brahmaputra. During this period, the low-lying areas remain under flood. After a medium shower, the Bharalu overflows and submerges many parts of RG Baruah Road, GS Road, Anil Nagar, Nabin Nagar, Rupnagar and Santipur by creating flash floods. The Bharalu water after washing all the trash of the city enters the households creating health hazards, loss of property and lives. In addition, such flash floods possibly contaminate the drinking water sources.
The Bharalu is an extremely polluted river and as a consequence, environmental degradation has become a challenge to human health. The sources of pollution in the Bharalu are sewage and solid waste, which are cruelly discharged into the Bharalu. The water parameters of the Bharalu indicate highly polluted water which is not suitable for any use and the survival of biodiversity is almost impossible. To rejuvenate the Bharalu, the municipal authority issued orders/guidelines to the public not to throw garbage and plastics to the river, yet the public behaviour has not changed. All residential and industrial wastewater generated in the catchment areas of the Bahini and the Bharalu should be treated before discharging into the river. Though there is an occasional flow of clear water in the Bahini, no such flow is noticed in the Bharalu. If an arrangement for pumping the Brahmaputra water from the Narengi area and discharging it to flush out the Bharalu water with 200-300 litre/sec in dry season, it will help revitalize the dead river. A treatment plant is mandatory to treat the Bharalu water before discharging it to the Brahmaputra.
The Government has adopted many ways to check flash floods in Guwahati. The authority can consider some points to be included in the Smart City programme. Dredging of the Bharalu by 1 to 3 metres will increase the carrying capacity of the river and shall help in reducing flash floods. Due to the dense population in Guwahati, the canals like in Amsterdam are not possible. If a tunnel, 20 m wide and 10 m deep, can be constructed below the three km stretch of the RG Baruah Road, it can hold 6 lakh cubic metres of water. This water reserve can be discharged into the Bharalu when the water level comes down. Japan is controlling flash floods by constructing huge underground reservoirs in the cities.
If an underground/over-ground reservoir of size 30 m diameter and 100 m depth/height is constructed on the bank of the Bharalu, it can store 70,000 cubic metre of water. For underground reservoirs, when the river water level reaches a certain mark, water will enter the reservoir automatically and can be pumped out to the river when the water level recedes. Because of underground structure, the land above it can be used for any other construction activities. If the reservoir is over-ground, water has to be pumped to store in it and by opening gates at bottom, the water can be discharged back to the river. The construction of 6-7 such reservoirs by the banks of the Bharalu will relieve flash floods.
When will the Bharalu in Guwahati be flowing like the Amstel in Amsterdam?