Degeneration of Jalangi River: An Investigation Based on Maps and Satellite Images

Jalangi is a distributary of the Padma River which has opened up within the last few hundred years to flow actively in the southern and south-western direction through the districts of Murshidabad and Nadia in West Bengal. Initially, its source was the original Jalangi offtake located near Jalangi village, Murshidabad district. Earlier, it used to meet Bhairab River at two different points 5 km apart. But due to irregular flow of water, this part of the Jalangi River has become a palaeochannel and the discharge through Jalangi River is now maintained by Bhairab River. So, the lower part of the Bhairab River is actually the present Jalangi River. It flows into the Bhagirathi-Hugli River near Mayapur in Nadia district. The part of Jalangi River in Nadia district is considered for this study which is representing the lower course of the river. Jalangi is active during the monsoon season and Nadia district is quite susceptible to the flooding of Jalangi and Bhagirathi-Hugli rivers. Jalangi River is otherwise suffering from lack of supply of water to maintain its flow during the drier part of the year. This study is an ·endeavor to map the behavior of the Jalangi River in the past two hundred years. The database for detecting the changes in the Jalangi river course consists of J. Rennell's Bengal Atlas (1780), Atlas of India maps (1855?56), and topographical maps of 1: 63,360 scale (1914- 18); satellite database includes Landsat (MSS, TM, ETM+) images (1973:2010) and LISS IV Mono images (2007). Discharge data of different periods have been used for identifying the variation of water flow through the main channel. The main channel of Jalangi is characterized by intense meandering and the channel has shifted a few times in the recent past. This fact is confirmed by the presence of ox-bow lakes, meander scars etc. near the main channel. It can also be found from the old maps of the 18th and 19th century that width of the Jalangi river channel-which was at a par with the Bhagirathi-Hugli river until a couple of centuries back has been decreasing.
The main reason behind decreasing water flow in the Jalangi River is the shifting of the main channel of Ganga coupled with rapid siltation occurring at the off-take of Jalangi River. This prevents the discharge to enter through the course of Jalangi except during the monsoons. The other factors disturbing the main channel are sediment quarrying from the river bank and -dry river bed, land-use changes, contaminationof river water through the release of effluents into the river, garbage dumping etc. The presence of water hyacinth is a common phenomenon in the lower course of the river indicating eutrophication. The anthropogenic impact is mostly ,visible in the areas near Krishnanagar city. In spite of bankful and sometimes overbank discharge during the monsoon season, there is a possibility that the river could turn into an abandoned one in near future. Mitigation measures with proper planning should be implemented to regenerate the river environment.