River Kollong is a spill channel of river Brahmaputra having its intake point near Jakhalabandha in between Kukurakata hill and Hatimura hill. The river traverses about 199.67 Km through Nagaon and Morigaon district and finally outfalls into the river Brahmaputra near Chandrapur in Kamrup district. The river meets streams like Diju, Missa and rivers like Killing, Kopili and Digaru along its course. Historically, the river served to be the route of trade and military movement during the reign of Ahoms and British. The British colonial administration almost established the district headquarters in Puranigudam on the bank of the river.In earlier days, Kollong was the only source of potable water and villages developed on the banks of the river.
The hydrology and topography of the catchment area of the river was such that apart from receiving water from the hilly streams, the river carried the flood water from the over flooded Brahmaputra river inundating the low-lying areas of Nagaon and Morigaon district and creating havoc among the people. Even the Nagaon town was under threat due to such flooding by Kollong river. In the year 1972, a news item with photographs was published in the daily “The Hindustan Times” regarding flood and erosion problem due to river Brahmaputra and Kollong in undivided Nagaon district at Jakhalabandha area. Subsequent to the news item, the then Hon’ble Minister, Govt of India Dr. K.L.Rao visisted the flood and erosion affected areas and a high level committee comprising of experts from both the Central Govt and State Govt was formed. The Committee, in their report, suggested for closure of Kollong river at the mouth with construction of an embankment from Kukurakata Hill to Hatimura Hill and accordingly the embankment was constructed during 1974-75. The flood inundation problem of river Kollong was mitigated after closure of the mouth of the river as well as construction of the embankment.
The river Kollong had become dead for a length of about 37Km upto Missa town after it was choked at the mouth due to continuous deposition of debris, water hyacinth etc. year after year. Two nos. of streams namely Missa and Diju feed Kollong at upstream of Nagaon town.
To study the status of the river Kollong, a team of State Technical Advisory Committee visited the site of mouth of the river Kollong on 27th July, 2014. The team observed that reopening the mouth of the river Kollong without comprehensive survey, study and hydrological investigation and data collection is not feasible. The team further observed that the channel is dead for all practical purposes and only the traces of bank is visible. The local inhabitants encroached the area for cultivation. However, the river starts activated after being fed by rivers Missa and Diju at downstream.
As a conclusion, the TAC team opined that revival of Kollong for augmentation of water flow is quite complex and require comprehensive feasibility study with survey and hydrological investigation and data collection and if required mathematical model study may be taken up.
Recently, in a workshop of Government of Assam, the issue was broadly discussed among experts from various agencies to chalk out possibilities of restoring the lost flow of river. Possibilities of re-linking the Kollong river with Brahmaputra river with the help of flow regulators alongwith resectioning and regrading the river at suitable stretches was discussed. Exploring and studying possibilities of holding the high monsoon discharge of Diju and Missa river so that the same can be fed to the Kollong river during lean period was also highlighted in the workshop.