Bed aggradation in the lower reach of the Jia Dhansiri River, India

This study aims at estimating the rate of bed aggradation of the Jia Dhansiri River in Assam, India. It is carried out using two methods: (1) measurement of channel cross section in the field, and (2) measurement of variously dated maps for the period 1995–2006. Following these two methods, data on parameters pertaining to bed aggradation are generated and authenticated by comparison. Data on total bed aggradation during 1995–2006 are extrapolated from cross section graphs and again verified with a model proposed in this paper based on average water level of base year and current year and total bed aggradation. The rates of bed aggradations are 5.27 cm/y at Dhansiri Khuti village, 5.09 cm/y at Barigain village, 5.27 cm/y at Bagishakash village, and 2.64 cm/y at Thalthali village. No degradation zones are found in between during the study period except in minor magnitude and localized cases. If these rates of bed aggradation are continued and no significant changes in the channel morphology occur, then the river bed may merge with the low river bank after 11 years at Dhansiri Khuti village, 17 years at Barigaon village, 6 years at Bagishakash village, and 7 years at Thalthali village. The average channel aggradation during 11–years of period in the 16–km reach has estimated to be 3.65 cm/y. Again, if this rate is continued then the river bed will overtop low banks of the 16–km reach after 16 years. At this situation the river may attain a state of geomorphic threshold which may be channel shift following vulnerable slope(s).