The Kopili River, which is the largest south-bank tributary of the river Brahmaputra, is primarily responsible for the frequent floods in the Morigaon and Nagaon districts of Assam, a northeastern state of India. The area of Dharamtul in Morigaon district is particularly susceptible to floods every year. Therefore, the current study aims to examine the hydrological characteristics of the Kopili River at the Dharamtul site so that insights can be drawn regarding the annual flooding patterns in the region. In this research, historical time series data has been utilized to create a comprehensive hydrological database. The database includes information such as peak discharge, design discharge for different return periods (10 years, 25 years, 50 years, and 100 years), stage-discharge rating curve, return period, and annual hydrograph for the Kopili river at the selected site, which is also a designated gauge site for the Water Resource Department of the Government of Assam. The findings of this research will be valuable in formulating flood models and implementing flood mitigation measures in the region in the long run. Additionally, it will pave the way for further hydrological studies in the area.