International Journal of Engineering Research ISSN:2319-6890 (online),2347-5013(print) Volume No.6, Issue No.6, pp : 307-311 1 June 2017 DOI : 10.5958/2319-6890.2017.00025.3 Page 307 A Study on Seasonal Variation of Hydro-Morphodynamic Parameters of Jamuna River Probir Kumar Pal, Afeefa Rahman, Dr. Anika Yunus Department of WRE, Bangladesh University of Engineering and Technology (BUET), Bangladesh, e-mail: probirpal10@gmail.com, afeefa@wre.buet.ac.bd, anikayunus@wre.buet.ac.bd Abstract :Owing to heavy sediment deposition, Jamuna River, the largest braided river in Bangladesh changes its hydro- mophodynamic characteristics rapidly. Due to the changes, we lost thousand hectares of mainland floodplain causing thousands of people landless. Therefore study on the variation of the hydro-morphodynamic parameters is immensely important. In this study, the hydro-morphodynamic changes of Jamuna River has been investigated by using HEC-RAS 1D and historical data analysis. Data has been sorted, analyzed and plotted for the investigation of variation of various parameters during pre-monsoon, monsoon and post-monsoon seasons for a 80 Km reach of Jamuna River. The model is calibrated (in 2004) and validated (in 2008) at Kazipur station by using manning’s n 0.025 for which the correlation factor (r), NSE and RSR are respectively 0.9889, 0.9144 and 0.2926 that indicates the performance of this model “very good”. Results reveal that between 1980 to 2014 during monsoon period discharge, water level, sediment transport rate and velocity significantly increase than pre-monsoon and post- monsoon period. From analyses, maximum discharge, water level, velocity and sediment transport rate found as 103129 m 3 /s, 15.11 m, 2.84 m/s and 32662117 tons/day respectively in 8 th September 1998, 30 th August 1988, 29 th August 2005 and 9 th October 2013 in monsoon. During this time, discharge, water level and sediment transport rate decreases in pre-monsoon and post-monsoon period respectively 66%, 70%; 38%, 40% and 87%, 72% with comparative to monsoon. The analysis also shows that velocity in monsoon increases about 45% to 75% than pre-monsoon and post-monsoon period. Velocity, flow area, top width and water surface elevation have been found to be decreased about 35%, 50%; 61% ,70%; 55%, 66% and 29%, 36% during pre-monsoon and post-monsoon period with respect to monsoon period. It is hoped that this study will help in understanding the seasonal change of hydro-dynamic characteristics of Jamuna River and will help to predict future situation and undertake appropriate future development activities. Key words: Jamuna River, Hydro-dynamic, Pre-monsoon, Monsoon, Post-monsoon, HECRAS 1 Introduction Bangladesh is a riverine country with hundreds of rivers overlaying its landscape. Because of its inherent alluvium nature, the rivers of Bangladesh are morphologically dynamic characterized by erosion and sedimentation, which results in changes in hydraulic geometry; plan form and longitudinal profile of the rivers (Habibullah, 1987). Aggradations, degradation or change in plan forms; change in river bed and meandering characteristics are most common features in the rivers of Bangladesh, affecting the major rivers as well as the medium and the minor ones. The Jamuna river, one of the major rivers of Bangladesh, originates from the Chemayung-Dung glacier, approximately at 31'30'N and 82'0'E (Hadi, 2015). The river is a major contributor to building up of the delta. Within Bangladesh territory, Brahmaputra-Jamuna is 280 km long, of which Jamuna is 205 km. The width of the river varies from 3 km to 20 km with average value of 10 km. During monsoon period it is about 5–8 miles (8.0–12.9 km) from bank to bank. Even during the dry season when the waters subside, the breadth is hardly less than 2–3 miles (3.2–4.8 km). The average annual flood of the Jamuna River is about 60,000 m 3 /s, and the discharge during low flow lies between 4,000 and 12,000 m3/s; the water level slope gradually decreases from 10 cm/km at the Indian border to 6 cm/km near the confluence with the Ganges River with a mean value of 7 cm/km (Laz,2012). Variables influencing the geometry of alluvial rivers according to Simons (1971) are velocity, discharge inflow, channel depth and slope, apparent dynamic viscosity of the water sediment mixture, grain size distribution of bed materials, sediment density, shape factor of the reach of the stream, cross-section and the seepage force. All the above mentioned factors make the river Jamuna morphologically active causing change in water level, discharge and velocity from time to time. Most of the rivers in northern region of Bangladesh depend on water flow from Jamuna River. The flow volume declines during dry season and it impacts the surrounding region. Maximum discharge in monsoon period is around 100,000 m 3 /s whereas minimum discharge in post monsoon is around 4000 m 3 /s (Hossain, 2016). The water level rises rather abruptly during April–June, fluctuates slightly during the next three months, and falls rapidly during October–November. Several discharge peaks can often be observed due to the dependence on rainfall and the distribution of the tributaries along the river in Assam and Tibet (Jagers, 2003).Therefore it is important to understand the seasonal change of hydro-morphodynamic characteristics of Jamuna River. Being an important water course for Bangladesh, Jamuna River has drawn attention of different national and international researchers. Coleman (1969) studied the riverbed erosion and deposition in the Jamuna River. Baki et al. (2012) studied riverbank migration and island dynamics of the braided Jamuna River of the Ganges-Brahmaputra basin using Landsat images. Ali et al. (2002) investigated the effect of the changes in the plan form and bed topography of the Jamuna River in the form of a stability analysis by perturbation technique. Several modeling studies have been conducted to understand the behavior of river. Laz (2012) studied on morphological assessment of Jamuna River by using Delft3D model. Shahed