Abstract:
Bangladesh is situated at the most downstream region of the GBM basin where the major
three rivers meet. Only 7 percent of the basin area lies within Bangladesh. Most of the water
flowing through Bangladesh is beyond the nation’s control. Besides, owing to flat lowlying geological formation, Bangladesh is a very flood prone country where flood stays for
longer period. In the northwest region Teesta is a flashy river in nature for which the water
level of river Teesta shows several peaks during the monsoon both at Dalia and Kaunia.
During the monsoon, Teesta River overflow its banks. For this severe flooding is caused
multiple times by Teesta River during monsoon in Bangladesh. Besides, Teesta is a
morphologically active river which shows significant shifting of bankline and change in
width over the years resulting from erosion and deposition. Therefore, the study is carried
out to understand the hydrological and morphological nature of Teesta River and the flood
characteristics of the river using mathematical model. For hydrological analysis, water level
hydrograph for Dalia, Kaliganj and Kaunia stations and Discharge hydrograph at Dalia
Station is prepared using historical data of daily water level and discharge from 2000-2022
year. Besides flood frequency analysis is also done using Gumbel’s distribution to
determine the maximum discharge and water level for a return period of 50 and 100 years.
For morphological analysis, planform analysis is done using satellite image to evaluate the
bank line shifting and amount of erosion-deposition of both banks of Teesta River for the
period 2000-2022. Cross section analysis is done to determine the changes in width of the
river and thalweg movement over the year using cross section data from left bank of the
river. As a part of the study, flood inundation maps were generated for monsoon season of
2020 using HEC-RAS 2D model. Later, the model generated map is also compared with
Satellite based inundation map prepared by FFWC of BWDB. HEC-RAS 2D model is
developed and calibrated for the year of 2020 August-September and validated for the year
of 2013 August-October with a manning’s roughness n=0.032. Lastly, the model is
simulated to generate flood inundation map for Teesta River of 2020 flood to compare it
with the actual scenario to understand the model performance.
