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    HYDRO-MORPHOLOGICAL ANALYSIS OF TEESTA RIVER USING HISTORICAL DATA AND FLOOD INUNDATION MAPPING USING HEC-RAS 2D MODEL
    (2023-02) ALI, MALIHA; ISLAM, RAFIA
    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.