A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering, School of Civil and Engineering

Thesis (M. Eng.) - Asian Institute of Technology

Flash floods in the Northeast region of Bangladesh are usually generated from the hilly catchments of India from where no hydrometeorological as well as hydrological data are available to forecast these. In such circumstances this study has the objective to analyze the possibility to forecast flash floods of the Northeast region of Bangladesh with the help of available data inside Bangladesh by using the user friendly computer model MIKE 11. Two flashy river systems Manu-Dhalai and Khowai, originated from the Indian state of Tripura have been selected for this purpose. The Indian subcatchments, contributing floods to these river systems have been calibrated (as NAM catchments) with respect to the discharge stations available inside Bangladesh border. The HD models were schematized by using discharge as upstream and water level as downstream boundary. The NAM models were incorporated to the HD models by distributing the NAM inputs through 20 kilometers of lengths in the Indian side assuming zero discharge at the upstream point. The HD models calibrations and validation gave quite good results. In case of NAM model the calibration was difficult and hence only the high peaks were considered for the calibration. After calibration of NAM and HD models some test forecasts were carried out to see the stability of the models. The forecasting points were in Moulvibazar and Shaistaganj for Manu-Dhalai and Khowai river systems respectively. Before flood forecasting exercise the updating parameters were calibrated. The flood forecasting exercise for the Manu-Dhalai river system showed it is possible to forecast the flood peaks accurately with short lead times (24 hrs.<). Where as the results of the Khowai river system indicated, however it is not possible in all cases. The long-term forecasts (>24 hrs.) were not too accurate for both the river systems. Finally this study concluded with the recommendation that forecasting flash floods of the Northeast region of Bangladesh may be possible if all the necessary required data as well as the cooperation from the Indian side is available.