Drainage congestion is the major problem for the study area. The Baggar Dona River is the main drainage channel of the study area, and Maradona Khal is the main drainage artery for Char Maradona. All the channels are silted up badly and cause drainage congestion during the monsoon. Drainage problems are mainly caused by accretion of coastal mudflats and lengthening of the drainage channel due to rapid morphological changes. Silt deposition on tributary khals is also a contributing factor. The Baggar Dona River a wide mouth where Boyer Char formed. In order to arrive at a comprehensive solution to the drainage problem and to study various options for drainage improvement and structure location, SWMC was contracted by the Main Consultants (CDP/Haskoning) of the Char Development and Settlement Project (CDSP) to carry out relevant mathematical modelling.

The objectives of mathematical modelling study are :

• support the Feasibility Consultant and decision makers to understand the causes of drainage congestion in the Baggar Dona area, and

• identify the size and location of the regulating structure and comparative benefit of the location to overcome/reduce the problem in a comprehensive way.

Major outputs of the modelling exercise consists of the following:

• A one-dimensional mathematical model was developed for the project area using MIKE 11 river modelling software;

• Using the model and design hydrometeorological events, optimum size of the regulators and drainage channels to mitigate water logging in the area were assessed through a series of simulations of the project model studying different options;

• Inundation maps showing the area of different classes of land (F0, F1, F2 & F3) under the existing situation and different options weregenerated to indicate the extent of benefit with respect to drainage improvement due to the implementation of the project;