Bangladesh maps can be used as an effective tool

Bangladesh is situated in a region which is highly vulnerable to
flood. To the north-west of the country, the world’s largest mountains – the
Himalayas is located. Around 80% of the country involves the combined delta of
the Ganges, the Brahmaputra and the Meghna river basin with a total catchment
area of 1.8 million km2. There are as many as 700 tributaries of
these rivers. The ultimate effect of the rivers is next to that of Amazon
(Islam, 2011). The most severe flood occurs
during the months of July and August and regular river floods affect 20% of the
country, increasing up to 68% in extreme years. The floods of 1988, 1998, 2004
and 2017 were particularly catastrophic, responsible for large-scale destruction
and loss of lives. Land use/human activities are directly related to land,
making use of its resources or having an impact upon it. Land cover is the
physical characteristics of the land, while land use is a basis of human
activities under a socio-economic context. Flood hazard maps can be used as an
effective tool for water resource as well as urban planning by design engineers
to assess the vulnerability of the infrastructure and residents of that area to
flood events (Fernandez and Lutz, 2010). Approximately 40% of the total natural
disasters worldwide are due to flooding (Ohl and Tapsell, 2000). The land use pattern
change is the main reason for ecosystem
change (Waroux, 2011; Owrangi et al., 2014). Although the flood hazard
disasters caused by natural calamities cannot be prevented, the magnitude of
impact can be reduced (Dewan et al., 2006). A small intensity of rainfall
coinciding with high tide causes a major part of the north-eastern Bangladesh
(upper Meghna Basin) to get flooded, during the rainy season, because it is
influenced by the tidal effects. To overcome these difficulties, and for the
effective design of drainage system, the flood-prone areas in the catchment
have to be identified. For the flood mitigation and evacuation system planning,
preparation of flood hazard maps for the maximum flood extent of different flow
conditions is necessary.

The impact of the land-use pattern change and rainfall on flood
hydrographs for different return periods considering best adaptation options
for flood hazard mitigation have not yet been systematically investigated in
the upper Meghna basin of Bangladesh. Therefore, it is needed to investigate the
impacts of land use change and rainfall on the flood peak discharge and flood
hydrographs for different return periods and needed to adopt best mitigation
options to minimize flood hazards for irrigated agriculture in the upper Meghna
basin of Bangladesh.Delineation of the basin and sub-basin boundary:

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The Digital Elevation Model (DEM) will be used for the delineation of the river basin boundary in the proposed study. The surveyed data of river basin will be collected for generating a perfect geometric profile along the cross sections of the river basin. From the DEM, the stream networks will be developed that may coincide with river alignment position. The basin, sub-basin and drainage networks will be generated using the Arc GIS extension of HEC-GeoHMS software based on the DEM data. Thus, basin and sub-basin delineation will be carried out.


Human activities changes scenarios and hydrological soil:

In the proposed study, land use patterns change will be assessed between 1997 and 2016. The land use patterns data may be collected from the land use map developed by toposheet and remote sensing satellite images. The land use map for 1997 will be considered as the base map when it will be compared with land use patterns change. The observed land use patterns are the paddy field, woodland, water body, dry land, and vegetation. The future human activities on the agricultural land will be predicted in the river basin according to the trends of land-use patterns from past to present using the CLUE (Conversion of Land Use and its Effects) model. The future land use will be simulated in 2035 according to variation trend of land-use patterns change between 1997 and 2016. The hydrological soil will be surveyed from the soil map of 1997 and 2016 years, will be collected from different Government organizations in Bangladesh.


Assessment of flood hydrograph and peak discharge:

The HEC-HMS model includes basin model, precipitation model, and control model. The basin model contains hydrologic elements such as – the delineation of sub-basin, sub-basin area, stream length, elevation, and junction etc., will be developed by using HEC-GeoHMS. The proposed basin model will be then exported to the HEC-HMS model. In the proposed study, kinematic wave method will be used for flood routing. The observed streamflow and rainfall data for different return periods will be used as input to the HEC-HMS model. Finally, the flood hydrograph and peak discharge will be determined at each junction under land use pattern change and flow conditions.


Adaptation/mitigation options for flood hazard management:

The Analytic Hierarchy Process (AHP), a Multi-Criteria Analysis (MCA) technique will be used to prioritize selected adaptation options related to minimize flood hazards for irrigated agriculture in upper Meghna basin of Bangladesh. The AHP will be developed (Saaty, 1980) to find the best adaptation options against a set of criteria using stakeholders’ experience and judgment about the issue of concern. Before doing MCA, several adaptation options will be selected. The selection will be based on the outputs of the model, review of literature about adaptations proposed by the respective department of the government, related research documents, etc. In order to assess the selected options, some criteria will be identified by stakeholders through a participatory approach. Each adaptation will be numerically scored against specific criteria by experts’ judgments. Scores or weights given to each option will then be aggregated to examine results. Finally, sensitivity analysis of the results will be done and prioritize adaptation options to recommend.