Abstract
The north-eastern part of Bangladesh is famous for rice production and fishing. A lot of bawl shaped depressed areas are located in this region which is locally called as haor area. Among seven haor districts Sunamganj has the maximum extent of haors and net cultivable area. The flash flood which is recurrent during April and May is the number one ranked hazard that affects agriculture in Sunamganj severely. Flash flood in 2017 was the most devastated in the recent past. Different researchers predicted that the rainfall during April/May will increase here due to the impact of climate change in future. The objective of present study is to evaluate the impact of rainfalls on inundations owing to flash floods using rainfall runoff inundation model (RRI-model) proposed. Ten rainfall events are prepared for computations of inundation, using reference rainfall in April in 2017, and their sizes normalized by the reference event range from 0.6 to 2.0, respectively. The size level of a flash flood is determined by means of RRI-model by water surface elevation at Sunamganj station in the Surma river and it is translated into return period. The inundation proc ess were computed for each of the specified rainfall events, together with inundation depths in Tahirpur upazilla (sub-district) in Sunamganj district in order to investigate the relation between the sizes of rainfall event, flash flood event and extents of inundation. The computed results suggest that the return periods of the computed flash floods are determined as 3.7,10, —,142.86 years corresponding to the normalized rainfall sizes such as 0.6, 0.9, —, 2.0 and suggest that inundated areas increase with the size of normalized rainfall and increase sharply in the range of rainfall size larger than about 1.1-1.2. Such results are useful to identify and quantify the associated inundated areas due to temporal variation of rainfall which is necessary for disaster preparedness and management.
Highlights
Flash flood is the common hazard in the north eastern part of Bangladesh due to upstream hilly topography and steep slope of the rivers flowing through the area
The objectives of this study are 1) to find out a relationship between rainfall amount and water level return period, 2) to evaluate the impact of rainfalls on inundations owing to flash flood, and 3) to identify the vulnerable area which will be inundated in future due to the increased rainfall amount
This study considers the flash flood in 2017 as reference rainfall pattern to evaluate the impact of rainfall variations in Tahirpur upazila
Summary
Flash flood is the common hazard in the north eastern part of Bangladesh due to upstream hilly topography and steep slope of the rivers flowing through the area. Many bawl shaped depressed areas are situated in this region. These bawl shaped flood plains are known as haor area. Boro rice is the only major crop in the haors. It accounts for most of the region’s income and providing most of its employment [1]. Flash floods suddenly inundate boro crops, damage infrastructures and often cause loss of lives and properties in haors region [2]. Almost 80% of haors area is covered by boro rice during January to May (pre-monsoon), which produces 18% of the total rice production in Bangladesh [3,4]
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