Abstract:
The Sylhet haor basin is bounded by the hills of Meghalaya in India to the north, the hills of
Tripura and Mizoram to the south and the high lands of Manipur to the east. The total area of
Sunamganj district, some part of Habiganj, Moulavibazar, Kishoreganj and Netrakona
districts are covered by major Haor Systems in the north east region. Flash flood is the most
commonly occurring water related disaster in the haor area. The main cause of flash flood is
the heavy rainfall that normally occurs in the hilly region and ultimately discharges with high
flow velocity through downstream river network in Bangladesh. Flash flood usually occurs
during the pre-monsoon season (March-April-May). During the flash flood it is very common
that people lost their primary agricultural productions which are the only source of their
livelihood. The main objective of this study is to assess flood damage and risk of agricultural
boro crop due to pre-monsoon flash flood.
Annual maximum and pre-monsoon maximum water level data were used for flood
frequency analysis. Inundation information is extracted from an existing 2D hydrodynamic
flood model (MIKE 21) for 2year, 10year, 20year and 100year recurrence intervals. Arc-GIS
is used to generate the flood hazard map. Flood hazard map has been developed considering
two combinations of hazard parameter. In the first combination, flood depth and flooding
duration were considered, where a critical date ‘120 julian date of year’ is used to determine
flooding duration. Hazard maps were prepared on the basis hazard magnitude. In the hazard
magnitude depth and duration index were used corresponding to four different depth and
duration ranges. From the hazard assessment it is found that flood area increased with flood
intensity. Higher flood depth increased and lower flood depth decreased with an increase in
flood intensity. Flooding of cultivable land indicated potential damages in boro crop
production and negative effects on the livelihoods.
Agricultural boro crop loss is estimated by developing a crop damage assessment model for
haor basin. A typical depth damage curve is formed for the study area. Depth damage curve
has been used to formulate damage function which is represented here by a stage damage
curve. Also crop loss function is developed on the basis total production cost which is the
secondary data of market price. Maximum damage occurs at the end of April which is the
harvesting time of boro crop. For risk assessment, risks of 2Year, 10Year 20Year and
100Year return period flood events are calculated by developing a risk model. Risk map for
the selected haor basin is developed that shows risk free, low risk, medium risk, high risk and
very high risk zone based on different ranges of expected damage or risk. To reduce the
expected damage some steps may be taken as, changing varieties of paddy, starting time of
cultivation be changed, invest higher harvesting force before flooding, repairing damage
location of submersible embankment.
