Abstract

Flooding Pattern

ConclusionStudy Area

Acknowledgement

Maps and charts

Flooding in Bangladesh coast is generally classified into four

types. These are fluvial flood, tidal flood, fluvio-tidal flood and

storm surge flood. Except storm surge flood, the other three types

of flood are caused by fluvial flows from the upstream rivers

systems of Ganges-Brahmaputra-Meghna and tides from the Bay

of Bengal. Polders are constructed in the coastal region as a

protective measure from tidal flood and salinity. These protective

measures divided the coastal floodplains into protected and non-

protected areas. It is generally expected that protected part inside

the polder will remain flood-free from the types of flood mentioned

above except during the situation when polders are overtopped by

the surrounding river water. Depending on the flood protection

measures and sources of flood water, flooding patterns in the non-

protected part of the coast behaves in a complicated manner. So

far there is no comprehensive study to investigate this flooding

pattern. In this study we have applied the Delft 3D model to study

the coastal flooding pattern in both protected (when polders are

overtopped) and non-protected part of the region. It is found that

fluvial flooding is characteristically different from the fluvio-tidal

flooding and tidal flooding. Fluvial flooding is confined in the

northern part of the coast whereas tidal flooding is confined in the

southern part. There are scattered part in the region where

flooding is found to be caused by both fluvial flow and tide. These

floods are considered to fluvio-tidal. This information will be useful

for the planning purpose when further interventions are planned in

the coast.

Fluvial Flooding

Tidal

Flooding

Fluvio-tidal

Flooding

Fig 1: ESPA Study Area

Inundation Map

1998 2000

1998 2000

Fig 2: Inundation Maps

Fig 3: Three types of Flooding

Flooding patterns in Bangladesh Coast

There are 4550 Unions in Bangladesh from which a subset of 653 Unions

are selected for ESPA study area. Here all these 653 unions are

categorized with respect to their flooding pattern in the non-protected part

and are shown in Fig 4. Year 1998 is selected as an extreme flood event

and year 2000 is selected as an average flood event in the region.

Fatin Nihal, Shanjida Noor, Anisul Haque, Munsur Rahman, Delowar Hossain

Institute of Water and Flood Management (IWFM)

Bangladesh University of Engineering and Technology

Three types of flooding patterns have found in the non-protected

part of the study area. Among 653 unions in the study area,

fluvial flood is the most dominating flood type followed by fluvio-

tidal and tidal floods. Fluvial flooding is confined in the northern

part of the coast whereas tidal flooding is confined in the

southern part. There are scattered part in the region where

flooding is found to be caused by both fluvial flow and tide. In an

average flood event 20%, 5% and 6% areas of the region is

flooded by fluvial flood, tidal flood and fluvio-tidal flood

respectively which is increased to 38%, 6% and 11% during an

extreme event.

Fig 4: Maps and pie charts for 653 unions

1998 2000