Performance of Flood Control Works around Dhaka City during Major Floods in Bangladesh (Part-1) A.K.M. Saiful Islam Institute of Water and Flood Management (IWFM) Bangladesh University of Engineer and Technology (BUET) Water Club 18 th March, 2010, IWM, Dhaka

Outline Hydro-Meteorology and Drainage System of Dhaka City Hydrological Characteristics of Major Floods Recent Extreme Rainfall event in Dhaka City

The Ganges, Brahmaputra, and Meghna (GBM) River Basins 93% water comes outside of Bangladesh

Recent Major Floods in Bangladesh  Flood is a reality for Bangladesh.  Devastating floods like 1954, 1987, 1988, 1998, 2004 and 2007 are considered to be the worst ones affecting the majority of the population of the country and severely disrupting the social and economic activities.

Floods in Major Rivers

Height of Peak above DL Brahmaputra Ganges Meghna

Duration of flood above DL Brahmaputra Ganges Meghna

TRMM Rainfall (May-Sep, 2004)

TRMM Rainfall (May-Sep, 2007)

Flood Inundation Map 2007 based on MODIS Satellite Data

Location of Dhaka City with regional river system

Greater Dhaka City : Rainfall  Four climatic seasons:  Pre-monsoon (March-May)  Monsoon (June-September)  Post-monsoon (October-November)  Dry (December-February)  Mean annual rainfall: 2060 mm (70% occurs during monsoon)  Mean monthly rainfall during monsoon: 300 to 450 mm  Peak monthly rainfall usually occurs before the surrounding rivers attain the highest stage Source: Khan et al., 2010 IWFM, BUET

Height of Peak above DL Turag Balu Buriganga Tongi Khal

Duration of flood above DL Turag Balu Buriganga Tongi Khal 20---

Recent Events of Urban Flooding

14 September 2004 Recorded highest daily rainfall (341 mm) and 5-day cumulative rainfall of 600 mm Both 1-day and 7- day rainfall had return period of about 100 years Kallyanpur Gulshan Rayer bazar Motijheel Source: Khan et al., 2010 IWFM, BUET

Storm water flooding in 14 September 2004 Mirpur Road Motijhee l Source: Khan et al., 2010 IWFM, BUET

BUET Campus on 14 September 2004

Heavy rain storms on May 22, 2006 The metrological office recorded 52 mm rainfall in Dhaka since the midnight of Thursday till 6:00 pm at May 22, The city experienced 38 mm rainfall 3 hours from 6:00 to 9:00 am in the morning at May 22, 2006.

Water logging on July 23, 2007 The worst affected were Azimpur, and the old parts of the city. The Meteorological Office recorded 134 millimeters of rain in Dhaka between 6:00am and 3:00pm WASA sources said the drains can deal with only 10 millimeters (mm) of rain an hour. The city has 150 square kilometers of storm drains, whereas it needs at least 260 sq kms to collect runoff from heavy shower.

July 28, 2009 The heaviest rain in 53 years battered Bangladesh's capital Tuesday, leaving at least six people dead and stranding thousands in their swamped homes. The national weather office said 333 mm of rain fell in 12 hours in Dhaka, an overcrowded city of about 10 million people - the most in a single day since 1956

Causes of Aggravated Stormwater Flooding Unauthorized development on the drainage routes Encroachment of the lakes, detention areas and retarding ponds Reduced conveyance capacity of storm sewers by accumulation of solids Inadequate passage for storm runoff through newly constructed roads Source: Khan et al., 2010 IWFM, BUET

Late starting of temporary pumping operation when detention storages are already filled up from antecedent rainfall Malfunction and power outage of permanent pumps Unauthorized discharge of domestic sewage into storm sewers Contd.. Source: Khan et al., 2010 IWFM, BUET

The Way Forward Integrated management of water supply, wastewater, stormwater, solid waste and aquatic ecosystem is necessary to ensure sustainable management of urban water systems. This will lead to reducing pollution and health problems, reducing flood impacts and improving the water quality in waterbodies. Source: Khan et al., 2010 IWFM, BUET

Thank you