100 Year Flood Simulation forDhaka City Using Multiple Models

Ismat Pervin, Md. Feroz Islam, Imtiaz Taher, David Khan

Institute of Water Modelling (IWM)

Outline• System Introduction

• Model Development Process

• Result Interpretation

• Conclusions

(SWMC)

Introduction• Service Nature: Research and EngineeringConsultancy

• Expertise: Water Resources Engineering

• International Office: Malaysia

• Products and Services:• Computational Models• Decision Support Systems• Feasibility Studies

History1986

• SWSMP, MWR

1988

• Surface WaterModelling Centre

1996

• SWMC Trust

2002

• Institute of WaterModelling (IWM)

IWM Expertise in urbanwater management

Sewer Master Plan

IWM involved in rehabilitation of water lines using trenchless technology and establishment of District metered Area (DMA) in Dhaka city. It is expectedthat it will allow 24-hrs pressurized reliable water to the city by 2015

Horizontal Directional Drilling

New Concept in Urban WaterDistribution Management

Water Supply Source AssessmentComputer models used in IWM

Bangladesh in the context of GBM Basin

Area:1.72 Mkm2

93% Area Outside of Bangladesh

75 to 80% oftotal flow in5 months ofmonsoon

Ganges

Brahmaputra

Meghna

Bangladesh in brief

Area: 147,570 km2

Population: 150 millionNo. of rivers: 57 trans boundary

rivers

Area:360 km2

Rivers Around DhakaCity

Population:About 15 million Dhaka

City

Model for Central & EasternDhaka

EasternDhaka

CentralDhaka

Pragati Sharani as Drainage Divider

Model for Central & EasternDhaka

Pragati Sarani

EasternDhaka

CentralDhaka

Types of Flood River FloodWater intrusion to the low lying areas of city from Surrounding Rivers. Since the internalDrainage network discharges to the rivers, at high water level in the river, the drainage system becomes dysfunctional.

Urban FloodCaused by high intensitystorm rainfall runoff in the city area. The incidentrunoff

overwhelms existing drainage infrastructure, both natural and man made. This leads to water logging for an extended period of time.

Dhaka ContextEastern Dhaka is unprotected. It is usually effected by river flood caused by high water levelin the rivers.

As the Central Dhaka is protected by embankments, it is usually effected by Urban flood caused by drainage congestion.

Rain

fall

(mm

)

Rainfall Pattern of DhakaCity

450

400

350

300

250

200

150

100

50

0

Average Rainfall (mm)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rainfall Pattern of DhakaCity

Rain

fall

(mm

)2004 Precipitation Event:100 year return period

350

300

250

200

150

100

50

0

Rainfall Hytograph in Dhaka

The design rainfall in the hydraulic design criteria for drainage structure for Dhaka city is 245 mm, which is2-day cumulative rainfall having a 5- year return period.

However, in 2004-

The recorded highest daily rainfall of341 mm compared to a

mean monthly rainfallof264 mm in September,

and a 5-day cumulative rainfall of 600 mm occurred duringthis period. Both the 1-day and 7-day cumulative rainfall during this

1-Jun-04 1-Jul-04 1-Aug-04 1-Sep-04 1-Oct-04 1-Nov-0 Da

te event had return periods of about100 ye ars .

Source: Islam, A. K. M. Saiful, Haque, Anisul and Kumar, Sujid, “Performance of Flood Control Works Around Dhaka City During Major Floods in Bangladesh”, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, 2009.

Skeleton of Methodology

Data Collection: GIS data

Landuse map of 2015 accordingLanduse map of 2004 to DAP of Dhaka city

Source: Capital Development Authority (Rajuk)

AS BUILT DRAWINGS

Data Collection: As builtdrawing

s

UnderstandingExisting DrainageSystem:

Literature Review• Japan International Co-operation Agency (JICA), “Study on Storm Water

Drainage System Improvement Project in Dhaka City”, Department of Public Health and Engineering, Bangladesh, 1987.

• Rahman, Rezaur, et al, “Investigation of Hydrological Aspects of Flood – 2004 With Special Emphasis on Dhaka City”, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, 2005.

• Rahman, S.M., et al, “Study on Drainage Master Plan for Dhaka City”, Institute of Water

Modelling (IWM), 2006.• Islam, A. K. M. Saiful, Haque, Anisul and Kumar, Sujid, “Hydrological Aspects of

Flood 2007”, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, 2008.

• RAJUK, “Integrated Development of Hatirjheel Area Including Parts of Bagunbari Khal”, Mid- term report, Bangladesh University of Engineering and Technology, 2008.

• Islam, A. K. M. Saiful, Haque, Anisul and Kumar, Sujid, “Performance of Flood Control Works Around Dhaka City During Major Floods in Bangladesh”, Institute

of Water and Flood Management, Bangladesh University of Engineering and Technology, 2009.

• Murshed, Sonia Binte, Islam, AKM Saiful and Khan, M. Shah Alam, “Impact of Climate Change on Rainfall Intensity in Bangladesh”, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, 2011.

Central Dhaka 1-DModel

Water Level at Outfall of Mike Urban from Mike 11

Rampura Gate & Pump• Gate is closed when W/L rises to 4.5m• 20 pumps start at W/L 4.8m & stop at 4.5m• Additional 30 pumps start if W/L reaches 5m• Pump capacity ranges from 0.007 to 0.01 m3/s

Maniknagar Gate & Pump• Gate is closed when W/L rises to 4.5m• 10 pumps start at W/L 4.8m & stop at 4.5m• Additional 11 pumps start if W/L reaches 5m

• Pump capacity ranges from 0.01 to 0.03m3/s

Manda Sluice Gate• Gate is closed when W/L rises to 5.4m• No pump is available

Wat

er L

evel

(mPW

D)

Eastern Dhaka 1-D Model

• Truncated from North-Central regional model

• 1-D model was calibrated• Coupled with 2-D model• 1D-2D couple model was

calibrated & validated

Calibration Point

CalibrationPoint

7

6.5

6

5.5

5

4.5

4

3.5

3

Water level Hydrograph at Demra

1-Jun-04 1-Jul-04 31-Jul-04 30-Aug-04 29-Sep-04 29-Oct-04

Date

Water Level at Demra on Balu River from Mike 11

1-DModel Simulation

Coupling 1-D and2-DModels

MIKE212-D Analysis

Simulating hyraulic conditions

(water depth, velocity, etc.)

on flood plain

MIKE FLOODCombining 1-D and 2-D

▪ Interrelating 1-D and 2-D

models▪ Defining overflows

along interrelated reaches

MIKE111-D Analysis

Simulating hyraulic conditions

(water depth, velocity, etc.)

in river channels

Flood plain defined by MIKE21

River channel defined by MIKE11

Lateral Link defined by MIKE FLOOD

Source: Danish Hydraulic Institute (DHI)

Data for 2-DModel

Land level survey data of Survey of Bangladesh (SOB)

Developing 1-D 2-D Couple Model

in Mike Urban

Model simulation: Central Dhaka Model

Gulshan

Dhanmondi

Matijheel

Flood Depth (m)

Coupling 1-D and2-DModels

forEastern DhakaBathymetry for

MIKE21River/Khal Network in MIKE11

Model Calibration: Eastern Dhaka Model

Results Interpretation: Flood Exposure

Flood Duration (min)

Results Interpretation:VelocityGradient

Challenge: Resolution ofDEM

10m x 10m 5m x 5m

No flow area

MH Pocket

Road Flow Path

Flow area

Road

Conclusion• Development of Sophisticated model. In fact, the first 1D-2D model for Dhaka

City.

• The Models were successfully utilized to imitate the extreme flood event of

2004.

• Detailed model development required data collection from different agencies.

Data consolidation and conversion to model format willeventually lead to

standardized data format.

• The model will be a useful tool that can factor in ongoing and proposed changes in urban landscape. The scenario runs in the model can correctly describe the impacts upon drainage infrastructures. This will help policy makers in adopting better strategies and infrastructure solutions.

• Integrated models require more detailed data, computational resources and skill development. The CORFU initiative is only the beginning!

ThankYou

Land Development

)s/3(m ffonRu

Area

(km

2 )

Results Interpretation:Eastern Dhaka

Model

Flood Depth Comparision for 1D and 1D-2D couple model35

30 1D-2D couple model1D model

25

20

15

10

5

-

0-0.5m 0.5-1m 1-2m 2-3m 3-3.5m 3.5-4m >4m

Flood Depth

Floo

d Du

ratio

n(ho

ur)

Results Interpretation:

CentralDhakaModel

35.00

30.00

Flood Depth Comparison

1 in 10 year event 1 in 30 year event 1 in 100 year event Actual event

80.00

70.00

Flood Duration Comparison

1 in 10 year event 1 in 30 year event 1 in 100 year event Actual event

25.0060.00

20.00

15.00

50.00

40.00

30.00

10.0020.00

5.0010.00

Area

(km

2 )0.00

Flood Free 0.1-0.25 0.25-0.75 0.75-1.5 >1.5Flood Depth (m)

0.00Average Maximum