INDIA’S FIRST REAL-TIME INTEGRATEDURBAN FLOOD FORECASTING SYSTEMFOR THE CITY OF CHENNAI

National conference on Flood Early Warning for Disaster Risk Reduction 30-31 May 2019, Green Park Hotel, Hyderabad, India

Presented by

Subhankar KarmakarProfessorCentre for Env. Sci. and Engg. (CESE)Associated Faculty member: IDP in Climate Studies (DST-CoECS)Associated Faculty member: Centre for Urban Science and Engineering (C-USE) Indian Institute of Technology Bombay, Mumbai

RECENTLY COMPLETED RESEARCH PROJECTS ON FLOOD RISK MAPPING

A comprehensive mapping of flood risk in changing climate: An application to Jagatsinghpur District, Orissa

Collaborators: IIT Bombay and National Remote Sensing Centre, Hyderabad

Sponsored by: STC-IITB-ISRO (2014-18, Completed)

Main deliverables: Projection of extreme rainfall events rainfall from GCM outputs, using

statistical and robust downscaling techniques. Combined 1D and 2D hydrodynamic flood modelling using MIKE

FLOOD Evaluation of Social vulnerability of the entire study area based on the

available demographic information and recent census data To generate flood risk map for the entire study area aggregating

information from flood lines, social vulnerability and LU/LC.

Near-Real-Time Urban Flood Forecasting System Collaborators: IIT Bombay, University of Maryland, Northeastern

Univ., and CDAC, PuneSponsored by: MoES, GoI (2014-2018, Completed)

Main deliverables: Improving global forecast system of extreme precipitation events

with regional statistical model: Application of quantile-basedprobabilistic forecasts over Mumbai

Optimal selection of canopy layers, physics options for WRFparameterization for an urban catchment: An application to aflood forecasting system for Mumbai, India

Generation of flood inundation maps under extreme rainfallscenarios

Design of an expert system for flood forecasting and management for the city of Chennai

Collaborators: IIT Bombay, IIT Madras, IISc Bangalore, Anna University, National Remote Sensing Centre (Hyderabad), ICMOM (Chennai),

Sponsored by: Office of the Principal Scientific Advisor, GoI (2016-19, Completed)

Main deliverables: Design of an real time expert system of flood forecasting 3-D visualization of flood propagation

Riverine

Urban

Urban

CHENNAI FLOOD FORECAST TEAM

30 Scientists from 8 Institutes First of its kind in India Institutes

IIT Bombay IIT Madras IISc Bangalore Anna University NCCR (formerly ICMAM), MoES IMD, MoES INCOIS, MoES NCMRWF, MoES

3<Rivers+Estuary+Coast+Urban infrastructure+Water structures>

OVERVIEW OF THE PROBLEM AND COMPLEXITY

CHALLENGES Simulations of urban precipitation: challenging task due to

multiple factors Fine-resolution urban DEM: either classified or not

available The Storm Water Drainage (SWD) for Chennai is a

complex system and the lack of necessary data like invert level, crown etc.

The complex building layer for an urbanized city like Chennai to be modelled using the Flexible Mesh approach.

Forecasted precipitation: spatial bias 3-way coupled flooding modelling: instability Lack of integration between multiple factors High computing time requirements for simulations of flood

inundation and velocity

5

Chennai Municipal Area (CMA)

LiDAR extent

Greater Chennai Corporation (GCC)

Figure. Selection of study area (as per the available data) for flood modelling

Selection of study area

HEC-HMS & HEC-2DIIT MADRAS

Hydrological Modelling

HydraulicModelling

• Chennai Metropolitan Area (CMA) excluding the portion covered by the LiDAR data• The discharge from the hydrological modelling is used as input data to MIKE FLOOD

MIKE FLOODIIT BOMBAY

• The LiDAR extent (orange shaded portion) is considered as the study area• A comprehensive 1D-2D flood modeling framework (flexible mesh)

Overall Framework

For Chennai: Forecasts Available from NCMRWF• 44 ensemble forecasts released on everyday around 3 PM with 0 hrs

GMT initial condition• Deterministic Forecasts released every 6 hours with updating the

initial condition• Challenges:

• Modeling Uncertainty• Understanding forecasts at a

fine resolution• Qualitative assessment of

forecasts based on users’ choice

Year Dates Ensembles2007 Nov 1-Dec 31 232008 Nov 1-Dec 31 232009 Nov 1-Dec 31 232010 Nov 1-Dec 31 232011 Nov 1-Dec 31 232012 Nov 1-Dec 31 232013 Nov 1-Dec 31 232014 Nov 06-Dec 31 112015 Nov 01-Dec 27 11

HINDCAST DATA AVAILABILITY (NCMRWF)

RG Stations in and around Chennai

Station ID Station Name Location Years43278 Minambakkam 13°, 80° 11' 2007, 2008,

2010, 2012, 2013, 2015

43279 Nungambakkam 13° 4', 80° 15' 2007, 2010, 2011, 2013(Dec), 2014, 2015

HOURLY DATA AVAILABILITY

SL Station Location Data

1 TIRUPATI 13° 40', 79° 35' 2009-14

2 KANCHIPURAM 12° 48', 79° 42'

2007, 2009, 2010-14

3 MINAMBAKKAM 13° 4', 80° 15' 2007-2014

4 TIRUTTANI 13° 12', 79° 36'

2007,2009-10, 2012-14

5 TIRUVANNAMALAI 12° 18', 79° 06'2009-2014

6 NUNGAMBAKKAM 13° 4', 80° 15'

2007,2010,2011-14

Daily Rainfall Data Availability (Year 2000 onwards)

Rainfall forecast: training algorithm

44 Ensemble• Ensemble 1• Ensemble 2• Ensemble 3

• Ensemble 44

Maxima

Mean

Minima

Quantile Regression

Station Level Data

Initial Condition: 20171031

Nungambakkam

Date: 2015/12/01

Initial Condition: 20180221

Minambakkam

Initial Condition: 20171031

Flood Data Bank

• Cases• Return Periods (2, 5,10, 25, 50, 75, 100 and 200 years)• Storm Duration (1, 3, 6, 12, 18, 24 hours)• Past Condition (Wet, Normal and Dry)• Tide Conditions (6 conditions, HH and LL with 3 types of

cyclones)• Simulations Completed: 796

Forecast Lead Time

Day 1 Day 2 Day 3

Day 03 PM IST

Meteorological Forecasts Released

Day 05 PM IST

Max Flood Inundation for Next

3 days from Data Bank

44 ensemble forecast with 0 hrs GMT IC

Tide Forecast

U/S Hydrologic Forecasts

Past Conditions

Algorithms (0-72 Hours Prediction)

Peak Rainfall

Total Rainfall

Highest Tide

Past Condition

Flood Inundation Level

Forecasted Rainfall

80pc

85pc

90pc

95pc

99pc

Forecasted Tide

Past Condition:Based on past 3 days rainfall

Look up table

Search in Data Bank

Flowchart with Real Time Flood Simulations at 6 hrs Interval with Single Member Forecast

Forecasted Inundation (Different Percentile)

95 and 99 PC Showing Flood Inundation

Yes No

Real time simulations at ICMAM at 6 hour interval

No Real time simulation

Tide-Surge modeling

Scenarios

WORK GROUPWORK GROUP Dr. K SrinivasaMr. PLN Murty

Prof. Manasa R. BeheraMs Maneesha SebastianMr. Gowrishankar C

Computational Domain

Discretization with unstructured mesh

Bathymetry and bottom friction

Computational Domain

Discretization with unstructured mesh

ADCIRC+SWAN (Ocean Circulation +

Wave Model)

Storm Surge

Model computed storm tide (surge + tide) ANIMATION

PAST PROGRESS

Tide-Surge modelingComputational

Domain

Discretization with unstructured mesh

Bathymetry and bottom friction

Computational Domain

Discretization with unstructured mesh

Scenarios

ADCIRC+SWAN (Ocean Circulation +

Wave Model)

Storm Surge

Maximum water level for Cyclone

VALIDATION

Tide-Surge modelingComputational

Domain

Discretization with unstructured mesh

Bathymetry and bottom friction

Computational Domain

Discretization with unstructured mesh

Scenarios

ADCIRC+SWAN (Ocean Circulation +

Wave Model)

Storm Surge

SCENARIOS

CYCLONE CATEGORY

Cyclonic Storm (CS)Severe Cyclonic Storm (SCS)

Very Severe Cyclonic Storm (VSCS)

TIDE LEVEL

Highest High Water Spring (HHWS)

Lowest Low Water Spring (LLWS)

SCENARIOS

1. HHWS-CS 4. LLWS-CS

2. HHWS-SCS 5. LLWS-SCS

3. HHWS-VSCS 6. LLWS-VSCS

U/S Hydrologic Modeling

• Used Model: HEC-HMS

Flood Modeling Framework A complete three-way hydrodynamic flood modeling in a coastal urban catchment

1D river flow

2D overland flow

River-overland flow interaction (1D-2D)

Tide-river interaction

Sewer-overland flow interaction (1D-2D)

1D sewer flow

Sewer -river interaction (1D-1D)

Schematic diagram of a coastal urban catchment

Rain

SW treatment plant

1. Overland flow2. River/channel flow3. Sewer flow

MIKE FLOODMIKE FLOODMIKE 11 MIKE 21 MIKE URBAN

• MIKE 11 is a fully dynamic one-dimensional modelling tool for bothsimple and complex river and channelsystems flood simulation.

• Tidal and storm surge studies may beperformed using MIKE 11 in rivers andestuaries.

• MIKE 11 has in-built rainfall-runoffeditor which provides facility ofparameterization, data inputting, evenediting of final results.

• various models in-built in MIKE 11 areNorth American Mesoscale Model (NAMModel), Unit Hydrograph Module(UHM), Soil Moisture Accounting Model(SMAP), Urban rainfall-runoff model [a.Time/area method b. Non- linearreservoir (Kinematic wave) method],Flood estimation handbook model (FEHModel).

• MIKE 21 Flow Model is a modeling system for2D free-surface flows.

• MIKE 21 is used in wide range of hydraulic andrelated phenomenon.

• Modelling of tidal hydraulics• Storm surges

• MIKE 21 is having capability to model floodingscenarios considering tidal impact in river.

• This module is commonly called as TidalAnalysis and Prediction Module [MIKE 21 usermanual, 2007].

• This tool analyse time series of hourly tideheights for a specified period of time usingAdmiralty method and Institute of OceanSciences (IOS) Method.

• Majorly this tool is used for:• Analysis of tidal heights• Analysis of tidal currents• Prediction of tidal heights• Prediction of tidal currents

• MIKE URBAN is a complete integration ofGIS and water modelling especially for urbanwater modelling applications.

• Some important applications are:• Storm water management• Prediction of local flooding• Contingency planning and risk

assessment• Water quality assessment

• SWMM and EPANET is in-built in MIKEURBAN for storm water & sewer modellingand water distribution modellingrespectively.

• MIKE URBAN collection system-rainfall-runoff module includes MOUSE engine forrainfall-runoff computation.

• In-built Rainfall-runoff models in MIKEURBAN are: (a) Time-Area method (b)Kinematic wave model (c) Linearreservoir model (d) Unit Hydrograph model.

Input: DEM, Rainfall time series, Tidal time series , Bathymetry, Drainage network layout, River cross section, Time series of river stage data

Output: Discharge-velocity relationship curve, Flood inundation map

Research component: No past effort on urban flood modelling considering extreme rainfall and tidal influence using MIKE Flood

Urban Flood Modeling

Performance of Flood Model

We acquired the maximum observed depth for407 points during the December 2015 floodevent in Chennai. These 407 validation pointswere used to validate the MIKE FLOOD model.

Real Time Data Collection

10 Automatic Weather Stations (AWS)5 Automatic Rain Gauges (ARG)6 Radar type Automatic Waterlevel recorders

ForecastDay

80percentile

85percentile

90percentile

95percentile

99percentile

01.12.2015

How does the model work for 2015 flood?

InitialCondition

ForecastDay

80percentile

85percentile

90percentile

95percentile

99percentile

31.10.2017

01.11.2017 No Flood No Flood

02.11.2017 No Flood No Flood No Flood

03.11.2017 No Flood No Flood

A Recent Example

Visualization of Flood

Acknowledgements

• Organizers: National Remote Sensing Centre (NRSC), ISRO & Central Water Commission (CWC), MoWR RD & GR Under National Hydrology Project

• Office of PSA, GoI• IIT Madras, IISc Bangalore, Anna University, INCOIS, NCCR, IMD• Greater Chennai Corporation• Centre for Environmental Science and Engineering /// Department of

Civil Engineering /// IDP in Climate Studies /// Centre for Urban Science and Engineering; Indian Institute of Technology Bombay

• Ph.D. students• Danish Hydraulic Institute (DHI), New Delhi and Pune

Thank you<skarmakar@iitb.ac.in>