PowerPoint Presentation

Presented By:Group XShazzadur Rahman 1116016Abir Mohammad 1116017Sabiha Tabassum - 1116025FLOOD FORECASTINGPresented To:Dr. Md. Mostafa AliAssociate professor,Department of Water Resources Engineering, BUET.

OverviewIntroductionRole of Flood Forecasting in Flood MitigationDesign ConsiderationsData RequirementsFlood Forecasting Methods & ModelsChallenges in BangladeshCase Studies

Introduction

What is Flood Forecasting?Flood forecastingis the use of forecastedprecipitationandstreamflowdata inrainfall runoffandstreamflow routingmodels to forecast flow rates and water levels for periods ranging from a few hours to days ahead.

What is Flood Warning?Flood warning is the task of making use of these forecasts to make decisions about whether warnings of floods should be issued to the general public or whether previous warnings should be rescinded or retracted.

Relation Between Flood Forecasting and Flood WarningFlood forecasting is the prerequisite for flood warning.Flood warning is the outcome of flood forecasting.

Components of Flood Forecasting & Warning System

Collection of Real Time DataPreparation of Forecast Warning & Information MessagesCommunication & Dissemination of Such MessagesInterpretation of The Forecast & Flood ObservationsResponse to The WarningsReview & Improvement of The System

Role of Flood Forecasting in Flood Mitigation

Prerequisite for successful mitigation of flood damage. Can be effectively combined with other measures for flood prevention such as retention, land use and structural measures, flood emergency and public awareness.Plays vital role in flood management when no preventive or defence measures can be completely effective.Increases flood resilience of the flood affected people.

Evacuation of Vulnerable Groups And Moving of AssetsShelter

Installation of Flood Resilience Measures (e.g. Sandbags, Property Flood Barriers)

Temporary Flood Defence

Design Considerations

Basic ConsiderationHydromorphological Characteristics of The Basin, Topography, GeologyShape, Boundaries And Content of A Water Body.

Main Physical Processes Occurring During Hydrometeorological Events

The Type of Service That is Required or Can be Achieved Technically And EconomicallyThreshold-based flood alert: qualitative estimation of the increase in river flow or levelFlood forecasting: more definitive service based on the use of simulation tools and modellingVigilance mapping: development of the site-specific warning approachInundation forecasting: It requires the combination of a hydrological or hydrodynamic level-and-flow model with digital representation of the flood plain land surface

Forecast Lead TimeBasic Principle: minimum period of advance warning necessary for preparatory action to be taken effectively Concept of lead time has to be flexible

DATA REQUIREMENTS

Hydrological dataMeteorological dataTopographic dataOther information and data

Hydrological DataDischarge & Water level

Stream Gauge

Meteorological dataRainfall intensity and duration, precipitation forecasts and past data

RAINGAUGE

56 Raingauge stations of Bangladesh

Rainfall Measurement Using Radar

Topographic dataInformation about the elevation of the surface of the Earth

Topographic map of Bangladesh

DEM of Bangladesh

(a) Population and demographic data to indicate settlements at risk;(b) Inventories of properties at risk;(c) Reservoir and flood protection infrastructure control rules;(d) Location of key transport, power and water supply infrastructure;(e) Systematic post-flood damage assessments.

Other information and data

FLOOD FORECASTING METHODS AND MODELS

The multi-model approach to rainfallrunoff modelling and forecasting

SPECIAL-CASE MODELSStorm surge Two types of models, statistical and dynamic, can be used to forecast storm surgesFlash floodsdistributed hydrological modelsUrban Floodingvery high spatial and temporal resolution in data, modelsReservoir flood controlEstimates incoming flood and incorporates it with d/s riparian area

ExamplesMIKE FLOODDelft-FEWS

MIKE FLOODIncludes 1D and 2D flood simulation enginesmodel any flood problemthree-way coupled modelling toolMIKE HYDRO River + MIKE URBAN+ MIKE 21

Delft-FEWSprovide an open shell for managing the data handling and forecasting process

In Bangladesh, FFWCuses GIS techniques extensively to display water level and rainfall status flood forecast model MIKE 11 FF

LIMITATIONSnot sufficient on its own to reduce riskModels require continuous improvisation (calibration)Cost of running the systemCost of sourcing meteorological datasystem inaccuracies may lead to complacencyavailability of communication channels requires resource

Challenges in Bangladesh

Data Collection57 transboundary river Location of Bangladesh in GBM basin

Tidal Influence on RiverUncertainty in Forecast of Rainfall

Other ChallengesLimited ResourceLimited Skilled Manpower

Case Studies

Case Study: BANGLADESH

Study Area: Bangladesh

Performed by: FLOOD FORECASTING & WARNING CENTRE (FFWC) of BWDB

Model Based on: MIKE11 FF conceptual Hydrodynamic model

DEM Used: 300m SRTM

Objectives of FFWCForecasting: Predicts the occurrence/magnitude of flood.

Interpretation: Warn people about the extent of flooding.

Dissemination: Communication/distribution of warning messages to disaster management agencies & vulnerable communities.

Response: Preparation/action by concerned agencies and threatened communities for protection against flood hazards.

Review & Analysis: Continuous monitoring of the performance of the various components.

StationsRainfall Stations: 56

Overview of Flood Forecasting

Internet

Data Entry & Retrieval System

Water Level Status shown in FFWC Website

Types of Flood ForecastingProbabilistic Method (10 days)

Deterministic Method (5 days)

FLOOD FORECAST EVALUATION, 2014EVALUATION CRITERIA OF FLOOD FORECAST PERFORMANCE:

Two statistical criteria considered:Mean Absolute Error, MAECo-efficient of Determination, r2

MAE: Mean of absolute difference between Observed and Forecast levels.

r2: Co-efficient of Determination for the correlation of Observed and Forecast water levels.

PRE-DEFINED SCALES TO EVALUATE FORECAST PERFORMANCE

Simulations were made for maximum 120 hrs.Flood Forecast generated at 54 stations/points.For 1-day forecast 98.15% for the stations are within the range of Good and Average.For 5-days forecast 59.26% stations are in the range of Good and Average.

Deterministic Forecast Performance (2014)

Weaknesses

Estimation of upstream inflows from India Quality of the data Inadequate rainfall radar stationsFlood mapping accuracy limited by DEM resolution of 300mModest investment in software and staff resourcesUpstream boundary estimationLack of integration between the organizationsForecast lead time 3-5 days, for rural areas to support agricultural activities, long term forecasts needed.

Case Study: ENGLAND & WALES

Study Area: England & WalesPerformed by: Flood Forecasting Centre (FFC), a partnership between the Environment Agency & the Met Office.

Separate operational forecasting rooms in each of the eight Environment Agency Regions.

Warning Time: 30 minutes to 72 hours.

ObjectivesMonitoring of environmental variables that may lead to flooding

Forecasting of possible flood

Warning, in the sense of decision making when flooding risks are realizable

Dissemination of warning messages

Response to the threat.

Monitoring Network4500 locations across England.

1100 Rain gauges1300 River flow2000 River level

Performance Evaluation (2013-14)

FIG: Flood Risk Matrix & Probability of Detection (Hits & Misses) for 2013/14

Coastal Flood Forecasting on 5 & 6 December, 2013The largest coastal flood for 60 years on the east coast and for 30 years on the west coast.A deep Atlantic storm brought severe gale force winds with gusts up to 100mph forcing a huge surge down both the west and east coasts of the UK.Increased WL & wave heights over three successive tides starting on the afternoon of Thursday, 5 December until Saturday, 7 December.

Potential surge was first spotted 7 days ahead.

The risk level in the Flood Guidance Statement was escalated during that week up to high likelihood of severe flooding (red).

Government contacts & emergency responders were given good notice of the developing situation.

Coastal surge & wave models developed were hosted on the Met Office supercomputer, helped inform critical decision-making.

As the surge moved down the North Sea the FFC maintained a round the clock commentary on live observations against the forecast.

How Flood Forecast Saves Lives19532013307 people deadNo Death24,000 properties flooded along the East Coast.Only one tenth of the level of property flooding.

Thank You