Civil engineering,

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HR Wallingford

• Civil engineering,
• environmental hydraulics, and
• water resources management

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Flood Forecasting and Warning UK and Overseas
Experience
James Dent Technical Director - HR Wallingford
Ltd
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Synopsis

• Examination of steps and sources of forecast
  material
• Information used to link rainfall and flood
  forecasts and warnings
• European research projects in flood forecasting
  and warning
• Bangladesh the first full-time flood forecasting
  and warning service

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How do we forecast?

• Using weather forecasts, weather radar and
  satellite imagery
• Rainfall-runoff model (using radar or raingauge
  data)
• River level-to-level correlations using upstream
  gauging stations
• Time of travel relationships
• Real time hydraulic river model (ISIS model)

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Types of weather forecast

• Seasonal/monthly too generalised
• Medium range,5 - 10 days. ECMRWF numerical
  weather forecasts, global model
• 2 - 5 day forecasts. Global model, daily weather
  charts
• 6hrs - 2-days. Mesoscale model charts and
  quantitative precipitation forecasts (QPF)
• 0 - 6hrs. Nowcasts mesoscale model and radar for
  QPF

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Weather forecasts for the Environment Agency

• - Daily Weather Forecast
• Days 1 and 2 sub-daily periods, 6 or 12 hours
• Quantity as a most likely maximum point fall
• Indication of confidence as or high, medium or
  low
• On area basis
• Days 3-5 24 hour totals Area or Region
• - Heavy Rainfall Warning
• Forecast for 12-24 hours ahead, on Area basis
• pre-set triggers on accumulations or intensities
• total accumulation
• peak intensity and timing of heaviest rainfall
  period

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Environment Agency river forecasts

• Flood Watch flooding from any river in a
  catchment is possible
• - use Met Office forecasts - particularly Heavy
  Rainfall Warnings
• - add value with knowledge of catchment
  conditions
• (Severe) Flood Warning flooding from a river is
  expected
• - river levels expected to reach a threshold when
  flooding to properties will commence
• - forecast of time when a given level will be
  reached
• - can be applied to a river reach or area

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FORECASTING PRECIPITATION FROM THE FLOOD
HYDROLOGISTS PERSPECTIVE
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Issues and Problems

• Definition in time and space
• Scale differences the mesoscale QPF model grid
  and the catchment size are seldom compatible
• How to apply QPF figure to a model lumped or
  distributed
• Accuracy the need for a consistent method in
  verification and assessment
• Operational limitations when and to what purpose
  can a QPF be applied?

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The next steps

• Achieve a high degree of consistency across
  Regions
• Clearer identification of purpose
• Match QPF information with flow forecast model
  requirements
• Apply QPF at various stages during the
  forecast/warning operation to establish benefits
• Implement an agreed method of verification and
  assessment

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Flood warning in Europe

• Catchments are considerably larger than UK. Time
  of travel models are effective.
• Problems of upper reaches within major
  catchments two tiers of flooding
• Trans-border rivers
• - data acquisition and sharing
• - compatibility of forecast methods
• - establishment of river basin management units
• - European Commission Research

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European Flood Forecasting System

• European flood forecasting system with 4-10 days
  lead time
• 1 km grid square basis
• Model small and large river basins
• Develop a large scale hydrological model
• Include uncertainties in the discharge forecast
• Set-up a prototype system
• Explore dissemination of results

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MITigation of Climate induced Hazards

• Concerted Action to cluster FP4 results (Jan 2001
  - May 2003)
• Floods, droughts and landslides
• Four workshops
• Climate change, forecasting, planning
• Emergency management in summer 2002 floods
• www.mitch-ec.net

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AChieving Technological Innovation in Flood
Forecasting

• Integrating results from several EC research
  projects
• Promotion of sustainable development reducing
  economic loss
• Improved public safety by non-structural methods
• Interdisciplinary links between meteorology,
  hydrology, hazard managers and users
• Forecast dissemination requirements

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Flood Forecasting and Warning in Bangladesh

• The author gratefully acknowledges Executive
  Engineer, Mr Salim Bhuiyan and his staff at the
  Bangladesh Flood Forecasting and Warning Centre
  for permission to use slides and material from
  their programme

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Features of flood forecasting in Bangladesh

• Floods happen every year, and are a significant
  feature of national activity
• Flood generating catchments lie 90 outside the
  country
• Time of travel and area inundation models
  (MIKE11/12)
• Rainfall flooding high volume, high intensity
• Radar rainfall and satellite imagery for QPF

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72 HOURS(11,12,13 August)CUMULATIVE RAINFALL
SURFACE MAP
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Features of flood forecasting in Bangladesh

• Dhaka local model - detailed monitoring and
  management
• Boundary conditions from main river model
• Sub-daily time steps
• Un-protected areas outside main flood embankment

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DHAKA CITY EXPERIMENTAL FLOOD MAP
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Features of flood forecasting in Bangladesh

• Extensive public dissemination
• Reporting network also serves as warning network
  to local authority
• Daily bulletin to high level government
  administration
• Web-site, giving tabular and graphical reports
  (hydrographs)
• Situation and seasonal review reporting

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The Flood Forecasters dream

• An isohyetal map of total and short period
  accumulations over catchment areas
• A set of limited area hyetographs at short time
  steps
• Accuracy within /- 2-5mm or /- 15?
• A full flood hydrograph
• These match the methods which a hydrologist would
  use in calculating a design flood.

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HR Wallingford
Knowledge to shape solutions