Challenges in fluvial and coastal forecasting in Wales Andrew How and Sam Mitchell
A story in four chapters An introduction to Natural Resources Wales Influence of FEWS on flood forecasting River Flood Forecasting challenges ; solutions and examples Coastal Flood Forecasting challenges ; solutions and examples
A story in four chapters An introduction to Natural Resources Wales
Where is Wales? We are here!
What is Wales? Area of 20,779 km 2 Mostly mountains Also 1200 km of coastline
Who are Wales? Population of around 3 million
The Environment in Wales Wales has had its own government, the National Assembly for Wales, since 1999 Prior to April this year (2013), Environment Agency Wales had responsibility for the environment in Wales Since April 2013, Environment Agency Wales separated from the rest of the EA, and merged with the Countryside Council for Wales and the Forestry Commission Wales to form: Natural Resources Wales Cyfoeth Naturiol Cymru
Natural Resources Wales Our purpose is to ensure that the natural resources of Wales are sustainably maintained, enhanced and used, now and in the future. We are the principal adviser to the Welsh Government on the environment We have over 2,000 staff, an operating budget of 177m, and we manage 7% of the land area of Wales We are one of the biggest providers of outdoor recreation in Wales: We are a 24 hour emergency responder and deal with approximately 9000 reported incidents a year that include flooded homes, polluted rivers and illegally dumped waste
Wales Flood Forecasting Team Andy Wall, Flood Forecasting Team Leader Andrew How, Technical Specialist Sam Mitchell, Technical Specialist Christopher Williams, Technical Specialist Rachel Skinner, Team Member 1 Sian Hurley, Team Member 1 Lisa Davies, Team Member 1 Sara Lane, Team Member 2
A story in four chapters Influence of FEWS on flood forecasting
Before Natural Resources Wales 2007 April 2006 2005 2004 Pre-2004 First centralised flood forecasting service for Wales (coastal) NFFS configuration training and go live Site acceptance testing of NFFS first introduction to FEWS (National Flood Forecasting System NFFS) Dispersed forecasting service. Correlations / unit hydrograph calculations / coastal lookup tables
Forecasting Origins
Before Natural Resources Wales 2007 Sept 2007 April 2006 2005 2004 Pre-2004 Start of a centralised river flood forecasting service in Wales First centralised flood forecasting service for Wales (coastal) National Flood Forecasting System (NFFS) configuration training and go live Site acceptance testing of NFFS first introduction to FEWS (National Flood Forecasting System NFFS) Dispersed forecasting service. Correlations / unit hydrograph calculations / coastal lookup tables
Forecasting Origins
Before Natural Resources Wales 2011 April 2007 Sept 2007 April 2006 2005 2004 Pre-2004 Boundary change with Environment Agency Midlands Start of a centralised river flood forecasting service in Wales First centralised flood forecasting service for Wales (coastal) NFFS configuration training and go live Site acceptance testing of NFFS first introduction to FEWS (National Flood Forecasting System NFFS) Dispersed forecasting service. Correlations / unit hydrograph calculations / coastal lookup tables
Before Natural Resources Wales 2011 Sept 2011 April 2007 Sept 2007 April 2006 2005 2004 Pre-2004 Roll out of Wales Coastal Model Boundary change with Environment Agency Midlands Start of a centralised river flood forecasting service in Wales First centralised flood forecasting service for Wales (coastal) NFFS configuration training and go live Site acceptance testing of NFFS first introduction to FEWS (National Flood Forecasting System NFFS) Dispersed forecasting service. Correlations / unit hydrograph calculations / coastal lookup tables
Before Natural Resources Wales 2013 April 2011 Sept 2011 April 2007 Sept 2007 April 2006 2005 2004 Pre-2004 Creation of Natural Resources Wales Roll out of Wales Coastal Model Boundary change with Environment Agency Midlands Start of a centralised river flood forecasting service in Wales First centralised flood forecasting service for Wales (coastal) NFFS configuration training and go live Site acceptance testing of NFFS first introduction to FEWS (National Flood Forecasting System NFFS) Dispersed forecasting service. Correlations / unit hydrograph calculations / coastal lookup tables
HYADES!
HYADES!
HYADES! Issues for NFFS Point forecast - non-continuous times series Non-cardinal timestep Need to compare non-continuous, noncardinal time series with thresholds Four possible run-off factors one of which includes a baseflow
HYADES! Flood Forecast at 11:00 Flood Warning threshold will be exceeded at 12:30
HYADES! What actually happened Flood Warning threshold exceeded just before 12:30
Summary NFFS key component of flood forecasting More complex does not necessarily equal better Different solutions to different problems important to be able to adapt
A story in four chapters Coastal Flood Forecasting challenges ; solutions and examples
Challenges Large storm surge risk Sections of coastline exposed to large Atlantic swell waves and strong onshore winds 1200km of coastline Significant coastal communities 2 nd largest tidal range in the world with complex tide / surge interaction
Utilising latest meteorological data
Improving data sets / Performance measures
Wales Coastal Model Model built using NFFS and is integral to the system Chainage calculations done within config files Imported gridded data inputs to wave transformation models This data is re-imported and combined with chainage calcs to drive an overtopping model
Wales Coastal Model Analyse data at each stage Able to calibrate model post-event Required changes can be effected through the NFFS config
Verification
Summary Incremental improvements Verification vital to understanding strengths and limitations of coastal forecasting Understand processes as well as modeled results Longer range forecasts may bring uncertainty but this can bring an understanding of the level of risk Improving communication around forecasts builds understanding and effectiveness
A story in four chapters River Flood Forecasting challenges ; solutions and examples
Challenges of flood forecasting in Wales 220,000 properties at risk from rivers & sea 1 in 6 live or work on the floodplain 8 billion worth of assets at risk Steep topography = fast responding rivers
Typical river response From normal to severe event in less than 2 hours
Weather radar coverage in Wales
Wales fluvial model coverage 2007
Wales fluvial model coverage 2010
Wales fluvial model coverage 2013
Wales fluvial model coverage 2016
Wales fluvial model coverage 2019
Using NFFS for Model Performance Testing Forecast 5 hours before peak (with perfect rainfall knowledge) Hourly forecast runs Performance testing using observed data up to time of forecast (T0) Hour by hour model runs tell you your lead time & accuracy only 1 hour here
Using NFFS for Model Performance Testing
Using NFFS for Post Event Analysis
Using NFFS for Post Event Analysis
St Asaph floods case study November 2012
St Asaph floods case study November 2012
St Asaph floods case study November 2012
St Asaph floods case study November 2012 Elwy catchment rainfall 26th to 27th Nov 12 1.8 1.6 1.4 1.2 Rainfall (mm) 1 0.8 0.6 0.4 0.2 0 26/11/2012 06:00 26/11/2012 12:00 26/11/2012 18:00 27/11/2012 00:00 27/11/2012 06:00 27/11/2012 12:00 Date/time Merged Rainfall forecast Observed rainfall at Gwytherin
St Asaph floods case study November 2012 Forecast timeline: Sunday 25 th 1800 GMT
St Asaph floods case study November 2012 Forecast timeline: Monday 26 th 0600 GMT
St Asaph floods case study November 2012 Forecast timeline: Monday 26 th 1800 GMT
St Asaph floods case study November 2012 Pont y Gwyddel to St Asaph correlated levels Developed Nov 2009 5 4.5 4 St Asaph (mald) 3.5 3 2.5 y = 1.1591x + 0.7024 R 2 = 0.9586 2 1 1.5 2 2.5 3 3.5 4 Pont Y Gwyddel (mald) Correlated levels Nov 26/27 event RES FAL N208 [...] RES FW N208 RES FW N204 Linear (Correlated levels)
St Asaph floods case study November 2012 Actual recorded peak level at St Asaph gauge from site survey
St Asaph, 27 November
St Asaph floods case study November 2012 Conclusions If no forecasting service, only two hours lead time from correlation warning at 3 am of overtopping at 5 am However: Met Office forecast was timely, accurate and consistent between NWP model runs Good communication between forecasting duty officers and professional partners Well calibrated model 9 hours lead time in which to prepare for evacuation If only all flood forecasting was that easy...
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