Progress on work package 1 Changing Coastlines: data assimilation for morphodynamic prediction and predictability Progress on work package 1 University of Reading: Tania Scott, Sarah Dance, Mike Baines, Amos Lawless, David Mason, Nancy Nichols, Polly Smith and Peter Sweby POL: Roger Proctor

Will it work? Data assimilation for a coastal area morphodynamic model: Morecambe Bay Tania Scott & David Mason Objective: to improve a medium-term morphodynamic model of Morecambe Bay by assimilating waterline observations of bathymetry into the model run

The method We developed a morphodynamic model to predict changes in Morecambe Bay bathymetry caused by tide induced sediment transport This model was very simplistic compared to the best engineering models because we wanted to investigate the benefits of using data assimilation in the model rather than develop a state-of-the-art model in itself We ran the model for 3 years with and without data assimilation

The data - waterlines An image of the land-sea boundary Water elevation ( bathymetry) An image of the land-sea boundary (satellite SAR image © ESA) Water elevation predicted along the boundary by a hydrodynamic model with surge component

The data assimilation For the data assimilation we used 13 waterlines acquired at intervals over the 3-year period Each waterline was assimilated at its validity time using a method called optimal interpolation More weight was given to the observations than to the model background Information from each waterline was spread to a distance of approximately three model grid cells

Examples of assimilated waterlines Difference between initial and observed bathymetries cool colours – model bathymetry needs to be lower green – model bathymetry is good warm colours – model bathymetry needs to be higher

Results for our 3-year model run Observed change in bathymetry Modelled change in bathymetry without data assimilation Modelled change in bathymetry with data assimilation Qualitative assessment: data assimilation successfully introduced erosion along the Ulverston channel Quantitative assessment: data assimilation improved both the current bathymetry and the predictive performance of the model

Conclusions Which led to the Changing Coastlines project! We showed that a morphodynamic model of Morecambe Bay could be improved by using data assimilation Results suggested that data assimilation could benefit morphodynamic models by improving the current model bathymetry helping to better predict future bathymetry Thus we should continue to develop this technique Which led to the Changing Coastlines project!

Work package 1 Develop morphodynamic models for each study site Develop data assimilation schemes for each model Acquire and process data for generation of initial bathymetries data assimilation model validation Evaluate model performance predictability and uncertainty with and without data assimilation Develop an aggregate morphological model

The models The Morecambe Bay model The Dee estuary model will be based on our old Morecambe Bay model The Dee estuary model will be similar to the Morecambe Bay model they are both enclosed tide dominated environments The east Lincolnshire coast model will be different from the others it is an open coastline environment different physical processes may dominate e.g. waves are likely to be more important

The Morecambe Bay model We have been considering improvements to our old Morecambe Bay model, in consultation with the Proudman Oceanographic Laboratory HR Wallingford The consensus is that the old model works OK so don’t break it by making it too complicated However we should increase the resolution (what impact does this have?) include a critical current for sediment transport possibly include waves (by possibly using SWAN)

Computing platforms We have ported the old Morecambe Bay model to newer platforms: My Linux workstation the model now runs much faster than before (approximately 12 hours per model year) which is good for development and testing The University of Reading Condor pool (with assistance from the Reading e-science Centre) on which we can run large numbers of models simultaneously which will be good for generating data assimilation statistics

The data We need lots of observations of bathymetry for generation of initial model bathymetries data assimilation model validation Possible data sources are airborne LiDAR ship-based swath bathymetry waterlines ground surveys shore-based X-band radar

The Dee estuary Each LiDAR survey covers most of the estuary Date Data type Source April 2003 LiDAR Environment Agency July 2003 Swath bathymetry of main channel February 2004 May 2004 October 2006 Apr 2003 – Aug 2006 30 SAR images European Space Agency ? X-band radar of estuary mouth Proudman Oceanographic Laboratory Each LiDAR survey covers most of the estuary We will run the Dee model from April 2003 to October 2006 the April 2003 LiDAR data will be used for initial model bathymetry the October 2006 LiDAR data will be used for model validation all other data will be used for both model validation and data assimilation

LiDAR images of the Dee estuary April 2003 October 2006

Observed change in bathymetry, April 2003 to October 2006 Dee estuary Observed change in bathymetry, April 2003 to October 2006

SAR image - georeferencing Get a root mean square location error of about 25m (2 SAR image pixels) Digital Ordnance Survey map from EDINA Digimap Look along edge of estuary for road/rail/ditch junctions field corners

SAR image - waterline extraction Automatic waterline extraction software previously developed by David Mason The extracted waterline needs correcting for false waterlines - missing waterlines The corrected waterline then needs to be assigned height values, by running a hydrodynamic model with surge component

Morecambe Bay Each LiDAR survey covers only a small amount of the Bay Date Data type Source December 2003 LiDAR Environment Agency November 2004 March 2005 November 2005 February - May 2006 2003 - n SAR images European Space Agency Each LiDAR survey covers only a small amount of the Bay mainly along the shore but some over the channels We will start the Morecambe Bay model run sometime in 2003 the initial model bathymetry will be generated from waterlines

LiDAR image of the Ulverston channel, Morecambe Bay, November 2004

Next steps We need to get the models up and running for the Dee estuary Morecambe Bay To do this we need to acquire SAR images for Morecambe Bay generate initial bathymetries (which includes lots of SAR processing for Morecambe Bay) determine tidal forcing parameters at the open boundaries implement a critical current for sediment transport possibly include waves Then we can start work on the data assimilation

Morecambe Bay at sunset Scott T.R. and Mason D.C., 2007. Data assimilation for a coastal area morphodynamic model: Morecambe Bay. Coastal Engineering, 54(2), 91-109.