Reducing regional flood and erosion risk from wave action on the Channel Coast

Reducing regional flood and erosion risk from wave action on the Channel Coast Jack Eade, Channel Coastal Observatory Travis Mason, Channel Coastal Observatory Uwe Dornbusch, Environment Agency Tim Pullen, HR Wallingford Jonathan Simm, HR Wallingford

The story for today (the scientific approach) Flood and coastal erosion management New understanding and guidance Something is not right Present experiment Hypothesis and evidence gathering Other studies

Flood and Coastal Risk Management Astronomical Water level Surge Bi-modal Setup Broad Multimodal Water Period spectrum Complex Narrow Wind Waves Height Swell Will water go over the defence if yes, how much? Narrow band Direction Broad band Hard Constant Bi- or multimodal Defence Mixed Sand Soft Profile shape change Total volume change Gravel Mixed

The issue

What are bi-modal waves (simple) Wind wave (5 seconds) Swell wave (15 seconds) Bi-modal waves

Wave examples Wind waves Swell waves

Chesil Beach 15-02-2011

Other studies I [Bi-modal] conditions are believed to be important to the design of shingle beach recharge schemes and to some coastal structures. As yet little work has been done on defining the physical processes involved in the interaction between complex sea conditions and beaches. The results of this study can be used by coastal engineers to improve beach design, but no formal design tools have yet been developed. Coates, T.T., Hawkes, P.J., 1989. Beach recharge design and bi-modal wave spectra. Hawkes, P.J., Bagenholm, C., Gouldby, B.P., Ewing, J., 1997. Swell and bi-modal wave climate around the coast of England and Wales (No. SR 409). HR Wallingford Ltd. Bi-modal conditions appear to have a particularly significant effect on the profile performance of beaches, impacting on run-up, crest cut-back, and overwashing of gravel barriers and on the overtopping of seawalls. Longer-term data sets are required to develop a robust empirical framework to quantify the impacts of these conditions. Bi-modal wave conditions may need to be considered as a design variable for some areas of the English Channel coast, in addition to the usual extreme wind-wave conditions. Alterative definitions of wave climates are needed to enable a statistical description of bi-modal conditions. New design methodologies are required to consider the impacts of bi-modal conditions on the design of coastal structures. Bradbury, A.P., Mason, T.E., Poate, T., 2007. Implications of the spectral shape of wave conditions for engineering design and coastal hazard assessment - evidence from the English Channel. Presented at the 10th International Workshop on Wave Hindcasting and Forecasting, 11-16 Nov. 2007, Oahu, Hawaii.

Other studies II large scale experiments López de San Román-Blanco, B., Coates, T.T., Holmes, P., Chadwick, A.J., Bradbury, A., Baldock, T.E., Pedrozo-Acuña, A., Lawrence, J., Grüne, J., 2006. Large scale experiments on gravel and mixed beaches: Experimental procedure, data documentation and initial results. Coastal Engineering 53, 349 362. Williams, J., Masselink, G., Buscombe, D., Turner, I., Matias, A., Ferreira, Ó., Bradbury, A., Metje, N., Coates, L., Chapman, D., others, 2010. BARDEX (BARRIER DYNAMICS EXPERIMENT): A LABORATORY STUDY OF GRAVEL BARRIER RESPONSE TO WAVES AND TIDES.

Recent projects Run-up Tool for Southeast Coast Beach Management Plan (EA, HR Wallingford, Coastal Groups), 2013 Field data to develop empirical prediction tool explicitly looking at wave spectrum

Recent projects New Understanding and Prediction of Storm Impact on Gravel Beaches (CCO, HR Wallingford, EA), 2014 Focussed on gravel to develop a process based prediction tool

SMP Name SMP Number SMP Lead Authority Approval Date Policy Unit ID Policy Unit Name (Location) Action Reference Action Description Activity North Solent 13 New Forest District Council May-11 SMP wide SMP wide 22 Commission region-wide wave climate risk studies to identify impacts of bimodal wave period conditions on design risk of all structures and beach systems and assess overtopping and breach potential based on uncertainties identified in SMP2 and SCOPAC studies, in partnership with neighbouring SMPs Regional Studies Isle of Wight 14 Isle of Wight Council May-11 SMP wide SMP wide 0.15 Region wide wave climate risk studies to identify impacts of bimodal wave period conditions on design risk of all structures and beach systems; to include assessment of overtopping and breach potential. Based on uncertainties identified in SMP2 and SCOPAC studies, in partnership with SMPs for North Solent and Poole and Christchurch Regional Studies Continued evidence gathering Poole and Christchurch Bay 15 Bournemouth Borough Council Aug-11 SMP wide SMP wide 0.16 Region wide wave climate risk studies to identify impacts of bimodal wave period conditions on design risk of all structures and beach systems; to include assessment of overtopping and breach potential. Based on uncertainties identified in SMP2 and SCOPAC studies, in partnership with SMPs for North Solent and Isle of Wight. Regional studies FDGiA funds

Present project Systematic approach to bi-modal waves using generic and site specific set-up Beach response to continued waves

The way forward Guidance from this project EurOtop update Defra / EA R&DD projects: Tools for better prediction of mixed beach responses (AM) Beaches may need to be bigger (wider / higher) Beaches may need to be replaced with hard structures (complete / partially) Beaches need space to move back Alternative adaptation to increased risk required

Questions