Session B.6: Understanding Hydro/Morpho-Dynamic Impacts for Design

Storm hours may not equate to coastal impact if water level is not included. Did you include the water levels at which the storms occurred?

At Great Yarmouth the tidal range is 2m reducing the significance of water level regarding beach exposure compared to other places around the UK shoreline. However, the more important point is that it is incorrect to consider the beach as a separate unit for storm exposure. At Great Yarmouth the on-offshore transport for a single storm event has been measured to equate to around 15% of the net alongshore annual sand movement. As a consequence, the behaviour of the shoreline is directly affected by storm activity occurring during water levels over the 2m tidal range acting on the sea bed from around the 5m below Chart Datum (CD) contour to the shoreline. The extent of on-offshore movement of sand from the beaches at Hopton was modelled using XBeach validated by beach profile data collected before and after a significant storm event in October/November 2010. It is therefore reasonable to ignore local water level fluctuations in any initial assessment of storm exposure - indeed to include such consideration as suggested is likely to effectively filter out important influences of storm activity on beach and shoreline behaviour.