Formation, development and movement of ords along the Holderness coast (UK): A comparison between 1994–1998 and 2010–2020 in response to changing morphodynamic and hydrodynamic conditions

Abstract

Sediment input from the rapidly eroding Holderness till cliffs and shore platforms forms irregularly spaced higher inter-ord and lower ord beaches. The ords, by allowing increased tidal access and wave attack on the cliff toe and cliff face, increase erosion rates. This paper compares the formation, development and movement of ords in 1994–1998 and 2010–2020. Taken in spring and autumn, stereo-aerial photographs were used in 1994–1998 and aerial LiDAR and ortho-rectified aerial photographs in 2010–2020. To compare hydrodynamic conditions in the two periods Immingham tide, Leconfield wind and Hornsea wave data were used. The main results are consistent with earlier findings that ords form near Barmston where the shelter of Flamborough Head in northerly storms ceases and causes a longshore sediment movement divide. Coastal defences had a similar effect at Hornsea and Mappleton. Ord length measurements showed ords covering 23–35% of the coast in 1994–1998 and 20–40% in 2010–2020. Average cliff toe height in the later period was 3.05, 2.24 and 3.27mAOD in the north, centre and south ord parts, respectively. This allowed all High Water Spring Tides to reach the cliff toe at the ord centres under calm conditions on the survey dates. Higher beach levels north and south provided more cliff protection. Slower annual net average ord movement southwards of 0.36 km in 1994–1998 contrasted with 1.1 km in 2010–2020. Although the storm surges over 0.9 m at Immingham increased from 12 in the earlier period to 58 in the later period, of these only four and six, respectively raised the tide level to over 4.0 mAOD, above the cliff toe height throughout the ords. No major storms occurred in 1994–1998 compared with three in 2010–2020. No rhythmic inter-tidal features closely resembling ords have been found globally in the extensive literature, but more research into morphodynamic processes within ords is needed.