SAND ACCRETION

Sand accretion is the most significant factor in the current development of the beach, which is currently rising at over 30cms per decade. It is important to note this is the underlying beach level. Windblown sand levels rise and drop but the overall trend is a significant rise, which therefore exacerbates windblown sand impacts.

Figure 13: This aerial image shows most of what we’ll call the ‘profile area’, which covers the area from Red Rocks to the new Lifeboat Station. Using satellite and other highly accurate ‘LIDAR’ scanning technologies, Wirral council have access to a wealth of useful data, including beach ‘profiles’. These are cross sections of the beach running 1,000 metres out from the promenade wall at nine points, each 200 metres apart, from the new lifeboat station to Red Rocks. Click here to view a high resolution version of this image, zoomable to 1,000%.
Figure 14: This chart shows the level of sand accretion at the Hoylake foreshore between 1982 and 2002. During these years the council conducted an annual ‘Beach Volume Analysis’. This showed a steady increase in rise until the late 1980s, after which the rate of sand accretion accelerated significantly. By 2002, the beach was rising at a rate of 30cms per decade. The chart discounts what was thought to be an ‘exceptional’ 70,000 cubic metre sand accretion in 1999. However in 2003, accretion of over 120,000 cubic metres was recorded.
Figure 15: This chart shows the beach profile from the bottom of Trinity Road, showing beach levels between 2000 and 2018. The ‘y’ (horizontal) axis shows chainage (distance) from the promenade wall. We can see that in 2000, at a Mean High Water Spring tide, we would need to walk out 60 metres to get our toes wet (a). By 2018, we would need to walk 190 metres to get our toes wet (b); a high tide tide cover reduction of 130 metres in less than 20 years.
The Mean High Water Spring tide cover of the beach is therefore receding by 75 metres every decade. Since the beach is getting higher, and tides are covering much less of the beach each year, it is inevitably getting drier.
Alderley Road Drainage 2015 Alderley Road Drainage 2020
This comparison image shows dramatic accretion since 2015. Although the sand closest to the wall is soft, windblown sand which may be removed by a subsequent high tide or storm event, the underlying level here has increased significantly. This surface water drain is now clearly below the underlying, compacted sand level.