Surveying and Investigations

To support the option development process, we need to collect data to better understand the current risk from coastal flooding and erosion from the sea. This is called the 'Surveying and Investigations' phase of the project. This will help us to make decisions about how best to manage the risk now and in the future.

Ground Level and Ground Penetrating Radar (GPR) Surveys - June 2022

Our contractors will be completing survey work using GPS equipment to obtain accurate land level measurements. They'll also be using ground penetrating radar to survey beneath the surface of the existing sea wall.

Ground investigation work - January 2023

Ground investigation work starts on Monday 16 January 2023. Specialist equipment will be used to drill boreholes through the sea wall and retrieve concrete cores which are sent to the laboratory for analysis. Machine excavated trenches located at intervals along the sea wall and next to the groynes will also be required. The results from the investigations will give the project team information about the composition of the ground and existing foundations where the coastal defence refurbishment is being proposed. It will increase our understanding of the existing structures and help us plan refurbishment work. Further details can be found here

Findings of the ground investigative work

• A total of nine concrete cores were extracted at strategic locations along the concrete sea wall. The cores showed that the Wessex Formation is present as bedrock across the whole site. At the western end of the site, the Wessex Formation is reported to alternate between a Clay and a Mudstone of various degrees of weathering. The Wessex Formation is notably multicoloured, in places mottled brown and purple, reddish brown, greenish grey and bluish grey. Its strength varies with the degree of weathering from a soft Clay to a very weak Mudstone, with bands of sand and Sandstone which is highly erodible. The presence of a stepped revetment around Yaverland car park demonstrates that erosion risk through scour at the toe of the sea wall has been a concern in the past. The soft erodible bedrock will need to be a consideration as the team draw up the design.
• The sea walls are much thinner than modern engineering standards. This tells us that works to the foundations will be needed as part of the refurbishment work.
• Borehole cores extracted from the ground have been donated to the British Geological Society. Their data sets provided useful information for our projects, and we hope our contribution will help others in the future.

The below image shows two of the borehole cores extracted from the ground and stored in their wooden containers:

Coastal processes assessment

We completed a coastal processes assessment to get an understanding of the sediment movement across the beach.

• The historic trends in beach profile from 2004 to 2020 were reviewed. The min/max envelope in the image above shows the beach level overall remains relatively stable across the survey period.
• Short term fluctuations are observed and indicate seasonal changes. Photographic records taken by Swim the Wight provide supporting evidence of this:

• The overall stable condition is attributed to the constant nourishment of sediment received from the south-north net sediment transport rate of 25,000m3/year on average.
• Satellite imagery captured evidence of North-South longshore sediment transport in 2005, 2014, and 2015. This is opposite to the predominant direction.
• Accumulation of sediment on the northern side of most of the groynes in Yaverland indicates the groynes are functioning well.
• Past storm events have caused beach levels to lower by up to 1metre in front of the sea walls.
• One of the major physical impacts of a rise in sea level includes erosion of beaches. Our coastal processes assessment shows that beach levels are expected to lower by 0.5m by 2040 and up to 3m by 2125. It is expected that the toe of the sea wall will have sufficient beach cover to protect it from erosion for the next 50 years. After this point, works to prevent scour at the toe of the sea wall may be needed.