Topographical Survey: Protecting the East Rhyl Coastline

​Protection of our coastal communities is an ongoing challenge.  Hard engineering techniques including rock armour and concrete structures are used throughout the UK to deflect the power of waves, helping to reassure coastal communities and protect our beaches. Working with such structures carries many challenges and risks meaning that surveys are a vital step in any repair, renovation and improvement works.
 
Back in 2017, working alongside Balfour Beatty and JBA Consulting, we were commissioned to provide survey works to assist in the repair and improvement of sea defences consisting of rock armour revetment and sea wall in East Rhyl.

Revetments are sloped structures built along coastal frontages that absorb the energy of waves breaking against them, thus helping to reduce coastal risk.
 
Rock armour involves placing large boulders in front of a cliff or sea wall to absorb the energy of waves. Used in conjunction these structures are a powerful means of energy absorption and protection.

​Our role as part of this project was to provide detailed topographical surveys with both 2d and 3d outputs compliant with BIM level 2 to inform the improvement works.

Using a combination of techniques including, GPS, total station and laser scanning we performed a mixture of high density and low density surveys as follows:

• High density topographic survey of boundary wall, promenade, existing sea wall and 50m onto foreshore, including all visible features and services
• Low density topographic survey of foreshore to low tide on a 10x10m grid and picking up major features such as groynes and major changes in beach composition
• Cross sections at 50m intervals through an extended frontage extending from the rear boundary wall/bund to 50m onto the foreshore, including each individual step riser and top of the sea wall
• High density topographic survey of the flow control structures with intermittent points surveyed showing changes in shape and level.

Our laser scanner was utilised to capture the sea wall and immediate foreshore, GPS units were used to capture remaining beach levels. Total stations were used to survey the promenade and landward features
 
Whilst seaside working provides a beautiful setting, it also carries with it challenging weather conditions and lots of risk factors. Working near a tidal body of water meant that timing was of the essence, both in terms of survey accuracy and health and safety. Being November, we also had weather factors to contend with.
 
During the course of the survey it was identified that the beach level change significantly between tides. An indication of which area of beach was surveyed each day was added to the final drawings
 
 Below: Laser scan data covering sea wall, rock armour and foreshore. Draft survey data showing areas of levels surveyed on individual days

Below: 3D model generated from the laser scan alongside traditional total station promenade survey

“Grantham Coates have been invaluable in supporting the development of a 3D model suitable for the construction of the East Rhyl defences.  We were able to discuss through our requirements and explore relative advantages and disadvantages of different survey techniques. This meant that the deliverables provided by GCS met our needs and avoided any need for further post-processing.”
Alec Dane
JBA Consulting
 
To read more about out topographical survey work, click here. If you’d like to discuss a project of your own, contact us on 01789 764 420 or email [email protected]
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