Increase in storms and flood incidents can destabilise structures with foundations underwater
The devastation caused earlier this year when the UK was hit by some of the worst storm surges in 60 years was evident for all to see. Thousands of homes and businesses across the country were flooded, roads were damaged and sea defences were battered.
But while the clean-up continues on land, the potentially devastating impact of the tidal surges underwater is not so clear. Flooding and swiftly moving water is one of the main causes of scour: the erosion of sediment and soils from the base of underwater structures which can lead to destabilisation.
With scientists predicting that flooding will increase, especially during winter as a result of water vapour known as atmospheric rivers*, loss of integrity and damage to structures such as offshore wind turbines, bridges and piers, could also escalate.
It is an issue that marine technology specialists Kongsberg Maritime Ltd believes will become increasingly prevalent in the years to come. The company, which is based near Aberdeen at Westhill – the hub of Europe’s subsea industry – saw the potential for scour monitoring services as a result of its involvement with the offshore renewables sector.
It has a strong track record in delivering solutions for subsea environmental monitoring for the development of offshore wind turbines and tidal and wave power installations.
This has by and large involved provision of acoustic monitoring for environmental impact assessments that are required as part of the feasibility and planning process, however Kongsberg Maritime Ltd has realised the potential to harness its technology for subsea inspection and long-term scour monitoring.
Business development manager Mark Baldwin says that more clients are now becoming aware of the potentially devastating consequences of scour and are responding by implementing a programme of regular inspections on structures with underwater foundations.
He explains, “Scour is an issue affecting structures which have been constructed both on the sea bed and river bed or river bank, and it is fair to say that it is perhaps not an issue which has previously been given much consideration.
“Essentially, scour holes around the base of underwater structures are caused by storms, fast flowing water or wave action. These can happen over a significant period of time or, especially during very extreme weather, can occur instantaneously.
“Therefore, we recommend that a long term programme of inspection and monitoring is undertaken as this allows for ongoing assessment and early warning on the potential loss of integrity. Most organisations will carry out post-storm surveys of structures, but evidence or scour holes are not always apparent in the immediate aftermath of a storm.”
As part of its scour monitoring operations, Kongsberg Maritime Ltd uses the Kongsberg Mesotech Dual Axis Scanning sonar as a profiling tool. It is deployed to detect possible erosion around the structure and potential loss of integrity. This continuous real-time data can be transmitted and displayed at a remote monitoring station via wireless telemetry infrastructure.
The information gathered by DAS, which is designed to cover a large area of approximately 300m, provides a snapshot of the dynamics of scour and sediment aggregation. It also provides a 3D profile point acquisition for digital records.
Mr Baldwin adds, “The fact that the DAS can be deployed on a wide range of structures, for example, bridges, piers and offshore wind turbines, has meant that we are also now working with clients that are not in Kongsberg Maritime Ltd’s traditional markets, such as civil engineers, local authorities and highways agencies to provide monitoring services.
“While diving inspections can be costly and there are often inconsistencies in the data being reported, the DAS system accurately visualises the base of the underwater structures and relays that information to engineers to allow them to make a full assessment as to the loss of supporting capability in the sea bed.
“The continuous monitoring of the structure is extremely important as sediment may quickly refill the scour hole, but, as it is not consolidated, it will have very little or indeed no load-bearing capacity. The ongoing assessment allows operators to take immediate protective measures such as rock dumping.
“Not only is DAS more cost-effective than frequent diving inspections, the continuous monitoring results in lower intervention costs for maintenance and increases the lifespan of the structure.”
Kongsberg Maritime Ltd is the UK subsidiary of global marine technology company Kongsberg Maritime. Kongsberg Maritime Ltd employs 142 people in Aberdeen, along with a further 9 in Southampton.