Case Cromer coast protection scheme

  • The town on the stormy North Sea coast needed to rebuild its crumbling sea defenses and prepare for rising sea levels.
  • Saltwater poses a unique integrity problem; stainless steel’s critical chloride threshold level is ten times greater than carbon steel rebar and requires less concrete cover to ensure a long lifespan.
  • Located in Cromer, UK

Supporting North Sea defenses

Courtney TenzDaniel AllenNortheast of London, England’s Cromer coast is a well-known North Sea retreat with a historic sea front and beloved beach.

With rising sea levels and intense storms threatening the area, the Cromer Coast Protection Scheme was launched in 2013 in order to refurbish the sea defenses and make them battle-ready for the anticipated sea level rise to come over the next 100 years. The sea defenses already in place have protected the area against the stormy North Sea for over 150 years. They were originally built in 1845 as a series of walls and timber groynes to fend off the force of the sea.

“In the new protection scheme, our brief to the consultants required that walls and groynes need to be designed to maintain not only the existing level of defense but they would also need to hold up against rising sea levels. At the same time, keeping the visual character of the seafront and preserving both a stable beach and beach access were important for us,” says Brian Farrow, North Norfolk District Council Coast Protection Engineer.

outokumpu-cromer-sea-wall-9

Designed to last

The protection scheme’s plans included refacing the concrete sea walls that were badly damaged after tidal surges in 2013. Furthermore, parapet walls were improved where necessary and timber groynes repaired.

Because of its superior corrosion resistance, stainless steel rebar played a central role in the refurbishment, with Outokumpu delivering 335 tonnes of Forta DX 2304 for the project. The use of stainless steel rebar within the wall will help to reduce the sea’s impact on the coastal frontage by providing added corrosion resistance. With a critical chloride threshold level ten times greater than carbon steel rebar, stainless steel has the added benefit of requiring less concrete cover while retaining its integrity and strength in spite of chloride ingress from the saltwater. Virtually maintenance-free, stainless steel rebar has a low lifecycle cost and will maintain its corrosion resistance over the design life of the scheme.

Absorbing the force of waves

An important element in coastal protection is the timber groynes that are often seen jutting into the sea, including at Cromer coast. They function as a means of trapping the sand and flint on the beach in areas where the sand is continually shifting due to wind and waves. At Cromer, that shifting with the tide is predominantly eastward. The groynes play a vital role as they keep as much sand near the beach as possible, to absorb the force of the waves before they hit the sea wall and cliff.

To provide added strength and keep them protected against the elements, stainless steel was added to the groynes as they were replaced. Says Brian Farrow: “Now completed, the coast protection scheme ensures that the Cromer Coast beach and sea front is there for the next generation to enjoy.”

Case facts

Challenge

Upgrade the current defenses − sea walls and timber groynes − at the Cromer coast to withstand storms on the North Sea and predicted sea level rises for the next 50 years.

Solution

Outokumpu delivered Forta duplex stainless steel, a virtually maintenance-free material with the exceptional chloride resistance that is ideal for marine environments and made to withstand the elements for 100 years.

Delivery

Steel grade: 335 metric tonnes of Outokumpu Forta DX 2304
Product form: rebar

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