Sandy Bay coastal defences, Gibraltar

This case study explores the coastal management practices adopted in Gibraltar to reduce the impact of erosion at Sandy Bay.

Sandy Bay Coastal Defences and Beach Replenishment, Gibraltar
Sandy Bay Coastal Defences and Beach Replenishment, Gibraltar

Project details

Location: Sandy Bay, Gibraltar
Value: £9M
Date of completion: June 30th 2014
Duration: 15 months
Client: HM Government of Gibraltar
Contractor: Van Oord (Gibraltar) Ltd
Project manager: Emil Hermida CEng MICE

Introduction

Gibraltar stands near the junction of the continents of Europe and Africa and close to the boundary of the Mediterranean Sea with the Atlantic Ocean. It forms a narrow peninsula 5.2km in total length and 1.6km in maximum width, protruding southwards from southern Spain.

Sandy Bay Beach is the southernmost of the three beaches which line the eastside of Gibraltar. It has historically been a wide sandy beach popular with locals and tourists alike.

Over recent years there has been a steady loss of sand at Sandy Bay leading to the virtual disappearance of the beach in 2010/11.

As part of its ongoing coastal management policy Her Majesty’s Government of Gibraltar set up a programme to review the coastal processes affecting the beach at Sandy Bay with a view of identifying long term mitigating measures to control the effects of beach erosion, provide shoreline control and encourage sand nourishment in the area.

History

In the 1970’s Sandy Bay was an established beach that varied in width between 10-20m. Due to its geometry, there was gradual erosion of the beach profile and loss of sand caused by cross-shore transport (displacement of sediment perpendicular to the shore by the combined action of tides, wind, waves and shore-perpendicular currents) and longshore/littoral drift (transport of sediment along the foreshore and shore face via the action of the breaking waves and longshore currents).

In 2006 investigative work regarding this sediment loss was carried out and concluded that the rate of erosion was in the order of 0.2 to 0.3m per annum which would have amounted to a loss of 8-12m over 40 years from the 1970’s to the present day. The combination of long term erosion and increased storm activity from 2008 onwards meant that the beach had been completely depleted of sand by 2010.

In August 2010 HM Government of Gibraltar carried out some emergency strengthening works to the existing sea wall to the rear of the beach as there were concerns over its continued structural performance under wave attack. These works basically consisted of the placing of rock armouring along the toe of the wall, along its entire length.

In May 2011 HM Government of Gibraltar carried out beach replenishment works by pumping in approximately 50,000m3 of dredged sand onto the beach however without any means of controlling beach erosion the replenished beach did not survive the effects of winter storms.

In 2013 HM Government of Gibraltar opted to review the coastal processes affecting the beach and engaged Lievense, a Dutch coastal Engineering consultant, to review the coastal processes affecting the beach and to identify long-term mitigating measures to address the coastal erosion problems affecting the beach.

A long term solution

Lievense was tasked with identifying design solutions which would establish beach stability and shoreline protection using hydraulic structures such as groynes and breakwaters. The design had to optimise marine biodiversity and take into account any possible impact on adjacent coastlines. The design solutions had to be sensitive to the cost of construction given that all materials required for the project would need to be imported.

The preferred design would see the construction of extensive off shore defences in the form of curved groynes located at each end of the beach as well as the construction of a submerged breakwater connecting both ends of the groynes. The project would also see the importation of 80,000 tonnes of Saharan sand to replenish the beach following the construction of the coastal structures.

The Contract was awarded to Van Oord (Gibraltar) Ltd who were tasked with value engineering the preferred design solution to optimise overall construction costs and speed of delivery.

Due to restrictions imposed by the Spanish Authorities at the Spain-Gibraltar land frontier all rock required for the project was imported from Nador, a city located in the north-eastern Rif region of Morocco.

The project commenced on March 10th 2013 and was completed on June 30th 2014.

The combination of these structures together with the final placement of sand has proven very effective in stabilising the beach at Sandy Bay and very few signs of coastal erosion have been noted since completion.

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