La Valette harbours (Malta)

Protection of La Valette natural harbours

Client: Infrastructure Malta - Scales: 1/32.6 (2D) - 1/46.6 (3D)

Background

The two natural harbours on either side of Valletta, Marsamxett Harbour to the north-west and Grand Harbour to the south-east, have significant heritage interest. They are also deep, steep-sided, rocky and exposed to waves from three different directions (north-west, north-east and east), making protecting them a particularly complex matter. They accommodate pleasure boating, trade, transport, cruise and naval activities, within severely limited space. There is hence an urgent need to improve operability conditions and protect them during winter storms.

3D model: vertical impact of a wave beneath the bridge deck at the level of the abutment | Artelia Hydraulics
3D model: vertical impact of a wave beneath the bridge deck at the level of the abutment

 

In this context, Infrastructure Malta commissioned Artelia to perform comprehensive hydraulic studies to characterise the current situation, define protection scenarios, draw up a preliminary dimensional design of the solution selected, and check the hydraulic performance and stability of the structures on a physical model.

 

 

 

Numerical model: diagram of wave disturbance in Grand Harbour with N75° chop, Tp= 5s | Artelia Hydraulics
Numerical model: diagram of wave disturbance in Grand Harbour with N75° chop, Tp= 5s

 

Activities

Artelia performed the hydraulic studies (offshore waves and onshore transformation, wave disturbance inside the harbours, and hydrodynamics), proposed protection solutions, assessed the hydraulic performance of the submerged breakwater using a numerical wave flume, produced the conceptual preliminary dimensional design of the proposed structures (overall layout and sections) and validated this design by performing wave flume and wave tank studies at its Hydraulics Laboratory near Grenoble.

 

2D wave flume model: waves breaking on the submerged breakwater | Artelia Hydraulics
2D wave flume model: waves breaking on the submerged breakwater

2D physical tests of the submerged breakwater:

  • hydraulic stability under extreme wave conditions
  • Wave energy dissipation under operational conditions

3D physical tests of the outer breakwater:

  • hydraulic stability and overtoppings under extreme wave conditions
  • interactions between waves and existing structures
  • wave agitation propagating into the harbor entrance

The 3D model in 100-year storm conditions | Artelia Hydraulics
The 3D model in 100-year storm conditions

 

Specific project feature

Protection scenario for Grand Harbour, combining :

  • a rubble-mound breakwater in 8 and 12 m3 Accropode™ II units outside the harbour to block the propagation of NW waves
  • a detached submerged breakwater in 4 and 6 m3 Accropode™ II units along the shore allowing a significant decrease of the natural shore reflection and consequently the wave disturbance in the harbor entrance
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