Taking the pain out of ports
Wave riders: Calshot Harbour's rehabilitation has been hampered by extreme wave climate conditions and frequent storms.
Consultants can deliver the planning pill to solve complicated design problems. Alex Hughes investigates how two challenging schemes have been tackled
Overseeing its implementation is consultant Royal Haskoning,where director Tom Smit says that the huge scale of the undertaking will result in the adoption of several innovative initiatives to ensure the scheme complies with two major environmental impact assessment (EIA) studies.
Asked whether this is a particularly difficult project to implement, Mr Smit says it is. "There are a lot of technical issues to be resolved, beside the fact that there are huge interests involved. In addition, we are having to liaise with the various government agencies involved, which is very time consuming."
He explains that dredging will form a central tenant of the work, although initially a temporary dyke will have to be put in place enclosing the area into which Maasvlakte harbour is being extended. As part of the second stage work, this dyke will then be dismantled.
"We have to undertake the work in distinct phases, because of environmental factors in that area," says Mr Smit. He says that such is the potential for environmental damage that two major EIAs are being undertaken, with results due to be published in April. "We will have a lot of issues to solve once we have seen the conclusions from these,"he says.
While he concedes that storms will inevitably cause some disruption to the work, these have been factored into the overall implementation timetable. On the other hand, no extreme geological problems are foreseen. Mr Smit's overall management of the project is also eased by the fact that access from both land and sea is comparatively easy, although he promises that a lot of new construction techniques will be used in the early stage of the project.
Once up and running, Maasvlakte 2 will enable Rotterdam to consolidate its position as Europe's leading container and chemical facility, says Mr Smit.Were it not to go ahead, then the Dutch port would lose its central position in these two trades.
However, not all port consultancy work involves large-scale big budget projects. Halcrow Group, for example, has been contracted by the UK's Department for International Development to devise a way of rehabilitating Calshot Harbour on the small South Atlantic island of Tristan da Cunha. This isolated territory is situated 1,750 miles east of Cape Town, which is also the nearest port.
The primary purpose of the rehabilitation work is to prevent further deterioration of the existing harbour by improving both the stability of the western breakwater and also the wave climate in the harbour. An initial study of the harbour facilities in 2004 noted that the existing breakwaters were of unusual configuration. This was because a standard design would not have been able to resist the wave climate and would have failed catastrophically.
The current contract involves project studies to be carried out on the harbour,including survey work,wave climate assessment, risk assessment, and environmental assessment. Following this a design for rehabilitation and upgrading of the existing breakwaters will be produced to enable the work to be tendered by qualified contractors. As part of a second phase, Halcrow will oversee construction and supervision of the harbour rehabilitation works, although this is dependent on the project's viability and on the availability of sufficient finance.
According to project manager and maritime engineer Ruwaida Edries, the island's location introduces numerous challenges associated with working in such a remote location. The lack of an airfield means that the only regular mode of access is via fishing vessels, of which there are just nine trips per year. In addition, there is the South African Antarctic Relief Service supply vessel, which makes a single trip each year. The island is also visited by passing cruiseships, the odd navy vessel and very occasionally by yachts.
"Sourcing contractors, plant and equipment, materials,manpower and so on is not simple,as none of these are located within reasonable distance," comments Mr Edries."The contractor's labour force will have to be housed on the island for the duration of the construction. All plant will also have to be shipped to the island and any critical equipment may need to be duplicated or alternate plant would have to be shipped later delaying the works. Furthermore, all construction plant will have to be land-based as there is no sheltered area in the harbour for the safe mooring of water-based plant during storms."
The extreme wave climate conditions experienced at the island, where frequent storms occur preventing access into/out of the harbour,complicates construction work in the harbour. "If any of the core material for the breakwater is put down first as per normal working methods, it would be washed away before the armour units are placed. To make matters worse, the volcanic nature of the seabed, which has pinnacles and holes,makes any alterations to the existing breakwaters difficult and also adds risk to navigation into the harbour,"says Mr Edries.
To date, bathymetric, hydrographical, topographic surveys have all been undertaken, as have aerial, underwater and boat-based photographic surveys, along with a condition survey."Despite generally very poor surveying conditions, results exceeded the minimum requirements of the Phase 1 works," says Mr Edries.
Following the site survey and investigation, desktop modelling ensued, which involved numerical modelling - both locally and globally - of the harbour to determine the inshore wave climate as well as the wave heights and wave directions.This information will be used in the physical modelling, where various technically feasible rehabilitative options can be obtained. Design work will then commence, which could comprise preparing a specification for the required repair work to the harbour and breakwaters.
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