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dredging, environmental and marine engineering N.V.
As already mentioned, the location of the marine borrow area is of the utmost importance for the evaluation of possible interventions. It can be concluded from the plan be-
low which intervention zones may be considered, taking into account the location of existing marine quarries.
Technical Information Sheet
DEEP DREDGING Opportunities for Jumbo-type trailing suction hoppers with deep-sea dredging installation (- 100 m): the practice of beach nourishment Abstract: Until the end of the 1980’s, the maximum dredging depth for the trailing suction hopper dredgers (TSHD’s) was directly linked to the maximum draught of these vessels. At about the mid 1990’s, a new generation of TSHD’s made their appearance. They were commonly called ‘Jumbo’, and had a capacity between 16.000 and more than 35.000 m³. The main sector of activity and operation of these vessels is the dredging and the transportation of large volumes of sand, used in vast reclamation projects - in particular in the Middle East and the Far East. Owing to the length of their hull, this new generation of dredgers has allowed to take very long suction pipes on board – hence making deep-sea dredging beyond 100 metres feasible. Distance of marine quarries to possible intervention sites
Conclusion Taking into account the increasing concern for respecting the environment, it is safe to predict that future tendencies for the realisation of beach nourishment projects by way of hydraulic reclamation of marine sand, will ultimately evolve towards the exploitation of borrow zones at big depth. A few projects have already been realised, and a lot of research is being done – in particular in the Mediterranean Sea.
AUTHORS Pierre Catteau Area Director Dredging and Environmental Marine Engineering (DEME) E-mail : Catteau@sidra.it Malik Boukebbous Proposals Manager Società Italiana Dragaggi S.p.A. E-mail : Boukebbous.malik@dredging.com
However, it is necessary that these projects have a sufficiently big dimension. They must fully benefit from the advantage of scale in order to guarantee an attractive operation. In order to realise projects of a sufficient dimension, it is advisable that coastal defence problems and related works would be managed, not by local authorities, but at a regional, interregional or even national level.
This Technical Information Sheet is based on the experience and “know-how” of Societá Italiana Dragaggi S.p.A. member of the DEME group and aims to give a technical contribution for the future beach nourishment projects. Società Italiana Dragaggi S.p.A. Via Carlo Zucchi, 25 - 00165 Roma Tel. 066604951 - Fax 0666049549 www.sidra.it - segreteria@sidra.it
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dredging, environmental and marine engineering N.V.
This new generation has led to the search and the exploitation of sand borrow areas at a depth of 100 metres and more, allowing the realisation of beach nourishment projects (coastal protection) while substantially limiting
the environmental marine impact. Indeed, the presence of marine vegetation almost always stops at depths of 35 to 40 metres. In addition, realising this kind of projects with Jumbo-type trailers allows to use borrow areas at a much bigger distance, i.e. up to 100 to 200 km between the borrow area and the beach nourishment area. Even then, dredging is done within acceptable economic limits. However, assigning Jumbo trailing suction hoppers can only be justified if total volumes involved match the depreciation for the costs of mobilisation and starting up the site. Indeed, this kind of dredging vessel would traditionally be assigned in areas such as the Far and the Middle East in the first place. In order to reach profitability, it is thus advisable that several beach nourishment projects would be clustered, for instance at a regional level, so that a project of several millions of m³ can be realised. Key words: Jumbo, deep-sea dredging, marine sand borrow areas.
Introduction The technological evolution in the field of trailing suction hopper dredger (TSHD) building has been driven by hydraulic engineering markets worldwide, and in particular by some specific needs in the dredging industry. On the other hand, the appearance of new plant and new technology has stimulated, and made possible new infrastructure projects, which were considered not to be feasible or profitable before the introduction of this new plant. It is this continuous movement between markets and
plant, which is the driving engine behind the recent strong technological evolution as well as the important investments that were recently made by the dredging industry. In particular, the appearance in the world fleet during the last decade of the past century of some ten dredgers that were commonly called ‘Jumbo’ (i.e. with a hopper capacity in excess of 16.000 m³), nowadays allows to dredge aggregates dredging at depths of more than 100 metres and gives a very concrete answer to some important problems in the field of coastal defence.