The Northern Sea Defence of Maasvlakte 2
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The northern sea defence of Maasvlakte 2 Hydraulic boundary conditions and design Author D. van Rooijen Date June 2005 Version Final Graduation committee Professor Dr. Ir. M.J.F. Stive TU Delft Ir. J.G. de Gijt TU Delft / Ingenieursbureau Gemeentewerken Rotterdam Ir. H.J. Verhagen TU Delft Ir. A.J. van der Westhuysen TU Delft MSc thesis D. van Rooijen The use of trademarks in any publication of Delft University of Technology does not imply any endorsement or disapproval of this product by the University. Accropode is a registered trademark of Sogreah Consultants, France; XBloc is a registered trademark of Delta Marine Consultants, Netherlands. MSc thesis D. van Rooijen Preface This study was performed within the framework of research on the land reclamation of the port of Rotterdam, Maasvlakte 2. This report deals with the design of a sea defence for the northern side of Maasvlakte 2. This research is the final requirement before receiving the Master’s degree in Civil Engineering at Delft University of Technology (DUT). For the hydraulic boundary research, I performed simulations with SWAN. During the model set-up and calibration phase I worked together with Michiel Muilwijk: An informative and humorous experience. I would like to thank the members of my graduation committee for their critical advice and my colleagues at Ingenieursbureau Gemeentewerken Rotterdam (IGWR) for their practical support. Furthermore I would like to use this opportunity to thank both IGWR and the section Hydraulic Engineering of DUT, for placing a work station and many more facilities at my disposal. Daan van Rooijen May 2005 Graduation committee: Professor Dr. Ir. M.J.F. Stive TU Delft Ir. J.G. de Gijt TU Delft / Ingenieursbureau Gemeentewerken Rotterdam Ir. H.J. Verhagen TU Delft Ir. A.J. van der Westhuysen TU Delft MSc thesis D. van Rooijen ii iii MSc thesis D. van Rooijen Summary In 1996 the Dutch government started a national discussion about the necessity of the expansion of the port of Rotterdam. It was concluded that a lack of space would occur in the near future. Therefore, the development of a project called “Maasvlakte 2” was initiated. The total area of waterways, sea defences, infrastructure and industrial areas of Maasvlakte 2 will be 2000 ha. The sea defence of Maasvlakte 2 will consist of two parts: the western and northern sea defence. To compensate for the loss of beaches, the western sea defence will be constructed as an artificial dune. This type of sea defence is not preferred for the northern sea defence, because of its more adverse orientation to potential maximum storms (design storm), that will necessitate frequent maintenance operations. These dredging operations will cause hindrance to navigation and will result in uncertainties in the total life cycle costs. This thesis research focuses on the design of the northern sea defence. The primary objective is to design an innovative, feasible and cost friendly sea defence. Sub objectives are firstly to find accurate hydraulic design conditions in the vicinity of Maasvlakte 2 and secondly to determine the possibility of two cost reducing methods for the northern sea dike. The research was divided in three phases: the modelling of the incident waves with the SWAN model, a literature study of the project history, and finally the design and economic optimisation of the northern sea defence. Combined statistics of wave height, wave period, still water level and wind speed were obtained by applying physical relations between the parameters at Europlatform and IJmuiden measuring stations. Wave propagation from relative deep water towards the location of the future sea defence was simulated with the SWAN model (Simulating Waves Nearshore). Maximum hydraulic conditions that are exceeded with a probability of 1/10,000 per year will occur at the North West corner of Maasvlakte 2. The maximum parameters are: significant wave height, 6.9m; peak period, 13.8s; and water level, NAP+4.8m. The significant wave height decreases with 15% towards the eastern end of the structure. Good estimates of the combined statistics of wind, waves and water levels were found by using physical relations. For the purpose of this thesis, the results of the simplified formulas were used as the input of the SWAN model. Previous studies proposed large and therefore expensive designs due to the adverse orientation of the northern sea defence. This thesis studies the feasibility of two cost reducing methods for the northern sea dike. Firstly the feasibility of a low crested sea dike with discharge canal; secondly the feasibility of allowing a certain amount of damage to the structure by applying a relatively light, less expensive, armour grading. The safety in the area will not decrease because the water return level with an exceedance frequency of 10-4 is lower than the designed terrain height, thus flooding will be highly improbable. For both methods an optimisation of the total life cycle costs was made for two types of armour layers: Interlocking elements and quarry stone. For the interlocking elements a comparison was made between the Accropode and the XBloc elements; this showed that the latter is most economical, mainly because of its less dense packing method. Unit costs, representing purchase and construction costs of building MSc thesis D. van Rooijen iv materials, were used to make an efficient comparison of design alternatives. By applying the concept of a low crested sea dike with an armour layer of XBloc elements, unit costs are reduced by 20 %. No cost reductions are obtained for a sea dike with a quarry stone armour layer. The reason is that the asphalt top layer must be replaced by heavy, expensive rock to ensure the stability of the top part of the construction in the case of overtopping waves. In the proposal of allowing damage, the application of XBloc armour units will make the construction fail in a progressive way when design conditions are exceeded, due to the interlocking of the elements. Therefore, application of XBloc elements in combination with the method of allowing damage is not possible. The non standard 3-7 ton graded armour layer leads to the lowest life cycle costs of a quarry stone sea dike. Costs are reduced by 20 % in comparison with a traditional designed armour layer. The construction of a low crested sea dike with a crest level at NAP+14.0m and use of interlocking element armour layer is recommended. Costs for construction and building materials are €21,000 per running metre. This is €11,300 less than the optimised sea dike with a quarry stone armour layer and a crest level at NAP+13.0m. v MSc thesis D. van Rooijen Table of contents PREFACE............................................................................................................................................................. II SUMMARY .........................................................................................................................................................IV TABLE OF CONTENTS....................................................................................................................................VI LIST OF SYMBOLS .......................................................................................................................................VIII LIST OF FIGURES ..............................................................................................................................................X LIST OF TABLES ............................................................................................................................................ XII 1 INTRODUCTION...................................................................................................................................... 14 1.1 BACKGROUND ...................................................................................................................................... 14 1.2 PROBLEM ANALYSIS ............................................................................................................................. 15 1.3 APPROACH ........................................................................................................................................... 16 2 DESIGN REQUIREMENTS..................................................................................................................... 18 2.1 INTRODUCTION..................................................................................................................................... 18 2.2 BOUNDARY CONDITIONS ...................................................................................................................... 18 2.3 GENERAL REQUIREMENTS .................................................................................................................... 18 2.4 PERFORMANCE REQUIREMENTS............................................................................................................ 18 2.5 CONSTRUCTIVE REQUIREMENTS ........................................................................................................... 18 2.6 RECREATION AND ENVIRONMENTAL REQUIREMENTS ........................................................................... 19 3 HYDRAULIC BOUNDARY CONDITIONS........................................................................................... 20 3.1 INTRODUCTION..................................................................................................................................... 20 3.2 ACCURACY..........................................................................................................................................