· · · Repository Hydraulic Engineering Reports

In 1989 the Dutch government decided to build a storm surge barrier in the New Waterway near Rotterdam being a good and cheap alternative for the necessary strengthening of dikes along the lower regions of the Dutch rivers Rhine and Meuse. To be feasible the barrier had to meet several goals. The most important ones being : * closing frequency less then once every 10 years now and once every 5 years after 50 years from now (including 25 cm sea-level rise) * prescribed reduction of design water-levels at two representative locations, being Rotterdam and Dordrecht. These and other parameters are calculated by means of a probabilistic calculation method. This method involves a mathematical open-channel network model of which the results are combined with the statistical properties of input parameters. A risk-analysis of the performance of the barrier is included. Finally the model is adapted to study operational aspects.

The Manly Hydraulics Laboratory, of of the Public Works department of New South Wales, Australia, on behalf of the Coastal Branch, has carried out an inspection of gabion coastal protection structures in the Sydney area to assess their condition following the August 1986 storm. This report has been made available via Maccaferri Gabions.

In deze notitie wordt een globale indicatie gegeven van het waterstandsverloop tijdens storm ten behoeve van de bepaling van de reststerkte van dijken.

On the 28th of February 2010 at 2 a.m. the storm Xynthia hit the French Atlantic coast. The storm surge combined with the high tide and large waves caused flood defences to fail along the coastline from the Gironde (Bordeaux) to the Loire Estuary. A significant amount of land, (>50 000 ha) was consequently flooded and 47 people died as a result of the storm. Most people died due to the flooding (they drowned, were exhausted or died from hypothermia). A number of people died as a result of the storm itself (storm debris). The French departments of Vendée and Charente Maritime suffered the most. Some parts of the departments Gironde and Loire Atlantique were also flooded. Since 1953 the Netherlands has not had any experience with major floods. Large parts of the Netherlands are also prone to coastal flooding, even though we have very high safety standards. The Netherlands can learn from this flood in a neighbouring country with a common history and legal system. The foundation of the legal system in the Netherlands and France was laid down in the Napoleonic period with the introduction of the book on common law. Jurisprudence plays a minor role in Napoleonic law. The flood was not caused by natural phenomena alone, organisational failure plays a large role in understanding the flood. This book describes the Xynthia storm and its consequences. Using multiple viewpoints of the “multy-layer safety”: flood warning, flood prevention, special planning and disaster management, this book gives lessons from the storm for the Netherlands. Please note: We have used all available public sources up to the beginning of August 2010. The official facts about the storm have been assembled in three French public enquiries, by each house of parliament and by the French ministry of Ecology, Energy Transport and Development MEEDEM. Our purpose is to give lessons for the Netherlands and not to give a perfect list of facts about the storm. The Dutch, French and English versions differ slightly. Some background information has been added in each language.

Comme c’est le cas pour la plupart des législations des autres états européens, la législation néerlandaise relative à la gestion du risque d’inondation a été contingente des catastrophes; cette attitude du législateur est classique et concerne aussi d’autres types de risques. L’infl uence européenne sur cette législation grandit constamment, ainsi on bénéfi cie aussi des expériences des autres états membres. La clef de notre réussite actuelle réside moins dans les ouvrages mêmes que dans notre système organisationnel, juridique et fi nancier. Faute de budget pour son entretien et son réaménagement régulier, un ouvrage ne tiendrait pas longtemps. En faisant en sorte que la gestion de l’eau et la gestion du risque d’inondation soient regroupées au sein d’une même structure, on s’assure que ce soient les mêmes personnes, maîtrisant et connaissant parfaitement les cours d’eau et les systèmes de protection concernés, concernés, qui sont impliquées. Des progrès substantiels restent encore à faire et ont été entamés en 2007 en matière de communication de crise entre les services de gestion des cours d’eau d’une part, et ceux en charge de la gestion de crise d’autre part. Ce livre décrit de façon large la spécifi cité de la situation des Pays-Bas, les institutions, les événements majeurs qui ont mené à la politique contemporaine de protection contre les risques et de la gestion de crise, le niveau de sécurité fixé par la loi, la gestion, le fi nancement du secteur de l’eau, les grands travaux, l’urbanisme et l’absence intentionnelle d’assurance contre l’inondation, les directives européennes sur le risque d’inondation, et les particularités de notre système de gestion de crise. Un certain nombre de sujets ne sont pas encore résolus, notamment le fi nancement de la réfection des digues, dunes et ouvrages d’art d’ici 2023, les choix à prendre ou à laisser dès aujourd’hui pour l’horizon 2050/2100, et les « confl its » entre l’application des différentes directives européennes en matière de gestion des risques et de protection de la nature.

Le 28 février 2010, vers 2 heures du matin, la tempête Xynthia atteint la côte occidentale de la France. A plusieurs endroits, les digues, dunes et d’autres ouvrages cédèrent, donnant lieu à des inondations du littoral. Plus de 50.000 hectares de terres furent inondées. Au total, la France compta 47 morts suite à la tempête, la plupart d’entre eux suite à la crue. Essentiellement les régions de la Vendée et de la Charente-Maritime endurèrent de terribles privations. Les dégâts et les victimes ne sont pas uniquement la conséquence du phénomène naturel, mais également des interventions de l’homme ou le manque de celles-ci. Les Pays-Bas pourraient tirer des leçons de ces inondations côtières françaises. Les circonstances aux Pays-Bas et en France sont, dans une grande mesure, comparables. La France, elle aussi, connaît des zones côtières à basse altitude sensibles aux inondations. Certes, le niveau de protection aux Pays-Bas est plus élevé, mais une inondation aux Pays-Bas est aussi bien concevable. Tout comme en France, une inondation du littoral néerlandais est causée par une combinaison de la marée, d’une tempête et d’une surcote. Les législations et les réglementations présentent des concordances ; leurs bases datent de l’époque de Napoléon. Ce livre décrit l’inondation par la tempête Xynthia et ses conséquences. Nous en tirons des leçons et nous formulons des avis pour les Pays-Bas. Nous cherchons à nous associer à une protection contre l’inondation à trois volets: la prévention, l’aménagement du territoire et la maîtrise des catastrophes.

Model to determine storm surges due to typhoons along the Vietnmase coast using Delft3d.

The numbers of easterly gales that occurred in the North Atlantic Ocean north of 25°N been estimated by using a selection criterion involving minimum values for the meridional pressure gradient, for each day of the period 1881-1970. To do this use has been made of magnetic tapes from the "Deutscher Wetterdienst" with daily pressure values (for 12 hours GMT) in grid points. This method is not without shortcomings, because the wind field depends on more factors than the pressure gradient only. When the pressure difference indicates an easterly gale there are two possibilities: the statement is correct or not correct. By applying a statistical method an estimate could be made of the percentages of (in)correct statements. The percentage of correct statements appeared to be around 80% in the area between 70°N and 35°N. South of 35°N this percentage decreases considerably. On the North Atlantic Ocean January is the month with the most frequent and July the month with the least frequent easterly gales. In general the maximum number of easterly gales is found in the area between Iceland and Greenland, while a secondary maximum is found south of the American coast between New York and Newfoundland. From the maxima southwards the numbers of easterly gales gradually decrease. In autumn a secondary maximum occurs in the area between the Azores and the English Channel, while in spring to the contrary a secondary minimum is found in this area. More interesting is the following. Looking at the number of days per year on which an easterly gale did occur it appears that especially in the area between 70°N and 50°N there are considerable differences between the successive periods 1881-1900, 1901-1920, 1921-1940, 1941-1960 with a minimum in the second period and a maximum in the last period. The differences between these periods are often highly significant. The fluctuations in the numbers of days per year with an easterly gale can be explained by the climatic fluctuation connected with the cycle of solar activity with a period of 80-90 years.

Lecture note for the course on flood protection, dikes and other water retaining structures at Unesco-IHE in Delft.

Memo met samenvatting van de effecten van stormvloed, dijkdoorbraken en overstromingen in Frankrijk door de storm Xynthia op 28 februari 2010. Overzicht schade, slachtoffers, staat van onderhoud waterkeringen en politieke implicaties. In Bijlage korte beschrijving effect Xynthia in Nederland

Computation of large waves generated by hurricanes and other low-pressure systems moving towards the coast.

In hoofdstuk 3 worden de situatie en de belangrijkste hydraulische randvoorwaarden omschreven voor het onderzoek van de spinakerkering. Het principe van dit nieuwe type keringsmiddel vol gens het huidige schetsontwerp wordt beschreven. Daarna worden te onderscheiden bedrijfsfasen - achtereenvolgens de transport-, de sluitings-, de kerings-, de openings- en opbergfase uitgelicht. In hoofdstuk 4 komt de beschrijving aan de orde van de faciliteit en van het eigenlijke schaalmodel van landhoofden, inkassingen en spinakerdoek. Hoofdstuk 5 geeft de opzet van het modelonderzoek weer, met alle te onderscheiden varianten uit het gerealiseerde meetprogramma. In hoofdstuk 6 tenslotte worden voor elke bedrijfsfase de belangrijkste onderzoeksresultaten beschreven. Paragraaf 6.6 geeft een kort resume van de resultaten.

The Dutch defence line appeared to be inadequate to withstand stormsurges of exceptional strength. In 1916 a heavy storm caused severe floodings and damage in the northwestern part of Holland, a disaster which led to the closing of the dangerous Zuyderzee. And in 1953 a stormsurge of even greater strength, with a floodlevel which surpassed all the floods of the past, hit the south-western delta, formed by the rivers Scheldt, Meuse and Rhine. After this new disaster a plan was immediately adopted, a plan somewhat similar to the Zuyderzee project, providing in the closing of three dangerous inlets, the Haringvliet, the Brouwershavensche Gat and the Eastern Scheldt. The location of the dams was planned as close as possible ta the sea, thus achieving maximum shortening of the coast-line and the largest protected area behind the dams. Needless to say that both the entrance ta the ports of Antwerp (Western Scheldt) and Rotterdam (Nieuwe Waterweg) should remain open for the ever increasing shipping, which entailed however that the dykes along these waterways should be modified and/or improved in accordance with the new stormsurge criteria. The dykes mentioned above and of course the new dams are ta be made to withstand a 'superstorm' having a frequency of occurrence of once in 10,000 years, (1% in 100 years). Once built, the plan ensures the safety against an attack an the south-western part of the Netherlands (see figure on pages 6 and 7). Naturally the main purpose and the leading policy of the plan is safety but other advantages are: the shortening of the coast-line, meaning less maintenance and fewer risks, whereas the existing dikes along the enclosed basins form a secondary defense, strang enough to withstand floods; the improvement of the watermanagement by restricting the salt intrusion from the sea; with the sluices in the Zuyderzeedike and three weirs in the lower Rhine (Lek) the Haringvlietsluices form a system by which the freshwater from the Rhine and the Meuse can be distributed according to the needs.

For two historical storms the water levels and currents in the Wadden Sea were simulated using the so-called model-train of Rijkswaterstaat. The first storm of 1 Nov. 2006 generated exceptionally high water levels in the Eems-Dollard estuary. The second storm of 18 Jan. 2007 was also scaled up to represent a 1 in 4000 year design storm. In general the simulated water levels agree rather well with the measured ones, except for levels near the Eems-Dollard estuary during the Nov. 2006 storm. The main effect of the storm wind is to increase the current magnitudes. In the case of very strong winds, an overall flow southwest-northeast flow occurs in the Wadden Sea that crosses the shallow areas south of the Wadden islands. The wave computations indicate that the tidal inlets effectively block North Sea waves and that the wave conditions are mostly locally determined and depth limited under storm conditions. The flow conditions in the tidal inlets determine the amount of wave penetration through them.

The first in a four-volume study to assist the Netherlands government in a policy analysis of alternative control strategies for operating the storm-surge barrier across the Oosterschelde basin. For each alternative, the project analyzed several consequences or "impacts," including the safety of the dikes along the Oosterschelde; the effects on the ecology and the shellfish and fishing industries of the region; the impacts on water management and shipping in the basin; and the implications for the design of the barrier and its control system. This volume describes the approach and summarizes the results of the complete analysis. It first presents an analysis of hydraulic conditions and closure frequency, then describes the rationale for selecting three alternative strategies for detailed evaluation, and finally illustrates the impacts of the strategies, category by category, through the use of a matrix display device--a colored scorecard.

The second in a four-volume study to assist the Netherlands government in a policy analysis of alternative control strategies for operating the storm-surge barrier across the Oosterschelde basin. This volume describes the sensitivity analysis and shows why two specific strategy representations were selected for further evaluation from the three promising barrier control strategies. It explores the effects on performance of varying specific elements of the control strategies: basin inside water levels, their durations, and head differences across the barrier while closing and while closed. Inside water level and duration are surrogate measures for the impacts discussed in Vol. I--dike safety, ecology and commercial fishing, and water management and shipping. Head difference is used to assess impacts on barrier loads.

The third in a four-volume study to assist the Netherlands government in a policy analysis of alternative control strategies for operating the storm-surge barrier across the Oosterschelde basin. This volume describes and evaluates several models for predicting North Sea water levels outside the barrier. The models include prediction based on observed local water levels (correlation over time); on observed remote water levels (correlation over space); on observed weather conditions, ranging from very short predictions (1 to 2 hours) to longer predictions (6 to 12 hours) for operational control of the barrier with different potential strategies; and on long-term weather forecasts (24 to 48 hours) for conducting maintenance, providing alert, etc. The statistical techniques explored here are intended to provide the Dutch with a basis for further study of hydraulic conditions in the North Sea as relates to the control of the storm-surge barrier. 90 pp. Ref.

The fourth in a four-volume study to assist the Netherlands government in a policy analysis of alternative control strategies for operating the storm-surge barrier across the Oosterschelde basin. This volume describes the simulation model of the storm-surge barrier and basin used to estimate the variation with time of different water levels inside the Oosterschelde, given specified sets of storms outside the barrier. It discusses the capabilities of the model (called SIMPLIC), the storm sets and tidal shapes used, and the model's inputs and outputs. Two sets of storm scenarios were represented in SIMPLIC: a historical storm set comprising 44 storms from 1921 to 1970, and a design storm set including 12 variations of two extreme storm surges. The first storm set was used to evaluate ecological, water management, and shipping impacts and the second to assess safety impacts of the alternative barrier control strategies, as discussed in Vol. I. 92 pp. Ref.

Construction of two hurricane barriers to protect the coastal communities of New Bedford and Fairhaven, Massachusetts and Providence, Rhode Island is nearly complete. The projects include navigation gates, pumping stations, street closures, cooling water canal, and numerous utility gates. Operation of these various features introduces many problems not generally encountered in flood control projects on rivers. Delineation of responsibilities, with close coordination and cooperation between governmental agencies and local interests is essential to assure full effectiveness of the structures during hurricane conditions.