· · · Repository Hydraulic Engineering Reports

This report about the Dutch coast was written in the context of the experimental phase of the programme CORINE of the Commission of the European Communities. The programme CORINE (COoRdination of INformation on the Environment) is a programme for the gathering, coordinating and ensuring of the environment and natural sources in the Community. The objective of the project ' coastal erosion', as part of the CORINE-programme, is to provide a cartography and a database of the risks of coastal erosion in the Community. This report has grown out of the objectives of the project and the activities and agreements of the working group involved. However, some parts of the contents may be interesting to a wider group. In the text you will often find the notation NUTS followed by a number. The NUTS (Nomenclature of Territorial Units for Statistics) is an interlocking system of territorial units at three levels. The used level III is the finest one.

The description of the transformation of shore in larger scales, i.e. the far-field effects, is summarized in Chapter 2 while the near-field mechanisms, encompassing different overall and local failure modes, stability and performance are dealt with in Chapter 3. Both are foliowed by Chapters 4 and 5 with design computations and examples, respectively. Unconventional design is illustrated in Chapter 6, and national policies of coastal management and defence are depicted in the closing Chapter 7. The design procedures for coastal structures should include geometrical design and structural design reflecting respectively the far-field and near-field requirements imposed on structures. This corresponds to our division of design procedures into two basic groups concentrating on • overall layout and configuration of a structure as a whole, and its interaction with the coastal environment to produce desirable sedimentation patterns and coastal management effects • stability and reliability of the structure and its components, hence dimensioning of structural constituents, associated with possible unavoidable and undesirable hazards due to the loadings exerted by the coastal environment. In other words, the first group involves design parameters producing the best environmental effectiveness of a structure in 'ideal' conditions, i.e. upon negligence of possible 'harmful by-effects' such as different modes of failures and instabilities, both overall and internal. The second group is concerned about these 'by-effects' and provides the tools which secure the integrity and proper operation of the structure and its components.

A mathematical theory about phenomena that occur if on a coastal area groynes are constructed. The theory is a simplification: it just deals with one aspect. The starting point in the coastal equation of Pelnard-Considère and a linearisation between the transport along the groyne and the size of the 'step' in the coastline at the groyne. The change of the coastline, caused by changing boundary conditions, by stationary transport and by the 'straightening' of the coast are considered. The conclusion is drawn that in the middle of a row of groynes the same process occur as without groynes, but on a larger time scale. Near the edge of the row there are edge effects, that cause bigger erosion and accretion than without groynes.

Mangroves are productive ecosystems, that sustain important fisheries, provide a variety of forest products and harbour millions of resident and migratory birds as well as endangered mammals and reptiles. Reclamation for aquaculture and agriculture is currently considered the main way to achieve development of mangrove areas. These types of reclamation are costly, often unsustainable, and have adverse environmental effects. They mainly benefit outsiders, and to a lesser extent local communities, to the prejudice of those traditionally engaged in fisheries and the gathering of forest products. Partial reclamation may be beneficial and cause limited environmental damage provided that activities are properly designed, judiciously located (Le. largely outside the mangroves, and on suitable soils), implemented on a small scale and controlled by the local population. However, reclamation is certainly not the only option available and priority should be given to the development of mangrove-related activities such as fisheries, forestry, open water aquaculture and nature-orientated tourism. These activities require less investments, are easily taken over by local communities and offer more opportunities for conservation. However, most of them may induce environmental risks and need proper management and control. Integrating sustainable development of mangrove coasts with conservation may take place along three different lines: optimising mangrove-related activities, while maintaining the integrity of mangrove ecosystems as wildlife habitat and naturally functioning ecosystems, optimising reclamation activities while maintaining the integrity of adjacent mangrove ecosystems, integrating conservation into coastal development.

The study into the feasibility o f the construction of islands off the coast of Israel is being conducted jointly between teams from Israel and The Netherlands as part of agreements for collaboration dating from 1996 and 1997. From early 1997, work began on defining the details of the project plan for the feasibility study. Since late 1997 and through 1998 data collection and analysis was undertaken by the Israel counterparts and modelling preparations were conducted by WL|Delft Hydraulics. In March 1999 the data required for the proposed models had been transferred to WL|Delft HydrauKcs where 2-dimensional flow, wave and morphological computations were conducted. From March to April 1999 the first of three schemes proposed for detailed modelling was investigated in the models. This report describes the overall methodology o f the assessment, by modelling, of the impacts o f island schemes on the central coast o f Israel and in particular the result o f the modelling of the impacts of each scheme, the "airport island scheme off Tel Baruch" plus the "single island scheme off Bat Yam" and the "triple islands scheme off N. Herzliya". The modelling of impacts focused on erosion /accretion of the seabed and coastline caused by the scheme and on proposed remedial measures.

This brochure presents low cost ways for the shorel ine property owner to control or slow down shoreline erosion. lt will also be of interest to community leaders, local government officials, and contractors and engineers involved in erosion control. Prepared as a public service by the U.S. Army Corps of Engineers, the brochure is part of a program to demonstrate low cost erosion control measures. The methods described here apply to all protected and inland shores of the United States where wave height does not usually exceed six feet and severe storms or hurricanes are not annual events. These sheltered areas are the only oneswhere low cost, owner-implemented protection is likely to be successful. The measures described here should not normally be used on open coastlines exposed to heavy ocean waves. The useful lifetimes of these methods vary from a year or two, for temporary structures, to over ten years, for longer-lasting installations. These numbers are approximate: unpredictable factors such as weather could shorten or prolong the expected lifetime of any shoreline structure. While all these methods have been used to reduce erosion problems, no erosion control device will ever be completely successful in all applications. The government cannot guarantee, therefore, that a particular method will be successful in your case. If you think it is likely that one or more of the measures described here could help with your erosion problem, we urge you to seek further information and assistance in designing a solution that meets your needs. In addition to this introductory brochure, the Corps of Engineers has prepared detailed reports to assist those who need further information. To obtain one of these reports, send in the postcard attached to the back cover. Additional sources of help are described in the back of the brochure under Where To Go From Here.

Field investigation by Vuong Van Quynh on the dissipation of wave energy in a mangrove field off the coast of southern Vietnam. Based on regression analysis a formula has been developed to determine the wave height decrease as function of the tree density and the tree sizes.

Storm surges occur when high winds and low atmospheric pressure raise water levels at the coast, causing sea water to surge onto the land. They are a major threat to low-lying coastal areas and their inhabitants. The largest storm surges are caused by tropical cyclones (also called hurricanes and typhoons in different regions); peak water levels can exceed 7 m in height, and can result in extensive flooding, loss of life and damage to property. Global climate change may result in increased storm surge flooding in some areas, through intensification of the cyclones driving the storm surges and as a result of sea level rise. Mangroves can reduce storm surge water levels by slowing the flow of water and reducing surface waves. Therefore mangroves can potentially play a role in coastal defence and disaster risk reduction, either alone or alongside other risk reduction measures such as early warning systems and engineered coastal defence structures (e.g. sea walls). Measured rates of storm surge reduction through mangroves range from 5 to 50 centimetres water level reduction per kilometre of mangrove width. In addition, surface wind waves are expected to be reduced by more than 75% over one kilometre of mangroves. Few data are available on surge reduction rates through mangroves because of the difficulties associated with measuring water levels during storm surges. All data currently available are from the south-eastern United States, where networks of recorders have been placed in wetland areas. Numerical models and simulations, validated using this data, provide the only means of exploring the importance of different factors in reducing storm surge heights. The numerical model of Zhang et al. (2012; Estuarine, Coastal and Shelf Science 102: 11-23) suggests that mangroves are more effective at reducing the water levels of fast moving surges than those of slow moving surges. The model also indicates that water level reduction through mangroves is non-linear, with the greatest reduction in surge height occurring near the seaward edge of the mangroves. Seaward of mangroves, a bulge of water can form as the water piles up in front of the mangroves; this can increase storm surge levels in this area. Several topics relating to storm surge reduction by mangroves are yet to be explored, such as the effect of mangrove density, species composition and vegetative morphology. Dense mangrove forests, including species with aerial roots, are expected to increase storm surge reduction rates. By reducing water levels and wave energy, mangroves can save lives and reduce storm-surge related damage to infrastructure: during a typhoon in north-east India, mangroves reduced the number of lives lost, as well as reducing damage to houses, crops and possibly coastal defence structures. Mangroves can also help people recover after coastal disasters by providing firewood, building materials and food sources (e.g. fish and shellfish that live among mangrove aerial roots). Cyclones and storm surges also impact mangroves themselves; some trees may be defoliated or uprooted. Extreme events with very high water levels and wind speeds may severely damage or destroy mangrove areas, rendering them less effective at reducing surge heights. Natural recovery can take many years to decades; restoration projects may speed up recovery. Further data on storm surge reduction by mangroves and further refinements to numerical models and simulations will improve our ability to understand and quantify the coastal defence services provided by mangrove forests against storm surges. Such information is needed to ensure that the coastal defence functions of mangroves are utilised appropriately, either alone or in combination with other measures, to reduce risk to people and infrastructure from storm surges.

Coastal populations are particularly vulnerable to the impacts of extreme events such as storms and hurricanes, and these pressures may be exacerbated through the influence of climate change and sea level rise. Coastal ecosystems such as mangrove forests are increasingly being promoted and used as a tool in coastal defence strategies. There remains, however, a pressing need to better understand the roles that ecosystems can play in defending coasts. This report focuses on mangrove forests and the role they can play in reducing wind and swell waves. While mangrove forests are usually found on shores with little incoming wave energy, they may receive larger waves during storms, hurricanes and periods of high winds. Large wind and swell waves can cause flooding and damage to coastal infrastructure. By reducing wave energy and height, mangroves can potentially reduce associated damage. All evidence suggests that mangroves can reduce the height of wind and swell waves over relatively short distances: wave height can be reduced by between 13 and 66% over 100 m of mangroves. The highest rate of wave height reduction per unit distance occurs near the mangrove edge, as waves begin their passage through the mangroves. A number of characteristics of mangroves affect the rate of reduction of wave height with distance, most notably the physical structure of the trees. Waves are most rapidly reduced when they pass through a greater density of obstacles. Mangroves with aerial roots will attenuate waves in shallow water more rapidly than those without. At greater water depths, waves may pass above aerial roots, but the lower branches can perform a similar function. The slope of the shore and the height of the waves also affect wave reduction rates through mangroves. To understand the level of protection provided by mangroves, and to plan how to increase it, the passage of waves through mangroves has been modelled numerically using both a standard wave model used by coastal engineers called SWAN (Simulating WAves Nearshore) (Suzuki et al., 2011), as well as a model developed specifically for waves in mangroves called WAPROMAN (WAve PROpagation in MANgrove Forest) (Vo-Luong and Massel, 2008). These models are able to predict typical levels of wave attenuation given a knowledge of the mangrove characteristics, the wave parameters and the local bathymetry and topography. A statistical model has also been developed to explore the relationship between some standard forest measurements (tree height, tree density and canopy closure) and wave attenuation with distance (Bao, 2011). This model has been able to predict wave reduction within the Vietnamese mangroves where it was developed, and could be used to determine the width of mangrove belt needed to deliver a predefined level of protection from waves. While there is a general confirmation that mangroves can attenuate wind and swell waves, research has focused on small waves (wave height < 70 cm), and there is a need to measure the attenuation of larger wind and swell waves associated with greater water depths, which may occur during storms and cyclones. More datasets are also needed to test the wider validity of the existing wave models under different wave conditions and in areas with different types of mangrove forest and different topographies.

Coastal rock structures are widely used in coastal engineering for a variety of purposes, including controlling the morphological development of beaches and providing protection against coastal erosion or flooding by wave overtopping. Strict adherence to existing design guidance has resulted in many of these structures being built using multiple layers of different rock sizes, high quality imported rock and carefully prepared foundations. Some innovative structures have, however, used locally available rock with simpler cross-sections placed on unprepared foundations, apparently without significant reduction to the overall performance of the scheme. This report gives guidance from a short research project which examined practical experience on rock structures from around the UK, with particularly emphasis on those that depart from conventional design rules. The report demonstrates that there are opportunities for lower cost rock structures for beach control and coast protection. Established design guidance provides a good degree of confidence in predictions of performance of coastal structures, but it is widely perceived that simple design rules can be overly prescriptive, particularly for nearshore structures in shallow water depths. The opportunities for lower cost structures principally relate to improved assessment of armour size for depth-limited waves, reduction in armour size for closer armour packing, and the need for complex underlayer / filters. The report emphasises the need to understand the performance of individual structures in the context of the overall scheme and ultimately national objectives, which provides an incentive to re-explore the balance between cost and structure performance. It also encourages the consideration of cost issues during the design of rock structures. Although the use of lower cost structures may also provide safety and environmental advantages, the structures described are envisaged to be of greatest benefit in locations where conventional structures would not be economically justified.

Manual for reporters with factual information related to the coasts of the USA. Includes legal information, environmental requirements.

This document outlines the Cabinet's position on water management policy in the 21st century. Immediately fuelling this is my concern about increasing water levels in the rivers, flooding, and the accelerated rise in sea level. In a country like the Netherlands, the geography of which is dominated by the sea and the mouths of four great rivers, water and natural space are inextricably bound to one another. For centuries, spatial planning in the low-lying Netherlands has been a matter of separating and maintaining the separation between land and water. And we have benefited from this, considering the fact that two-thirds of the gross national product (around NLG 400 billion annually) is generated domestically. But changes are brewing. Climatic changes are increasing the likelihood of flooding and water-related problems. In addition, population density continues to grow, as does the potential of the economy and, consequently, the vulnerability of the economy and society to disaster. Two undesirable developments that, in terms of safety, potentiate one another - a growing risk with even larger consequences. As such, the safety risk is growing at an accelerated pace (safety risk = chance multiplied by consequence). In 1999, together with the president of the Association of Water Boards (UvW), I requested an independent Committee to determine whether current water management policy is sufficiently equipped for the future - an effort that came none too soon. Across Europe and abroad, we have witnessed the consequences of superfluous water. The events in Switzerland, Italy and the UK have shown us the importance of looking ahead. The Committee concluded that the current water management system was not capable of responding to future developments. In order to keep the Netherlands safe, liveable and attractive in terms of water for inhabitants and investors for the century to come, a change in water management policy and in the way we approach water is required. This change involves the idea that the Netherlands will have to make more frequent concessions. We will have to relinquish space to water, and not win space from it, in order to curb the growing risk of disaster due to flooding, limit water-related problems and be able to store water for expected periods of drought. By this, I do not mean space in terms of the height of ever taller dykes or depth through continued channel dredging, but space in the sense of breadth. This will cost space, but in return we will increase safety and limit waterrelated problems. Safety is an interest that must play a different role in spatial planning. Only by relinquishing space can we set things right and if this is not done in a timely manner, water will sooner or later reclaim the space in its own, perhaps even dramatic, manner. My argument to innovate water management policy appears to be widely accepted, but more is required. It demands creativity, energy, time and money. Protecting the Netherlands from flooding will require repeated investments over a long period of time.

Summary of the Dutch coastal zone policy for the years 2000-2001