1 

Stable Channels
The form and size of a channel in cohesionless material stable against erosion for a definite discharge are studied. The angle of internal friction and the limiting tractive force 'tmax are taken as known. Distribution of shearing stresses is assumed to be such that they are proportional to the distance between bottom and water surface, measured at right angles to the bottom. In addition to the action of gravity and shearing stress the grains are acted upon by a hydrodynamic lift force.
proving to be proportional to the shearing forces. The differential equation of the bottom form is established and integrated numerically; the form depends on internal friction.
Based on the logarithmic law of velocity distribution and the assumed distribution of shearing stressea, the velocities in all parts of the cross section can be found, and the total discharge is found by numerical integration. A profile consisting of thé curved "bankpart"of the above mentioned cross section and a "middlepart" of indefinite width and of constant depth y would be stable for the same tractive force. On the assumption however that nature will produce that cross section which has a minimum of area, only one definite solution, viz. the equilibrium profile, is found. The dimensions depend not on internal friction alone but also on the relative roughness of the bottom. Provided that the hydraulic roughness is assumed Ymax to be in conformity with that of natural watercourses, it is found that the area of the equilibrium profile varies slowly with <f and must be proportional to (~0.9 . V"'maxJ The above assumptions are checked by calculation of a complete set of isovels. Further three model tests, carried out in Vienna in 1916. are studied and compared with profiles calculated according to this theory.

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2 

Experimental study of wave forces on rubble mound breakwater crown walls
This paper has two main objectives: (1) to describe the experimental work carried out in order to verify the theoretical method from Martin (1995) for the calculation of wave forces on crown walls and (2) to show some results from field and lab measurements and compare these data to calculations from several analytical methods.
The Principe de Asturias Breakwater at Port of Gijon has been taken as the reference structure in this study. The experimental work (prototype and scale models) has been carried out over the same cross section, corresponding to this breakwater. Three scales have been used here: scale 1:1 (prototype measurements), scale 1:18..4 (tests done at Laboratorio de Ingenieria Maritima, UPC, Barcelona) and scale 1 :90 (tests done at Laboratorio de Ingenierfa Oceanogratica, Universidad de Cantabria). Therefore, data from the same phenomena in three different scales are available, which will provide the basis to analyse scale effects in the lab. The main part of the experimental work was carried out from 1995 to 1998 .. Due to the large costs of such a long experimental project, several organisations (referred in the acknowledgements section) were asked for financial support to the study. This is a good example of longterm project which was possible by the joint effort of, several institutions (public and private) within the European Research Framework.
In the paper, forces from the tests are compared to calculations done from the method proposed by Martin (1995). The comparison shows good agreement between the calculations and the measurements from the lab, and notsogood agreement to prototype data. From these results, it can be stated that the method is working well as it was developed from lab data From this study, it can be stated that differences to prototype forces are due to scale effects between lab and prototype measurements.

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3 

Fenderconstructies
Afmeerkrachten bij centrisch en excentrisch botsen van een schip tegen fenderpalen en bij aanvaren van een verend remmingwerk; invloed traagheid van het water op afmeerkrachten, aanvullende beschouwing betreffende botsen van schepen tegen remmingwerken (rekenen in tijddomein)

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4 

Floating breakwaters: State of the art, literature review
A multitude of conceptual models of floating breakwaters have been proposed without extensive or complete evaluation of most of these concepts. The technical literature regarding floating breakwater applicability and design procedures is fragmentary and sometimes confusing. Clear, concise guidance does not always exist for those responsible for planning and developing wave protection measures which utilize floating breakwaters. This study reviewed and evaluated the existing technical literature (theoretical, field, and laboratory) on floating breakwater concepts.
While floating breakwaters provide a lesser assurable degree of protection than a permanently fixed breakwater, they are in general less expensive and can be moved from one location to another. The cost of a floating system is only slightly dependent on ,.,rater depth and foundation conditions. Adequate wave reduction or energy attenuation can be attained by a floating breakwater only if the incident wave is of a relatively low height. A reasonable magnitude appears to be an incident wave height not exceeding 4 feet, with a corresponding wave period not exceeding 4 seconds. Floating breakwaters can attenuate waves with these incident characteristics to a magnitude tolerable in a smallcraft mooring area (wave heights up to 1.5 feet). Openocean applications of a distinctly different concept can be formulated to withstand substantial increases in the incident wave characteristics.
A group of prismatic structures contains the simplest forms of floating breakwaters. This group offers the best possibilities for multiple use as walkways, storage, boat moorings, and fishing piers. In addition to mass, the radius of gyration and the depth of submergence appear to significantly influence the attenuation characteristics. As the ratio of breakwater widthto wavelength increases to values greater than 0.5, the wave attenuation features of the structure not only improve markedly, but the net result of the forces on the mooring and anchoring system becomes substantially less. This occurs because the wave dynamics are exerting forces on a part of the structure in a direction opposite to those forces on other parts of the breakwater.

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5 

Shock Pressures Caused by Waves Breaking against Coastal Structures
Shock pressures of high intensity and short duration may occur during breaking of waves on coastal structures, slamming of ships, landing of seaplanes, and water entry of naval projectiles with flat nose. The phenomenon of shock pressures resulting from the impact between a solid and a liquid can better be described as a water hammer phenomenon wherein the elasticity of the solid and the compressibility of the liquid are the governing factors. The water hammer theory predicts the extreme values of shock pressures since it neglects the effect of air that might be entrapped between the solid an the liquid at the moment of impact. Analytical formulations of shock pressures as a water hammer phenomenon and as the compression of a thin layer of air entrapped between the solid and the liquid at the moment of impact are presented in this report.
Tests were conducted by dropping a steel, aluminum or plastic plate whose edge was hinged at the water surface into a 3 by 3 by 6ft steel tank that was partially filled with water. The shock pressures were measured at two locations by means of strain gage and piezoelectric type pressure cells mounted in the plate with special adapters.
The ratio between the recorded and theoretical pressures when treated statistically was found to fit the Poisson distribution well. Correlation between the recorded pressures and the shape of the surface of contact between the solid and the liquid at the moment of impact indicated that although shock pressures have a great intensity, they have a short duration and occur only at some spots on the surface of the solid. Therefore (a) they should not be applied as static pressure for checking the stability of the coastal structure as a whole, (b) they may be absorbed by flexible structures, (c) they may cause cracks in rigid structures such as steel caissons filled with rock, and (d) they may affect the stability of structures that have natural frequencies within the range of duration of shock pressures. Equations and diagrams for the prediction of the magnitude and duration of shock pressures resulting from the impact between a solid and a liquid are presented herein.

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6 

Loads on fender structures and dolphins by sailing ships
Fender structures and dolphins form an important part of the navigable canal. They have many functions: they must be able to guide and slow down ships, they must protect structures aft of ships against impacts from ships, and must protect ships from these structures. In addition, they must act as berthing or waiting places for ships. Fender structures and dolphins are installed where one or more of these functions are required, generally when passing nearby sluices, bridges, harbour entrances, etc. The costs of constructing and maintaining fender structures and dolphins may be considerable, thus savings in construction or maintenance costs, together with efficient operation, are very important.
Up until recently schematised calculation methods, with dimensioning approach velocities and angles of the ships, obtained from practical observation, were used by the Netherlands Ministry of Public Works, Locks and Weirs Directorate, for designing fender structures and dolphins. The fender structures built meet the requirements previously laid down.
However, at a time when fender structures and dolphins must be designed as economically as possible, and when ships are increasing in both size (e.g. push tows) and speed, there is a need to provide better calculation methods and more broadly based general conditions.
For these reasons a study has been carried out to determine the loading of fender structures and dolphins by sailing ships. This Rijkswaterstaat Communication gives a survey of the study carried out.
This Rijkswaterstaat Communication is drawn up in two parts. The first part contains an introduction to, and summary of, the study (Chapt. 1), and a determination of the data required for determining the impact forces (Chapters 2 to 5 inclusive). The second part contains the determination of the impact forces by calculations and model investigation (Chapters 6 to 9 inclusive).

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7 

Dwarskracht in ingegoten basalt tijdens golfaanval

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8 

Belastingen op remmingwerken door schepen, varend onder een hoek tegen het remmingwerk

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9 

Influence of Ambient Air Pressure on Impact Pressures Caused by Breaking Waves
Experimental research to the influence of the air pressure on the impact pressure cause by breaking waves.
The research shows that there are three factors which load the structure during the breaking of waves: the water layer over the structure, the shock due to the impact of the water jet from breaking and the air pocket entrapped in the water mass. The influence of all of the factors is determined.

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10 

Mound Breakwaters under Wave Attack
Research on rubble mound breakwaters when confronted with waves. The rapport covers the flow characteristics and mound stability under regular waves and under oblique wave attack.
The authors find a formula for rough, permeable slopes, flow characteristics under the action of a regular wave train by a function of the type. Furthermore they conclude that the distribution of flow characteristics in sea state can be obtained on the basis of interaction curves and joint probability density function of wave heights and periods.
The conclusions on the mound stability of breakwaters are:
Stability conditions of an undefined, rough, permeable slope are governed by the stability function.
The stability function depends only on Iribarren's number.
Randomness can be accounted for by using confidence bands for the stability function.
For each type of armour unit, an optimum slope of maximum stability exists. The greater the interlocking among armour units the steeper the optimum slope and the more peaked the stability maximum.
Given a rubble mound breakwater a minimum sea state exists which produces a significant failure probability. If a sea state is presented which is the same or higher than this minimum, failure of the structure is only a question of the duration of the sea state.
Conclusions on the characteristics and stability of rubble mound breakwaters under oblique wave attack:
There is a dangerous lack of experimental data on the subject.
Runup and rundown under small oblique incidence of waves (angle lower than 45 degrees) are function of Ir.cos(theta). For higher incidence angles the hypothesis is unreliable.
The stability of steep slopes under oblique wave attack is not worse than under perpendicular wave incidence. For milder slopes the opposite may be true.
The failure of probability of a rubble mound breakwater under a sea state with oblique incidence, can be calculated by taking into account the breaking limit, the interaction curve and a joint distribution of wave heights and periods.

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11 

Rekenmodellen voor het botsen van schepen tegen remmingwerken: theoretische benaderingen voor de invloed van het water

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12 

Recent Italian Experience in the Design and Construction of Vertical Breakwaters
Italy is often considered as a mother country of vertical breakwaters for harbour protection, since they have been widely used all along our coasts long since. An updated location map is given in fig. 1, which also shows the position of the directional wave recording stations of the existing Italian network. The most common vertical breakwaters are in fact composed by prefabricated monolithic cellular r.c. caissons, which are typically floated and sunk with seawater ballast upon a rubble mound foundation and then filled with sand and/or concrete. They are also called "upright" or "composite" breakwaters. New research work (including largescale physical models and advanced numerical models) is being addressed to the dynamic behaviour of vertical structures, particularly under breaking wave impact loading, as within the ECfunded MAST G6S project (199092), which already produced many new contributions (see references). Also a new PIANC working group (n.28) is just about to start.
This report gives useful information on the most recent caisson breakwaters designed and constructed in Italy, which include particular solutions for the configuration of the caisson walls and superstructure in order to reduce the main "drawbacks" of vertical structures, such as wave reflection and toe scour, wave forces and wave overtopping.
This report concludes that vertical breakwaters are still very popular structures in Italy, despite the dramatic failures occurred to a few old breakwaters in the last 60 years. The main reasons for this "success" can be attributed to:
 the progress in construction technology of prefabricated monolithic concrete caissons which ensures reduced costs, shorter installation times and better quality and durability of the structure (with low maintenance);
 a favourable environmental impact in relation to spatial and visual obstruction, potential removability of infilled caissons and smaller air/water/acoustic pollution during construction compared to a rubble mound;
 the greater confidence in the design which takes advantage of the recent advances of knowledge in maritime hydraulics and of the extensive use of laboratory model testing;
 the introduction of new alternative caisson geometries (e.g. cylindrical fronts, perforated absorbing chambers, sloping parapet walls) which can reduce the wave forces, wave reflection, overtopping discharge and toe scour effects.
The safety against wave overtopping in particular is gaining importance for the increased recreational use of breakwaters which should he easily accessible to the public.
Further improvement of knowledge of the complex wavecaissonfoundation interaction are being achieved from new research activity (particularly within the present European MAST G6S project) and increased practical engineering experience. Useful information is also expected from new prototype measurements, just about to start in two instrumented caissons of the West Breakwater at Porto Torres industrial harbour.
A better insight of the effective dynamic response of vertical structures under high impact forces due to breaking waves will undoubtedly promote a wider application of the caisson technology even in shallow waters and will lead to safer and more economic breakwaters.

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13 

Mathematical Model to Predict the Behavior of DeepDraft Vessels in Restricted Waterways
Presently deepdraft navigation channel analysis, design and review is based on empirically derived ratios of the design vessel's dimensions. Because of radical changes in vessel operation purposes and characteristics, these ratios can no longer be safely or economically applied.
The mathematical model and related theory described in this document provide the engineer with a comprehensive tool in the design and review of deepdraft navigation channels. Through its use he will be able to predict values of squat, bank suction forces and moments, equilibrium drift and rudder angles, and heights of shipgenerated waves for varied channel configurations, ship positions and ship velocities. Through the determination of channel section configuration sensitivity, an optimal design both operationally and economically can be achieved.

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