Pedro Lomonaco

PROTOTYPE ANALYSIS OF STABILITY OF RUBBLE MOUND PROTECTIONS FOR SUBMARINE OUTFALLS

This paper presents the construction, surveying and results of a prototype experiment on stability of rubble mound protection for submarine outfalls. Taking advantage of the Santander outfall construction, financial support from the European Community was obtained to carry out the experiment that consisted of covering the outer layer of the outfall’s protection with two extra layers of rubble with a stone weight smaller than that of the project. Three stone weights were tested in three different stretches of the outfall. The experiment lasted two years, during which waves and stone movements were surveyed. Damage and wave data were analyzed and the damage parameter is presented here as a function of the mobility parameter. To take into account the random characteristics of waves in the sea states, a Montecarlo simulation is used here to calculate the mobility parameters corresponding to all the waves of all the sea states that reached the experimental sections. The use of the average of the 50 biggest mobility parameters that reached the test sections at the survey date is proposed here to represent damage results against the mobility parameter. Using this mobility parameter, prototype results compare well with laboratory experiments carried out with regular waves. INTRODUCTION Submarine outfalls for wastewater are economical alternatives in coastal areas to wastewater treatment plants. In coastal areas of high wave energy like the northwest of Spain and in those sites were the bottom characteristics do not allow the burial of the pipe, the outfalls are protected by several layers of rubble. 1 Associate Professor, University of Cantabria, Avda. de los Castros, s/n 39005 Santander, Spain. vidalc@unican.es 2 Assoc. Researcher, University of Cantabria, Avda. de los Castros, s/n 39005 Santander, Spain. lomonacop@unican.es 3 Associate Professor, University of Cantabria, Avda. de los Castros, s/n 39005 Santander, Spain. martinfl@unican.es Vidal, Lomonaco, and Martin 1 The existing methods for the assessment of the armor layer stability against wave action are based on extrapolations of formulas developed for submerged breakwaters or for the determination of sediment transport on horizontal bottoms. The existing uncertainty about their applicability to the deep outfall protections may result in conservative, oversized designs. During the 1990’s, the application in Spain of the European Union regulations for wastewater emissions generated a high number of outfall projects for coastal cities in the North Atlantic waters of Spain. Most of these outfalls were designed with rubble protections. The application of the existing formulas showed great differences among the prescribed weights of the stones required in those sections of the outfall where the water was deep enough to prevent the rubble from the direct action of the breaking waves. To cover this lack of stability formulations, the Ocean & Coastal Research Group (hereafter GIOC) of the University of Cantabria started in 1997 several R&D Projects founded by the Spanish Commission for Science and Technology (CICYT) and by the European Founds for Regional Development (FEDER). After extensive experimental work in wave tank, a methodology for the assessment of the stability of near bed rubble protections, based on the mobility parameter, was presented in Vidal et al. (1999). In 1999, the GIOC obtained FEDER founding to carry out the construction and survey of several prototype test sections over the outfall of Santander that was being built at that time. The outfall’s building company, Dragados y Construcciones, S.A, collaborated in the Project, building these test sections after the main protection was completed. The prototype experiments started in September 1999 and ended in August 2001. The objective of the test was to measure the stone movement due to wave action. This paper presents the prototype experiment and their results. SITE DESCRIPTION AND WORK PLAN The prototype experiment was designed to take place over the outfall of Santander that extends 2 Km into the Cantabrian sea from the cliffs of La Virgen del Mar (6 Km to the northwest o the city) up to 40 m water depth, were the diffusion section is located, see figure 1. The pipe is buried in the rocky bottom at a 15-m water depth. Deeper than this, the pipe lays over the bottom, protected by a core of 5 cm gravel, a filter of two layers of 200-300 Kg of quarry stones, and an armor of two layers of 3,000 Kg quarry stones, see figure 2. Vidal, Lomonaco, and Martin 2 ATLANTIC OCEAN PENAS EMOD Diffusion section REMRO Test section Santander Figure 1: Location of test section and wave buoys. The prototype experiment was planned to start just after the protection of the pipe was completed. Test sections were built using the same equipment and type of rock used by the building company.

Wave Height, Pressure and Velocity DCF's around Rubble Mound Protections for Submarine Outfalls

A statistical comparison is presented between measured and computed cumulative distribution functions of wave height, pressure and velocity around and inside rubble mounds for submarine outfalls. The data set is obtained from laboratory and prototype experiments, originally designed to determine the stability of the stones protecting the pipeline. From the experiments, it was found that the peak horizontal velocity at the crest of the structure is continuously underestimated during the design stages. Generally speaking, although all cumulative distribution functions follow reasonably well the Rayleigh distribution, the largest waves deviates, yielding an increased maximum value for pressures and velocities. Since the stability of the stones is directly linked with this velocity, an enhanced formulation to assess it has been tested successfully, although the performance of the model has to be improved.

ON PERMEABLE RUBBLE MOUND COASTAL STRUCTURES

The morphodynamic effect of permeable jetties at tidal inlets and adjacent beaches is discussed in the paper. A thorough description of the different morphologic aspects of inlets stabilized with groins and jetties is also presented. It is shown that a deep understanding of the sediment fluxes and identification of the sedimentary units is required, in order to analyze the sediment budget, long-term behavior and proper management practices of an inlet and its adjacent beaches. The available experience related to sites with permeable groins is reviewed, and an understanding of the processes of leaking water and sediments through the rubble mound structure is developed. Physical model tests performed for a specific jettied inlet site are also described, gaining a closer understanding of the main parameters involved in the process.

Tsunami Response in Semienclosed Tidal Basins Using an Aggregated Model

An aggregated model to evaluate tsunami response in semienclosed water bodies is presented in this work. The model is based on one-dimensional shallow water equations and can include long-wave external forcing such as a tsunami. It has been successfully validated against experimental data from a physical model, and its predictions for a case study have been compared with results from the Cornell multigrid coupled tsunami (COMCOT) model. The model can be used as a predictive tool because a calibration using a theoretical value for expansion and contraction losses has been performed and differences with the typical calibration are less than 10%, which is considered acceptable. This allows using the model in the absence of measured data, which is very difficult to obtain in case of a tsunami event. A case study for the Gulf of Cadiz (Spain) has been simulated with the COMCOT model. The aggregated model predicted the response for a harbor more accurately than for estuarine systems with tidal flats. Nevertheless, the aggregated model has been demonstrated as a useful general tool to predict the response of semienclosed tidal basins to a tsunami event, and hybrid models coupling advanced models to simulate ocean tsunami propagation with the model presented here would be useful in developing coastal warning alert systems.

Flow Measurements and Numerical Simulation on Low-Crested Structures for Coastal Protection

A series of laboratory and prototype experiments have been performed to measure and model the flow around and inside low-crested structures and submerged breakwaters. The results of the tests are used to improve the understanding of the wave-structure interaction and its effect on the near-shore dynamics. The database become the core to develop an empirical model to determine dynamic pressure and velocity profiles for design purposes, and to assess the laboratory scale effects on coastal structures. Finally, the large amount of measured information is used to calibrate and validate COBRAS, a 2DV, VOF-type, RANS numerical model, proven to be a powerful tool for the functional and structural design of low-crested and submerged breakwaters, as well as a numerical wave flume to increase the applicability of empirical models.

STATISTICAL ANALYSIS OF DIRECTIONAL SEA STATE PERSISTENCE

A statistical model for the long-term distribution of wave height duration is developed in this work. The relationship between directional sea state intensity and sea state duration is obtained by means of a mathematical model that describes the bivariate distribution of significant wave height and the duration of the persistence. The application of the methodology to a particular site on the northern coast of Spain shows that the proposed model can be used to determine the wave climate, improving the results from existing formulations. INTRODUCTION Historically, the evaluation of the wave conditions at a particular site has only focused on frequency analysis of the intensity alone, typically significant wave height, H. Wave measurement programs have contributed to the longer duration of available data sets allowing the study for other climate variables. In port engineering operations and also in offshore and coastal engineering, the duration of persistence (D) of the sea state intensity is of considerable interest since it makes the planning of engineering operations possible from a statistical viewpoint. Recently, the new “Recommendations for maritime and harbour works in Spain (ROM 0.0)” (Puertos del Estado, 2001) establish new conditions for the design of maritime works. This handbook establishes that “All maritime work is constructed to comply, during an interval of time, with specific functions, according to certain requirements of reliability, functionability and operativity”. In particular, the operativity, which defines the working 1 Postdoctoral Researcher, Ocean & Coastal Research Group, Dpto. de Ciencias y Tecnicas del Agua y del Medio Ambiente, Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander, Spain. mendezf@unican.es 2 Professor, Ocean & Coastal Research Group, Dpto. de Ciencias y Tecnicas del Agua y del Medio Ambiente, Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander, Spain medinar@unican.es 3 Postdoctoral Researcher, Ocean & Coastal Research Group, Dpto. de Ciencias y Tecnicas del Agua y del Medio Ambiente, Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander, Spain. lomonaco@puer.unican.es Mendez, Medina, and Lomonaco 1 conditions of the maritime structure, must be defined using three indicators: a) the minimum operativity; b) the average number of admissible technical breakdowns and c) the maximum duration of the technical breakdowns. The minimum operativity is usually expressed in terms of a sea state parameter (in general the significant wave height). The technical breakdown is produced when the significant wave height, H, is greater than a value given by the Recommendations. This information is usually represented by the cumulative distribution function (cdf) of the significant wave height , that is, the long-term distribution. So, for the threshold which defines the technical breakdown, the probability of non-exceedance of significant wave height defines the minimum operativity. ( ) H F H As technical breakdown is defined by the significant wave height, the average number of breakdowns and the maximum duration of technical breakdowns can also be calculated using the significant wave height. Nevertheless, in this case it is necessary to consider the sea state curve. Given a threshold that defines the minimum operativity, there is a number of events N and a duration of exceedance, D, different for each one. Both the significant wave height, H, (or the intensity) and the duration of the exceedance, D, above the threshold H are random variables. Therefore, it will be necessary to obtain the long-term distribution of wave height duration, that is, the joint probability density function pdf fH,D(H,D) (see figure 1).

Impact du port sur la plage de Gijón

ABSTRACT The construction of Torres breakwater, as part of the expansion plan of the industrial port of Gijón (Spain), requires a previous evaluation of the structure morphodynamic impact on the beaches in the vicinity of the port. This paper contains the specific study of the San Lorenzo beach morphodynamic behaviour, directly affected by the presence of the new breakwater. The changes on wave propagation, namely a reduction of the incident energy and diffraction of the wave fronts, induce a beach profile steepening and a clockwise rotation of the coastline. This configuration change, coupled with a sand nourishment, would permit to overcome the current lack of dry beach and, as a consequence, to improve the functionality of the beach.