Paolo De Girolamo

Application of wavelet transform analysis to landslide generated waves

The aim of this paper is to illustrate the results of a preliminary study on aerial landslide-generated waves, which has been mainly intended to establish a method for analyzing water surface records. Some simple physical experiments, reproducing the Scott Russells wave generator, were carried out in a small two-dimensional wave flume; the Wavelet Transform (WT) is applied to analyze wave measurements and it is shown that useful information can be obtained by means of this technique. The celerity of impulsively generated waves, reflection by an overflow structure and seiching phenomena of the flume are studied. A discussion of the results along with some remarks about ongoing research is also given.

An experiment on harbour resonance induced by incident regular waves and irregular short waves

It is generally accepted that bound long waves generated by wind waves excite harbour resonance. Nevertheless it is not clear if there are differences in the harbour response when resonance is induced by incident regular free long waves or by incident bound long waves. This experimental investigation aims at determining these differences for a narrow long bay. The finite water depth inside and outside the narrow bay is constant. For incident bound long waves, two cases have been studied: in the first case bound long waves are generated by carrier bichromatic short waves which form regular wave groups; in the second case bound long waves are generated by irregular short waves. The experimental setup allows the characteristics of the forcing waves to be defined with a good degree of accuracy. The bay response is obtained for the three cases of regular free long waves and bound long waves for regular and irregular groups.

Internal generation of waves in 2D fully elliptic mild-slope equation FEM models

Abstract This paper looks at an alternative approach for the treatment of open boundaries in linear wave field simulations by means of fully elliptic mild-slope equation (MSE) finite elements models. In these kinds of models, the domain of investigation is traditionally contoured both by reflecting–absorbing boundaries, which simulate the coastline or the structures that emerge from the sea, and by an ‘open’ or ‘artificial’ boundary, which separates the sea region included in the domain from the semi-infinite region that extends outward to infinity. The approach presented here assumes the domain to be completely contoured by reflecting–absorbing boundaries. A total absorbing boundary is, in particular, assumed to separate the inner (finite) from the outer (semi-infinite) sea region. Sources of energy, which generate waves of specified height and period, are located within the domain along a line in the proximity of the inner–outer sea region boundary. Reflected and scattered waves can propagate over the generation line and are absorbed at the open boundary. Numerical tests have been carried out to simulate progressive and stationary waves in a channel and long waves around a fully reflecting circular island on a parabolic shoal, and to evaluate the amplification factors of a long and narrow bay. All these validation tests show a very good agreement with the available analytical solutions. A discussion is finally carried out on the advantages and disadvantages of the presented approach with respect to traditional ones.

Forecasting Landslide Generated Tsunamis: a Review

When earthquakes occur, suddenly bottom deformations will induce water response that is almost instantaneous. Then, bottom displacements affect wide areas and generate transient waves (tsunamis) usually characterized by a relatively small heightwith respect to their length, i.e. by a small steepness. Indeed, just after the earthquake, the water free surface mimics the final bottom deformations, that can be of the order of some meters, and small amplitude long waves start to propagate resulting in a potential transoceanic devastation (Synolakis et al., 2002). When either subaerial or submerged landslides occur, thedisplacementswill takeplace onboth larger temporal-, and smaller spatial-scale. The deformations are of the order of hundreds of meters and the generated waves are quite different from those induced by submarine earthquakes. Hence, landslide tsunamis tend to be a local phenomenon, although extreme. Since two centuries ago, submarine failures were related to “sea waves without earthquake” when great waves were observed without any account of earthquakes (e.g. Mallet & Mallet, 1858; Milne, 1898; Montessus de Ballore, 1907). In an illuminating reasoning Mallet & Mallet (1858) argued that “great underwater slippage takes place [...] the effect upon the surface of the sea is at the same moment to originate a positive and a negative wave. [...] The magnitude of the wave raised is dependent upon that of the mass of solid material that has suddenly changed its place, upon the depth of water in which the slippage has occurred, upon the rapidity of the transposition, and in minor degree upon the form and material of the portion of the bank that has slipped.” One of the more meaningful event occurred at Lituya Bay (Alaska, July 9, 1958), when a subaerial landslide triggered by an earthquake entered the water at the Gilbert Inlet and generated an impulse wave (Miller, 1960). The induced run-up was the highest known: the water rose up to 524m at the slope in front of the landslide, then thewaves propagated into the Bay and eventually radiated offshore through the Bay inlet with minimum effects outside the Bay itself. Another example, related to submarine failures, is the well documented tsunami generated by an underwater slump triggered by a magnitude 7 earthquake on July 17, 1998 close to the Sissano Lagoon, Sandaun Province, Papua NewGuinea (see Synolakis et al., 2002). The tsunami struck about 30 km wide area, i.e. rather small, by inducing a maximum run-up of about 15 m and killing over 2100 people. Landslide generated impulse waves can occur not only at the sea boundaries, but also in enclosed basins (i.e. reservoirs and lakes). The event that took place at the Vajont Valley (Italy) on October 9, 1963 is perhaps the more sorrowful one. A subaerial landslide of about 6

Algorithms for Automatic, Real-Time Tsunami Detection in Sea Level Measurements

Automatic, real-time tsunami detection in sea-level measurements is a main component of a tsunami early warning system (TEWS). Although a great effort has been recently undertaken by the scientific and engineering community in developing new technologies (e.g. satellite altimetry, detectors of low-frequency elastic oscillations associated to a tsunami) capable of increasing the awareness of potential tsunamis in the minimum amount of time, at present direct detection in sea level measurements is still the main mean to confirm their actual generation and propagation. Clearly, the device used to collect these measurements has to be chosen between those equippedwith sensors capable of detecting sea-level oscillationswithin the tsunami frequency band. At present, the main devices that can be actually used should belong to the following classes:

Influence of Dredged Channels on Wave Penetration into Harbors: The Malamocco Inlet Case

A natural or dredged channel extending outwards and harbor entrance may strongly influence wave penetration into the harbor itself. Bottom refraction and diffraction induced by the channel boundary slopes can actually cause either concentration or dispersion of wave energy at the harbor entrances, depending on the direction of the incoming waves. Wave penetration may therefore depend on directional spreading of incoming wave energy more than on its frequency spreading. The paper illustrates the results of an investigation carried out on the Malamocco inlet of the Venice lagoon in Italy by means of a 2D fully elliptic mild-slope equation FEM model, alongside a study intended to support barrier-system design aimed at protecting Venice from storm-surge flooding. Being characterized by a natural channel extending outwards its entrance actually makes this inlet as particularly suitable case study. Both frequency and directional spreading have been simulated by means of the superposition principle, either taking into account or not taking into account wave breaking. The results confirm the smoothing effect on both wave concentration and attenuation due to the directional spreading, and show that wave attenuation is to be expected for waves traveling along direction nearly parallel to the channel axis while wave concentration arises when the wave direction is about 20 to 30 degrees to the channel axis.

Evaluation of design waves along the Adriatic coast of the Venice lagoon

The prevention of flooding inside the Venice lagoon requires a system to disconnect the North Adriatic sea and the lagoon hydraulically in order to control the water level. This requires the definition of extreme design wave conditions for the various structures. This paper describes numerical modelling using a parametric wave prediction model to derive the design wave conditions outside the inlets to the lagoon. This includes a description of a verification study using buoy measurements and a sensitivity study into the effect of uncertainty in the model parameter settings.

Engineering Tools for the Estimation of Dredging-Induced Sediment Resuspension and Coastal Environmental Management

In recent years, increasing attention has been paid to environmental impacts that may re‐ sult from resuspension, sedimentation and increase in concentration of chemicals during dredging activities. Dredging dislodges and resuspends bottom sediments that are not captured by dredge-head movements. Resuspended sediments are advected far from the dredging site as a dredging plume and the increase in the suspended solid concentration (SSC) can strongly differ, in time and space, depending on site and operational condi‐ tions. Well-established international guidelines often include numerical modelling appli‐ cations to support environmental studies related to dredging activities. Despite the attention that has been focused on this issue, there is a lack of verified predictive techni‐ ques of plume dynamics at progressive distances from the different dredging sources, as a function of the employed dredging techniques and work programs, i.e., spatial and temporal variation of resuspension source. This chapter illustrates predictive techniques to estimate the SSC arising from dredges with different mechanisms of sediment release and to assess the spatial and temporal variability of the resulting plume in estuarine and coastal areas. Predictive tools are aimed to support technical choices during planning and operational phases and to better plan the location and frequency of environmental moni‐ toring activities during dredging execution.

Met-ocean and heeling analysis during the violent 21/22 october 2014 storm faced by the sailboat ECO40 in the gulf of lion: Comparison between measured and numerical wind data

On 19 October 2014 Matteo Miceli, a known italian oceanic sailor, left the Port of Riva di Traiano (Rome, IT) with the italian sailing boat ECO 40, for the Roma Ocean World Project. This ambitious challenge consists of a non-stop sailing alone around the World in energy and food self-sufficiency. ECO 40 is a Class 40 oceanic vessel (LOA of 12,0 m) that has been equipped with a data acquisition system for measuring both the met-ocean parameters recorded (apparent and real wind speed and wind direction, atmospheric pressure, current velocity, air temperature, sea temperature, etc.) and the kinematic characteristics of the boat itself (i.e., speed and course over ground). Furthermore, the boat has been equipped with three high precision GPS receivers, provided by Leica Geosystem, for measuring the motion of the boat and an inertial platform. Due to these high-precision instruments it is possible to fully measure and characterize the six degrees of freedom of the boat, and accordingly to use her as a sailing wave buoy. Within this paper we present the analysis of the met-ocean data measured by the boat during the storm occurred in the Gulf of Lion on the 21–22 October 2014 that ECO 40 has faced just few days after her departure. Furthermore, by analyzing the GPS signals by means of an innovative application of differential kinematic positioning technique, a detailed analysis of the boat heeling during the Gulf of Lion event has been carried out. The boat heeling measurements have been used to correct the measured wind data that have been compared with the hindcast time series.