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Shingle beach response to swell wave action
Published in Zhao-Yin Wang, Shi-Xiong Hu, Stochastic Hydraulics 2000, 2020
Kaiming She, Paul Canning, Sally Sudworth
Swell waves are commonly perceived to result in onshore transport of sediment, leading to deposition of material at the beachhead. Swell waves thus act as a natural coastal defence measure. This was shown to be the case under the condition that the wave height did not exceed a certain value. Figure 1 shows the beach profiles at the end of four tests with the same wave period of 2.5 s. As the wave height was increased, the volume of material buildup at the beachhead due to onshore transport was increased. At a wave height of 80 mm, the onshore transport did not take place. The sediment movement took place in the offshore direction instead, resulting in a loss of beachhead material. The net change of the beach profile with respect to the initial profile are shown in Fig. 2, providing a clearer view of the beach material movement.
Design wave specification
Published in Dominic Reeve, Andrew Chadwick, Christopher Fleming, Coastal Engineering, 2018
Dominic Reeve, Andrew Chadwick, Christopher Fleming
A straightforward way of understanding swell is to return to Figure 2.1. Swell is a generic term applied to waves experienced at a point far from wave generation. Swell waves are characterised by being long-crested (focused in direction) and having long periods and relatively small wave heights. What makes these waves different from waves generated nearby is: (1) spreading – waves generated from afar will tend to be long-crested as waves propagating in different directions will not reach the observation point; (2) dispersion – in deep water, wave speed depends on wave period not water depth (see Section 2.2.4) and are ‘dispersive’. Thus far from the generation region, waves of different periods will be separated according to their speed, with the longer period waves travelling faster than shorter period ones. Due to the spreading and dispersion swell represents a fraction of the total energy that is imparted to the sea by storms, and the wave heights are correspondingly small. However, the energy within a single swell wave can exceed that in a single storm wave by virtue of its larger wave length. For example, a 1 m high swell wave of period 15 s has approximately the same energy as a 2 m high 7 s wind wave.
Intensifying swells and their impacts on the south coast of Java, Indonesia
Published in Coastal Engineering Journal, 2019
Wakhidatik Nurfaida, Takenori Shimozono
The study clarified the characteristics of the intensifying swells and their current impact level on coastal communities in the south coast of Central Java. A number of studies projected an increase in wave energy in the extra-tropical region of the southern Indian Ocean over the next decades. The further intensification of the swells may lead to an extreme event with severe damage to residential areas along the coastline. This issue is significant not only for the present study area but also for a broad region under the influence of the same swell source. Further studies will be needed to clarify the increasing coastal flood risk in the broad region and overcome the uncertainty in the future.
Effect of potential swell pressures on anchored sheet pile walls
Published in International Journal of Geotechnical Engineering, 2022
Numerous studies have been performed and methods have been developed to measure and predict the potential vertical swell (heave) magnitudes of expansive soils. Al-Shamrani and Dhowian (2003) list the indirect and direct methods used to predict the potential heave of expansive soils. The indirect methods are based on empirical and semi-empirical correlations relating swelling magnitudes or swell pressures to a soil property, such as Atterberg limits. The direct methods involve experimental measurement of swell parameters using oedometer or triaxial swell tests.
Indian Ocean wave forecasting system for wind waves: development and its validation
Published in Journal of Operational Oceanography, 2022
P. G. Remya, T. Rabi Ranjan, P. Sirisha, R. Harikumar, T. M. Balakrishnan Nair
High swell events and coastal flooding are quite frequent in the Indian coastal areas. The link between such events and the Southern Ocean meteorological conditions are already explored in the study of Remya et al. (2016). Hence forecast evaluation during the swell event is very important and one such case is analysed here. High swells from the Southern Ocean affected the regions of Kerala, south Tamil Nadu and West Bengal from 31st July to 4th August 2016 (furnished based on user feedback). A storm developed in the Southern Ocean (near50°S and 90°E) on 26th July 2016 was responsible for the high swell generation. The wind speed and Hs at the generation area was 24 m/s and 12 m respectively (not shown). The swell waves with period 18.13s hit the Kozhikode location on 1st August 15 UTC. As per model results, the first swell wave with period 18.8s hit the location on 1st August 3 UTC. Model simulation shows a lead of 12 hours in the arrival time of swells at the buoy location. An overestimation in wave periods is also seen along with a lead of 12 hours. In the deep ocean, the group velocity can be directly linked to the wave period and hence any overestimation in the wave period can lead to an increase of wave velocity. An increase in the velocity will cause a lead in the time of hit of swell trains in different places. Spatial validation of wind shows a positive bias in the SIO and hence the error in the swell waves might be due to the error in the swell source wind (Figure 9(a)). The time evolution of spectra for both observation and model at Kozhikode location is shown in Figure 12(a,b). Spectral shapes show a good agreement with an underestimation in maximum energy (>0.5m2/Hz) during the period. Figure 12(c) shows a comparison of spectra at 00UTC of 2nd August. A very good match of spectral shape can be seen in both low and high frequencies. The dominant low frequency peak was seen around 0.06 Hz in both model and observation, but the model could not accurately reproduce the maximum energy at the low frequency and it shows an energy underestimation of ∼0.8m2/Hz in dominant frequency. Also at the deep ocean location BD14, the model simulation shows a lead of 21 hours in the travel time and overestimation in the periods. In the model results, the first swell wave with period 17.79s hit the location BD14 on 1st August 03 UTC whereas the observations 16.8s on 2nd August 00 UTC (Figure 12(d,e)). Model Hs shows good agreement with observation till 3rdAugust. The underestimation seen in Hs during 3–4 August was attributed to the wind error (not shown). Tp also shows a very good match with observation with a lead of 18 hours in the swell arrival time. A detailed comparison of southern ocean wave conditions may reveal the reason for the lead which cannot be performed in this study due to the lack of observed data. Overall analyses suggest that the model is able to predict the swell events with a good level of accuracy and can be used for operational high period swell predictions.