DEVELOPMENT OF A NEARSHORE EXTREME EVENTS RECONNAISSANCE COMMUNITY

Extreme events have significant impacts on the nearshore water-land system - where ocean, sound, and estuary processes interact with the nearby land - that pose high risk to society. Observations before, during, and after these events are critical to improve understanding of the interactions and feedbacks among the natural and built environments during major storms, and the corresponding human actions and reactions. The goal of the Nearshore Extreme Events Reconnaissance (NEER) Association is to organize and coordinate a national network of scientists spanning many disciplines to perform rapid, pre-and post-event site characterization, to deploy instruments to observe event processes, and to gather virtual data about the event and provide support to field teams. This presentation provides information about NEER's motivation, event-response and coordination activities, data-distribution plans, and lessons learned to date. Funding for NEER is provided by the U.S. National Science Foundation Coastlines and People Program.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/9I9Z3OLGszU

ANALYSIS OF THE IMPACT PROCESS AT DIKES WITH CROWN WALLS AND PARAPETS

This paper is focused on the analysis of the impact process at dikes with crown walls and parapets under breaking and non-breaking waves. A small-scale laboratory campaign was performed at the Hydraulic Laboratory of Bologna. The experiments were aimed to analyze the vertical pressure distribution along the crown wall and the resulting wave forces, by varying geometrical and hydraulic parameters. The tested configurations included different off-shore slopes, dike crest widths, crown-wall heights, dike crest freeboards and the inclusion of the parapet. The measurements were combined with the image analysis of the run-up and of the wave impact process. A sub-set of the experiments was numerically reproduced, with the openFOAM modelling suite, to support and to extend the experimental results. The results confirmed the link between the air content, the shape and the magnitude of the pressures according to the breaker type, already observed for larger-scale experiments.

MODELLING OF WAVE OVERTOPPING FLOW OVER COMPLEX DIKE GEOMETRIES: CASE STUDY OF THE AFSLUITDIJK

Grass cover erosion by overtopping waves is one of the main failure mechanisms of dikes. Transitions in cover type and geometry can increase the hydraulic load and are therefore identified as vulnerable locations for grass cover erosion. Two models are applied to the inner slope of the Afsluitdijk in the Netherlands to show how transitions can be included in overtopping models. Firstly, the analytical grass-erosion model is used to simulate the erosion depth along the profile for a six-hour storm. The model results show that the erosion depth is maximal at the end of the two slopes in the profile. Secondly, the effect of transitions on the hydraulic load is computed with a detailed hydrodynamic model. The model results show that geometric transitions significantly influence the shear stress, the normal stress and the pressure. Four vulnerable locations for grass cover erosion are identified based on the model results that are related to slope changes along the profile. Furthermore, the model results show that the overtopping flow is mainly affected by geometric transitions, while no effect of roughness transitions on the modelled forces was observed.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/t1cPJwf72nE

COASTAL ENGINEERING ANALYSIS AND DESIGN OF A FETCH-LIMITED STORM-TRACKED LACUSTRINE MARINA

A marina for small crafts is being planned to be built within Caliraya Lake situated at an elevation of 290m above Mean Sea Level (maMSL). Unlike sea-connected water bodies, the water level of Caliraya Lake is largely influenced not by tidal fluctuations, but by the operational water level requirements of the hydroelectric power plant that it caters to. Due to the large difference in the Normal High Water Level (NHWL) and Minimum Operating Level (MOL) of the lake of 2.5m, a floating pontoon marina with guide piles was contemplated to be used. The marina analysis and design approaches implemented in this study considered waves generated by prevailing winds and ship-generated wakes to assess the wave climate and tranquility within the marina. Since the project area is also frequently tracked by typhoons, wind- and pressure-driven storm surges were also used for the vertical siting of the guide piles. Lastly, based on the geographic appearances of the lake shoreline and with the small size of the lake, the fetch limitations resulted to very small wind-generated waves and wind setup considered as wind-driven storm surge components. In comparison to open seas where wind-driven storm surge accounts for approximately 95percent of the total storm surge, the wind-driven storm surge components for the potentially critical historical typhoons which traversed within 200-km radius of the project area only generated 10-30percent of the total storm surge considered for the vertical siting.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/m-XEEw6r99g

NUMERICAL SIMULATIONS ON INFLUENCE OF LONG-TERM FLUCTUATION OF MEAN WATER LEVEL ON SAND WAVES IN THE KANMON WATERWAY, JAPAN

In this study, the numerical simulation of tidal current and sediment transport in the Kanmon Waterway were performed by using a numerical simulation model FVCOM (Finite Volume Community Ocean Model (Chen et al. 2003)), in order to discuss the influence of the long-term fluctuation of mean water level on the sand waves. The numerical simulation results suggested that the spatial difference of the long-term fluctuation of mean water level in the Kanmon Straits slightly changes the tidal current around Tanoura Area, and consequently affects the development of sand waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/kfMfIVGiLKM

ROLE OF SPATIAL VARIABILITY OF SOIL RESISTANCE IN ALONGSHORE VARIABILITY OF COASTAL BARRIERS RESPONSE TO SUPERSTORM SURGES

Sand dunes and other natural coastal barriers (e.g. barrier islands) represent important components of the defense system against consequences of storm surges. However, in many coastal systems, major storm surges represent important drivers of coastal erosion. Increased extreme events potentially result in accelerated coastal erosion, coastal barrier breaching, and coastal flooding. The response of a barrier to a storm surge is often determined by mutual interaction among the driving hydrodynamics, the subsequent morphodynamics, and the local geology, including spatial variations of subaqueous bathymetry and subaerial topography. However, the effect of alongshore variability of soil properties on the alongshore varying response is not yet considered. Therefore, this study examines soil parameters that may affect coastal erosion during major storm surges. Moreover, it applies a novel extension of the numerical model XBeach that accounts for spatial variation of soil properties to an artificial dune system of spatially varying soil permeability. Results showed that variability of soil permeability alongshore the dune results in alongshore varying resistance to erosion so that breaches may occur at the locations of less resistance that are corresponding to locations of higher soil permeability. Outcomes of the numerical simulations proved also that reduced soil permeability represents a nature-based solution that increases the resilience of natural defense systems during major storm surges by mitigating rates of coastal erosion.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/1ERwbW5BmYA

ROUND ABOUT MACHINE LEARNING

In this talk I will review the use of Machine Learning in studies of coastal morphodynamics. I will discuss a number of problems where ML tools have been used and why it makes sense to use ML methods. I will also outline recent advances in ML algorithms and applications, and discuss possible areas for future research.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/X5QnAdD1-T8

PRELIMINARY ASSESSMENT OF WAVE ENERGY IN SRI LANKA

Preliminary results of a numerical model developed to detail spatial and temporal assessment of theoretically available near shore wave energy, and potential wave energy extracting sites, along the Sri Lankan coast is presented in this paper. Wave energy is estimated applying Danish Hydraulic Institute's Mike 21 Spectral Wave (SW) module. The model is developed and applied covering an area along the coast line of entire country extending from 315000 to 640000 mE, and 602000 to 1164000 mN. Model was run with boundary inputs of wind and wave, based on long term measured, and long term hindcast directional wave data available at seven locations, which are well distributed around the country. Model calibration and validation are carried out based on long term measured directional wave data at Colombo, Sri Lanka. Based on the estimated wave energy density maps, and spatial and temporal energy variations, Hambantota, in South East coast is identified as the most feasible location for wave energy harnessing. Annual and seasonal availability of the wave energy, for Hambantota area, at 25 m depth, were looked into in detail. In the above area, mean annual energy potential was estimated as 10 kW/m at 25 m depth, whereas maximum annual potential energy was estimated as 36 kW/m. During South West monsoon, where high waves are present, the mean energy potential is estimated as 15 kW/m.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/dPa9istaB7A

RECOVERY OF SANDY BEACH AFTER TYPHOON WAVES - CASE STUDY ON CHIGASAKI COAST

Beach topography quickly changes in response to the action of storm waves, resulting in erosion of the foreshore with accretion under a calm wave condition after a storm. These seasonal beach changes may occur on beaches with protective measures or artificial beaches produced by beach nourishment. On these beaches, the shore protection function of a sandy beach is reduced when a trough is formed immediately offshore of the shoreline and the foreshore slope increases, indicating the importance of the study on topographic changes. Moreover, the time required for a beach recovery in response to wave conditions has not been sufficiently studied, along with the 3-D topographic changes associated with beach cycles. In this study, we aim to investigate these issues using the Narrow Multi-Beam survey data, wave data, and seabed materials data, taking the Chigasaki coast as an example. It was found that a seabed shallower than 2 and 3 m depths was eroded by rapid offshore sand transport during a storm event with the deposition of sand in a zone between 3 and 5 m depths, and then the beach recovered within 1-2 years after the storm. It was also confirmed that a bar and trough disappeared in 1-2 months under the conditions of HE = 0.5 m, TE = 8 s, and H/L = 0.005 when the crown depth of the bar was smaller than approximately 2 m. Thus, the topography after the storm waves recovers within several months or 1-2 years depending on wave conditions and the crown depth of the bar.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/W_P_3p_xd8U

CIRCULAR SHAPED ROUGHNESS ELEMENTS TO MITIGATE OVERTOPPING OF COASTAL REVETMENTS

This paper presents preliminary design guidelines for wave overtopping when circular-shaped roughness elements (ring-type revetment) are placed on the upper slope of a coastal revetment. Such a type of revetment was designed during the tendering phase of the Afsluitdijk reinforcement in 2017 as an innovative and highly effective way of reducing overtopping rates along coastal revetments. The design combines a relatively smooth lower slope (~1 in 2.5), wide storm berm (~1.5x wave height) and the roughened upper slope (~1 in 3) with a specific pattern of circular elements, resulting in a roughness comparable to that of a double layer rubble mound slope with an impermeable core. To effectively reduce overtopping rates, the circular elements require an average height of ~1/10 of the wave height and diameter of ~1/3 of the wave height, as well as a specific placement pattern (staggered pattern and spacing ~1/10 of the wave height).Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EYxSI9ymYa4