Coastal structures IV

The severity of damages to riverine structures across German estuaries has increased in the past years due to the increase in the ship-induced loads. Here, the field data of a riverine rock-armored groyne tracked for a year is analyzed; the campaign began after the structure was rebuilt and finished when the structure presented severe damage. The ship-induced primary waves and water levels were recorded, and laser scans of the groyne armor were taken. Damage curves were derived and each increment of damage (ΔSe) was related to a ship-wave event and a passing ship. The most significant variables to describe ΔSe were the primary wave height, the partial blockage factor, the ship length and width and the relative velocity of the ship. The shape of the dependence between these variables is also analyzed, concluding that models more complex than the commonly used Gaussian copula might be needed.

Coastal zones have consistently been among the most appealing settlement areas due to their proximity to the sea, rich natural resources, and the high quality of life they offer. However, these regions are affected to climate change impacts, such as sea-level rise, storm surges, and an increased intensity of extreme weather events. Rubble-mound breakwaters, especially low-crested structures, are frequently utilized among the portfolio of potential typologies. However, it is expected that the variability of climate conditions will induce loss of functionality and structural integrity in the coming decades. The objective of this study is to propose a portfolio of alternative solutions for emerged or quasi-emerged rubble-mound breakwaters that are perceived as highly impacting structures. To achieve this goal, a hybrid approach is followed, including the best of physical and numerical investigations to get a better insight of their hydraulic performance.

Rock bags are a product developed in 1987 by Kyowa in Japan to protect against erosion from hydraulic processes in riverine, lake, coastal and marine environments. Within Australasia, the rock bags are imported and distributed by Bluemont Pty Ltd. However, the behaviour of rock bags in shallow water, coastal environments had not previously been assessed in a physical modelling study. This is despite the use of rock bags since 2020 as a temporary or emergency coastal protection unit for seawalls located at the back of some beaches in Australia (e.g. Wamberal Beach and Collaroy Beach). Since this is an emerging erosion protection application for rock bags, Bluemont wanted to assess their hydraulic stability in this arrangement using scale model laboratory tests. The UNSW Water Research Laboratory was engaged by Haskoning Australia to partner in carrying out a physical modelling study for Bluemont for shallow water seawalls constructed from rock bags.

A modification to the Keofloat system has been developed to address the effect that rotation about its vertical axes may have on the measurement accuracy of the system. The effect of rotation was found to rarely occur for some three-dimensional models. Consequently, the Keofloat design was modified from having a single suspension string to a double suspension string supporting it. A single and double suspension string Keofloat was tested in a and compared in a wave flume. Tests were conducted for regular waves between 0.5 mm and 23 mm and wave periods of 0.8 s and 1.6 s. 
The tests show that the double suspension string Keofloat compared extremely good to the single suspension string Keofloat and can reliably be used to measure small waves in a harbour basin where factors causing rotation of the Keofloat might be present.