Experimental Study on Toe Scouring at Sloping Walls with Gravel Foreshores

M Salauddin,J M Pearson

doi:10.3390/jmse7070198

Abstract

Sea defences, such as urban seawalls can fail due to the development of a scour hole at the toe of the structure. The scour depth or the information on ground levels at the structure toe is required for the sustainable management of coastal defences, due to its influence on the structural performance. This research reports and summarises the main findings of a new laboratory study on toe scouring at a smooth sloping wall with permeable gravel foreshore. A set of small-scale laboratory experiments of wave-induced scouring at sloping seawalls were conducted. Two gravel sediments of prototype d50 values of 13 mm and 24 mm were used to simulate the permeable 1:20 (V:H) gravel beach configurations in the front of a smooth 1 in 2 sloping wall. Each experiment comprised of a sequence of around 1000 random waves of a JONSWAP energy spectrum with a peak enhancement factor of 3.3. The relationship of the scour depth with toe water depth, Iribarren number, and wall slope were investigated from the test results of this work and through a comparison with available datasets in the literature. The results of this study showed that the relative toe water depth and Iribarren number influence the relative toe scour depth at a sloping structure on a shingle beach. Within the experimental limitations, the maximum toe scour depths were observed for the experiments under spilling and plunging wave attack.

Highlights

Toe scouring at a coastal structure is usually defined as the development of a scour hole at the toe of the structure
The reflection co-efficient varied from 0.25 to 0.45 at a relatively deep water, near the structure the distribution of wave heights for deep water conditions for two test configurations, and compares the results with the estimated Rayleigh distribution. It is clearly seen from the graphs that the resulting data points show a good agreement with the Rayleigh distribution for both low and high wave steepness the measured wave heights were found to deviate from the expected Rayleigh distribution for very high waves, which may be a result of the Jl.iMmairt.aStciio. nEnsgo. 2f0p19a,d7,d1l9e8 generation, such as the wave paddle stroke or wave breaking on the pa5dodf l1e2
The relationship of scour depth with toe water depth, Iribarren number, and wall slope were investigated from the test results of this work and through a comparison with the available dataset in the literature

Summary

Introduction

Toe scouring at a coastal structure is usually defined as the development of a scour hole at the toe of the structure. Based on a laboratory study on scour depths at vertical structures with a sandy slope and two gravel slopes, [19] proposed an empirical relationship between the maximum wave height at the toe of the slope, submergence of the berm, and local wave length to estimate the scour depth at this type of sea defence. Two gravel sediments of prototype d50 values of 13 mm and 24 mm were used to simulate the permeable 1:20 (V:H) gravel beach configurations at smooth 1 in 2 sloping walls The findings of this laboratory study provide the data and comprehensive knowledge that are required to understand the toe scouring phenomenon at a sloping structure with a gravel foreshore

Laboratory Set-Up

Inshore Wave Conditions

Variation of Toe Scour Depth with Iribarren Number

Conclusions