Velocity and water-layer thickness of overtopping flows on sea dikes: Report of measurements and formulas development
The study aims to establish a set of formulas estimating velocity and depth of overtopping flows at sea dikes including seaward-side slope, crest and landward-side slope. These formulas are applicable to flows which are generated by natural waves and the simulator giving associated characteristics of any arbitrary value of exceedance probability. Note that the probability is based on the total number of incident waves and not to be confused with the total number of overtopping events. The difference between the fictitious wave run-up level and the crest level (Ru2% - Rc) is widely considered as a measure of the (potential) energy of wave overtopping. This term is therefore used to estimate values of the mean overtopping discharges, ow velocities, water-layer thickness and overtopping volumes. In line with many existing research works and guidelines, the potential term is crucial to derive other parameters. Experimental data of Van Gent [2002] is reanalyzed with a slightly different perspective to achieve the study objective. The analysis procedure basically consists of three main steps:  from wave conditions and dike cross-section to calculate wave run-up levels;  from wave run-up levels to estimate flow parameters on the dike crest;  from flow parameters on the dike crest to further compute the corresponding parameters on the landward slope. The obtained equations are verified with flow measurements of the simulator on real dike slopes. Consequently, feasible values representing the roughness of different grass coverings are determined.
Damage to Grass Covered Slopes Due to Overtopping
Many dike failures have been ignited by damage due to erosion on the landward slopes. This paper investigates how grass covered slopes perform when being attacked by overtopping flow during storm surges. Based on observations during a number of simulator tests, damage is classified into three types 'head-cut', 'roll-up' and 'collapse' depending on the combination of grass, material components and corresponding layer thickness. To quantitatively predict the potential types, strength ratio and thickness ratio are proposed. Besides, erosion usually starts at weak spots so their spatial distributions are evaluated along dike stretches with various lengths. Finally, the overtopping resistance of a grass turf is presumably represented by critical velocities depending on soil cohesion and apparent cohesion induced by roots. The computed results are comparable to erosion on Bermuda and Carpet grass slopes tested with the simulator.
Facies and microfacies of slope deposits
Abstract This paper reviews the facies and microfacies of the main types of slope deposits. Lamination and sorting, when preserved, are good evidence for overland flow. Features due to deformation (folds, boudins, coatings and tails due to the rotation of clasts) are associated with the early stages of deformation in earth slides. Other mass-movements such as debris flows, rock avalanches, earth flows, and to a certain extent, dry grain flows may be characterised by similar microscopic facies, typically a poorly sorted, porphyric material. Porosity gives evidence for both liquefaction (debris flows) and frost-induced mass-movement (solifluction). However, this criterion is thought to be irrelevant for fossil deposits owing to the rapidity and scale of post-depositional changes (wetting and drying, freezing and thawing, bioturbation). At present, only a detailed analysis of both the macro- and micromorphological characteristics of the deposits allows an accurate identification of past slope dynamics.