Scour and Erosion. Proceedings of the 7th International Conference on Scour and Erosion

This paper introduces an experimentally based study into backward erosion piping. The motivations for and aims of the study are outlined and the experimental setup and procedures are described. Experimental challenges are highlighted and innovative methods to overcome them presented. New experimental techniquespresented include: a constant head tank capable of providing continuous head variation between 0.3 to 4.0m in 5mm increments; measurement of water velocity in inaccessible, small sand channels; preventing bio-clogging from interfering with the backward erosion process; and drying large quantities of sand in an inexpensive, time efficient manner. An account of experiment observations is given which groups the backward erosion process into 5 stages: fluidisation, tip progression, equilibrium, forward deepening and failure. Initial results are provided and compared to similar testing from other researchers to demonstrate repeatability and accuracy of the experimental setup and procedure. An outline of the intended future experiments is given including major test groups and their respective objectives and variables

Proceedings of the 34th Hydrology & Water Resources Symposium

This paper presents a review of the engineering techniques currently available for assessment of scour of rock by water. Such techniques are typically applied for design of unlined rock spillways or sections of channel downstream of chute or plunge spillways. The current techniques, while numerous, each apply to limited and specific conditions, which in this paper have been categorised into four distinguishable hydraulic conditions common to spillways. Commentary on the options relevant to design of Australian spillways is given, and important uncertainties and limitations in the existing techniques are highlighted

A physical model study of culvert blockage by large urban debris

© 2015 Engineers Australia. Abstract: A large-scale laboratory study has been completed to characterise the impacts of large urban debris blockage on a representative box culvert. A formal definition of hydraulic blockage is proposed: Hydraulic blockage(%) = Hblocked - Hunblocked/ Hblocked × 100% where Hblocked and Hunblocked are the upstream total energies for the blocked and unblocked conditions respectively. The study shows that hydraulic blockage values can be considerably different from perceived values of traditional visual blockage. Stochastic testing allowed the behaviours of large urban debris on approach to a culvert to be observed. Debris tends to align with its long axis parallel to the direction of flow. A common observation was that floating debris impacts the culvert headwall and then is dragged downwards by the flow so that it becomes tilted up towards the headwall with its upstream end supported by the bed. The hydraulic blockages of different debris types and orientations were quantified. The data provided in this study were obtained to allow worst-case estimates of hydraulic blockage to be determined. Blockage conditions of 100% were not observed during this study. Incorporating waterway hoods increased the efficiency of culvert priming and reduced the blockage by up to 17%. For conditions where large-scale debris is a major risk, culvert hoods will improve overall hydraulic performance of culverts and may be a cost-effective option for mitigating debris risk

Experimental investigation of global backward erosion and suffusion of soils in embankment dams

Many embankment dams constructed with a core of nonplastic or very low plasticity silt–sand–gravel (typically of glacial, fluvioglacial or alluvial origin) have experienced internal erosion. This has often expressed itself with the development of sinkholes or with intermittent episodes of increased leakage, which then reduces. In this investigation 22 soil samples with gradations representing the range of the soils used in embankment dam cores have been tested in the laboratory. All 22 soils tested were shown to be internally unstable with particle movement within the soil after placement. Some soils exhibited global backward erosion (GBE), others suffusion, and some internal instability but with no erosion from the sample, indicating self-filtering. The internal erosion process was very rapid for suffusive soils, typically occurring within minutes of test commencement, and at a gradient of 1. For soils subject to GBE and no-erosion soils, the internal movement of particles continued for weeks and months, and re-activated when the overall gradient was increased. For GBE, the erosion process occurred over a range of gradients. A method for predicting the amount of erosion and the erosion mechanism based on the gradation of the soil has been developed that is related to the ability of the soil to self-filter

Managing Adaptation of Urban Water Systems in a Changing Climate

Current evidence is that climate change is occurring, it is largely manmade and it will have significant implications for human civilisation. Australia is particularly vulnerable to the anticipated effects of climate change, creating major challenges for water resource management and water supply security. Climate change adaptation offers a means by which we can reduce our exposure to future climate change risks, whilst at the same time exploiting any potential benefits that may arise from climatic changes. This review outlines the current major climate change adaptation challenges facing the water supply industry at large, with a particular focus on these challenges in an Australian context. It also aims to highlight the critical knowledge gaps and strategies required to assist in the formulation of adaptation responses to the range of potential impacts on water infrastructure and future water security. A diverse range of management and assessment techniques are used by relevant professions in industry. Here, an adaptive management approach is presented highlighting the important information required for robust assessment

On the threshold for wave breaking of two-dimensional deep water wave groups in the absence and presence of wind

The threshold for the onset of breaking proposed by Barthelemy et al. (arXiv:1508.06002v1, 2015) has been investigated in the laboratory for unidirectional wave groups in deep water and extended to include different classes of wave groups and moderate wind forcing. Thermal image velocimetry was used to compare measurements of the wave crest point (maximum elevation and also the point of maximum) surface water particle velocity (Us) with the wave crest point speed (C) determined by an array of closely spaced wave gauges. The crest point surface energy flux ratio Bx = Us/C that distinguishes maximum recurrence from marginal breaking was found to be 0.840 ± 0.016. Increasing wind forcing from zero to Uλ/r/C0 = 1.42 systematically increased this threshold by 2 %. Increasing the spectral bandwidth (decreasing the Benjamin-Feir index from 0.39 to 0.31) systematically reduced the threshold by 1.5 %

CContemporary challenges for dams : conference proceedings : 2015 / ANCOLD

The method of Annandale (1995) is widely used by Australian practitioners for the assessment of erosion in unlined spillways. This method is based on comparison to various case studies, where the geology at each site is characterised using the Kirsten index (a rock mass index previously developed to assess the rippability of rock), and the hydraulic conditions are characterised using the unit stream powerdissipation. In this paper, the historical development of this comparative design technique is traced and is critically reviewed against the original geotechnical and hydraulic data, and against a new, independent,dataset gained from unlined spillways in fractured rock in Australia, South Africa and the USA. It is shown that, while erosion can be usefully correlated against rock-mass indices and hydraulic indices, this‘comparative’ design technique has been promoted beyond its reach - the data do not support the inference of an erosion ‘threshold’ as presented by Annandale (1995). It is argued that this type of analysis should be used only as an initial ‘first indication of erosion potential’, as originally proposed by van Schalkwyk (1994b)