Research on Hydraulics and River Dynamics

This Special Issue includes nine original contributions focused on river hydraulics. Four of these resulted from cooperation between universities from different countries: (a) Russia and Poland , (b) Taiwan and the USA , (c) Iran and Italy, and (d) India and Italy . The other contributions resulted from research carried out in universities from South Korea [5], Greece [6], China , and Japan

Beach development behind detached breakwater.

Merged with duplicate record 10026.1/2650 on 06.20.2017 by CS (TIS)Concurrent wave and morphology data were collected around a coastal protection scheme on the U. K. south coast. The scheme consists of eight detached breakwaters protecting a renourished sand and shingle beach, and is situated in a strongly macro-tidal environment. The development of the beach morphology is described. The beach trapped sand and shingle moving eastwards into it, and lost material from the eastern end. While the beach was designed to maintain a shingle beach, it was found that the scheme was most effective at trapping sand, which led to tombolo formation behind the updrift breakwaters. Current engineering design methods for describing beach development were applied to the scheme. Empirical techniques were found to be poor predictors of the salient length, although the simplest methods were reasonable guides to the scheme response over a variety of tidal levels. The US Army Corps of Engineers one-line model GENESIS (Hanson, 1989) was applied to the scheme. Using observed values of beach, structure and wave conditions, it was necessary to exaggerate transport due to longshore gradients in wave height relative to transport due to oblique wave approach to correctly describe salient formation. While it was possible to reduce model calibration errors, model validation was not successful. This was due to the inability of the model to allow tombolo formation, and also due to the lack of a 'constant! beach profile, due to the different behaviour of the sand and shingle. Empiricalo rthogonafl unctiona nalysisw as carriedo ut on the beachs urveyd ata.F rom the limited records available, it was clear that the scheme reduced profile variance behind it, compared to the updrift and downdrift shorelinesT. he schemea lso led to morec omplex3 D seasonaml ovementso f beachm aterial,i n contrastto the predominantly2 D responseu pdrift

Performance-based management of flood defence systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Mixed sand and gravel beaches: accurate measurement of active layer depth to develop predictive models of sediment transport

This thesis addresses the need to calibrate longshore sediment transport equations for use on heavily managed mixed sediment beaches, which are becoming increasingly common but are still relatively understudied. This is achieved through the use of active layer measurements, tracer pebble experiments, and monitoring of morphodynamics over a total period of 16 months. It is unique in investigating a complex, artificially replenished, groyned mixed sand and gravel beach in this way. The groynes have a significant impact on beach morphology and sediment transport at Eastoke. Beach levels were monitored using repeated profiles at three main locations within a groyne cell, allowing for the effect of these structures on beach profile shape and response to changing wave climates to be assessed. This provides a more accurate representation of morphodynamics than would otherwise be available from semi-annual profile surveys. The beach response to hydrodynamic conditions was shown to be rapid, and not always indicative of drift direction. Sediment sorting was observed, but was not strongly correlated with wave conditions. A vast dataset of active layer measurements indicated significant variability, which has not been made clear by previous studies of active layer depth. The key finding of this thesis is that active layer depth as a percentage of wave height can be predicted from significant wave height using the equation ln(y) = -0.797x + 3.565 (R2 = 0.578), and this value can then be converted into a depth measurement. The prediction can be applied at a daily scale to the combined upper and mid beach as an estimate of the average active layer depth. Further field sites should be investigated to determine whether this equation can be applied to other mixed sediment beaches. Short- and medium-term pebble transport patterns were observed using passive integrated transponder (PIT) tagged pebbles, deployed in stages throughout the research. Sediment transport volumes were estimated based on field data, and hydrodynamic data used to calculate a range of drift coefficients (k) for the commonly used CERC transport formula. Low detection rates ultimately limit the confidence which can be applied to final calculations of longshore transport volumes and values of k, but this study provides insight into the complexities associated with studying a site like this, and suggestions for improvements which could be made to future research

Coastal Morphology Assessment and Coastal Protection

Sediment, which collects in rivers and seas to secure a large amount of aggregate, reduces the supply of earth and sand to coasts. Dams and breakwaters constructed in various places also impede the transportation of earth and sand. Furthermore, the maintenance dredging of dam lakes and waterways will also disrupt the supply of sediment to coasts if the dredged sediment is not released back into the water system. Due to these development activities, coastal erosion has become a serious problem in many beaches around the world. Moreover, due to the excessive industrial activities of human beings, the exacerbation of natural disasters caused by global warming is becoming a real problem. In addition, because great earthquakes with a magnitude of 9 or more have occurred about three times per 100 years at boundaries of the Pacific Crust Plate and the Nazca Crust Plate since 1700, the possibility of losing many lives and assets in the Pacific coastal areas due to a huge tsunami caused by a great earthquake should not be underestimated. Therefore, research into the prevention and mitigation of coastal erosion and coastal disasters is becoming increasingly important. This Special Issue, “Coastal Morphology Assessment and Coastal Protection”, consists of five peer-reviewed papers, collected to contribute to the technological progress on the prevention of coastal erosion and coastal disaster resulting from large waves and tsunamis

Mathematical modelling of shoreline evolution under climate change

This study focuses on the impact of potential changes in the wind-wave climate on shoreline change. The `one-line' model for medium to long-term prediction of coastline evolution is employed. New analytical and numerical solutions of this important model are described. Specifically: 1) original semi-analytical solutions are derived that relax the unrealistic assumption of existing analytical work that a constant wave condition drives shoreline change and, 2) a more general form of the one-line model is solved with a novel application of the `Method of Lines'. Model input consists of 30-year nearshore wave climate scenarios, corresponding to the `present' (1961-1990) and the future (2071-2100). Winds from a high resolution, (12km x 12km), regional climate model, obtained offshore of the south-central coast of England at a dense temporal resolution of 3 hours, are used to develop the aforementioned wave climate scenarios, through hindcast and inshore wave transformation. A hypothetical shoreline segment is adopted as a `benchmark' case for comparisons. Monthly and seasonal statistics of output shoreline positions are generated and assessedfo r relative changeso f `significance' between `present' and future. Different degrees of evidence that such changes do exist are found. This study is the first application of such high resolution climate model output to investigate climate change impact on shoreline response. Major findings include: 1) shoreline changes of `significance' are strongly linked to `significant' changes in future wave direction, 2) future changes appear smaller for entire seasons than for individual months, 3) shoreline position variability is often smaller in the future, 4) different climate model experiments produce diverging results; however, general trends are largely similar. The present study, at a fundamental level, offers analytical solutions of the 'oneline' model that are closer to reality and a numerical solution that is of increased effciency.. At a practical level, it contributes to better understanding of the patterns of shoreline response to changing offshore wave climate through: 1) the use of fast and straightforward methods that can accommodate numerous climate scenarios without need for data reduction, and 2) the development of a methodology for using climate model output for coastal climate change impact assessment studies