Browsing by Author "Hollander, Liza"
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- ItemWave runup on rocky coasts(Stellenbosch : Stellenbosch University, 2022-04) Hollander, Liza; Theron, Andre Karl; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: This study investigated wave runup on rocky coasts by considering both boulder beaches and rocky platform beaches. The wave runup height is a key component in determining coastal flooding hazard levels and coastal setback lines. Wave runup can be observed and measured along a shoreline but can also be predicted by several numerical prediction methods. Methods have been developed to predict wave runup on natural sandy shorelines and coastal protection structures, such as the Nielsen & Hanslow (1991), the Mather et al (2011) and the Stockdon et al (2006) models, the Coastal Engineering Manual (2006) and the EurOtop (2016) Manual, but there are no prediction methods explicitly developed for natural rocky shorelines. A characterisation of rocky coasts was developed to investigate wave action and runup on boulder and rocky platform beaches. Topographic surveys, site observations and drone photogrammetry products, namely Digital Terrain and Surface Models and Orthomosaic maps were used. These were obtained at three boulder beach and three rocky platform sites, located in Strand and Kogelbaai in False Bay, South Africa. A morphodynamic classification method was applied along with an analysis of the structural characterisation factors, namely the profile gradient, roughness and permeability. The Terrain Ruggedness Index and Vector Ruggedness Measure in ArcGIS and a slope deviation method was used to analyse the roughness. The permeability was based on the percentage of stationary rocks versus the percentage of sand and cobbles and pebbles. Thereafter, a wave runup scoring system was developed based on the forementioned structural characterisation factors. Wave runup measurements were conducted at the Kogelbaai sites. The wave conditions were recorded at the time of the tests and were used as inputs for the five forementioned prediction methods. The measured runup heights were also used to test the wave runup scoring system. The first application of the scoring system showed that it was useful, accurate and easy to use and could be applied as a first estimate of the relative wave runup potential of different sites. Physical modelling was conducted at the Stellenbosch University Hydraulics Laboratory in a 2D wave flume equipped with an HR Wallingford wavemaker. The model was a representative profile based on Kogelbaai Site 1. Wave runup tests were conducted on a smooth impermeable profile and an impermeable profile with boulders. Video footage of the wave runup tests were visually analysed to obtain the wave runup heights above still water level. The field data and physical modelling wave runup results were used to evaluate the prediction methods. The initial analysis showed that the Stockdon (2006) Model and the Mather (2011) Model had the most accurate prediction values for the field data and the physical modelling data sets respectively. Thereafter, further analyses were done by proposing a roughness influence factor to adapt the prediction models, which enabled a significant improvement in the prediction results at boulder beaches. The final recommendation was that the Stockdon (2006) Model should be applied to predict wave runup on natural boulder beaches and the adapted Stockdon (2006) Model, using ๐พ๐,๐๐ก๐๐๐๐๐๐,๐ต๐ต = โ0.26 ร ๐0 + 0.99, should be applied to predict wave runup on impermeable profiles with boulders.