Configurations of a piled row breakwater for a protected shallow water marina

[摘要] ENGLISH ABSTRACT:For the safekeeping or harbouring of small craft, whether for leisure or commercial use, atranquil basin is the principle requirement in designing a functional harbour facility. Wavestransmitted through the perimeter structures of a marina result in agitation of the basin andthereby a reduction in tranquillity. Similarly, waves reflected off the perimeter structures that lineentrance channels could result in difficulty when manoeuvring through the entrance channelwater areas.An alternative to the conventional breakwater becomes a necessity when the conventionalmass-filled or caisson breakwaters are not feasible in technical or financial terms. One of thealternative options could be to consider a piled row breakwater. In broad terms, this consists ofclosely spaced piles that attenuate wave energy whilst not forming an impermeable barrier,allowing for currents and sediment to pass through. When comparing the different options forcreating a piled row breakwater the quantity of material used to achieve a desired level of wavedissipation could be the most important aspect in considering possible alternatives, as this wouldrelate directly to construction costs and time when considering implementation.A literature review revealed multiple references to theories that predicted the transmitted andreflected waves for various breakwater porosities and wave conditions. However, there is limitedcoverage in literature enabling prospective designers. For example, literature describing theapplicable ranges of shape configurations that one should start off with when developingconcepts is not readily available.This thesis study used physical modelling to compare the wave transmission properties ofbreakwaters comprised of three different piled element shapes, namely round, square anddiagonal square piles. The pile element shapes are compared for varying porosity values over arange of input wave parameters. A comparison of the transmission incurred by theseconfigurations with previous work is presented and it was found that the physical modelexperiment closely simulated the predicted values. The tests were scaled from actual conditionsin possible marina locations and therefore the performance criteria measured could be applied inreverse to potential site locations.From analysis of the physical model results, it was clear that the highest energy loss was found,in general, to occur with low porosities (below 10%), as could be expected. For a fixed screenconfiguration in terms of pile element shape and porosity, the performance is heavily dependenton wave steepness, the steeper waves incurring a lower transmission coefficient than the lesssteep waves. For a given porosity, circular piles performed the best (transmit the least) followedby square piles and then diagonal square. When comparing the material used, diagonal squarepiles yielded better performing breakwaters due to the expanded cross section gained inelevation.The work has provided useful insight into the performance of piled row breakwaters in restrictingtransmission of wave energy. Design guidance has been provided when considering theparameters for deriving conceptual layouts for piled row breakwater structures.Recommendations were put forward for further work in this field, including potential study areas,data gathering, and study methods, as well as more applied uses of piles, for example incombination with other elements in a marina.

[发布机构] Stellenbosch University