J.D. Pitt, P. Ackers


This paper describes the performance of test panels of riprap on an offshore island in the Wash estuary, UK, for the first 2h years after their construction, by which time all but one had failed. It outlines the methods used in obtaining and analysing data on stone size, wind, tides and waves. The techniques used in surveying the test panels for damage and the reduction of the survey data to yield quantitative estimates of damage are described. Comparisons are made between the damage to the riprap panels and what might have been estimated using laboratory data. Results do not support any scale effect causing riprap sized on laboratory data to be larger than necessary, and this conclusion is supported by the outcome of model tests carried out retrospectively by the Hydraulics Research Station (now HRS Ltd) at Wallingford, UK. Slope protection is sensitive not only to wave height and stone size but also to construction methods and, bearing in mind possible departures from the desired specification, a cautious approach to the design of riprap protection is advisable.


prototype tests; riprap; random wave; wave attack

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