Hydraulic Roughness and Mobility of Three Oyster-Bed Artificial Substrate Materials

Abstract

Laboratory and field studies were conducted, for applications by resource managers, to examine how proposed artificial oyster bed substrate replenishment materials, tire chips and heat expanded shale, compare to oyster shells in terms of hydraulic roughness and ease of transport by currents and waves. Under steady undirectional flows, beds composed of tire chips and oyster shells produce similar large roughnesses that cause appreciable form drag and reduce skin friction thereby reducing mobility. However, oscillatory wave- and boat-wake-induced flows, typical of shallow field situations, easily transport tire chips but not oyster shells or heat-expanded shale. It is concluded that tire chips are unsuitable for use as a substrate material in shallow estuarine environments exposed to wind waves or recurrent large boat wakes. In contrast, heat- expanded shale is roughly equivalent to oyster shells in terms of physical stability.