A Silt-Salinity-Depth Profiling Instrument

Abstract

The planning of new port facilities in muddy estuaries often calls for the acquisition of velocity, salinity and suspended solids data throughout the length of the estuary at several stages of the tidal cycle. The tidal regime in most estuaries causes periodic scour, transport in suspension, and deposition of fine grained sediments. Interaction of the tidal and fluvial flows may generate a pattern of saline stratification and longitudinal density currents which are important in determining the zones of maximum siltation in the navigation channel. Each estuary has a unique tidal current-salinity-sediment transport regime. It is a major exercise to organise the simultaneous measurement of these variables from a series of stationary barges or boats, especially if the salinity and sediment transport patterns depend on the occurrence of particular combinations of tides and fluvial flows. Because the measurement of salinity and suspended solids by conventional sampling techniques is a slow process, a profiling instrument has been developed at the Hydraulics Research Station, which permits measurements to be made rapidly from a high speed launch at several sites during substantially identical tidal states. This paper describes the design of the transducers used for salinity and suspended solids measurements, and how they have been incorporated into a simple low cost system for rapid indications of the results.