A Conductivity Sensor for Nearbed Sediment Concentration Profiling

Abstract

A new sensor that measures the vertical profile of nearbed sediment concentration is described. The conductivity-based sensor is composed of eight electrode pairs separated in the vertical by 2.5 ? 10?3 m. Electrode pairs are sampled at 16 Hz, with higher rates achievable. Each electrode pair response is linear over the range of conductivity tested from 0.2 to 0.65 mS cm?1 that exceeds the range of conductivity values corresponding to sediment?water mixtures from clear water to the packed bed limit of 0.65 m3 m?3. A laboratory test over a planar sloping beach indicates the capability of the sensor to simultaneously quantify sediment concentration profiles from roughly 0.01 m below to 0.1 m above the at-rest bed. The data indicate that the upper few millimeters of the bed are highly mobile and that bed dilation and sediment mobility vary considerably over a swash cycle.