A Conductivity Sensor for Nearbed Sediment Concentration Profiling

摘要

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 m~3 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.