The development of the POST system for in-situ intertidal measurements

A suite of instruments has been developed with the objective of providing accurate data on suspended sediment concentrations and profiles in the very shallow water (of depth <1.0 m) of intertidal estuarine mudflats. Such data on sediment movement is essential for the quantification of erosion and accretion processes on intertidal mudflats, particularly to calibrate the sediment transport models used for environmental management. Miniature electromagnetic current meters (EMCMs) were constructed, comprising 2-cm diameter discus shaped sensors. These sensors had a linear response to flow speeds of at least 1.0 m s^-1. Which was unaltered by sediment concentrations to 15 g l^-1. The accuracy was ±3% for measurements within 2 mm of the bed. Miniaturised optical turbidity probes were developed using a narrow band infra-red source and spectrally matched receiver (λ=960 nm). Optical backscatter sensors (OBS) measured mud concentrations from 0 to 50 g l^-1. With a resolution of at least 1% depending upon calibration. The equipment was called POST (Profiles Of Sediment Transport) and has been deployed successfully during both the MAST II and III programmes and the results have been published