Doi.org/10.1006/ecss.2000.0635

From WikiLetters
Jump to navigation Jump to search

Target Article

Ridd P., Day, G., Thomas, S., Harradence, J., Fox, D., Bunt, J., Renagi, O., Jago, C. (2001). Measurement of sediment deposition rates using an optical backscatter sensor. Estuarine Coastal and Shelf Science. 52(2), 155-163 Available at: https://www.sciencedirect.com/science/article/pii/S0272771400906358 doi: 10.1006/ecss.2000.0635

Significant Claim

This paper describes a sensor for measuring the deposition of sediment that could be applicable for a range of conditions including marine and freshwater systems, and potentially for industrial applications. The instrument uses an upward pointing optical backscatter sensor in which a bundle of optic fibres form an aperture in a smooth horizontal plastic plate. As sediment falls onto the plate, the response of the optical backscatter sensor changes. The bundle of optic fibres is divided into two groups: one group transits infra-red light into the water, while the other group receives the backscattered light from the deposited sediment. The sensitivity of the sensor is very high, which allows the sensor to detect the thicknesses of sediment deposition down to only a few tens of microns.

Possible caveat with this article

In this critique, a weakness of the instrument will be described that came to light after extensive testing, viz the system as described in Ridd et al. (2001), which is limited to use in systems where the water movement is very slow compared to the sediment fall velocity. The process of settling onto a horizontal plate is highly dependent on the boundary layer characteristics, and thus the roughness and shape of the surface upon which settling occurs. Horizontal flow changes the boundary layer, and thus the quantity of sediment that may fall onto a smooth horizontal plate. This deposition may not be the same as the quantity that would have fallen onto a surface such as the sea bed or a piece of coral. This dependence of sediment deposition on roughness has been discussed at length by Whinney et al. (2017) who developed a much-improved version of the sensor for the specific application of measuring deposition on coral. Whinney et al. (2017)[1] describe an instrument where the optical fibre backscatter sensor is mounted on a system with similar roughness and characteristics to real coral.

However, in determining the sediment deposition on the seabed, it is difficult to see how the upward pointing backscatter sensor can be mounted, so as to not interfere with the natural boundary flow characteristics.

For systems such as settling ponds or other industrial applications where the flows rates can be controlled to be very quiescent, the system described by Ridd et al. (2001) is useful.

References

  1. * [1] Whinney, J., et al., 2017. Continuous in situ monitoring of sediment deposition in shallow benthic environments. Coral Reefs, 36(2): 521-533., doi: 10.1007/s00338-016-1536-7

Comments

In WL-Letters you have the freedom to respond to any caveat that may be inaccurate.
-- Andutta (talk) 00:12, 7 July 2022 (UTC)