Instrument for Sediment and Siltation Monitoring
The SediMeter™ instrument measures a 35 cm long turbidity profile using 36 optical backscatter detectors (OBS). Based on the turbidity profile it estimates the bottom level to ±2 mm. An optional wiper allows for field monitoring.
The SediMeter can be used for measuring siltation, erosion, and sedimentation rate, the latter both in terms of sediment accumulation rate, and in terms of sediment settling from suspension. It can be used to get real-time data on the dynamics of the sea floor.
The patented instrument consists of a computer and a sensor. This sedimeter sensor consists of an array of 36 infrared optical backscatter detectors. The turbidity is measured every 10 mm, and the bottom level is interpolated with 0.1 mm resolution. The sensor is controlled by the LogDator™ computer, which is also available separately as an under-water data logger.
A temperature sensor is included, and two optional sensors can be fitted, e.g., pressure and light. These sensors can be sampled many times per measurement. Potential uses include measuring wave frequency spectra (wave period).
Model SM2A can be used both as a stand-alone logger and connected to a cable. It has USB, RS-485, user interface, built-in memory, accepts SD/MMC memory cards, and runs on batteries and external power. The instrument requires our free computer software. Hundreds of instruments can be operated along a single cable in a network stretching over several kilometers.
Designed from Experience
The instrument is designed based on long experience in collecting and analysing sedimeter data. The goal is overall cost-effectiveness in small as well as large organisations, taking into account all associated costs—not just the price. In environmental monitoring it can be used for continuously measuring the accumulation of sediment spill (or sinking fractions from an oil spill) on sensitive bottoms. An optional sensor-cleaning wiper is available for longer deployments in fouling environments.
Helcom recommends that monitoring of the sedimentation pattern be mandatory during marine dredging. A network of SediMeters can be used for that purpose as described in our sedimentation monitoring plan. Hundreds of SediMeters can deliver data to a single buoy-mounted LogDator, which stores the data as files on a memory card for easy retrieval. As an example of criteria, the accumulation of sediment spill on mussel banks around Saltholm in Øresund is limited to 10 mm at any given time (i.e., 15 kg/m2).
A finger screw secures the SediMeter™ in a holder that is first screwed down into the bottom.
SediMeter™ mounting — the video shows how easy it is to deploy the instrument.
Application Example: Spill Monitoring
Click to open these photos in a new window (design subject to change; some photos on this page show non-standard features):
The SediMeter reports turbidity in the unit FBU. It is a kind of Formazin Turbidity Units (FTU), similar to the ISO 7027 standard of FNU (Formazin Nephelometric Units). The difference is that the scattered light is measured at 180 degrees rather than 90 degrees, and that the near infrared (NIR) wavelength is 945 nm rather than 860 nm. The somewhat longer wavelength helps decrease the influence of ambient light, as does a new measuring and compensation procedure. The ISO standard—as well as the US standard with unit NTU—of 90 degree scatter are incompatible with measuring very high concentrations—they would report low concentration values rather than high when buried or in thick turbidity currents.
“...recommending that sedimeters be installed to monitor sedimentation on reef tracts..."
Coastal Engineering Administrator in Florida Department of Environmental Protection
"...dredge monitoring ... there is not much out there that is as simple and cost effective."
Senior Environmental Scientist in an engineering consulting company
"...we are excited about our new SediMeter. It looks very unique and a rather beautiful design."
"The SediMeter proved a reliable means of providing continuous measurements during the study period with respect to accuracy."
Kevin Daniel Denn, University of Iowa master thesis, p 84.