FAQ Topic

Is the SediMeter strong enough for my application?

The concern is usually that the narrow sensor tube will break when exposed to wave action in a nearshore or littoral (beach) environment, or to strong currents in a river. The old model of the SediMeter was admittedly not quite up to the challenges in those environments.

That is why we designed the new model to be virtually unbreakable. It may have other weaknesses, but the impact strength is very high. It will yield if exposed to very strong forces, and not break. Eventually, at some extreme point, the electronic circuits inside may get damaged, or the instrument may get torn out of its holder, but it is not likely ever to break (just do not tighten the finger screw so much that you crush the holder tube).

If it is to be deployed at a location where ropes, branches, or the like are prone to be carried by the water, so that they may get stuck on the logger house, we have another solution. Place the instrument upside down, burying the logger in the bottom so that only part of the sensor is protruding. While it will not prevent that things get stuck on it, it will increase the probability that these objects can slide over the top. In a river you may even opt to place the instrument at a slight angle as an extra precaution. The flip side is that it is more difficult to retrieve the data, why you may want to use a network SediMeter in this configuration, and place a connection box on land with batteries and a computer connection.

Another risk is that the anchor comes loose. When mounted so deep that the seafloor is half way up the sensor, the anchor is 60 cm below the bottom. Experience in sand shows that already when it is deeper than ca 20 cm down it is impossible to pull it straight up by hand. The effects that vibration might have in strong currents or wave oscillatory motion has been investigated in a tidal inlet off Miami during the passage of hurricane Paloma. No tendency to movement was detected (cf. data plot of tides and waves).

A word of caution: The downside of increasing the impact resistance is that the scratch resistance is impaired. Bedload particles coarser than sand may scratch the sensor under turbulent conditions. You may want to protect the sensor with an outer tube, or an optically transparent plastic film, even if it is not physically necessary when placing it upside down.

<a href="video/sensorstrength.mp4">[View using Helper Application]</a>
In this demonstration a dummy sensor is used to lift a 10 kg weight off the table. The outer tube has twice as thick walls as this tube, so the combination is rigid enough to hold the SediMeter in place even in the presence of a current.