Bedload sediment monitoring
Type: Helley-Smith
Bedload sediment sampler
Sampler catches bedload from the river bottom into the permeable bag through the aperture. Instrument is hydraulicly designed to minimally disturb the surrounding flow.
The illustrations below show how data is collected using a physical drift sensor and what the result looks like…
Sampler is lowered to the river bottom, where it rests to collect a representative sample. Duration of the measurements is recorded for a unit to calculate bedload discharge.
Samples are collected on at least 3 points for 1 cross-section, and processed in the lab to be weighted and calculated into unit bedload transport.
Measured values are integrated over cross-section length to calculate total bedload transport.
Type: StarOddi DST compass magnetic
Tilt Data Logger
Device for tilt measurement used to determine sampler’s compass heading, tilt over 3 axis (pitch, roll and misalignment), as well as depth and temperature
The illustrations below show how data is collected with a tilt sensor and what the processed results look like…
Sampler’s ideal position is alligned with the oncoming flow with the longitudinal axis. Deviation from the flow results with erroneous sample mass.
The graph shows that in some cases, the amount of sediment captured does not correlate with the flow velocity at the entrance to the trap opening, indicating an error.
Samples with misalignment angle greater than 25° from the flow and/or tilt greater then 10° are discarded because the bedload transport calculated from such samples are not representative.