Erosion and delivery of deposited peat sediment

Abstract

Erosion of deposited organic peat sediments from peat harvesting ditches was studied in both laboratory and field conditions. Peat sediments were placed in a recirculation flume at controlled pH levels and allowed to stabilize from 15 min to 10 d. Afterward, different flow velocities were applied and the peat erosion was measured. The erosion rate was related to the physical properties of peat: the particle size and form, settling velocity, peat type and degree of decomposition (von Post). The mean average settling velocity for the peat was measured to be 0.87 m h−1. The median sediment particle size was 42 μm, which indicates that the peat sediment is partly cohesive. The deposited sediment formed a loose layer overlaid by more stabilized layers. Critical shear stress for the surface of the loose peat layer was 0.01 N m−2 and for the more consolidated layer was 0.059 N m−2 after a stabilization of three days. The erosion coefficients determined during laboratory study varied between 3.7·10−4 and 4.1·10−6 kg m−2 s−1. The determined erosion and sedimentation rates were used to calibrate sediment erosion and deposition models. A new approach was then developed for the uses of these models to simulate peat sediment delivery from field ditches. The model was tested against measured values which were in accordance to observed sediment transport rates.