Influence of ambient temperature on erosion properties of exposed cohesive sediment from an intertidal mudflat

摘要

Intertidal flats regularly emerge and submerge in accordance with changes to the water level occurring over tidal cycles. The alteration between wet and drained states may affect the sediment water content, and so the erosion properties of intertidal sediments. This study examined the influence of ambient temperature on the erodibility of exposed cohesive sediment from an intertidal mudflat in the Firth of Thames, New Zealand, in December 2017 and March 2018. The EROMES device was used to measure the erosion potential of sediment (erosion threshold, tau(cr) Nm(-2), and erosion rate, ER gm(-2)s(-1)). Samples were drained and exposed to temperatures of 0, 8, 25 and 40 degrees C, chosen to mimic natural exposed conditions, while submerged samples simulated natural flooded conditions. Results showed that the cohesive sediment became more resistant to erosion when exposed to air compared with submerged samples as a consequence of decreased water content. The water content of exposed sediments decreased by 1.01-1.78 times, a rate which was a function of increasing temperature. The tau(cr) of exposed experiments was 1.2 to 2.2 times higher, whereas ER decreased 1.2 to 6.2 times. Both the December 2017 and March 2018 sampling dates showed a similar pattern of increasing resistance to erosion (higher tau(cr) and lower ER), which corresponded to depleted water content of the exposed sediment at higher temperatures.