Simulating Accumulation of Low-Conductivity Layer in Streambeds Under Moving-Bedform Conditions

Abstract:

Recent studies have shown that under moving-bedform conditions, a low-conductivity layer is formed below and within the scour zone. This clogging layer is the result of the combination of deposition due to HEF and erosion due to bedform scour. The layer accumulates over time as a result of the passage of many bedforms. Previous modeling studies of bedform-induced HEF have used a frame of reference that moves with the bedform while the bedform shape remains unchanged. This is a valid approach when studying the porewater flow induced by a bedform and the transport of solutes due to this flow. However, by definition it cannot simulate the accumulation of fine particles at a given location over time as a modeling outcome. Moreover, the above approach implies that the domain shape imposes a constant flow field on every point in the domain, while in reality each point is subject to a flow field that changes with the shape of the bed. In order to address these gaps, a simulation is presented which captures these factors using a stationary frame of reference. Passage of successive bedforms is represented by varying the shape of the top boundary of the domain. To our knowledge, this is the first simulation of bedform-induced HEF to use a stationary reference frame. Simulation results successfully reproduce experimental observations of the development of the low-conductivity layer near the scour zone.