Infiltration of fine sediment mixtures through poorly sorted immobile coarse beds

Abstract

Percolation of fine sediment is a common process in gravel bed rivers, which often exhibit extended and overlapping grain size distributions of the bed and the supplied fine sediment. Yet existing sediment infiltration theory assumes well‐sorted fine material with smaller grain size than the bed pores, and as such, is not suitable for many situations encountered in gravel bed streams. Previous developments for infiltration of uniform material are here generalized to consider poorly sorted sediment mixtures. Governing equations and a numerical solution to model the vertical distribution of infiltrating sediment are presented. The equations are solved as a function of a trapping coefficient, dependent on the relative size of infiltrating fines in relation to bed material. A method is developed to generate equivalent grain size distributions to calculate the trapping coefficient, when grain sizes of the infiltrating and bed materials overlap. Moreover, a bed cutoff size is defined and computed with a semiempirical packing‐porosity model, to distinguish particles smaller than the bed pores. Published experimental data are used to test the new model and calibrate the trapping coefficient. It is shown that this coefficient is highly sensible to the fine and coarse tails of fine and coarse materials grain size distributions. Accordingly, calibrated values of the coefficient are set as a function of a mean size ratio, computed from the geometric mean of the tails of the size distributions. Incorporating this relation, the model performed well in reproducing indirect observations of sediment infiltration from experiments reported in the literature.

A Physically Based Model of Deposition, Re‐Entrainment, and Transport of Fine Sediment in Gravel‐Bed Rivers

“…There has been substantial investigation of the range of factors which affect the transport of fine sediment over gravel beds of various types. For example, Núñez‐González (2016) found an empirical trapping coefficient was capable of summarizing observations on sediment storage within the pore space of gravel beds. Mooneyham and Strom (2018) investigated factors such as pore space and shear velocity on the deposition of clay in a variety of gravel bed types in a flume.…”

The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management

“…Vertical distributions of fine sediment quantity in the investigated chalk stream gravel beds (denoted by field data), compared with the results of fine sediment infiltration and accumulation in immobile gravel bed flume experiments (denoted by experimental data), where data on fine sediment accumulation was available (Wooster et al, 2008; Gibson et al, 2009, 2010, 2011; Huston & Fox, 2015; Herrero & Berni, 2016; Núñez‐González, 2016, Appendix ). Depths of both the field and experimental beds have been normalised by the bulk D 50 of each deposit, allowing for comparability between different depth profiles used in the original investigations.…”

Application of time domain reflectometry to high suspended sediment concentration measurements: Laboratory validation and preliminary field observations in a steep mountain stream

“…8c-g). These increases in SC potentially reflected the mechanical compaction of the deposit (Houseknecht, 1987) and/or the propagation of fine particles into pores of the deposit (Núñez-González et al, 2016).…”