Deposition of Suspended Clay to Open and Sand‐Filled Framework Gravel Beds in a Laboratory Flume

Abstract

Pulses of fine sediment composed of sand, silt, and clay can be introduced to gravel bed rivers through runoff from burn‐impacted hillslopes, landslides, bank failure, or the introduction of reservoir sediment as a result of sluicing or dam decommissioning. Here we present a study aimed at quantifying exchange between suspensions of clay and gravel beds. The questions that motivate the work are: how do bed roughness and pore space characteristics, shear velocity ( u∗), and initial concentration (C0) affect clay deposition on or within gravel beds? Where does deposition within these beds occur, and can deposited clay be resuspended while the gravel is immobile? We examine these questions in a laboratory flume using acrylic, open‐framework gravel, and armored sand‐gravel beds under conditions of varying u∗ and C0. Deposition of clay occurred to all beds (even with Rouse numbers ∼ 0.01). We attribute deposition under full suspension conditions to be an outcome of localized protected zones where clay can settle and available pore space in the bed. For smooth wall cases, protection came from the viscous wall region and the development of bed forms; for the rough beds, protection came from separation zones and low‐velocity pore spaces. Bed porosity was the strongest influencer of nondimensional deposition rate; deposition increased with porosity. Deposition was inversely related to u∗ for the acrylic bed runs; no influence of u∗ was found for the porous bed runs. Increases in discharge resulted in resuspension of clay from acrylic beds; no resuspension was observed in the porous bed runs.

The Dynamics of Suspended Sediment in a Typical Alpine Alluvial River Reach: Insight From a Seasonal Survey

“…This amount of bed erosion is realistic as suggested by the observed cross sectional changes (see Figure S4.1) and vertical scouring estimation in Misset et al (). This simple analysis supports the existence of efficient sediment exchanges between the flow and the bed subsurface as proposed by several authors (Mooneyham & Strom, ; Mueller & Pitlick, ; Park & Hunt, ) and discussed in the next section.…”

Quantifying bed‐related suspended load in gravel bed rivers through an analysis of the bedload‐suspended load relationship

“…This hypothesis is consistent with observations made in several flume and field studies considering sand, silt or clay particle infiltration in porous beds [Frostick et al, 1984;Glasbergen, 2014;Hamm et al, 2009;Harvey et al, 2012;Krishnappan and Engel, 2006;Mooneyham and Strom, 2018]. This infiltration process was found to occur even for very low Rouse numbers (~0.01), especially when pore spaces were empty [Khullar, 2007;Mooneyham and Strom, 2018].…”

“…Similar observations were made at the reach scale in the Isabena catchment where changes in fine sediment stocks were correlated with the maximum flood discharge [Buendia et al, 2016]. The strong interactions observed in these field studies between suspended load and the river bed were also demonstrated in several flume experiments [Glasbergen, 2014;Hamm et al, 2009;Krishnappan and Engel, 2006;Mooneyham and Strom, 2018]. Navratil et al (2010) estimated these stocks in a typical mountainous braided river by considering stocks in dried braided channels, bars and vegetated bars in addition to sediments stored in the wetted channel.…”

“…It is important to note that, even though it is often considered that only coarser materials interact with the bed, all of these field measurements used the Lambert and Walling or the Navratil technique and thus mainly concern the finest fraction (<63 μm) of fine sediments [Lambert and Walling, 1988;Navratil et al, 2010]. The strong interactions observed in these field studies between suspended load and the river bed were also demonstrated in several flume experiments [Glasbergen, 2014;Hamm et al, 2009;Krishnappan and Engel, 2006;Mooneyham and Strom, 2018].…”

Colloid transport and distribution in the hyporheic zone

“…Experiments and a physico‐chemical model demonstrated that advection (driven by hyporheic flow associated with interactions between stream flow and bedform), particle settling, and retention (filtration) are the major process that influence the colloid exchange between the stream and streambed (Jin et al, ; Packman et al, , ). Particle settling enhanced colloid deposition in the hyporheic zone (Fries & Trowbridge, ), which in turn changed the bed properties including porosity and hydraulic conductivity (Mooneyham & Strom, ). There were also simulations with considering particle aggregation effects on colloid exchange between the stream and streambed based on a pumping exchange model (Areepitak & Ren, ).…”