Understanding mass fluvial erosion along a bank profile: using PEEP technology for quantifying retreat lengths and identifying event timing

Abstract

This study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing, quantifying retreat lengths, and providing ranges of incipient shear stress for hydraulically driven erosion. Mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion, or the entrainment of individual grains or aggregates under lower hydraulic shear stresses. We explore the relationship between the two regimes in a representative, US Midwestern stream with semi‐cohesive bank soils, namely Clear Creek, IA. Photo‐Electronic Erosion Pins (PEEPs) provide, for the first time, in situ measurements of mass fluvial erosion retreat lengths during a season. The PEEPs were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes. This transition is postulated to occur when the applied shear stress surpasses a second threshold, namely the critical shear stress for mass fluvial erosion. We hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion. Selective entrainment of unbound/exposed, mostly silt‐sized particles at low shear stresses over sand‐sized sediment can armor the bank surface, limiting the removal of the underlying soil. The armoring here is enhanced by cementation from the presence of optimal levels of sand and clay. Select studies show that fluvial erosion strength can increase several‐fold when appropriate amounts of sand and clay are mixed and cement together. Hence, soil layers or conglomerates are entrained with higher flows. The critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion, and proceeded with higher (approximately 2–4 times) erodibility. The results were well represented by a mechanistic detachment model that captures the two regimes. Copyright © 2017 John Wiley & Sons, Ltd.

Equilibrium Cross Section of River Channels With Cohesive Erodible Banks

“…These measures are in fact time and resource consuming and still present a variety of limitations. In particular, the heterogeneity of cohesive materials (Arulanandan et al, 1980;Grissinger, 1982;Samadi et al, 2009) and the high variability of the critical shear stress along the bank profile (Papanicolaou et al, 2007(Papanicolaou et al, , 2017Sutarto et al, 2014) impose repeated sampling for an accurate description of erosion properties. In addition, the presence of vegetation can alter or invalidate the measurements, especially when varying seasonally during the year.…”

“…,Darby et al (2010),Nardi and Rinaldi (2010),Sutarto et al (2014),Papanicolaou et al (2017), we assume that, in the absence of vegetation, a reasonable range of variation for c is 0.5-4 Pa, while in the presence of vegetated banks c can increase by up to a factor of 2.5 for high vegetation density (see, e.g.,Figure 8fromParker et al, 2007).…”

The Intensively Managed Landscape Critical Zone Observatory: A Scientific Testbed for Understanding Critical Zone Processes in Agroecosystems

“…Photo‐electric erosion pins are used to capture the effects of this cementation in terms of changes in mass erosion (Papanicolaou et al, 2017). Photo‐electric erosion pins contain a series of photo‐diodes that are charged when they become exposed to sunlight as the bank retreats are able to identify the transition from surface to mass fluvial erosion when the applied shear stress surpasses a second threshold.…”

Understanding saturated hydraulic conductivity under seasonal changes in climate and land use

“…Soil crusts result from broken-down aggregate fragments that infiltrate into soil pores, causing the pores to clog. Additionally, the clays and sands mix forming a cement-like crust as the soil dries reducing the permeability of soil (Papanicolaou et al, 2017b). However, different soil textures and higher soil roughness can limit the crusting effect (Rawls and Brakensiek, 1985).…”

“…As aggregates breakdown from rain splash or runoff, some of the finer soil particles settle into the soil pores, blocking them. Additionally, the clays and sands mix forming a cement-like crust reducing the permeability of soil, and hence reduce the values of K br (e.g., Eigel and Moore, 1983;Sun et al, 2010;Hu et al, 2012;Sutarto et al, 2014;Papanicolaou et al, 2017b). Fig.…”