On the nonuniqueness of sediment yield at the catchment scale: The effects of soil antecedent conditions and surface shield

Abstract

The understanding of reasons leading to nonuniqueness of soil erosion susceptibility is still inadequate, yet indispensable for establishing general relations between runoff volume and sediment yield. To obtain relevant insights, we performed a series of numerical simulations with a detailed hydrodynamic model using synthetic storms of varying intensity, duration, and lag time between events as representations of different hydrologic response conditions in a zero-order catchment. The design targeted to generate surface flow and ''perturb'' soil substrate by a first rainfall event, creating a set of initial conditions in terms of flow and deposited sediment prior to the onset of a subsequent rainfall event. Due to the differential effect of (re)detachment and (re)entrainment processes on soil particles of varying sizes, the deposited sediment mass formed shielding layer. One of the essential results is that unless the initial condition of flow and sediment is identical, the same volume of runoff can generate different total sediment yields and their variation can reach up to $200%. The effect is attributed to two major conflicting effects exerted by the deposited ''initialization'' (soil antecedent condition) sediment mass: erosion enhancement, because of supply of highly erodible sediment, and erosion impediment, because of constrain on the availability of lighter particles by heavier sediment. Consistently with this inference, longterm simulations with continuous rainfall show that a peculiar feature of sediment yield series is the existence of maximum before the steady state is reached. The two characteristic time scales, the time to peak and the time to steady state, separate three characteristic periods that correspond to flow-limited, source-limited, and steady-state regimes. These time scales are log linearly and negatively related to the spatially averaged Shields parameter: the smaller the rainfall input and the heavier a given particle is, the larger the two scales are. The results provide insights on how the existence of shield operates on erosion processes, possibly implying that accurate short-term predictions of geomorphic events from headwater areas may never become a tractable problem: the latter would require a detailed spatial characterization of particle size distribution prior to precipitation events.

Climate change and uncertainty assessment over a hydroclimatic transect of Michigan

“…An example highlighting the issue is when the daily or hourly heavy rainfall intensity statistics are compared: there are various methods that attempt to disaggregate daily total to sub-daily intervals and can range from an assumption of uniform intensity in the simplest case, to more elaborate methods based on Multiplicative Random Cascades (Rupp et al 2009;Paschalis et al 2014). The differences in these assumptions are amplified when projections of hydrologic, or even more so, ecological and morphological processes are of interest (Ivanov et al 2008;Fatichi et al 2012;Kim et al 2012Kim et al , 2013Kim and Ivanov 2014). Clearly, climate change impact on precipitation process at finer temporal scales can be better addressed if climate model outputs are extended to finer temporal scale in combination with long-term precipitation data.…”

Soil erosion assessment—Mind the gap

“…Recent studies demonstrated potential clues to how the initial and temporal evolution of geomorphic internal variability can impact soil loss [ Sander et al ., ; Jomaa et al ., ; Zhong , ; Kim and Ivanov , ; Kim et al ., ]. Specifically, during a runoff event, rainfall and overland flow simultaneously drive erosion processes of detachment, entrainment, and deposition on original soil that is relatively intact and cohesive and in which contact forces bind the particles.…”

“…Further reentrainment and transport of deposited soil particles is thus promoted, leading to a complex intraevent and interevent temporal evolution of variations of surface erodibility. The deposited soil layer can exhibit two conflicting roles: it could both increase and decrease soil erosion of the subsequent event for the same magnitude and timing of overland flow according to the degree of shielding or exposure of fine loose material [ Sander et al ., ; Zhong , ; Kim and Ivanov , ; Kim et al ., ].…”

Determinants of modelling choices for 1-D free-surface flow and morphodynamics in hydrology and hydraulics: a review

“…On the other hand, many erosion controls have received attention within the SV or ASV formalisms, i.e. without explicit descriptions of particle-scale flow features: micro-scale variability (Risse et al, 1993;Kinnell et al, 2005), local sheltering effects Kim and Ivanov, 2014), slope effects (Polyakov and Nearing, 2003), particle-size effects (Van Rijn, 1984a;Hairsine and Rose, 1992a;Sander et al, 2007;Wainwright et al, 2008), flow stratification effects (Van Maren, 2007), the effects of hyperconcentrated flows (Hessel, 2006). Bedload transport (e.g.…”