Bank‐collapse processes in a valley‐bottom gully, western Iowa

Abstract

Widening and bank-slope reduction of a valley-bottom gully in western Iowa was correlated to increasing subsurface flow over a 36-year period. To study bank collapse at this gully, we measured rainfall, air temperature, hydraulic head near the banks and bank movement nearly continuously over a 2-year period. Styles of movement ranged from imperceptible creep to rapid slab collapses preceded by the formation of tension cracks parallel to the gully walls. Bank movement was commonly correlated to rainfall or snowmelt and associated head increases in the banks. If the banks are modelled as a twodimensional slab with an adjacent tension crack partly filled with water, measured heads were sufficient to cause bank failures through reduction of frictional support at the base of the slab. During winter months, air temperature variations across 0°C were correlated with bank movement: during mildly subfreezing periods banks expanded, and most, but usually not all, of this movement was recovered during above-freezing periods. This motion is attributed to frost heave followed by thawing. Deformation of the banks by heaving and thawing during winter may weaken them and prime them for failure during spring rains and snowmelt, when the frequency of mass-wasting events is highest.

Main types of soil mass failure and characteristics of their impact factors in the Yuanmou Valley, China

“…Mass failures due to undercutting in a plunge pool also caused headcut migration (Chen et al, 2013;Stein and LaTray, 2002). Mass failures not only accelerated the gully enlargement (Bull and Kirkby, 1997;Thomas et al, 2009), but also resulted in sediment production, sediment deposition in channels, and nutrient loading in higher order streams (Martínez-Casasnovas et al, 2003;Poesen et al, 2002;Vandekerckhove et al, 2003).…”

“…The occurrence of mass failure is attributed not only to the internal characteristics of lithology (Crosta and Prisco, 1999), soil type (Vandekerckhove et al, 2000), and terrain (Moeyersons, 2003), but also to external meteorological and hydrological conditions (Thomas et al, 2009), and human activities (Wilson et al, 2008). Mass failure in the development process of gullies was caused by flow hydraulics and gravity.…”

Spatial distribution and morphologic characteristics of gullies in the Black Soil Region of Northeast China: Hebei watershed

“…According to topographic positions, gullies were classified as hillslope gullies and valley-floor gullies. Similar classifications have been used in other studies (Bradford & Piest, 1980;Brice, 1966;Liu, Zhu, & Zhou, 1988;Thomas, Iverson, & Burkart, 2009). Hillslope gullies were called valley-side gullies, while valley-floor gullies were called valley-bottom gullies in some studies (Morgan, 2005;Morgan & Mngomezulu, 2003).…”

“…In addition, the removal of residue is known to make the surface much more susceptible to erosion (Dabney, Wilson, McGregor, & Foster, 2004;Moldenhauer & Langdale, 1995;Wilson, Dabney, McGregor, & Barkoll, 2004). Freezing and thawing cycles, common in the study area, tend to decrease soil resistance to concentrated flow erosion (McCool, Dun, Wu, Elliot, & Brooks, 2013) and promote mass wasting (Hu et al, 2007;Thomas et al, 2009). Freezing can also induce an impermeable (frozen) subsoil layer, which can restrict percolation and facilitate seepage conditions that foster gullies (Øygarden, 2003).…”

Application of a simple headcut advance model for gullies

“…(); in the western United States, Rieke‐Zapp and Nichols () and Rengers and Tucker (, ); and in the Midwestern United States, Burkard and Kostaschuk () and Thomas et al . (, ). In each case, the gully advance and eroded volumes were tied to easily measurable parameters that appeared to represent the major trends in gully advance such as drainage area, and daily rainfall, with and without thresholds or estimates of stream power.…”