Erosion thresholds and land surface morphology

Abstract

We propose a graphical technique to analyze the entirety of landforms in a catchment to define quantitatively the spatial variation in the dominance of different erosion processes. High-resolution digital elevation data of a 1.2 km2 hilly area where the channel network had been mapped in the field were used in the digital terrain model, TOPOG, to test threshold theories for erosion. The land surface was divided into-20 m2 elements whose shapes were then classified as convergent, planar, or divergent. The entire landscape plotted on a graph of area per unit contour length against surface gradient shows each planform plotting as a separate field. A simple steady-state hydrologic model was used to predict zones of saturation and areas of high pore pressure to mimic the extreme hydrologic events responsible for erosive instability of the land surface. The field observation that satu ration overland flow is rare outside convergent zones provided a significant constraint on the hydrologic parameter in the model. This model was used in threshold theories to predict areas of slope instabil ity and areas subject to erosion by saturation overland flow, both of which can contribute to channel initiation. The proportion of conver gent elements predicted to exceed the threshold varies greatly with relatively small changes in surface resistance, demonstrating a high sensitivity to land use such as cattle grazing. Overall, the landscape can be divided, using erosion threshold lines, into areas prone to channel instability due to runoff and stable areas where diffusive transport predominates.

Sensitivity analysis and implications for surface processes from a hydrological modelling approach in the Gunt catchment, high Pamir Mountains

“…on landscape evolution, by providing high spatiotemporal resolution data to deepen our understanding of climate/weather variability impacts on erosional processes (e.g. DiBiase and Whipple, 2011;Champagnac et al, 2012;Dietrich et al, 1992;Iverson, 2000;Montgomery and Brandon, 2002). The here presented conceptual model of interactions between water mobilisation and expected Earth surface processes also sheds some light on the very unusual discrepancy between erosion and incision rates in the Pamirs (Fuchs et al, 2013(Fuchs et al, , 2014b.…”

“…Rising temperatures during spring to summer lead to an increase in altitude where snowmelt occurs and thus affect the geomorphological boundary conditions, such as hillslope angles, which seem to affect the mobilisation of sediments (Iida et al, 2012;Ali and De Boer, 2010). The increase in soil moisture content that coincides with the snowmelt progression is known to contribute to hillslope mass wasting and landslides (Iverson, 2000;Dietrich et al, 1992). Intense precipitations generate strong direct runoff and sediment supply from hillslopes in the Himalayas (Andermann et al, 2012a).…”

“…But hydrology-related surface processes are manifold, including frost cracking intensities based on available water content (e.g. Andersen et al, 2015;Egholm et al, 2015), sediment mobilisation from snowmelt (Gao et al, 2014;Iida et al, 2012), glacier melt as a transport agent for sediment (Chernova, 1981;Ali and De Boer, 2010), river incision (Snyder et al, 2003;Lague et al, 2005), landslide triggering due to soil moisture content (Iverson, 2000;Dietrich et al, 1992), and suspended sediment transport in rivers (Andermann et al, 2012a, c;Dadson et al, 2003;Milliman and Syvitski, 1992). Therefore, obtaining spatiotemporal knowledge about water mobilisation in quantity and quality can provide further insights into the effects of climate and climate variability on mountain evolution (Champagnac et al, 2012;DiBiase and Whipple, 2011;Montgomery and Brandon, 2002).…”

Mechanism of Gully-Head Retreat - A Study at Ganganir Danga, Paschim Medinipur, West Bengal

“…A large variation in this channel head and process is observed, depending on many factors (i.e. source area, source basin length and contributing area per unit contour length) (Abrahams, 1984;Dietrich et al, 1992;Montgomery and Dietrich, 1989). The location of heads on steep slopes is controlled by subsurface flow, instability of colluvial fill, whereas on gentle slopes, head location is governed by overland flow (Montgomery and Dietrich, 1989;Montgomery, 1999).…”

Time, space, and episodicity of physical disturbance in streams

“…Dietrich et al, 2001) and surface erosion (Dietrich et al, 1992). Topography also determines where in the landscape colluvium will accumulate (Hack and Goodlett, 1960;Dietrich and Dunne, 1978) and dictates the points of delivery for water-eroded and mass-wasting derived sediment to the channel network (Swanson et al, 1988;Benda and Dunne, 1997b).…”