Analysis of Erosion Thresholds, Channel Networks, and Landscape Morphology Using a Digital Terrain Model

Abstract

To investigate the linkage between erosion process and channel network extent, we develop two simple erosion threshold theories driven by a steady state runoff model that are used in the digital terrain model TOPOG to predict the pattern of channelization. TOPOG divides the land surface into elements defined by topographic contours and flow lines, which can be classified as divergent, convergent and planar elements. The calibration parameter for the runott model is determined using empirical evidence that the divergent elements which comprise the ridges in our study area do not experience saturation overland flow, where as the convergent elements in the valleys do during significant runoff events. A threshold theory lor shallow landsliding predicts a pattern of instability consistent with the distribution of landslide scars in our 1.2 km2 study site and confirms the interpretation, based on field observa tions, that indicate the steeper channel heads to be at least partially controlled by slope instability. Most sites of predicted and observed slope instability do not, however, support a channel head, hence landslide instability alone is not sutficient for channelization. In contrast, most elements predicted to be eroded by saturation overland flow coincide with the observed location of the channel network. In addition, areas of predicted downslope decrease in relative sediment-transport capacity were found to correspond to locations where channels became discontinuous. The topographic threshold given by the saturation overland flow erosion theory varies with the third power of critical boundary shear stress, suggesting that critical shear stress, although difficult to quantify with much precision in the field, is a dominant control on the extent ot the channel network where saturation overland flow is significant. Current extent ot the channel network in our field site, tor example, may best \)c explained as resulting from grazing-induced reduction in surtace resistance.

A new method for the determination of flow directions and upslope areas in grid digital elevation models

“…The specific catchment area contributing to flow at any particular location is useful for determining relative saturation and generation of runoff from saturation excess in models such as TOPMODEL [Beven and Kirkby, 1979;Beven et al, 1984;Wood et al, 1990]. Specific catchment area together with other topographic parameters has also been used in the analysis of processes such as erosion and landslides [Dietrich et al, 1992[Dietrich et al, , 1993Wu, 1993 The earliest and simplest method for specifying flow directions is to assign flow from each pixel to one of its eight neighbors, either adjacent or diagonal, in the direction with steepest downward slope. This method, designated D8 (eight flow directions), was introduced by O'Catlaghan and Mark [1984] and has been widely used [Marks et Dispersion is inherent in any method (including the one I describe below) that assigns flow from one pixel to more than one downslope neighbor and manifests itself in terms of spreading of flow from a single pixel.…”

A flash flood hazard assessment in dry valleys (northern France) by cellular automata modelling

“…These studies underlined the difficulties encountered when linking local responses (sub-basins or hillslopes) to this global behaviour, and this aim has been one of the main issues for geomorphologists since the 1970s (Veltri et al 1996;Rodriguez-Iturbe and Rinaldo 1997;Schmitz and Cullmann 2008). A few studies have successfully shown that the network organization plays a key role on hydrological functionality (Dietrich et al 1993;Vogt et al 2003). The CA RUICELL partially overcomes such difficulties and also implicitly captures the channel network structure and its influence on flood through scales.…”

Delineating incised stream sediment sources within a San Francisco Bay tributary basin

“…teria (e.g., Montgomery and Dietrich, 1992;Dietrich et al, 1993) based on flow accumulation and surface slope, plan (contour) curvature, and flow length over which these criteria are met (Miller et al, 2002(Miller et al, , 2015.…”