An evaluation of the geomorphically effective event for fluvial processes over long periods

Abstract

[1] Fluvial processes erode landscapes in response to a wide range of discharges. The importance of a given discharge to the erosion of a basin can be calculated by multiplying the discharge's frequency of occurrence and the erosion rate produced by the discharge. The discharge that contributes the most geomorphic work is called the geomorphically effective event (GEE). In this paper, the behavior of the GEE is examined when a generic stream power model with a threshold is used to describe either the detachment or transport of sediment by flowing water. The results suggest that the return period of the GEE depends primarily on the threshold value when the exponent on discharge is less than 2. Otherwise, it depends primarily on the exponent. The GEE usually cannot be substituted for the probability density function of discharge because it produces a different long-term erosion rate. Furthermore, the return period of the GEE can vary spatially in a basin. For example, the return period can be different between locations where the fluvial process is dominant and subdominant if the threshold is nonzero. For a detachment-limited model the return period of the GEE is different upstream and downstream of knickpoints, and for a transport-limited model the return period is different along channel profiles even at steady state. Spatial variation in streamflow generation also produces spatial variations in the return period of the GEE.

Modelling landscape evolution

“…Willgoose et al (1989) justifi ed this approach by deriving a time-averaged sediment transport equation based on the Einstein-Brown formula (see Julien (1998)) in which the applicable discharge is the mean annual peak discharge; however, because some terms were discarded, the result is approximate rather than exact unless the discharge exponent is an integer. Huang and Niemann (2006) analysed the return period of the geomorphically effective event under a range of erosion laws and catchment states, and found that in general the event return period -and thus its intensity -varied systematically throughout the network in most cases. Several studies have explored the role of discharge variability in time (Willgoose, 1989;Tucker and Bras, 2000;Molnar, 2001;Tucker, 2004;Molnar et al, 2006;Lague et al, 2005).…”

“…In fact, there are many fascinating and unanswered questions regarding the feedbacks between climate, hydrology and landscape evolution. While models of drainage basin evolution have begun to address some of these, including issues of both precipitation distribution and phase (Beaumont et al, 1992;Roe et al, 2002;Anders et al, 2008) as well as runoff generation (Sólyom and Tucker, 2004;Huang and Niemann, 2006), the topography-hydrology-climate connection remains a rich problem to be explored.…”

Identification of tectonically active areas using DEM: a quantitative morphometric analysis of Mt. Medvednica, NW Croatia

“…Hence, the derived shape of hypsometric curves gives in for ma tion about the vol ume of orig i nal ba sin re mains, and in di cates an ero sional stage of drain age bas ins as out come of in ter ac tion be tween tectonic ac tiv ity, lithological het er o ge ne ity and cli ma tic con di tions (Willgoose and Han cock, 1998;Huang and Niemann, 2006). Keller and Pinter (2002) sug gested that hypsometric curves can be used for com par ing drain age bas ins of dif fer ent size and can be used to sep a rate phases in land scape evo lu tion.…”

Scaling Soil Erosion Models in Space and Time

“…For example, the assumption that flow may be parameterized as a function of upslope contributing area is inappropriate in semi-arid environments, where localized storms are mismatched with the area of the catchment. In addition, the assumption that erosion is driven by a single, representative discharge is flawed; numerous studies have demonstrated that assumptions of a single discharge produce different results compared with a range of discharges (Wainwright & Parsons, 1998;Zhang et al, 2002;Huang & Niemann, 2006).…”