Magnitude and Frequency of Forces in Geomorphic Processes

Abstract

Abstract:At the Satino site in the center of the Russian Plain, major events of the Holocene erosion history are concentrated on sides of river valleys incised into smooth moraine landscape. Valley sides are dissected by Pleistocene gullies. Extraordinary for the Holocene was formation of four new permanent gullies. Three of them had appeared in the Late Atlantic -Early Subboreal time. One gully permitted direct dating of the fan base, which gave estimation of its appearance between 4.3-4.6 ka BP (cal). Two other gullies were constrained within the two intervals 5.2-5.5 and 5.9-6.2 ka BP (cal), based on assumed correlation with extreme runoff events dated over the area. After a long break of erosion, two of the gullies had exhibited the second phase of activity between 3.0-3.7 ka BP (cal). As in the Bronze Age no settlements are known in the study area and surroundings; human reinforcement of erosion was minor if any. The four intervals of extraordinary linear erosion on valley sides coincided with extremely high runoff events in streams of various sizes, which left prominent geomorphic and sedimentological features: meander arcs, coarse-grained alluvium, buried floodplain soils, etc. Altogether, this is considered to indicate a highly irregular climatic pattern in the area in the interval of 3.0-6.2 ka BP (cal) with several phases containing a series of extreme downpours, which had no analogs throughout the Holocene.

Least action principle, equilibrium states, iterative adjustment and the stability of alluvial channels

“…In terms of their geometry, alluvial rivers are self-forming and operate most effectively by moving water and sediment from their drainage basins under conditions approximating bankfull flow (Wolman and Miller, 1960). They exhibit stable channel geometries, which can be predicted with reasonable accuracy using 'regime theory' for stable canals (Lacey, 1929(Lacey, , 1933(Lacey, , 1946(Lacey, , 1958Blench, 1952Blench, , 1969Blench, , 1970Simons and Albertson, 1960) and 'hydraulic geometry' for stable river channels (Leopold and Maddock, 1953;Parker, 1979;Huang and Warner, 1995;Huang and Nanson, 1995, 1998.…”

Applying bootstrap resampling to quantify uncertainty in fluvial suspended sediment loads estimated using rating curves

“…The question of whether, over the longer term, the total mass of sediment moved during periods of high flow (with their low frequency of occurrence) exceeds that transported by more frequently occurring, lower-flow conditions is a long-standing one in fluvial geomorphology [Wolman and Miller, 1960;Pickup and Warner, 1976;Nash, 1994]. Indeed, Pickup and Warner [1976] found that for bed load transport within a relatively small creek near Sydney, flows of moderate magnitude and frequency dominated net bed load transport.…”

A stochastic approach to modeling the role of rainfall variability in drainage basin evolution

“…The importance of the frequency spectra of g½omorphic events is a fundamental problem in g½omorphic research. Much of the previous research on this problem has focused on defining the recurrence interval of the most effective g½omo•hic event, with "effectiveness" defined either on the basis of denudation rate [e.g., Wolman and Miller, 1960 Wolman and Gerson, 1978]. Scant attention has been paid, however, to the question of how intrinsic variability in g½omo•hic forces impacts the morpholo• and ra•½ of evolution of landforms.…”