A simple model of river meandering and its comparison to natural channels

Abstract

Abstract:We develop a new method for analysis of meandering channels based on planform sinuosity. This analysis objectively identifies three channel-reach lengths based on sinuosity measured at those lengths: the length of typical, simple bends; the length of long, often compound bends; and the length of several bends in sequence that often evolve from compound bends to form multibend loops. These lengths, when normalized by channel width, tend to fall into distinct and clustered ranges for different natural channels. Mean sinuosity at these lengths also falls into distinct ranges. That range is largest for the third and greatest length, indicating that, for some streams, multibend loops are important for planform sinuosity, whereas for other streams, multibend loops are less important. The role of multibend loops is seldom addressed in the literature, and they are not well predicted by previous modelling efforts. Also neglected by previous modelling efforts is bank-flow interaction and its role in meander evolution. We introduce a simple river meandering model based on topographic steering that has more in common with cellular approaches to channel braiding and landscape evolution modelling than to rigorous, physics-based analyses of river meandering. The model is sufficient to produce reasonable meandering channel evolution and predicts compound bend and multibend loop formation similar to that observed in nature, in both mechanism and importance for planform sinuosity. In the model, the tendency to form compound bends is sensitive to the relative magnitudes of two lengths governing meander evolution: (i) the distance between the bend cross-over and the zone of maximum bank shear stress, and (ii) the bank shear stress dissipation length related to bank roughness. In our simple model, the two lengths are independent. This sensitivity implies that the tendency for natural channels to form compound bends may be greater when the banks are smoother.

Generic theory for channel sinuosity

“…underlying Brownian mechanics, with the strength of resistance (R) relative to slope (S) driving the transition between directed and undirected random walks. It is interesting to note that the upper range of planform sinuosities we generate with and without our iterated, minimumpath procedure are consistent with results of other numerical planform models whose channel patterns, with and without meander cutoffs, derive from parameterization of in-channel flow (3,4,22). However, unlike in other models, our flow paths are static once formed.…”

Status and Trend of Cottonwood Forests Along the Missouri River

“…and Greco 2002, Lancaster and Bras 2002, Richards et al 2002, Larsen et al 2007). We also suggest that the implications for cottonwood populations and broader ecosystem effects be considered for various flow and sediment release scenarios designed to support endangered species recovery (e.g., the spring pulse for pallid sturgeon) or other purposes (e.g., removal of sediment accumulations at the Lewis and Clark Lake delta).…”

A cellular model of river meandering

“…Where two lines touch, a cut-off can form, allowing the development of ox-bow lakes. More recent approaches (Lancaster and Bras, 2002) have used the concept of topographic steering. Instead of relating lateral erosion to planform curvature, they use the cross-stream angle of the river bed or the crosschannel slope to drive lateral erosion.…”