On the analysis of the medium term planform dynamics of meandering rivers

Abstract

The continuous wavelet transform is applied to the analysis of curvature signals from both synthetic meanders and 52 realizations from 16 natural meanders ranging from class B to class G (Brice classification), thus providing information on the spatial distribution of their arc-wavelength spectrum, and therefore, representing an objective characterization of meanders. Past research has studied the meander dynamics by using the centerline (short-term frame) and the valley centerline (long-term frame). The present study introduces a medium term frame, termed the mean center (MC), which is defined as the medium term coherent wave being present in the meander planimetry for a period that is strongly governed by the occurrence of cutoff events; although in the absence of them, it is present for $10 to $30 years. The MC is obtained by using a methodology that combines the capabilities of the principal component analysis and the discrete wavelet transforms. The application of wavelet cross correlation shows that peaks in the centerline curvature are strongly correlated with those of the MC suggesting that (1) a linear relationship between them may be associated to bank processes and, (2) in all other cases, a higher nonlinear relationship may be induced by autogenic hydrodynamic processes. In freely meandering rivers, compound bends, multiple loops, and cutoff events are associated to peaks in the MC local curvature. We define the planform amplitudes as the orthogonal distance of the centerline from mean center. Planform amplitudes (orthogonal distance of the centerline from mean center) are normally distributed and ranges from 2 to 20 river mean widths.

Multiscale structure of meanders

“…The tree can be used to recognize patterns in the planform at different scales. The patterns at different scales can interact among each other [ Gutierrez and Abad , ] and can potentially be matched with local geological confinement [ Frias et al , ; Mendoza et al , ], vegetation, or other factors that influence meander formation.…”

“…Until now most techniques are only in part suitable to determine the shape of meanders or are unsuitable to quantify meander characteristics [ Hooke , ]. These techniques often focus on different scales, typically the meander scale, valley scale, or more recently also a cutoff scale or mean center scale [ Gutierrez and Abad , ].…”

“…This can be done on a meander by meander basis [ Marani et al , ], which, however, involves the detection of inflection points first. More recently, the use of wavelet transforms of curvature series has been employed to describe meandering behavior to detect changes in meandering characteristics [ van Gerven and Hoitink , ], analyzing the change at different supermeander scales [ Gutierrez and Abad , ], and to characterize the wavelengths of meandering [ Zolezzi and Güneralp , ].…”

Are process nonlinearities encoded in meandering river planform morphology?

“…A bend therefore was defined as a reach of river between two inflection points. The number of bends was verified by eye and was noted to vary depending on the strength of the Savitzky-Golay smoothing filter due to the multiscale nature of meandering planforms [Gutierrez and Abad, 2014]. The smoothed centerline was then resampled with evenly spaced nodes with a density of 25N b such that each bend contained 25 nodes on average.…”

Dynamic characterization of meandering channels planform

“…The first criterion of meanders classification involving only the meander geometry is introduced by [7]. Then, [8] focus in a new description, which includes as the medium term coherent wave being present in the meander planform for a period that is strongly governed by the occurrence of cutoff events (medium-term frame). This new focus raised has a different position that the past research [7,10], which used the centerline (short-term frame) to describe the morphodynamics.…”