Spatiotemporal variations in channel changes caused by cumulative factors in a meandering river: The lower Peixe River, Brazil

Abstract

Channel changes in meandering rivers naturally exhibit complex behaviour, and understanding the river dynamics can be challenging in environments also subject to cumulative human impacts. Planform changes were analysed on four reaches of the lower course of the Peixe River, Brazil, at decadal scales over the period 1962-2008 from aerial photographs and satellite imagery, complemented by a historical map from 1907. Analysis of the spatial and temporal patterns of channel change mechanisms and morphometry of bends and of the sinuosity and morphodynamic variations of the reaches demonstrates major changes in planform characteristics. Sinuosity in all reaches decreased from~2.6 to~1.7, average wavelength of bends has increased from~200 to~500 m, and the planform has become much simpler. Changes have been progressive from downstream to upstream, with higher intensities of processes, particularly cutoffs first in downstream reaches then more recently in upstream reaches. It is suggested that channel changes represent a morphological adjustment to human interventions, such as reservoir construction and land use. However, evidence of the autogenic behaviour of meanders is highlighted in which the existence of compound meanders reveals control over the spatial variation in the reaches. The results suggest that geomorphic thresholds associated with the compound meander formation and the bend evolution should be considered, even in impacted meandering rivers, because they exert primary controls on the spatial-temporal adjustment of channels.

Temporal and spatial adjustments of channel migration and planform geometry: responses to ENSO driven climate anomalies on the tropical freely‐meandering Aguapeí River, São Paulo, Brazil

“…Morais et al . () observed that in 75% of the reaches major channel adjustments took place between 1962 and 1978, the first time period of their study, and this corresponds to the period of a step‐functional increase in mean annual and peak discharges on these two adjacent rivers. It is apparent that a significant shift in climate and associated flow regime at about 1971–1972, and not land‐use changes, has been the cause of correspondingly significant changes in the channel morphology of both these rivers.…”

“…In a study of the adjacent Peixe River catchment immediately to the southwest of the Aguapeí River, Morais et al . () have suggested changes in meander morphology have been caused by anthropogenic factors such as reservoir construction and land‐use changes. There has been no reservoir constructed in the Aguapeí basin but to examine the possibility land‐use changes may have caused significant channel change, the percentage of land in the basin cleared of forest is plotted in Figure for the years 1962, 1986 and 2010.…”

“…Also, Morais et al . () quantifying land‐use changes in the Peixe River basin found that by 1972, 90% of the basin had been cleared and this increased by just a further 3% by 2008. They assessed the rate of channel planform change at four reaches in the lower course of Peixe River over a 46 year period – 1962, 1978, 1997 and 2008 – and found that the sinuosity averaged for all four of their study reaches decreased from ~2.6 to ~1.7 with the average meander wavelength increasing from ~200 to ~500 m, the planform becoming essentially much simpler over that period.…”

“…The second objective is to examine if anthropogenic factors such as reservoir construction or land‐use changes have led to changes in migration rates and planform geometry over time, as has been proposed by Morais et al . () for an adjacent catchment, or whether ENSO (El Niño Southern Oscillation) driven climate anomalies over much of the south‐eastern region of South America as recognized by Amarasekera et al . () may have caused channel adjustments on this river over the 48 years to 2010.…”

Centurial Changes in the Depth Conditions of a Regulated River: Case Study of the Lower Tisza River, Hungary

“…These indirect impacts are characterized by spatial and temporal lags of varying intensities. The consequences of these human interventions have been well described on various rivers in the world (Rinaldi and Simon, 1998;Surian, 1999;Liébault and Piegay, 2001;Kondolf et al, 2002;Xu, 2002;Rinaldi, 2003;Yates et al, 2003;Antonelli et al, 2004;Harmar et al, 2005;Pinter and Heine, 2005;Chang, 2008;Kroes and Kraemer, 2013;Kiss and Balogh, 2015;Morais et al, 2016;Nagy and Kiss, 2016).…”