Lateral erosion of the Sacramento River, California (1942–1999), and responses of channel and floodplain lake to human influences

Abstract

This study focused on a spatial and temporal analysis of the active channel and associated floodplain lakes using aerial photographs spanning five decades (1942, 1962, 1985, 1999) over a 140 km long reach of the Sacramento. Planimetric changes were analysed longitudinally and temporally to highlight the spatial structures and their evolution through time. The results underline complex changes and space-time pattern in bank erosion, channel length and active channel width. The bank erosion and also channel lengthening were higher between 1962 and 1985 than in the two periods studied before and after. Active channel width significantly decreased from 1942 to 1999; partly progressively from upstream to downstream with local widening whatever the studied periods. Similarly the floodplain lakes observed before 1942-1962 were significantly different in size and geometry from those which appeared during the most recent period. The creation of lakes is less frequent after the 1940s, with a secondary peak of occurrence during the 1962-1985 period. The interpretation of these changes is complex because of various human pressures acting over different time scales (bank protection, flow diversion, sediment starvation, land-use changes) and various natural influences (flood sequences through out the period, geological setting). The findings are discussed by comparison with previous work, and highlight the important effect of dam impact on peak flow and sediment starvation modifying longitudinally hydraulic conditions within the channel, but also the increase in riprap protection which induced change in bank erosion, channel planimetry and floodplain lake characters (geometry, frequency of renewal). Variation in flood intensities is also observed as having positive effects on the bank erosion pattern. Secondarily, land-use changes also controlled bank erosion intensity.

Channel migration inferred from aerial photographs, its timing and environmental consequences as responses to floods: A case study of the meandering Topľa River, Slovak Carpathians

“…Similar floods in terms of magnitude and frequency, however, can produce dissimilar morphological responses (Fuller, 2008). Michalková et al (2011) point out the significant geomorphological effect of a critical shear stress, which is recorded under the influence of more frequent and prolonged floods. Hickin and Sichingabula (1988) highlight the importance of the flood duration.…”

“…The accuracy and precision of spatial data, methods for calculating lateral movement of the channel and the selection of consistent rules for identifying landform dynamics and delimiting the features of interest, significantly affect geomorphological interpretations (Zanoni et al, 2008). Not only do historical data serve to identify lateral migration (Hooke, 1979;Pišút, 2002;Gilvear and Bryant, 2003;Michalková et al, 2011), but they also contribute to the study of changes of channel and riparian zone patterns (Bryant and Gilvear, 1999;Gilvear and Willby, 2006). Floods and their erosional power affect the overall ecological diversity in the riparian landscape by eroding channel landforms or vegetation in the riparian zone, by depositing sediments and seed dissemination (Ward et al, 2002;Petts, 2002, 2006;Corenblit et al, 2007;Opperman et al, 2010;Corenblit et al, 2010;Erskine et al, 2012).…”

Response of lateral channel dynamics of a lowland meanderingriver to engineering-derived adjustments - an example of theMorava River (Czech Republic)

“…Mean channel shift for the period analysed is then calculated as a polygon area divided by half of its perimeter [30]. For a detailed description of spatio-temporal changes of Er, Ar and ∆W, lateral migration polygons were further divided into 25 m long segments, similar to the studies of [21,32,33], representing in the case of the Morava approximately half of the channel width. For every segment, a mean channel shift was calculated as its area divided by a half of the bank line length in times t and t + .…”

“…; (2) how should channel migration zones be delimited to mitigate the con icts between the dynamic changes of meandering channels and economic activities, typically arable land erosion and disruption of transportation infrastructure [18][19][20]? ; (3) what controls channel migration rates of meandering rivers [21][22][23]?…”

Variabilidad espacial de los cambios de cauce en una rambla mediterránea en las seis últimas décadas (1946-2006)

“…Channel width is considered in this work the result of measuring the total unvegetated width, that is, the sum of the single channel branches widths, plus the unvegetated gravel bars (Bertoldi et al, 2009;Michalková et al, 2010). Channel width was measured on the aerial photographs every 500 m along the entire study reach (16.5 km).…”