River channel cutoff dynamics, Sacramento River, California, USA

Abstract

We measured patterns of river channel migration and cutoff between 1904 and 1997 on a 160 km meandering alluvial reach of the Sacramento River by intersecting a sequential set of river channel centrelines mapped from a field survey and aerial photography. We identified approximate dates and locations of cutoffs and quantified cutoff dimensions. Twenty-seven chute and 11 partial cutoffs occurred over this 93-year time interval, with an average of one cutoff approximately every 2.5 years or 0.0029 cutoffs per kilometre per year. The average rate of lateral channel change was over the study period was 5.5 AE 0.6 m year À1 (approximately 0.02 channel widths per year) due to progressive migration and cutoff combined. An average of 5% of the total channel length moved laterally via chute cutoff at a rate of 22.1 AE 3.3 m year À1 versus 94% of channel length that moved via progressive migration at a rate of 4.7 AE 0.5 m year À1. The remaining 1% of channel length migrated via partial cutoff at a rate of 13.0 AE 2.8 m year À1. Although channel cutoff was less predominant mode of channel change than progressive migration in terms of channel length, an average of 20% of the total floodplain area change between successive centrelines was attributable to cutoffs. Peak cutoff frequency was concentrated temporally between 1964 and 1987 and was also spatially clustered in specific active sub-reaches along the valley axis over the entire study period.We hypothesize that the probability of channel cutoff is a function of both channel geometry and discharge. Bends that experienced chute cutoff displayed an average sinuosity of 1.97 AE 0.1, an average radius of curvature of 2.1 AE 0.2 channel widths and an average entrance angle of 111 AE 78, as opposed to average values for bends migrating progressively of 1.31 AE 0.01, 2.8 AE 0.1 and 66 AE 18, respectively. The sinuosity of Sacramento River bends experiencing chute cutoff appears to have been consistently declining from 2.25 AE 0.35 channel widths in 1904 to 1.54 AE 0.23 channel widths in 1987. We hypothesize that this trend may be due in part to the influence of land-use changes, such as the conversion of riparian forest to agriculture, on the 'erodibility' of bank and floodplain materials. For the post-dam flow regime (1937 on), cutoff frequency was significantly correlated with an estimate of cumulative overbank flow.

Dryland anabranching river morphodynamics: Río Capilla, Salar de Uyuni, Bolivia

“…The first explanation invokes a hydraulic gradient advantage for the potential chute channel (Howard, 1996) where the flow across the bar top follows a preferable hydraulic gradient as crevasse splays occur during overbank flooding and erodes into the top of the bar as it takes a shortcut across the bar instead of following the longer course around the meander bends. Studies of sand-bed meandering rivers show that chute cutoff like this is favoured by bend expansion as the sinuosity and the approach angle increase (e.g., Micheli and Larsen, 2010;Grenfell et al, 2012). Although these models are developed for sand-bed meandering rivers, we see no reason why they should not apply equally well to a braid bar developed between two meander bends.…”

Bifurcation instability and chute cutoff development in meandering gravel-bed rivers

“…Furthermore, chute cutoffs locally increase the sediment load causing deposition elsewhere, which affects navigation through the river (Zinger et al, 2011). Recently, significant progress was made in understanding the dynamics of chute cutoffs in field studies (Constantine et al, 2010b;Micheli and Larsen, 2011;Grenfell et al, 2012), while morphodynamic models have remained underemployed for this purpose (Howard, 1996;Zolezzi et al, 2012). Here we study the controlling factors for initiation and development of chute cutoffs based on field observations, a morphodynamic three-dimensional (3D) model, and a onedimensional (1D) model with a nodal-point relation for the partitioning of flow and sediment.…”

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

“…The most dynamic segment of the Morava River (segment 4) reached lateral migration rates of the same order of magnitude as substantially larger rivers (e.g. the Sacramento: 5.5 m/year [30], Prophet River: 2.34 m/year [39], the Fort Nelson: 4.44 m/year [39], the Brazos River: 3.28 m/year [40]). Similar behaviour was documented by [35] on the Dane River, which reached local maxima of Er of around …”

“…Based on the methodology of [30], lateral migration polygons (polygons delineated by the position of the bank line in times t and t + ) were constructed for every respective period for both bank lines ( Figure 5). In previous studies, authors used either bank lines or centrelines for describing the pattern of lateral channel migration.…”

“…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.…”