Changing river channels: The roles of hydrological processes, plants and pioneer fluvial landforms in humid temperate, mixed load, gravel bed rivers

Gurnell, Angela M.; Bertoldi, Walter; Corenblit, Dov Jean-François

doi:10.1016/j.earscirev.2011.11.005

Cited by 430 publications

(427 citation statements)

References 165 publications

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“…Its spatial extent, dynamics, and magnitude are determined by many factors including channel geomorphology (e.g., channel morphology, bank topography), flow and sediment dynamics (e.g., frequency, duration and magnitude of floods, and suspended sediment concentrations), and vegetation cover (Steiger and Gurnell, 2003;Benjankar and Yager, 2012;Gurnell et al, 2012). However, these features have been shown to be highly active and dynamic components of the reservoir fluctuation zone of the Three Gorges Reservoir affected by flow regulation.…”

Section: Sedimentation In the Reservoir Fluctuation Zonementioning

confidence: 99%

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

Tang

Bao

et al. 2016

Science of The Total Environment

104

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• Hydrological regime in the reservoir fluctuation zone has been significantly altered.• Grain-size variations are diagnostic for sedimentary stratigraphy differentiation.• Post-dam sedimentation processes were reproduced by chronology determination.• Regular flow regulation controls contemporary seasonal sedimentary dynamics. Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1 cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by G R A P H I C A L A B S T R A C T a b s t r a c t a r t i c l e i n f o Contents lists available at ScienceDirectScience of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may have profound implications in affecting sedimentary equilibrium in the reservoir fluctuation zone. The results herein provide insights of how big dams have disrupted the sediment conveyance processes of large scale fluvial systems.

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Section: Sedimentation In the Reservoir Fluctuation Zonementioning

confidence: 99%

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

Tang

Bao

et al. 2016

Science of The Total Environment

104

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“…As shown elsewhere, bar morphodynamics vary markedly for differing planform types, with key differences outlined here for braided, anabranching, and meandering channels (cf., Hooke, 1986;Kleinhans, 2010;Kleinhans and van den Berg, 2010;Church and Ferguson, 2015). Bar development and stability reflect the ability of vegetation to trap sediments and stabilize banks, which in turn is directly influenced by flow energy relationships (i.e., these are mutual adjustments; Corenblit et al, 2007;Gurnell et al, 2012;Gurnell, 2014;Osterkamp and Hupp, 2010;Pietsch and Nanson, 2011). In this study, riparian vegetation and its root network are considered to restrict channel width and increase hydraulic efficiency, inducing greater bedload transport capacity in multi-thread channels (Allmendinger et al, 2005;Huang and Nanson, 2007).…”

Section: Discussionmentioning

confidence: 99%

Vegetative impacts upon bedload transport capacity and channel stability for differing alluvial planforms in the Yellow River source zone

Brierley

et al. 2016

Hydrol. Earth Syst. Sci.

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Abstract. The influence of vegetation upon bedload transport and channel morphodynamics is examined along a channel stability gradient ranging from meandering to anabranching to anabranching-braided to fully braided planform conditions along trunk and tributary reaches of the Upper Yellow River in western China. Although the regional geology and climate are relatively consistent across the study area, there is a distinct gradient in the presence and abundance of riparian vegetation for these reaches atop the QinghaiTibet Plateau (elevations in the study area range from 2800 to 3400 m a.s.l.). To date, the influence of vegetative impacts upon channel planform and bedload transport capacity of alluvial reaches of the Upper Yellow River remains unclear because of a lack of hydrological and field data. In this region, the types and pattern of riparian vegetation vary with planform type as follows: trees exert the strongest influence in the anabranching reach, the meandering reach flows through meadow vegetation, the anabranching-braided reach has a grass, herb, and sparse shrub cover, and the braided reach has no riparian vegetation. A non-linear relation between vegetative cover on the valley floor and bedload transport capacity is evident, wherein bedload transport capacity is the highest for the anabranching reach, roughly followed by the anabranching-braided, braided, and meandering reaches. The relationship between the bedload transport capacity of a reach and sediment supply from upstream exerts a significant influence upon channel stability. Bedload transport capacity during the flood season (June-September) in the braided reach is much less than the rate of sediment supply, inducing bed aggradation and dynamic channel adjustments. Rates of channel adjustment are less pronounced for the anabranching-braided and anabranching reaches, while the meandering reach is relatively stable (i.e., this is a passive meandering reach).

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“…Longitudinal variations in vegetation cover along the 21-km lower reach may be explained by differences in floodplain width, channel form, and vegetation type. Some parts of the reach are relatively narrow and contain many islands heavily-vegetated with willow, which are likely to resist erosion during floods (Blom, 1999;Hering et al, 2004;Gurnell et al, 2012). Other sections are very wide (up to 3 km) and display a more typical braided river pattern, with large expanses of bare gravels or with pioneer lupins or grasses.…”

Section: Changes In Covermentioning

confidence: 99%

Flood Hydraulics and Impacts on Invasive Vegetation in a Braided River Floodplain, New Zealand

Caruso¹,

Ross²,

Shuker³

et al. 2012

ENRR

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This study evaluates the effects of floods and their hydraulic characteristics on invasive vegetation in the Ahuriri River floodplain, a braided gravel-bed river in the eastern high country of the South Island, New Zealand. Invasive vegetation alters the natural braiding tendency of rivers such as the Ahuriri and has severe negative impacts on threatened and endangered native wading birds and floodplain ecology. Aerial photographs for a 10-year period (1991 to 2000) that includes the largest flood on record in 1994 (recurrence interval of almost 50 years) based on a 46-year record were analysed to determine changes in aerial cover of water, bare substrate, and several different vegetation classes. This was complemented by hydraulic modelling using HEC-RAS software for a representative 1.1-km reach to evaluate flood hydraulic characteristics that can impact vegetation, including water inundation area, depth, velocity, and shear stress. The 1994 flood (570 m 3 /s) removed up to 25% of the invasive vegetation in the study reach, with preferential removal of lupin and less removal of willow and grassland. However, flood effects varied considerably with overall minor effects on total vegetation cover over the entire lower 21-km reach. The spatial distribution of vegetation cover changed considerably in response to this flood event, in a pattern resembling a shifting-mosaic steady state model. Modelling showed that a 600 m 3 /s (50-year) flood is likely to result in almost total inundation of the study reach floodplain and significant velocities and shear stresses on floodplain vegetation. Over the study reach linear models approximate the relationships between flood peak magnitude with average water area, depth, velocity, and shear stress. Depth and velocity do not increase as fast as flow area or shear stress, and differences between hydraulic characteristics for the 600 and 155 m 3 /s floods ranged from 37% for velocities to 179% for flow inundation areas. Much of the vegetation appeared to recover relatively quickly after flood events so that vegetation removal effects are short-lived. Although large floods can remove a considerable amount of invasive vegetation in some reaches of the river, natural flood events are unlikely to significantly reduce invasive vegetation cover throughout the river.

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Changing river channels: The roles of hydrological processes, plants and pioneer fluvial landforms in humid temperate, mixed load, gravel bed rivers

Cited by 430 publications

References 165 publications

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

Vegetative impacts upon bedload transport capacity and channel stability for differing alluvial planforms in the Yellow River source zone

Flood Hydraulics and Impacts on Invasive Vegetation in a Braided River Floodplain, New Zealand

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