Discussion of “The Importance of Fluvial Morphology in Hydraulic Engineering”

Lane, E. W.

doi:10.1061/jyceaj.0000048

Cited by 87 publications

(129 citation statements)

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“…Most dams trap sediment and limit downstream river discharge to some degree. The resulting geomorphic and sedimentary effects of dams depend upon the relative extent of alterations to sediment supply and transport capacity in any particular river (Dade et al, 2011;Lane, 1955), as many studies have shown. In alluvial rivers where dam operations reduce sediment supply more severely than transport capacity, the channel downstream of the dam typically becomes incised and attains a simplified planform morphology, and bed sediment coarsens because fine material is preferentially transported downstream without being replaced by upstream supply (Brandt, 2000;Galay, 1983;Grams et al, 2007;Schmidt & Wilcock, 2008;Williams & Wolman, 1984;S.…”

Section: Introductionmentioning

confidence: 99%

Geomorphic Evolution of a Gravel‐Bed River Under Sediment‐Starved Versus Sediment‐Rich Conditions: River Response to the World's Largest Dam Removal

et al. 2018

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Understanding river response to sediment pulses is a fundamental problem in geomorphic process studies, with myriad implications for river management. However, because large sediment pulses are rare and usually unanticipated, they are seldom studied at field scale. We examine fluvial response to a massive (~20 Mt) sediment pulse released by the largest dam removal globally, on the Elwha River, Washington, United States, in an 11‐year before‐after/control‐impact study of channel morphology and grain size. We test the hypothesis that for a given flow magnitude, greater geomorphic change occurs under sediment‐rich conditions than under sediment‐starved conditions. Channel response to flow forcing was significantly different during the sediment‐pulse peak, 1–2 years after dam removal began, than earlier or later. During peak sediment supply our hypothesis was supported; major geomorphic change occurred under low flows and unit stream power ≤60 W/m2. However, by 4–6 years after dam removal began, rates of geomorphic change and sensitivity to stream power had decreased substantially such that our hypothesis was no longer unequivocally supported. These findings are consistent with a two‐phase conceptual model of dam‐removal response, involving a transport‐limited state followed by a more supply‐limited state. From comparisons with other dam removals and natural sediment pulses, we infer that the longevity of sediment‐pulse signals in gravel‐bed rivers depends upon gradient, river discharge, valley morphology, and sediment grain size. Stream power associated with substantial geomorphic change varies with sediment supply, such that assigning a general threshold stream power to gravel‐bed rivers may be untenable.

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Section: Introductionmentioning

confidence: 99%

Geomorphic Evolution of a Gravel‐Bed River Under Sediment‐Starved Versus Sediment‐Rich Conditions: River Response to the World's Largest Dam Removal

et al. 2018

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“…In general, fluvial morphology and erosion-depositional patterns are governed by the differences between the energy available and the energy required for the transport of water and sediments. Available energy is mainly provided by the water supply that, in turn, is determined by the river discharge and gradient, while the amount and size of the sediment load determine the energy that is required to transport the sediments (Lane, 1955). These variables are a function of basin and climatic characteristics including topographical setting, frost and thaw, and vegetation.…”

Section: Introductionmentioning

confidence: 99%

Modern and ancient periglacial river types

Vandenberghe

Woo

2002

Progress in Physical Geography: Earth and Environment

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Climate has been proposed conventionally as the primary factor that determines periglacial river activity (aggradation) and pattern (braided). This concept does not explain the rich diversity in river patterns and morphological processes in both the present and past periglacial environments: besides braided rivers and sandur, meandering, anabranching, transitional and deltaic rivers also occur. A first attempt is made to combine past and present periglacial river types with regard to their morphology, processes and environments. The processes that control river energy and morphology are discussed especially for periglacial conditions. This approach permits an assessment of the responses of periglacial rivers to climatic conditions and the modulation of the responses due to changes in the basin properties. Examples drawn from palaeo- and present-day periglacial rivers and environments demonstrate that there is no unique type of periglacial river but rather an azonal fluvial system with a number of periglacial variants.

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“…The capacity of a stream to transport sediment is a function of flow, channel form (cross-section, slope, roughness) and sediment size (Lane, 1955). Flow and channel form together determine stream hydraulics (depth, velocity, shear stress), which drive the motion of sediment particles on the bed.…”

Section: Introductionmentioning

confidence: 99%

How urban stormwater regimes drive geomorphic degradation of receiving streams

Russell

Vietz

Fletcher

2020

Progress in Physical Geography: Earth and Environment

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For streams draining urban catchments, sediment transport capacity is the key driver of physical impacts including bed sediment removal and channel incision. The main unanswered question is the relative role of flow alteration compared to sediment supply in influencing sediment transport capacity. With this objective, we computed sand and gravel bed sediment transport capacity using the Wilcock and Kenworthy two-fraction bedload transport relation for nine streams in catchments covering a gradient of urbanisation. Computations were done for typical natural bed surface material, based on conditions in the least urban study streams. We compared transport capacity distributions and cumulative transport capacity over one-year between the streams. Transport capacity was up to three orders of magnitude higher in urban streams than in forested-catchment streams. This was driven overwhelmingly by the urbanisation-induced alterations to the flow regime, with only minor feedback from channel form changes. Transport capacity was two to three orders of magnitude greater than measured bedload transport in all but the least urban streams. This excess bedload transport capacity mobilises and removes bed sediment, produces channel incision and enlargement and reduces channel complexity. Rebalancing transport capacity with sediment supply therefore requires significant flow mitigation towards pre-urban conditions. Other responses, which may theoretically help to regain this balance – channel widening, grade control, increasing roughness, sediment augmentation – are either inappropriate or only feasible following flow mitigation measures.

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Discussion of “The Importance of Fluvial Morphology in Hydraulic Engineering”

Cited by 87 publications

References 0 publications

Geomorphic Evolution of a Gravel‐Bed River Under Sediment‐Starved Versus Sediment‐Rich Conditions: River Response to the World's Largest Dam Removal

Geomorphic Evolution of a Gravel‐Bed River Under Sediment‐Starved Versus Sediment‐Rich Conditions: River Response to the World's Largest Dam Removal

Modern and ancient periglacial river types

How urban stormwater regimes drive geomorphic degradation of receiving streams

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