River flood hydraulics

Knight, Donald W.

doi:10.1201/9781439824702.ch17

Cited by 24 publications

(21 citation statements)

References 60 publications

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“…Significant horizontal shear is predicted on the floodplain near the banks, with velocity gradients in a horizontal direction approximately 20% of the vertical gradients near the bed in the channel. This is in keeping with our understanding of compound channels (Knight and Shiono, 1996) where shear layers have been observed to develop in the bank regions.…”

Section: Flow In a Compound Channelsupporting

confidence: 60%

A mixing length model for estimating channel conveyance

Horritt¹,

Wright²

2013

Proceedings of the Institution of Civil Engineers - Water Manag

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This paper describes a simple, physically based mixing length model that explains the functional form of Manning's equation for mean velocity in open channels. Manning's equation has been used to describe mean velocity for over 100 years and is essentially an empirical result rather than being based on an understanding of physical processes.The model described in this paper uses Prandtl's mixing length hypothesis, with mixing length modelled at each point within the cross-section being proportional to the distance to the nearest solid boundary. The model solves equations for the along-stream velocity field using a simple numerical method on regular and irregular finite-

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Section: Flow In a Compound Channelsupporting

confidence: 60%

A mixing length model for estimating channel conveyance

Horritt¹,

Wright²

2013

Proceedings of the Institution of Civil Engineers - Water Manag

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“…Whilst there has been much research into the parameterization of fluxes from river to floodplain (e.g. Knight and Shiono, 1996), much less of this research has been incorporated into models that couple 1D river and 2D floodplain representations and this remains an area of significant uncertainty. Flows from floodplain to river are based upon evaluating the water surface elevation difference between 2D diffusion wave model predictions on the floodplain and the 1D model predictions in the river using the 2D diffusion wave approximation.…”

Section: Flood Inundation Modellingmentioning

confidence: 99%

Interactions between sediment delivery, channel change, climate change and flood risk in a temperate upland environment

Lane¹,

Tayefi²,

Reid³

et al. 2006

Earth Surf Processes Landf

213

183

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This paper uses numerical simulation of flood inundation based on a coupled one-dimensionaltwo-dimensional treatment to explore the impacts upon flood extent of both long-term climate changes, predicted to the 2050s and 2080s, and short-term river channel changes in response to sediment delivery, for a temperate upland gravel-bed river. Results show that 16 months of measured in-channel sedimentation in an upland gravel-bed river cause about half of the increase in inundation extent that was simulated to arise from climate change. Consideration of the joint impacts of climate change and sedimentation emphasized the nonlinear nature of system response, and the possibly severe and synergistic effects that come from combined direct effects of climate change and sediment delivery. Such effects are likely to be exacerbated further as a result of the impacts of climate change upon coarse sediment delivery. In generic terms, these processes are commonly overlooked in flood risk mapping exercises and are likely to be important in any river system where there are high rates of sediment delivery and long-term transfer of sediment to floodplain storage (i.e. alluviation involving active channel aggradation and migration). Similarly, attempts to reduce channel migration through river bank stabilization are likely to exacerbate this process as without bank erosion, channel capacity cannot be maintained. Finally, many flood risk mapping studies rely upon calibration based upon combining contemporary bed surveys with historical flood outlines, and this will lead to underestimation of the magnitude and frequency of floodplain inundation in an aggrading system for a flood of a given magnitude.

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“…Theoretical analyses by Knight and Shiono (1996) showed that the speed of a flood wave peaks at 0.67-1 · bankfull depth, and is drastically reduced when the floodplain is inundated. We can expect the floodplains in restored reaches to be flooded more frequently, and the cumulative effect of this would be a reduction in peak flow.…”

Section: Geomorphic and Hydraulic Responsesmentioning

confidence: 99%

Forecasting Environmental Responses to Restoration of Rivers Used as Log Floatways: An Interdisciplinary Challenge

et al. 2005

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Log floating in the 19th to mid 20th centuries has profoundly changed the environmental conditions in many northern river systems of the world. Regulation of flow by dams, straightening and narrowing of channels by various piers and wing dams, and homogenization of bed structure are some of the major impacts. As a result, the conditions for many riverine organisms have been altered. Removing physical constructions and returning boulders to the channels can potentially restore conditions for these organisms. Here we describe the history of log driving, review its impact on physical and biological conditions and processes, and predict the responses to restoration. Reviewing the literature on comparable restoration efforts and building upon this knowledge, using boreal Swedish rivers as an example, we address the last point. We hypothesize that restoration measures will make rivers wider and more sinuous, and provide rougher bottoms, thus improving land-water interactions and increasing the retention capacity of water, sediment, organic matter and nutrients. The geomorphic and hydraulic/hydrologic alterations are supposed to favor production, diversity, migration and reproduction of riparian and aquatic organisms. The response rates are likely to vary according to the types of processes and organisms. Some habitat components, such as beds of very large boulders and bedrock outcrops, and availability of sediment and large woody debris are believed to be extremely difficult to restore. Monitoring and evaluation at several scales are needed to test our predictions.

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River flood hydraulics

Cited by 24 publications

References 60 publications

A mixing length model for estimating channel conveyance

A mixing length model for estimating channel conveyance

Interactions between sediment delivery, channel change, climate change and flood risk in a temperate upland environment

Forecasting Environmental Responses to Restoration of Rivers Used as Log Floatways: An Interdisciplinary Challenge

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