Channel-Forming Discharge and Hydraulic Geometry Width Predictors in Meandering Sand-Bed Rivers

Copeland, Ronald R.; Soar, Philip J.; Thorne, Colin R.

doi:10.1061/40792(173)568

Cited by 19 publications

(22 citation statements)

References 10 publications

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“…The purpose of hydraulic geometry relationships is to relate a river's form to a single representative discharge. The representative discharge, or channel forming discharge, as defined by Copeland et al [2005], is a single discharge that over a long period of time would theoretically "produce the same channel geometry as the natural long-term hydrograph." Standard practice is to estimate the channel forming discharge with the bankfull discharge Q bf , that is, the discharge at which flow just spills from the channel onto the floodplain [Wolman and Leopold, 1957].…”

Section: Formative Shields Number and Bankfull Geometrymentioning

confidence: 99%

Numerical modeling of erosional and depositional bank processes in migrating river bends with self‐formed width: Morphodynamics of bar push and bank pull

2014

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Meandering rivers display active communication between bank erosion and bar deposition processes. How does this occur? How does the river select its width? To answer these questions, we implement a model for meander migration where both bank processes (erosion and deposition) are considered independently. Bank erosion is modeled as erosion of purely noncohesive bank material damped by natural slump block armoring; channel deposition is modeled via flow-retarded vegetal encroachment. Both processes are tied to a slope-dependent channel forming Shields number; banks with near-bank Shields number below this value undergo deposition, and those above it undergo erosion. Channel-forming Shields number must increase with slope, as dictated by available data and model performance. Straight channel modeling shows that a channel arrives at an equilibrium width from any initial condition. For the channel bend, the river always approaches an asymptotic state where width reduces slowly in time and where bank erosion and deposition occur at nearly equal rates. Before this state is reached, however, the river follows a phase-plane trajectory with four possible regimes: (a) both banks erode, (b) both banks deposit, (c) both banks migrate outward, but with a faster depositing bank (bar push), and (d) both banks migrate outward, but with a faster eroding bank (bank pull). The trajectory of migration on the phase plane depends on initial conditions and input parameters controlling the rate of depositional and erosional migration. All input parameters have specific physical meaning, and the potential to be measured in the field.

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Section: Formative Shields Number and Bankfull Geometrymentioning

confidence: 99%

Numerical modeling of erosional and depositional bank processes in migrating river bends with self‐formed width: Morphodynamics of bar push and bank pull

2014

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“…Various approaches have been used to formulate a representative steady water discharge that, given enough time, would produce the same channel geometry as the natural long‐term hydrograph [e.g., NEDECO , ; Prins and de Vries , ; Pickup and Warner , ; Pickup and Rieger , ; Hey , ; Emmett and Wolman , ; Copeland et al , ]. This natural long‐term hydrograph is here defined as the hydrograph that covers the flow rate statistics of several years or decades.…”

Section: Introductionmentioning

confidence: 99%

“…The concept of a channel‐forming discharge was first introduced in the design of irrigation channels, in which the variation of the flow rate is generally limited [e.g., Lacey , ]. Application of this concept to the design, maintenance, and restoration of natural streams, which are subject to a much wider range of flow rates, initiated a search for a single value of the water discharge representative in its effect on channel geometry [ Pickup and Rieger , ; Copeland et al , ; Gomez et al , ]. Although the terminology has not always been consistent, the following representative discharges have been proposed: First is the bankfull discharge, which is the flow rate at which the channel is just filled to the top of its banks and which therefore agrees to the condition of incipient flooding [e.g., Wolman and Leopold , ; Williams , ; Parker , ; ; Emmett and Wolman , ; Gomez et al , ; Parker et al , ; Phillips and Jerolmack , ].…”

Section: Introductionmentioning

confidence: 99%

The equilibrium alluvial river under variable flow and its channel‐forming discharge

et al. 2017

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When the water discharge, sediment supply, and base level vary around stable values, an alluvial river evolves toward a mean equilibrium or graded state with small fluctuations around this mean state (i.e., a dynamic or statistical equilibrium state). Here we present analytical relations describing the mean equilibrium geometry of an alluvial river under variable flow by linking channel slope, width, and bed surface texture. The solution holds in river normal flow zones (or outside both the hydrograph boundary layer and the backwater zone) and accounts for grain size selective transport and particle abrasion. We consider the variable flow rate as a series of continuously changing yet steady water discharges (here termed an alternating steady discharge). The analysis also provides a solution to the channel‐forming water discharge, which is here defined as the steady water discharge that, given the mean sediment supply, provides the same equilibrium channel slope as the natural long‐term hydrograph. The channel‐forming water discharge for the gravel load is larger than the one associated with the sand load. The analysis illustrates how the load is distributed over the range of water discharge in the river normal flow zone, which we term the “normal flow load distribution”. The fact that the distribution of the (imposed) sediment supply spatially adapts to this normal flow load distribution is the origin of the hydrograph boundary layer. The results quantify the findings by Wolman and Miller (1960) regarding the relevance of both magnitude and frequency of the flow rate with respect to channel geometry.

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“…In contrast to upland, gravel/cobble‐bed channels, sand‐bed channels are dominated by unconsolidated sediment mobilized at flows as low as mean annual discharge (Copeland et al. ), and associated rapid channel adjustments to altered hydrology (Simons and Simons ). Stream biota in the SE Plains strongly differ compositionally from that in upland ecoregions, likely reflecting contrasting instream habitat conditions (Feminella ; Kosnicki et al.…”

Section: Introductionmentioning

confidence: 99%

“…The Sand Hills (Level IV) ecoregion of the SE Plains (Level III) ecoregion in the southeastern United States (U.S.) is characterized by streams with low gradient, sand-bed channels (Omernik 1987). In contrast to upland, gravel/cobble-bed channels, sand-bed channels are dominated by unconsolidated sediment mobilized at flows as low as mean annual discharge (Copeland et al 2005), and associated rapid channel adjustments to altered hydrology (Simons and Simons 1987). Stream biota in the SE Plains strongly differ compositionally from that in upland ecoregions, likely reflecting contrasting instream habitat conditions (Feminella 2000;Kosnicki et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Hydrogeomorphic Reference Condition and Its Relationship with Macroinvertebrate Assemblages in Southeastern U.S. Sand Hills Streams

Sefick

Kosnicki

Paller

et al. 2018

J American Water Resour Assoc

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Defining stream reference conditions is integral to providing benchmarks to ecological perturbation. We quantified channel geometry, hydrologic and environmental variables, and macroinvertebrates in 62 low‐gradient, SE United States (U.S.) Sand Hills (Level IV ecoregion) sand‐bed streams. To identify hydrogeomorphic reference condition (HGM), we clustered channel geometry deviation from expectations given watershed area (Aws), resulting in two HGM groups discriminated by area at the top of bank (Atob) residuals <0.6 m2 and >0.6 m2 predicted to be HGM reference/nonreference streams, respectively. Two independent partial least squares discriminate analyses used (1) hydrologic/environmental variables and (2) macroinvertebrate mean trait values (mT) on 10 reference/nonreference stream pairs of similar Aws for classification validation. Nonreference streams had flashier hydrographs and altered flow magnitudes, lower organic matter, coarser substrate, higher pH/specific conductivity compared with reference streams. Macroinvertebrate assemblages corresponded to HGM groupings, with mT indicative of multivoltinism, collector‐gatherer functional feeding groups, fast current‐preference taxa, and lower Ephemeroptera, Plecoptera, and Trichoptera richness and biotic integrity in nonreference streams. HGM classifications in Sand Hills, sand‐bed streams were determined from channel geometry. This easily implemented classification is indicative of contemporary hydrologic disturbance resulting in contrasting macroinvertebrate assemblages.

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Channel-Forming Discharge and Hydraulic Geometry Width Predictors in Meandering Sand-Bed Rivers

Cited by 19 publications

References 10 publications

Numerical modeling of erosional and depositional bank processes in migrating river bends with self‐formed width: Morphodynamics of bar push and bank pull

Numerical modeling of erosional and depositional bank processes in migrating river bends with self‐formed width: Morphodynamics of bar push and bank pull

The equilibrium alluvial river under variable flow and its channel‐forming discharge

Hydrogeomorphic Reference Condition and Its Relationship with Macroinvertebrate Assemblages in Southeastern U.S. Sand Hills Streams

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