Geomorphic response of low-gradient, meandering and braided alluvial river channels to increased sediment supply

Kemper, John T.; Rathburn, Sara L.; Mueller, Erich R.; Wohl, Ellen; Scamardo, Julianne

doi:10.1016/j.earscirev.2023.104429

Cited by 10 publications

(5 citation statements)

References 273 publications

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“…Historical geomorphic conditions do not provide a blueprint for restoration to a reference condition. Persistent contemporary constraints as diverse as changing climate and flow regime, reduced riparian aquifer level, lateral confinement of the river corridor by land use (Blanton & Marcus, 2009), or substantially altered sediment regime (Kemper et al, 2023;Wohl et al, 2015) as a result of an upstream dam or land use change, may preclude full restoration to historical conditions. However, understanding the historical geomorphic context may provide information on the site potential and the ideal conditions for native species and different life stages of a species (e.g., Beechie et al, 2015Beechie et al, , 2021.…”

Section: Using Geomorphic Context To Inform Process-based Restorationmentioning

confidence: 99%

Geomorphic context in process‐based river restoration

Wohl,

Rathburn,

Dunn

et al. 2024

River Research & Apps

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Process‐based river restoration seeks to restore processes such as channel‐floodplain connectivity that create and maintain river corridor functions. Process‐based restoration can fail to produce the desired results if geomorphic context is not effectively incorporated into restoration design. Geomorphic context of a river reach refers to the controls on contemporary river form and process. Controls at the catchment‐ to reach‐scale include geologic history, biophysical characteristics, legacies of past human alterations, position within the river network, river corridor geometry, base level stability, disturbance regime, and contemporary human alterations of the river corridor. We conceptualize a river corridor as reflecting the interactions among fluxes of material and the geomorphic context. We discuss how an understanding of geomorphic context can be used to select a restoration approach and provide examples of how restoration can fail to achieve desired outcomes when geomorphic context is not considered. Within the toolbox of methods used to implement process‐based restoration, we differentiate the alteration of inputs to the river corridor and fluxes of material through the corridor from alteration of form and/or connectivity within the river corridor. Historical, biotic, geologic/geomorphic, and reference sites can be used to inform process‐based restoration targets. Restoration is strongly influenced by human perceptions of what is appropriate and achievable at a site and diverse communities influencing restoration at a site may differ in their perceptions. Geomorphically based conceptual guidelines, such as the River Styles Framework, provide an effective platform for incorporating an understanding of geomorphic context into process‐based river restoration.

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Section: Using Geomorphic Context To Inform Process-based Restorationmentioning

confidence: 99%

Geomorphic context in process‐based river restoration

Wohl,

Rathburn,

Dunn

et al. 2024

River Research & Apps

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“…The Yampa River in Deerlodge Park evacuated 12 ± 11 MT/m (downstream)/year of sand during our study period, yet the river maintained the same geomorphic character and behavioral regime, reflective of a river in equilibrium accommodating minor watershed disturbances. The arroyo-cutting event during the late nineteenth to early twentieth century , Kemper et al, 2023 and elevated stream flow during the twentieth-century pluvial period (Woodhouse et al, 2006;Woodhouse & Pederson, 2018) caused a period of increased lateral instability and widespread overbank sedimentation on the pre-1938 floodplain (Figure 15). Once the arroyo-cutting event ended, the supply rate decreased, and floodplain shaving began to slowly remove excess sediment stored in the overbank, a process which continues today, evidenced by eroding banks being a factor of ∼3 times taller than laterally accreted floodplains (Figure 15).…”

Section: How Do Rivers In Equilibrium Behave?mentioning

confidence: 99%

“…One way that a channel can absorb a disturbance without changing its form is to adjust the transport capacity. Internal adjustments, such as changes in bed material grain size and bar frequency, can change transport capacity without changing the average channel form (Fryirs & Brierley, 2012, 2022Kemper et al, 2023;Knighton, 1998). In cases where bed textural changes are significant, a channel may absorb the impact of an upstream disturbance in flow or sediment supply with little to no morphologic adjustment (Ahammad et al, 2021;Buffington & Montgomery, 1999;Cui et al, 2003;Ferguson et al, 2015;Kemper et al, 2023;Leonard, 2022;Rubin & Topping, 2001;Sklar et al, 2009;Topping et al, 2018Topping et al, , 2021).…”

Section: Introductionmentioning

confidence: 99%

A Sediment Budget for a Sand Bed River Partitioned by Sand Fractions

Leonard,

Schmidt

2024

JGR Earth Surface

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Sediment budgets are widely used to measure reach‐scale sediment accumulation and evacuation. Such measurements, however, cannot determine when the disturbance is major and the measured sediment mass imbalance is reflective of a river adjusting to a new equilibrium state, as opposed to situations when the disturbance is minor, and the mass imbalance is reflective of a river adjusting within its existing behavioral regime. Sediment sorting among channels and floodplains can have a large effect on how a river responds to a disturbance. Fine sediment may accumulate in the floodplains while coarser sediment erodes from the channel bed. We demonstrate that if a sediment budget does not account for the different behavior and destination of grain sizes, the budget cannot reveal important channel adjustments. In this study, we evaluated how a sand bed river responded to increases in sediment supply by partitioning a sediment budget among silt/clay and five sand fractions. On average, 12 metric tons/meter (downstream)/year of sand was evacuated from the system, but sorting caused channel margins to behave differently from vegetated islands, revealing how a river can slightly narrow while in deficit. Floodplain shaving and bed coarsening evacuated sediment while channel geometry barely changed, consistent with a river adjusting to a minor disturbance within its behavioral regime. This study is an important reminder that sediment mass imbalance does not always lead to channel change. Mechanisms such as floodplain shaving and bed textural change help rivers absorb minor disturbances and resist channel change.

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“…Sinuosity was measured by calculating the channel length divided by the straight-line valley bottom length. Additionally, braiding is a common and readily measurable fluvial response to increased sediment supply (Kemper et al, 2023). Braiding index was calculated by averaging the number of channels (including main and secondary) within the river corridor at five random transects.…”

Section: Measuring Potential Driving Factorsmentioning

confidence: 99%

Drivers of Geomorphic Heterogeneity in Unconfined Non‐Perennial River Corridors

et al. 2023

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River corridors along non‐perennial stream networks provide diverse physical and ecological functions that are thought to be related to the spatial and temporal variability of geomorphic units, also known as geomorphic heterogeneity. While studies on the characteristics and drivers of geomorphic heterogeneity have been developed in perennial streams, similar studies in ephemeral streams are lacking. Given the ubiquity of non‐perennial streams globally, we aim to answer questions regarding the magnitude and drivers of geomorphic heterogeneity in ephemeral river corridors as well as how geomorphic unit assemblages reflect processes related to flood disturbance. Geomorphic units were mapped in 30 unconfined river corridors within six non‐perennial watersheds in Utah and Arizona, USA. Landscape heterogeneity metrics—Shannon's Diversity Index, Shannon's Evenness Index, and patch density—were used to quantify geomorphic heterogeneity within each reach. Additionally, variables that potentially constrain or drive heterogeneity were quantified, including floodplain shape, grain size, large wood abundance, and proxies for flood disturbance. While heterogeneity positively correlated with metrics for morphology and disturbance, statistical models suggest that morphologic context, particularly river corridor width, was a more important predictor for estimating geomorphic heterogeneity. Still, geomorphic units reflected aggradation processes indicative of a range of flood energies, suggesting a strong tie between heterogeneity and disturbance. Results suggest that geomorphic heterogeneity may be resilient to changes in flood disturbance frequency or magnitude, but future studies investigating long‐term temporal heterogeneity are needed.

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Geomorphic response of low-gradient, meandering and braided alluvial river channels to increased sediment supply

Cited by 10 publications

References 273 publications

Geomorphic context in process‐based river restoration

Geomorphic context in process‐based river restoration

A Sediment Budget for a Sand Bed River Partitioned by Sand Fractions

Drivers of Geomorphic Heterogeneity in Unconfined Non‐Perennial River Corridors

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