Valley-scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes

Weber, Matthew D.; Pasternack, G. B.

doi:10.1016/j.geomorph.2017.03.018

Cited by 21 publications

(20 citation statements)

References 59 publications

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“…Further, both approaches were congruent in regard to the morphological alterations in the marsh area in the lower part of the creek in the BW zone. This suggests active banks with frequent erosion and deposition, indicating the presence of sediment transport in the BW zone from the river to the banks and vice versa [75,76]. Unlike the model results, the satellite images indicated the occurrence of some morphological alterations in the marsh area in the middle of BW zone (Figure 7).…”

Section: Analysis Of the Geomorphic Modelmentioning

confidence: 75%

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

Hosseiny

Smith

2019

Water

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Predicting morphological alterations in backwater zones has substantial merit as it potentially influences the life of millions of people by the change in flood dynamics and land topography. While there is no two-dimensional river model available for predicting morphological alterations in backwater zones, there is an absolute need for such models. This study presents an integrated iterative two-dimensional fluvial morphological model to quantify spatio-temporal fluvial morphological alterations in normal flow to backwater conditions. The integrated model works through the following steps iteratively to derive geomorphic change: (1) iRIC model is used to generate a 2D normal water surface; (2) a 1D water surface is developed for the backwater;(3) the normal and backwater surfaces are integrated; (4) an analytical 2D model is established to estimate shear stresses and morphological alterations in the normal, transitional, and backwater zones. The integrated model generates a new digital elevation model based on the estimated erosion and deposition. The resultant topography then serves as the starting point for the next iteration of flow, ultimately modeling geomorphic changes through time. This model was tested on Darby Creek in Metro-Philadelphia, one of the most flood-prone urban areas in the US and the largest freshwater marsh in Pennsylvania.the river increases gradually upstream to form a smooth transition between a quasi-normal flow and standing water, forcing an alteration of the hydraulic conditions. The segment of the river affected by this response-which might exceed hundreds of kilometers in low slope rivers-is called the backwater zone [12].The shift in BW hydraulics causes the water surface slope to decrease independent of the bed slope, resulting in a gradual longitudinal alteration of the flow depth and velocity [13]. The vertical velocity distribution in BW conditions is less divergent compared to the one in a uniform flow [14]. These changes in the hydraulics of the vertical and horizontal flow velocity in BW zones consequently alter the sediment transport processes.Current approaches to BW in morphological studies are primarily based on either measured or estimated hydraulic parameters coupled with the estimated sediment transport [9,11,[15][16][17][18][19][20][21]. The studies of sediment transport in BW conditions are scarce due to the complex dynamics of the sediment transport in BW zones and the lack of field-measured data. The presence of the BW complicates different types of hydrometric measurements including the water surface slope, velocity, and discharge [19]. A lack in measured data is even more severe for transitional areas where the flow state changes from normal to a gradually varied flow [18]. Nittrouer et al. used measured cross sections in the lower Mississippi River to back calculate velocity, shear stress and sediment discharge [22]. They concluded that where the flow transitions to the BW zone, the cross-sectional area increases in the downstream in low-moderate flows, resultin...

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Section: Analysis Of the Geomorphic Modelmentioning

confidence: 75%

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

Hosseiny

Smith

2019

Water

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“…In some cases the delineated valley bottom included this adjacent steep slope or rock outcrop. In these locations ALS interpolation errors and horizontal displacement errors (Hodgson and Bresnahan, 2004) can lead to errors in estimating ground locations and elevations, resulting in substantial errors in the DoD volume estimates (e.g., Heritage et al, 2009;Wheaton et al, 2010;Milan et al, 2011;Bangen et al, 2016). These inaccuracies in identifying valley margins also caused higher elevation points to be included within a given segment, which will lead to inaccurate estimates of valley bottom slopes.…”

Section: Uncertainty Errors and Methodological Issues In Dem Differmentioning

confidence: 99%

“…DEMs of difference (DoDs) were computed using the geomorphic change detection (GCD) tool add-in for ArcGIS (http://gcd.riverscapes.xyz/ (last access: 1 September 2018), version 6; Wheaton et al, 2010). GCD uses a fuzzy inference system (FIS) to propagate spatially explicit DEM uncertainties, and consequently the uncertainties in the DoD.…”

Section: Valley Changementioning

confidence: 99%

“…GCD uses a fuzzy inference system (FIS) to propagate spatially explicit DEM uncertainties, and consequently the uncertainties in the DoD. Spatially explicit errors are much more accurate than assuming a uniform uncertainty, as the latter can lead to large errors in the calculated volumes of erosion and deposition (e.g., Wheaton et al, 2010;Milan et al, 2011).…”

Section: Valley Changementioning

confidence: 99%

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Spatial and temporal patterns of sediment storage and erosion following a wildfire and extreme flood

2019

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Abstract. Post-wildfire landscapes are highly susceptible to rapid geomorphic changes, and the resulting downstream effects, at both the hillslope and watershed scales due to increases in hillslope runoff and erosion. Numerous studies have documented these changes at the hillslope scale, but relatively few studies have documented larger-scale post-fire geomorphic changes over time. In this study we used five airborne laser scanning (ALS) datasets collected over 4 years to quantify erosion and deposition throughout the channel network in two ∼15 km2 watersheds, Skin Gulch and Hill Gulch, in northern Colorado after a wildfire followed by a large, long-duration flood 15 months later. The objectives were to (1) quantify the volumes, spatial patterns, and temporal changes over time of erosion and deposition over a nearly 4-year period, and (2) evaluate the extent to which these spatially and temporally explicit changes are correlated to precipitation metrics, burn severity, and morphologic variables. The volumetric changes were calculated from a differencing of DEMs for 50 m long segments of the channel network and associated valley bottoms. The results showed net sediment accumulation after the wildfire in the valley bottoms of both watersheds, with greater accumulations in the wider and flatter valley bottoms in the first 2 years after burning. In contrast, the mesoscale flood caused large amounts of erosion, with higher erosion in those areas with more post-fire deposition. Only minor changes occurred over the 2 years following the mesoscale flood. Volume changes for the different time periods were weakly but significantly correlated to, in order of decreasing correlation, contributing area, channel width, percent burned at high and/or moderate severity, channel slope, confinement ratio, maximum 30 min precipitation, and total precipitation. These results suggest that morphometric characteristics, when combined with burn severity and a specified storm, can indicate the relative likelihood and locations for post-fire erosion and deposition. This information can help assess downstream risks and prioritize areas for post-fire hillslope rehabilitation treatments.

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“…We hypothesized that 25 stronger correlations might be present when the watershed data were stratified by valley bottom slope or drainage area, but this did not greatly improve the strength or magnitude of the correlations. Alternatively, it has been suggested that better relationships could be attained by parsing the valley into more discrete geomorphic units (e.g., channel, floodplain, terrace) to reflect different dominant processes (e.g., Weber and Pasternack, 2017), but there was no easy way for us to do this across our study watersheds. Nevertheless, the correlations still provide useful insights into the controls on the volumetric changes.…”

Section: Controls On Spatial and Temporal Patterns Of Geomorphic Changementioning

confidence: 97%

Spatial and temporal patterns of sediment storage and erosion following a wildfire and extreme flood

Brogan¹,

Nelson²,

MacDonald³

2019

Preprint

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Abstract. Post-wildfire landscapes are highly susceptible to rapid geomorphic changes at both the hillslope and watershed scales due to increases in hillslope runoff and erosion, and the resulting downstream effects. Numerous studies have documented these changes at the hillslope scale, but relatively few studies have documented larger-scale post-fire geomorphic changes over time. In this study we used five airborne laser scanning (ALS) datasets collected over four years to quantify valley bottom changes in two ∼15 km2 watersheds, Skin Gulch and Hill Gulch, after the June 2012 High Park fire in northern Colorado and a large mesoscale flood 15 months later. The objectives were to: 1) quantify spatial and temporal patterns of erosion and deposition throughout the channel network following the wildfire and including the mesoscale flood; and 2) evaluate whether these changes are correlated to precipitation metrics, burn severity, or morphologic variables. Geomorphic changes were calculated using a DEMs of difference (DoD) approach for the channel network segmented into 50-m lengths. The results showed net sediment accumulation after the wildfire in the valley bottoms of both watersheds, with the greatest accumulations in the first two years after burning in wider and flatter valley bottoms. In contrast, the mesoscale flood caused large net erosion, with the greatest erosion in the areas with the greatest post-fire deposition. Volume changes for the different time periods were weakly but significantly correlated to, in order of decreasing correlation, contributing area, channel width, percent burned at high and/or moderate severity, channel slope, confinement ratio, maximum 30-minute rainfall, and total rainfall. These results suggest that morphometric characteristics, when combined with burn severity and a specified storm, can indicate the relative likelihood and locations for post-fire erosion and deposition. This information can help assess downstream risks and prioritize areas for post-fire hillslope rehabilitation treatments.

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Valley-scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes

Cited by 21 publications

References 59 publications

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

Spatial and temporal patterns of sediment storage and erosion following a wildfire and extreme flood

Spatial and temporal patterns of sediment storage and erosion following a wildfire and extreme flood

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