Topographical change caused by moderate and small floods in a gravel bed ephemeral river – a depth-averaged morphodynamic simulation approach

Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes caused by floods. In most cases, the channel shape and bedform migration during different phases of a flood hydrograph cannot be identified from field evidence. This paper analyses the timing of riverbed erosion and deposition of a gravel bed ephemeral river channel (Rambla de la Viuda, Spain) during consecutive and moderate- (March 2013) and low-magnitude (May 2013) discharge events, by applying a morphodynamic model (Delft3D) calibrated with pre- and post-event surveys by RTK-GPS points and mobile laser scanning. The study reach is mainly depositional and all bedload sediment supplied from adjacent upstream areas is trapped in the study segment forming gravel lobes. Therefore, estimates of total bedload sediment mass balance can be obtained from pre- and post-field survey for each flood event. The spatially varying grain size data and transport equations were the most important factors for model calibration, in addition to flow discharge. The channel acted as a braided channel during the lower flows of the two discharge events, but when bars were submerged in the high discharges of May 2013, the high fluid forces followed a meandering river planform. The model results showed that erosion and deposition were in total greater during the long-lasting receding phase than during the rising phase of the flood hydrographs. In the case of the moderate-magnitude discharge event, deposition and erosion peaks were predicted to occur at the beginning of the hydrograph, whereas deposition dominated throughout the event. Conversely, the low-magnitude discharge event only experienced the peak of channel changes after the discharge peak. Thus, both type of discharge events highlight the importance of receding phase for this type of gravel bed ephemeral river channel.

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Topographical changes caused by moderate and small floods in a gravelly ephemeral river – 2D morphodynamic simulation approach

10.5194/esurf-2017-52 ◽

2017 ◽

Author(s):

Eliisa Lotsari ◽

Mikel Calle ◽

Gerardo Benito ◽

Antero Kukko ◽

Harri Kaartinen ◽

...

Keyword(s):

Morphological Changes ◽

Model Performance ◽

Total Load ◽

Channel Changes ◽

Morphodynamic Modelling ◽

Geomorphic Response ◽

Field Evidence ◽

Ephemeral Rivers ◽

Spatially Varying ◽

Low Magnitude

Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes performed by a flood. In most cases, the channel shape and bedform evolution during different phases of a flood hydrograph are not recognized from field evidence. This paper analyzes the capabilities of morphodynamic modelling (Delft 2D) for resolving the evolution of a gravelly ephemeral river channel during consecutive, moderate- and low-magnitude discharge events. We pursue for schematic concepts for simulations in ephemeral gravely rivers that provide an outcome with the closest similarity to the post-flood reality. Based on the simulations, we analyze the morphodynamic evolution of Rambla de la Viuda (Spain) to find out when and to what extent the channel changes occur during the phases of moderate- (March 2013) and low-magnitude (May 2013) discharge events, and what influence the discharge has on the rate of morphological changes. The model performance is examined with different parameterizations. The spatially varying grain size data and transport equations were the most important factors, in addition to the quality of recorded discharge, for the simulation results of the channel evolution. The total load equation worked better, compared to the deterministic equation. The erosion and deposition can be in total greater during the longlasting receding phase than during the rising phase. The deposition and erosion peaks are predicted to occur at the beginning of the moderate-magnitude discharge event, whereas deposition dominates throughout the event. On the contrary, the low-magnitude discharge event only experiences the peak of channel changes after the discharge peak. These different predicted erosion/deposition patterns suggest a hysteresis effect on the morphodynamic changes, and stress the importance of previous flood history (timing, succession and magnitude) in understanding the geomorphic response of gravelly ephemeral rivers.

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Kissimmee River restoration: a case study

Water Science & Technology ◽

10.2166/wst.2002.0379 ◽

2002 ◽

Vol 45 (11) ◽

pp. 55-62 ◽

Cited By ~ 28

Author(s):

P.J. Whalen ◽

L.A. Toth ◽

J.W. Koebel ◽

P.K. Strayer

Keyword(s):

Ecological Integrity ◽

Flow Characteristics ◽

River Channel ◽

Floodplain Wetlands ◽

Water Control ◽

Control Structures ◽

Meandering River ◽

Hydrologic Processes ◽

Kissimmee River

Channelization of the Kissimmee River transformed a 167 km meandering river into a 9 metre deep, 75 metre wide, 90 km drainage canal (C-38) that is compartmentalized with levees and water control structures into a series of five stagnant pools. Channelization dramatically changed water level and flow characteristics, drained 21,000 hectares of floodplain wetlands and severely impacted fish and wildlife populations. A $500 million dollar restoration project will restore the ecological integrity of the river-floodplain system by reconstructing the natural river channel and reestablishing hydrologic processes. Sixty expectations have been established to quantify the ecosystem's recovery. The first phase of reconstruction was completed in February 2001 and included movement of 9.2 million cubic metres of earth to backfill 12 km of C-38, the explosive demolition of one water control structure, construction of two sections (2.4 km) of new river channel, and reestablishment of 24 contiguous km of river. Numerous social, political, and technical challenges have been encountered during the project's evolution. Recommendations are provided for future restoration projects.

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Hohokam Political Ecology and Vulnerability: Comments on Waters and Ravesloot

American Antiquity ◽

10.2307/3557040 ◽

2003 ◽

Vol 68 (1) ◽

pp. 169-181 ◽

Cited By ~ 10

Author(s):

Bradley E. Ensor ◽

Marisa O. Ensor ◽

Gregory W. De Vries

Keyword(s):

Political Ecology ◽

Social Groups ◽

River Channel ◽

Cultural Changes ◽

Anthropological Perspective ◽

Channel Change ◽

Channel Changes ◽

Environmental Processes ◽

River Channel Change

Waters and Ravesloot (2001) test the assumption that natural river channel change caused periods of Hohokam cultural reorganization. However, they conclude that channel changes did not correlate with all periods and areas of significant cultural changes and that landscape alone cannot explain Hohokam transformations. An anthropological perspective on political ecology and disasters can explain why environmental processes and events differentially impact societies, differentially impact societies diachronically and differentially impact social groups within societies. We suggest that this perspective may explain the variability described by Waters and Ravesloot.

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Simulation of wind-induced snow transport in alpine terrain using a fully coupled snowpack/atmosphere model

The Cryosphere Discussions ◽

10.5194/tcd-7-2191-2013 ◽

2013 ◽

Vol 7 (3) ◽

pp. 2191-2245 ◽

Cited By ~ 7

Author(s):

V. Vionnet ◽

E. Martin ◽

V. Masson ◽

G. Guyomarc'h ◽

F. Naaim-Bouvet ◽

...

Keyword(s):

Laser Scanning ◽

Winter Season ◽

Coupled Model ◽

Deposition Process ◽

Atmospheric Model ◽

Horizontal Resolution ◽

Blowing Snow ◽

Erosion And Deposition ◽

Atmospheric Flow ◽

Snow Transport

Abstract. In alpine regions, wind-induced snow transport strongly influences the spatio-temporal evolution of the snow cover throughout the winter season. To gain understanding on the complex processes that drive the redistribution of snow, a new numerical model is developed. It couples directly the detailed snowpack model Crocus with the atmospheric model Meso-NH. Meso-NH/Crocus simulates snow transport in saltation and in turbulent suspension and includes the sublimation of suspended snow particles. A detailed representation of the first meters of the atmosphere allows a fine reproduction of the erosion and deposition process. The coupled model is evaluated against data collected around the experimental site of Col du Lac Blanc (2720 m a.s.l., French Alps). For this purpose, a blowing snow event without concurrent snowfall has been selected and simulated. Results show that the model captures the main structures of atmospheric flow in alpine terrain, the vertical profile of wind speed and the snow particles fluxes near the surface. However, the horizontal resolution of 50 m is found to be insufficient to simulate the location of areas of snow erosion and deposition observed by terrestrial laser scanning. When activated, the sublimation of suspended snow particles causes a reduction in deposition of 5.3%. Total sublimation (surface + blowing snow) is three times higher than surface sublimation in a simulation neglecting blowing snow sublimation.

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

10.5194/esurf-2018-98 ◽

2019 ◽

Author(s):

Daniel J. Brogan ◽

Peter A. Nelson ◽

Lee H. MacDonald

Keyword(s):

Laser Scanning ◽

Sediment Accumulation ◽

Temporal Patterns ◽

Burn Severity ◽

Spatial And Temporal Patterns ◽

Channel Network ◽

Valley Bottom ◽

Erosion And Deposition ◽

Downstream Effects ◽

Extreme Flood

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

Earth Surface Dynamics ◽

10.5194/esurf-7-563-2019 ◽

2019 ◽

Vol 7 (2) ◽

pp. 563-590 ◽

Cited By ~ 6

Author(s):

Daniel J. Brogan ◽

Peter A. Nelson ◽

Lee H. MacDonald

Keyword(s):

Laser Scanning ◽

Sediment Accumulation ◽

Burn Severity ◽

Spatial And Temporal Patterns ◽

Channel Network ◽

Erosion And Deposition ◽

Long Duration ◽

Extreme Flood ◽

Changes Over Time ◽

Over Time

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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