Drone Based Quantification of Channel Response to an Extreme Flood for a Piedmont Stream

Abstract

The influence of extreme floods on the form and functioning of upland systems has concentrated on the erosive impact of these flows. They are seen to be highly competent with coarse sediment transport rates limited by upstream supply and moderated by the ‘blanketing’ effect of an armour layer. This study investigates the effect of extreme events on the upland sediment cascade subjected to a recent extreme rainfall-induced flood event. The drone-based survey generated orthophotography and a DEM surface, which was compared with historic LiDAR data. This allowed erosion and deposition to be quantified and the surface micro-variation used to characterise stable and mobile sediment. The idealised model of sediment residence time increasing downstream is questioned by the findings of this study as relatively little coarse bedload sediment appears to have been transferred downstream in favour of initial local channel erosion (moderated by legacy large sediment), mid-reach palaeo-channel reactivation, sub-channel infilling and downstream deposition of the majority of mobilised sediment across berm and bar surfaces within the active inset channel margins. Channel margin erosion was largely limited to fine sediment stripping moderated by the re-exposure of post-glacial sediment. Only a weak relationship was found between local channel slope and deposition, with storage linked more to the presence of inset berm and bar areas within the inset active channel. Downstream fining of sediment is apparent as is a strong contrast between coarser active sub-channels and finer bar and berm areas.

Impacts of River Engineering on River Channel Behaviour: Implications for Managing Downstream Flood Risk

“…On a general level this study supports expert opinion of the recent review of flood processes and management in the UK [3], that coarse sediment transport processes and associated erosion, deposition and morphological dynamism are commonly overlooked in flood risk mapping exercises, but are likely to be important in any river system which receives high rates of sediment delivery and which in the past would have deposited much of its sediment on the floodplain. Coarse sediment storage is ubiquitous in naturally functioning gravel-bed river systems; an extensive alluvial fan on the River Wharfe developed after the valley widens at Hubberholme has been shown to act as a general aggregational zone [1] and a similar function associated with the smaller fan that has developed on Liza Beck, near Crummok Water in Cumbria has been reported [39]. This study adds to this evidence base, demonstrating coarse sediment storage through bed aggradation and overbank splay deposition, this time on an unconfined lowland sinuous single thread system.…”

Channel Evolution Triggered by Large Flash Flood at an Earthquake-Affected Catchment

“…In this study, the unit area is the square of the resolution of the high-resolution DSM. The error of DoDs (ε DoDs ) is estimated by the error propagation of Equation (9), where ε pre is the RMS error of the pre-flash flood DSM and ε post is the RMS error of the post-flash flood DSM [22,61] (Table A1).…”

“…DSM derived by sUAV, as one of the key data for quantitative analysis in this study, was processed and analyzed using uniform error analysis [22,61]. It has little effect on the overall trend and location distribution of channel evolution.…”

The Status of Earth Observation Techniques in Monitoring High Mountain Environments at the Example of Pasterze Glacier, Austria: Data, Methods, Accuracies, Processes, and Scales

“…The use of UAVs is also increasing for monitoring fluvial systems [119]. UAV are the basis for data collection for requested bathymetry of river sections (for numerical modeling) and the observation of morphodynamic processes, such as quantifying erosion and accumulation or stream bank failure [105,120]. On a smaller scale, UAV-based SfM analysis are used to determine: (i) the sediment composition and distribution; and (ii) hydraulic parameters, such as grain roughness, etc.…”