Real time measurements of sediment transport and bed morphology during channel altering flow and sediment transport events

Abstract

Real-time measurements of bed changes over a reach are a missing piece needed to link bed morphology with sediment transport processes during unsteady flows when the bed adjusts quickly to changing transport rates or visual observation of the bed is precluded by fine sediment in the water column. A new technique is presented that provides continuous measurement of sediment movement over the length of a flume. A bedload monitoring system (BLMS) was developed that makes use of pressure pillows under a false flume bottom to measure sediment and water weights over discrete flume channel sections throughout a flow event. This paper details the construction of the BLMS and provides examples of its use in a laboratory setting to reconstruct bed slopes during unsteady flows and to create a real-time record of sediment transport rates across the flume channel bed during a sediment transporting flow. Data gathered from the BLMS compared well against techniques commonly in use in flume studies. When the BLMS was analyzed in conjunction with bed surface DEMs and differenced DEMs, a complete transport and bed adjustment picture was constructed. The difference DEMs provided information on the spatial extent of bed morphology changes. The BLMS supplied the data record necessary to reconstruct sediment transport records through the downstream channel, including locations and time periods of temporary sediment storage and supply. The BLMS makes it possible to construct a continuous record of the spatial distribution of sediment movement through the flume, including areas of temporary aggradation and degradation. Exciting implications of future research that incorporates a BLMS include a more informed management of river systems as a result of improved temporal 3 predictions of sediment movement and the associated changes in channel slope and bed morphology.

Effect of morphologic and hydraulic factors on hysteresis of sediment transport rates in alluvial streams

“…Sediment‐feeding conditions were applied less frequently to sand‐bed experiments (e.g., Curran et al, ; Martin & Jerolmack, ; Reesink & Bridge, ; Reesink & Bridge, ) and more frequently applied in gravel bed experiments (e.g., Hassan & Church, ; Humphries et al, ; Madej et al, ; Mao, ; Wong & Parker, ). Analysis of the literature reveals that sand beds with sediment supply (i.e., sediment‐feeding conditions) show no dominant trend in type of hysteresis (Figure d).…”

“…The majority of the experimental research summarized used triangular‐shaped hydrographs (e.g., Ahanger et al, ; Curran et al, ; Madej et al, ; Nelson et al, ; Piedra et al, ; etc.). These triangular hydrographs can be classified as symmetrical or asymmetrical triangular‐shaped hydrographs of varying magnitudes and durations.…”

“…Specifically, knowledge of three‐dimensional bed form geometry (Nelson et al, ), rate of bed form migration (Reesink & Bridge, ; Reesink & Bridge, ), spatial pattern (Martin & Jerolmack, ), and grain size sorting of pre‐existing and superimposed bed forms (Reesink et al, ) is required to better understand of the effects of long‐term unsteady flow on hysteresis of bed morphological response. The mechanics of bed formation and bed form decay during more complex unsteady flow events could be achieved by determining the quantitative step length of bed load in relation to changing discharges (Nelson et al, ) or using innovative real‐time monitoring techniques (Curran et al, ; Waters & Curran, ). Hydraulic conditions can vary drastically (i.e., suspended and bed load can occur at higher discharge stages of the hydrograph) causing a shift in the balance between sediment diffusion and settling onto the bed, which can affect the overall morphology of the bed (Martin & Jerolmack, ; McElroy & Mohrig, ).…”

Capturing the spatiotemporal variability of bedload transport: A time‐lapse imagery technique

“…Measuring the sediment output in flume experiments is straightforward and has been widely used to estimate sediment transport flux through a downstream weighting system. Curran et al, 2015), despite providing continuous information at a larger scale, are very limited in terms of spatial detail. Image-based experimental techniques (e.g.…”

“…Other techniques (e.g. Curran et al, 2015), despite providing continuous information at a larger scale, are very limited in terms of spatial detail. Therefore, continuous and spatially accurate maps of bedload flux and active area over complex morphologies have not been produced yet, limiting the possibility of investigating the linkages between bed topography, flow field, and sediment flux at the reach scale.…”