Observations of bedload transport in a gravel bed river during high flow using fiber‐optic DTS methods

Abstract

The question: 'how does a streambed change over a minor flood?' does not have a clear answer due to lack of measurement methods during high flows. We investigate bedload transport and disentrainment during a 1.5-year flood by linking field measurements using fiber optic distributed temperature sensing (DTS) cable with sediment transport theory and an existing explicit analytical solution to predict depth of sediment deposition from amplitude and phase changes of the diurnal near-bed pore-water temperature. The method facilitates the study of gravel transport by using near-bed temperature time series to estimate rates of sediment deposition continuously over the duration of a high flow event coinciding with bar formation. The observations indicate that all gravel and cobble particles present were transported along the riffle at a relatively low Shields Number for the median particle size, and were re-deposited on the lee side of the bar at rates that varied over time during a constant flow. Approximately 1-6% of the bed was predicted to be mobile during the 1.5-year flood, indicating that large inactive regions of the bed, particularly between riffles, persist between years despite field observations of narrow zones of local transport and bar growth on the order~3-5 times the median particle size. In contrast, during a seven-year flood approximately 8-55% of the bed was predicted to become mobile, indicating that the continuous along-stream mobility required to mobilize coarse gravel through long pools and downstream to the next riffle is infrequent.Note: Bedload transport was calculated using three different formulae (Meyer-Peter and Müller [1948], Singer and Dunne [2004], and Wilcock and Crowe [2003]). Meyer-Peter and Müller equation was calculated assuming a τ Ã c value of 0.047 and an adjusted value of 0.02. BEDLOAD TRANSPORT AND DISENTRAINMENT USING DTS METHODS

Was That Assumption Necessary? Reconsidering Boundary Conditions for Analytical Solutions to Estimate Streambed Fluxes

“…An area of recent discussion is the nonstationarity of signal filtering (the transfer functions) because of changes in the vertical flux, which is important to monitor over time (e.g., Rau et al, ). Bed scour and sediment transport are important geomorphological and ecological processes (e.g., Goode et al, ; Tonina et al, ), and these equations have been applied for monitoring such processes as well (Bray & Dunne, ; DeWeese et al, ; Luce et al, ; Sebök et al, ; Tonina et al, ). Such changes in the bed also induce nonstationarity in the transfer functions (Tonina et al, ).…”

Measuring and Modeling Gravel Transport at Caspar Creek, CA, to Detect Changes in Sediment Supply, Storage, and Transport Efficiency

“…In particular, measuring bed load yields for the duration required to assess the effects of supply and storage is difficult as many common sampling techniques are labor intensive and not well-suited to long-term studies. Promising indirect measurement techniques such as fiber optic systems (Bray & Dunne, 2017;Selker et al, 2006), morphological analysis of the streambed and bars (e.g., Lane et al, 1995Lane et al, , 2003, geophones and seismic monitoring (e.g., Barrière et al, 2015;Burtin et al, 2011;Hsu et al, 2011;Rickenmann et al, 2012;Roth et al, 2017;Turowski et al, 2011), and bed load tracers (e.g., Klösch & Habersack, 2018;Phillips & Jerolmack, 2014;Schmidt & Ergenzinger, 1992) are under development and may prove useful for developing long-term bed load transport records. However, as promising as these new techniques may be for future studies, they are of little use for reconstructing historical transport records.…”

Special Issue: Gravel Bed Rivers 8

“…Acoustic signals analyzed with the proposed model are interpreted by comparison with Helley-Smith bedload data obtained during flood conditions on the large gravel-bedded Arc-en-Maurienne River, France, demonstrating that careful attention to acoustic propagation effects is required when estimating bedload grain size distribution with hydrophones in rivers. Bray and Dunne (2017) studied entrainment and disentrainment of bedload by using fiber optic distributed temperature sensing cables. In their study gravel and cobble particles were transported along a riffle and were re-deposited on the lee side of the bar while water discharge was constant.…”