DOI: 10.5061/dryad.tdz08kq2j
title: Influence of sand supply and grain size on upper regime bedforms

description: Notwithstanding the large number of studies on bedforms such as dunes and
 antidunes, performing quantitative predictions of bedform type and
 geometry remains an open problem. Here we present the results of
 laboratory experiments specifically designed to study how sediment supply
 and caliber may impact equilibrium bedform type and geometry in the upper
 regime. Experiments were performed in a sediment feed flume with flow
 rates varying between 5 l/s and 30 l/s, sand supply rates varying between
 0.6 kg/min and 20 kg/min, and uniform and non-uniform sediment grain sizes
 with geometric mean diameter varying between 0.22 mm and 0.87 mm. The
 analysis of the experimental data and the comparison with datasets
 available in the literature revealed that the ratio of the volume
 transport of sediment to the volume transport of water Qs/Qw plays a prime
 control on the equilibrium bed configuration. The equilibrium bed
 configuration transitions from washed out dunes, to downstream migrating
 antidunes for Qs/Qw between 0.0003 and 0.0007. For values of Qs/Qw greater
 than those typical of the downstream migrating antidunes, the bedform
 wavelength increases. Equilibrium bed configuration for fine sands is
 characterized by upstream migrating antidunes or cyclic steps, and
 significant suspended sand. At these high values of Qs/Qw the equilibrium
 bed for coarse sands is plane with bedload transport in sheet flow mode.
 Standing waves form at the transition between downstream migrating
 antidunes and bed configurations with upstream migrating bedforms or
 bedload transport in sheet flow mode. 
description: <strong>Experimental
 Overview</strong> Laboratory experiments were conducted in
 the Hydraulics Laboratory at the Department of Civil and Environmental
 Engineering, University of South Carolina. The main objective was to
 observe and quantify how bedform type and geometry are affected by
 sediment supply rate and grain size. Sediment supply and flow discharge
 were chosen with the intended goal to obtain equilibrium bed
 configurations that evolve from lower regime to upper regime bedforms,
 with upstream bedforms migrating in the upstream and downstream
 directions. Sediment geometric mean grain sizes ?? ranged between 0.22 mm and 0.87 mm, flow
 rates ?? varied between 5 l/s and 30 l/s, and
 sediment feed rates varied between 0.5 kg/min and 20 kg/min. Sediment
 sizes were chosen based on the range where sand waves occur and what
 material is locally available. <strong>Experimental
 Setup</strong> Experiments were conducted in a glass wall
 sediment feed flume. The flume is 13 m long, 0.5 m wide and 0.9 m deep. A
 custom sediment trap is placed 9 m downstream of the flume entrance and a
 tailgate controls the downstream water surface level. A calibrated orifice
 plate and a Dwyer series 490 wet-wet manometer were used to measure the
 flow rate from the head tank. To decrease the sediment supply needed for
 experiments and the occurrence of three-dimensional bedforms, the
 cross-section of the test reach was narrowed to 0.19 m with the use of
 marine plywood.  In the first 2 m of the flume, the cross-section is
 gradually narrowed to 0.19 m to obtain a 7 m long experimental test
 reach. <strong>Experimental
 Procedure</strong> All experiments started from a
 net-depositional or net-erosional (disequilibrium) condition and continued
 until the bed level averaged over a series of bedforms did not change in
 time (equilibrium). At equilibrium, suspended sediment concentration was
 measured at the downstream end of the test reach and the experiment
 terminated. Experiment 1-SS started with a 10 cm thick flat layer of
 sediment with ?? equal to 0.43mm. The equilibrium bed of
 one experiment was used as the initial condition for the next experimental
 run. For example, the initial deposit in experiments 2-SS and 5-SS, was
 the equilibrium bed of experiments 1-SS and 4-SS respectively. After
 experiment 3- SS, a ~3 cm layer of sediment mix with ?? equal to 0.34 mm was sprinkled over the
 existing deposit to perform experiments with a finer sediment grain size.
 This process was repeated once more before experiment 7-SS to use coarser
 sediment with ?? equal to 7 0.62 mm. The duration of an
 experiment varied between 45 minutes to two hours depending on the initial
 condition and the feed rate. As the sediment size decreased, the time it
 took to reach equilibrium conditions decreased. On the glass wall and at the top of the
 flume there are vertical and horizontal rulers which indicate the distance
 from the flume entrance and the elevation above the flume bed. Bed and
 water surface elevations were measured at every 10 cm interval moving
 downstream with ruler readings.  The first measurement was recorded at
 3.50 m from the flume entrance and the last measurement was taken at 8.90
 m from the flume entrance. During the experiments, measured values were
 reported in a spreadsheet, plotted, and the slopes of the best fit lines
 were computed to estimate the bed slope and the water surface slope. When
 the bed and water surface slopes did not significantly change in time, the
 flow and the sediment transport were deemed to be at
 equilibrium.
description: <strong>Pictures and
 Videos</strong> The
 folder entitled ‘Pictures’ contains pictures and videos from each
 respective experiment in .JPEG and .MOV files.  These files are
 unprocessed. <strong>Suspended Sediment
 Concentration and Velocity Profiles Measurements</strong>
 Raw suspended sediment concentration
 data is presented in EXCEL .xlsx files within the
 ‘Suspended_concentration’ folder.  This folder also contains raw data from
 velocity probes as ‘.xlsx’ files for supplemental information. 
   <strong>Experimental
 Data</strong> ‘CumulativeRunTable’ Excel file .xlsx,
 contains all variables found in the laboratory setting and ‘GSD_Design
 Mix,’ contains the sieve analysis for all experiments, suspended sediment,
 and parent material used for the dataset.  ‘Engelund phase diagram’ Excel
 file .xlsx, contains the current dataset with respect to datasets
 performed in the same laboratory facility.