Three-Dimensional Flow Fields and Bedform Migration in a Field-Scale Meandering Channel

The St. Anthony Falls Laboratory Outdoor StreamLab (OSL) at the University of Minnesota was constructed in 2008 as field-scale sand bed meandering stream channel within a vegetated floodplain. This state-of-the-art facility provides the unique opportunity to investigate physical, chemical, and biological stream and floodplain processes in a controlled outdoor environment with laboratory-quality measurement capabilities. The research presented here summarizes results from several experiments conducted in the OSL examining the effect of three-dimensional (3-D) flow fields on sediment transport and bedform development. Specifically, we examined bedform dimensions and flow fields in two scenarios 1) in the vicinity immobile rock structures, and 2) on the quasi-equilibrium bar that formed on the inner bank of a meander. A combination of methods were used for each study to determine the rate of scour hole formation, quasi-equilibrium bed elevation and variation in bed elevation, and bedform size and spacing. Bed topography data were collected at 1 cm resolution under live-bed conditions using a downward looking sonar probe attached to a mobile data acquisition (DAQ) cart. At each DAQ station, repeat scans were collected giving insight into the 3-dimensionality of bedforms in a meandering channel with and without rock structures. Supplementary data were collected at transects under two flow and sediment conditions (280 L/s and 6 kg/min and 199 L/s and 4 kg/min, for water and sediment, respectively) using an acoustic Doppler velocimeter (ADV) and a profiling ADV to measure 3-D flow fields and concurrent velocity and bed elevation data. These data were used in conjunction with data from optical remote sensing of bedform migration in the OSL to provide a validation dataset for a high-resolution 3-D hydro-morphodynamic model that is being used to simulate flow and sediment transport processes in meandering channels with embedded rock structures (Khosronejad et al. Adv. in Water Res. 2011). These OSL experiments examining flow fields and sediment transport in the vicinity of in-stream rock structures demonstrate the capability of field-scale experiments, coupled with numerical investigations, to provide insight on the complex interactions between flow fields and the streambed in meandering streams.; Measured velocity magnitude and quasi-equilibrium bed topography in the OSL (d50 = 0.7mm, width = 2.7m, depth = 0.3 m) with installed rock structures.