Comparison of Measured Bedload With Predictions From Transport Equations In An Unarmored Ephemeral Channel

The Arroyo de los Pinos is a tributary of the Rio Grande that transports relatively coarse sediment into the river annually through flash flood events. This coarse sediment can lead to problems for downstream infrastructure, such as sedimentation in reservoirs and increased channel maintenance requirements for flow conveyance. Over the last five years, a comprehensive database of bedload, suspended sediment, and meteorological-hydrologic measurements have been developed at the confluence of the channel to the Rio Grande. Bedload flux is monitored with Reid-type slot samplers at 1-minute resolution, flow stage is continuously monitored with pressure transducers, and surface flow velocity is measured periodically using large scale particle imagery velocimetry to produce a discharge rating curve. Bed material samples have been collected and sieved, and channel geometry has been mapped in detail using drone imagery and structure from motion (SfM) photogrammetry. This dataset enables assessment of predicted bedload using a wide range of well-established equations, including the modified Einstein procedure, the equations of Meyer-Peter and Müller, Wilcock and Crow, Parker, Rickenmann, and Recking. Crucially, we can compare the quality of prediction from these methods against the observed bedload transport at a range of flow depths between 5-50 cm (discharge at 0.25 – 10 m^3/s). The Pinos dataset provides an excellent opportunity to compare a range of transport equations and consider which performs the best in semi-arid, flash flood driven systems. Successful equation selection will enable the expansion of our estimates to approximate annual bedload yields to the Rio Grande from the Arroyos de los Pinos as well as from other ephemeral tributaries to the Rio Grande.