SURFACE VELOCITY VARIATIONS AND BAR FORMATION IN EPHEMERAL WATERWAYS

In arid environments, understanding river interactions with flash flooding is crucial for efficient irrigation and managing sparse water resources. While perennial rivers can be monitored routinely, ephemeral waterways that feed these major rivers can only be measured during flash flood events. Knowing the velocity of ephemeral streams is important for measuring sediment transport into connecting perennial rivers and for future flood management. The nature of these rivers makes typical data collection methods ineffective due to time sensitivity, and being on-site for long periods during extreme weather involves unnecessary risk, leading to the development of automated, remote methods of analyzing velocity and bedload.

To assess bedload movement and velocity during summer flood events, a field site was established at the Arroyo de los Pinos tributary of the Rio Grande River and outfitted with various sensors and remote data collection equipment. This study focuses on remote collection of velocity metrics through large-scale particle image velocimetry (LSPIV), utilizing video camera footage from on-site flood events to track changes in the water’s surface flow, and to calculate surface velocity. The current study aims to determine if surface velocities differ near one bank compared to the other and how these differences might relate to the position of bars and their formation on the streambed. To analyze variations in velocity, the program uses orthorectification reference points to reposition the point of view above the river, and trackers to create surface velocity vectors. Combined with the logarithmic law of the wall, this allows calculation of water velocity at different depths. Existing data on sediment transport at three points across the channel and on bars formed along the riverbed can be paired with the final velocity data to determine how such formations affect the velocity of the river as it flows. We expect to find evidence of decreasing velocity when the flood passes over or near bars, and an increase where the river bed is more uniform.