ASSESSING THE INFLUENCE OF SEDIMENT LOADS ON THE SURFACE VELOCITIES OF FLASH FLOODS

Studying the effect of sediment load on surface velocity during flash floods is crucial for understanding erosional processes and enhancing aquatic safety. The collection of data on ephemeral streams can be difficult; the use of handheld velocity meters requires close proximity to swift moving water. However, the use of video and digital software allows for remote, safe data collection. In this study, we analyzed two years of video camera footage of floods during 2022-2024 from the Arroyo de los Pinos, a Rio Grande tributary in central New Mexico. We compared water surface velocity with bedload sediment transport rates, across flow depths ranging from 15 to 65 cm. Sediment data was collected in Reid-type in-channel samplers. Surface velocity data was collected from video camera footage that was analyzed using Large Scale Particle Image Velocimetry (LSPIV) software (FudaaLSPIV). This open-source program analyzes each frame of a video and uses individual particle tracking to calculate surface flood velocity, allowing for safe and remote flood velocity analysis. We predict that our findings will indicate that higher sediment loads correlate with decreased surface velocity during flash floods of similar water levels, because of the additional roughness and momentum transfer or drag due to the mobile bed sediment. The results will provide valuable insights for the interpretation of surface velocity data, which is useful for flood risk management and erosion control strategies.