Seven Years of Sediment Measurements At The Arroyo de Los Pinos Monitoring Station

We present a seven-year summary of sediment transport data from the Arroyo de los Pinos sediment monitoring station. The channel, located in central New Mexico, is a direct ephemeral tributary to the Rio Grande, the main stem river system in the American Southwest. These data represent the most comprehensive transport measurements made in an ephemeral watershed in the U.S. and provide evidence of the capabilities of ephemeral channels to efficiently transport sediment. Bedload flux was captured using continuously recording Reid-type slot samplers. Suspended sediment derived using automated pump samplers and depth-integrated manual sampling. In addition to flow strength (water depth and velocity), the dataset contains a multitude of sediment transport measurements including surrogate suspended and bedload instruments.

More than 550 bedload flux measurements and 230 samples of suspended sediment have been recorded since 2016. Instantaneous bedload flux is high – up to 14 kg/s m – compared to global averages. Total sediment production was, on average, 380 t/km2 yr since 2018, of which suspended sediment is an estimated 80% of the annual yield. Due to their ephemeral nature and semi-arid climate, flows within the Pinos are relatively short and infrequent, 3-5 bedload transporting events occur annually. The onset of bedload transport begins at very low discharges (~0.1 - 0.25 m3 s-1), and almost all grains sizes are transported shortly thereafter during bore rises, near 2.5 m3 s-1. Taken in total, data collected at the Pinos station provide a new context concerning frequency and connectivity of flows, the efficiency of sand and gravel mixtures in transport, and the development of new, cost-effective monitoring techniques for sediment transport. These findings can aid river managers throughout the desert Southwest in understanding and forecasting sediment dynamics.