New Mexico Geological Society Annual Spring Meeting — Abstracts

One common source of uncertainty in sediment transport modeling of large semi-arid perennial rivers is sediment influx delivered by ephemeral, flood-driven tributaries. Large variations in sediment delivery are associated with these regimes due to the highly variable nature of flows within them. Flooding within these tributaries typically last on the order of hours, making it difficult to be present during an event. To better understand these regimes, automated systems are needed to continuously sample bedload and suspended load. In preparation for the pending installation of an automated site on the Arroyo de los Piños in New Mexico, manual sediment and flow samples have been collected over the summer monsoon season of 2017.

Eight flow events were recorded along the Piños from July to October. Of these eight events, data (including stage, velocity, and sediment samples) were collected from six. These events ranged in duration from 30 minutes to 4 hours and in maximum water depth of 10 cm to 75 cm. Bedload and suspended sediment samples data reveal a channel that is dominated by sand and gravel; more than 50% of the sediment in suspension is of sand size or larger. Flow data and flood wave arrival times indicate a complex system; flow is generated primarily in areas of exposed bedrock in the center and higher elevations of the watershed. These data will be used to inform future site operations, which will combine direct sediment measurement from Reid-type slot samplers and non-invasive acoustic and seismic measuring methods. Indirect methods for measuring of bedload have never been extensively evaluated in ephemeral channels in the southwest United States. Ultimately, this experiment will provide more accurate ephemeral channel sediment loads for stream restoration studies, sediment management actions, and reservoir sedimentation reports.