New Mexico Geological Society Annual Spring Meeting — Abstracts

Baseflow conditions in ephemeral streams are unable to winnow away fine sediment, preventing stable armor layers of coarse material that resist erosion from developing. These channels also feature a greater abundance of coarse sands and fine gravels that are easily mobilized but difficult to suspend. Consequently, low bed shear stress can generate much larger bedload fluxes in ephemeral streams than their perennial counterparts. These rapid influxes of sediment can dramatically alter the fluvial geomorphology in the receiving drainage system and pose significant challenges to river managers, particularly in arid climates or watersheds impacted by wildfire. Multidimensional hydraulic models offer a tool to forecast the magnitude and spatial distribution of sediment flux but are typically developed and validated using data from perennial streams. Using data from the Arroyo de los Pinos sediment monitoring station—located on a sand-rich gravel bed channel near Socorro, NM—we will validate sediment transport in ephemeral streams for two industry-standard models: HEC-RAS (which supports up to two dimensions) and AdH (up to three dimensions). We intend to apply the resulting modeling framework to two additional streams in the Socorro region, Arroyo de la Parida and Arroyo de la Cañas, to demonstrate how multidimensional modeling of sediment transport can better inform the management of infrastructure and aquatic habitat along the Middle Rio Grande.