New Mexico Geological Society Annual Spring Meeting — Abstracts

In large river systems such as the Rio Grande, sediment influx and water delivery from ephemeral streams is difficult to quantify and track. Yet is has major management implications to such diverse issues as reservoir sedimentation, sediment plugs and avulsions, flooding, and additions to streamflow. In the Arroyo de los Pinos watershed, one such ephemeral system, we have been monitoring discharge at 18 different points for two years in an effort to quantify water and sediment delivery from the ephemeral channels. The data collected in the past, present, and future will allow for a better understanding of how the network connects across a range of precipitation intensities and magnitudes, and how these interactions control water and sediment delivery to the watershed outlet. Preliminary data support the prevailing understanding that the primary controls on local runoff generation are rainfall intensity, lithology, and sub-basin size (Richards, 2020).

To investigate how these flow events influence sediment discharge, my proposed work will focus on building open channel flow models with sediment transport capability. The first step will be to build a model framework for a reach where sediment flux is monitored near the confluence of the Pinos and Rio Grande (Stark, 2018). Discharge, bedload, and topographic data collected during the monsoon seasons of 2018, 2020, and – if there are floods – 2021 will be used to calibrate open channel flow models with sediment transport capability. Initially we will utilize the sediment transport simulation capabilities within the Bureau of Reclamation’s BORAMEP model, because Reclamation has supported work at the Pinos and is interested in evaluating their model’s performance. Modeled sediment flux will be compared against monitored sediment flux near the confluence of the Pinos and Rio Grande. If successful, we will then be able to model sediment transport using the calibrated sediment parameters in other upstream reaches in the channel network. Combined with our flow connectivity data, this would enable an unprecedented quantification of sediment transport connectivity, and potentially disconnectivity, within ephemeral fluvial systems.