New Mexico Geological Society Annual Spring Meeting & Ft. Stanton Cave Conference — Abstracts

In large river systems such as the Rio Grande, water delivery from ephemeral tributaries is difficult to quantify and track. In the Arroyo de los Pinos watershed (32 km²) draining a variety of lithologies, we have been monitoring rainfall at five locations and discharge at 12-18 locations since 2018 to quantify flow patterns in ephemeral channel networks. These data allow for a better understanding of how the network connects across a range of rainfall intensities, magnitudes, spatial distributions, and storm track. These interactions are expected to control water and sediment delivery to the watershed outlet. Initial data support the prevailing understanding that the primary controls on local runoff generation are lithology, sub-basin size, and rainfall intensity. For monsoon storms that do not cover the full watershed, the lithology of the area experiencing rain largely controls whether runoff reaches the Rio Grande or becomes transmission loss.

Connectivity of a watershed describes how efficiently water and sediment are transmitted between geomorphic systems such as hillslopes and river networks. Flow generation is the primary indicator of the hydrologic connectivity or disconnectivity of a watershed and is controlled by the same factors – lithology, basin size, etc. Knowledge of the size and lithologies of the tributaries and sub-basins combined with the rainfall-runoff data will enable quantification of connectivity across scales. Analysis of three flood events with similar North-South storm track in the month of July 2021 illustrates the diversity of rainfall events and connectivity within the Arroyo de los Pinos.