SOURCES OF SEDIMENT IN THE CURRENT ARROYO CYCLE USING A SEDIMENT BUDGET FOR TWO SUBBASINS OF THE RIO PUERCO, NEW MEXICO

Several Holocene cut-and-fill cycles have been documented in alluvial valleys of the American Southwest. Many studies have concluded that climate change is a primary driver of cut-and-fill cycles. Studies that budget the sources of sediment in arroyos during the filling cycle are imperative for understanding arroyo cycles, yet are still uncommon. In this study, we developed a sediment budget for two small arroyos, Volcano Hill Wash (9.30 km²) and Arroyo Chavez (2.11 km²), which are subbasins to the Rio Puerco. The study objectives were to determine the significant sources of sediment over a 3-year period and to differentiate hillslope erosion from channel erosion. The findings indicated that channel erosion was the major contributor of sediment, constituting 98% of the total sediment budget in Volcano Hill Wash and 69% in Arroyo Chavez. Volcano Hill Wash and Arroyo Chavez are incising and widening through most upstream reaches while downstream reaches are aggrading. In each subbasin, the alluvial-valley floor had the lowest soil infiltration rates of runoff (64 and 67 mm/hr), the highest sediment concentrations measured in sediment traps (25,320 and 139,990 ppm), and common soil-piping features. The high rates of erosion may reflect soil properties and/or grazing as the alluvial-valley floor is the geomorphic surface where livestock congregate. The contribution of hillslope-derived sediment versus channel-derived sediment is a function of the arroyo cycle. Establishing the state of the arroyo within this cycle is important for determining if channels or hillslopes are the major contributors of sediment.