Contributions of moderately low flows and large floods to geomorphic change in the Rio Puerco Arroyo, New Mexico

Abstract

From the mid-1800s to around 1930, monsoonal floods incised an arroyo roughly 100 m wide and 10 m deep along the lower Rio Puerco, NM, from the confluence with the Rio San Jose downstream to the mouth at the Rio Grande, causing sedimentation and flooding downstream. Since the 1930s, the channel has greatly narrowed, a densely vegetated floodplain has developed, the arroyo has partly filled, and downstream sedimentation has greatly decreased. Application of herbicide to a 12-km reach of the arroyo in 2003 to control non-native saltcedar (Tamarix spp.) prompted ongoing studies of channel change in the presence and absence of dense, riparian, woody vegetation. We used digital terrain models and satellite imagery to quantify changes in channel width and location in the sprayed reach and in an unsprayed reach downstream during a moderately low-flow interval (November 2006 to March 2010) and during an interval with a large flood (March 2010 to January/February 2014). Channel width increased in magnitude and variability in the sprayed reach but not in the unsprayed reach over both intervals, continuing a pattern first observed in an earlier study of the period 2003 to 2006. Since the herbicide application in 2003, there have been a total of five meander cutoffs in the sprayed reach and none in the unsprayed reach. In kilometer-long sections of the sprayed reach, channel width is now approaching that at the beginning of the period of channel narrowing in 1935. 439