The landscape impact of unmaintained rangeland water control structures in southern Arizona, USA

Abstract

Water development has transformed the topography of rangelands. This study investigated the associated hydrologic and geomorphic impacts of structures such as earthen berms, stock tanks, and road drainages in a semiarid rangeland in the Altar Valley in the southwestern USA where land use has been dominated by livestock production since the late 1800 s. The condition of remnant and operational runoff and erosion control structures was inventoried, mapped, and assessed using aerial imagery and Light Detection and Ranging (LiDAR) data. A total of 377 stock tanks are distributed throughout the valley where they are a control on runoff and sediment transfer. Almost half of 59 identified lateral channel berms (41%) have been breached and 17% have experienced lateral scour; 15% of 667 shorter water spreader berms have been breached and 29% have experienced lateral scour. Although landscape evolution in the valley is ultimately driven by regional geomorphic instability caused by channel incision and land cover changes, manmade structures are currently an important control on hydrologic and geomorphic processes, especially where not operating as intended. Due to the spatial extent of rangelands managed for livestock grazing and the large number of manmade structures distributed within, the results of this study are important for informing the role of humans in altering even seemingly sparsely impacted lands.