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

Authors: Nichols, Mary; DEGGINGER, T. - University Of Arizona

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2021
Publication Date: 2/13/2021
Citation: Nichols, M.H., Degginger, T. 2021. The landscape impact of unmaintained rangeland water control structures in southern Arizona, USA. Catena. 201, Article 105201. https://doi.org/10.1016/j.catena.2021.105201.
DOI: https://doi.org/10.1016/j.catena.2021.105201

Interpretive Summary: Livestock graze extensively in the southwestern US, however, prior to the late 1800s, their distribution was limited by access to water. Water development was rapid once well drilling and pumping equipment became available in the late 1800s after which livestock numbers increased substantially. Water development included the construction of dams, stock tanks, and wells, and developing springs. In addition, earthen berms were constructed to control runoff and both surface and channel bank erosion. This research was conducted to assess the condition of remnant and operational runoff and erosion control structures and to inventory and map the structures using aerial imagery and Light Detection and Ranging (LiDAR) data. We found that many of these structures have been compromised and contribute to eroding the landscape. 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. 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 understanding the role of humans in altering even seemingly sparsely impacted lands.

Technical 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 1800s. 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.