The Geomorphic Legacy of Rangeland Water and Erosion Control Structures in the Altar Valley

Pima County Regional Flood Control District Monthly Brown Bag Series

Speaker: Mary Nichols, Research Hydraulic Engineer/Scientist USDA – ARS, Southwest Watershed Research Center, Tucson
Date/Time: Wednesday, May 9, 2018: 12:00 -1:00
Location: 201 North Stone Ave, 9th Floor

The Buenos Aires National Wildlife Refuge in southern Arizona was established in 1985 with a primary goal of restoring grassland habitat of the endangered Masked Bobwhite (Colinus virginianus ridgwayi), a subspecies of quail. Currently, channel incision, gullying, headcut advance, and erosion are challenges to grassland restoration. Prior to the establishment of the refuge, the landscape was managed as a commercial cattle ranch. Water supply for ranching operations was enhanced by construction of numerous stock ponds, water spreader berms, and lateral channel berms, and concrete spillways. Many of these structures have been compromised and contribute to eroding the landscape. An inventory of water control structures remnant of historic cattle ranching was assembled for the refuge and an assessment of structural condition based on aerial imagery was completed. Of 27 identified lateral channel berms, 48% have been breached and 18% of 190 shorter water spreader berms have been breached or flanked. Identifying the cause of recent gullying and channel incision is critical for future land management and habitat restoration on the BANWR, as well as for downstream restoration efforts. Although gullying induced by unmaintained structures threatens large areas of productive grassland habitat, in some cases onset of disturbance is recent enough that opportunities for mitigation can be identified and potentially damaging erosion trajectories can be altered.