Arlington Wildlife Area In-Lieu Fee Restoration Project: Gila River Streambank Stabilization

Arlington Wildlife Area In-Lieu Fee Restoration Project: Gila River Streambank Stabilization

Oxbow Ecological Engineering, in collaboration with Fred Phillips Consulting, was contracted by the Arizona Game & Fish Department to complete assessment & design services for 3,200 feet of eroding banks along the Gila River within Arlington Wildlife Area, with the goal of stabilizing the streambank using soil bioengineering techniques and native vegetation. As part of the work the design team completed detailed field work that included topographic and geomorphic mapping with RTK GPS and soil and groundwater sampling and analysis.

Based on the site inventory and analysis the restoration team developed a holistic set of site specific practices that could be used to mitigate against further streambank erosion from river flooding and upland stormwater flows while providing a favorable environment for native plant revegetation. The team developed construction documents, including drawings, technical specifications, and Engineer’s Opinion of Probable Cost.

Design elements included:

  • STREAMBANK SHAPING – Excavate/re-slope the existing cutbank to reduce bank erosion potential (BEP), resist surface erosion and subsurface soil piping from upland stormwater runoff, create a stable platform for soil bioengineering and native revegetation practices, and minimize impacts/disturbances to other phases of the overall restoration master plan. As part of bank re-sloping work, excavate or fill to create a “flood bench”. The bench is designed to break up the slope length and provide a zone of moisture accumulation to enhance plant growth as well as provide additional flood relief.
  • COIR LOG & WATTLE EROSION CONTROL – In addition to bank re-sloping biodegradable coir logs and wattles will be embedded and integrated into the slope and benches at key locations to break up the slope further and provide additional rill protection and water harvesting functions as the native vegetation establishes.
  • MAINTENANCE ROAD – A compacted and slightly elevated maintenance road will be constructed to divert upland stormwater runoff away from the streambank slope, provide site access for maintenance and monitoring, and act as an agricultural berm for future restoration flood cells.
  • FLOODPLAIN REVEGETATION AREA SITE PREPARATION – Clear, grub, strip, smooth, and shape the zone between the toe of the cutbank and the OWHM to provide a tamarisk free platform for native plantings. Plantings in this zone will serve as a pilot study for future restoration efforts in the lower floodplain.
  • NATIVE REVEGETATION PLANTING & IRRIGATION PLAN – Because of the high salinity concentrations of the soil and groundwater at the site, a specialized planting palette was developed using native salt tolerant species.