Gila River Restoration Project at Apache Grove

Gila River Restoration Project at Apache Grove

The Gila River Restoration Project at Apache Grove was developed in response to recommendations of a report from a previously funded Arizona Water Protection Fund (AWPF) project titled, “Upper Gila River Fluvial Geomorphology Study” (AWPF Grant Number 98-054WPF). The Gila River Restoration Project at Apache Grove focused on a 1.6-mile long reach of the Gila River on 200-acres of private farm and ranch land near Duncan, AZ. Objectives of the project include restoring natural floodplain function by removing existing partially breached agricultural dikes, reducing the risks of lateral erosion and land loss, managing salt cedar, and improving riparian habitats and stream function. Proper stream geomorphology/channel characteristics will be restored by allowing the main channel to reattach to its former floodplain thereby restoring floodplain conditions within the project area. This project includes excavating 3,000 feet of earthen dikes and returning the ground to natural grade and re-contouring the floodplain to add floodprone width to the river. Other proposed practices include implementation of bank stabilization measures, invasive vegetative species management, native species revegetation, monitoring, fencing, and development of a public outreach plan. [For more information see the Arizona Water Protection Fund Project Information Page]

The following is a summary of George F. Cathey’s technical contribution to the project (as an employee of Natural Channel Design, Inc.):

• Survey – Coordinated and conducted a supplemental survey of the river reach using a survey grade RTK GPS system to augment the photogrammetric data of the site with additional topographic and geomorphic data (profiles, cross-sections, and bankfull features).
• Permitting Assistance – Helped develop the permitting package for the project including ACE 404 permit, ADEQ 401 Certification and Stormwater Pollution Prevention Plan (SWPPP).
• Hydrologic and Hydraulic Modeling – Evaluated local and regional hydrology to develop flood frequencies/recurrence intervals and associated flows. Evaluated flooding under existing conditions and proposed conditions (with the removal of invasive vegetation, removal of the dike, and floodplain re-contouring operations) using vegetation mapping data, geomorphic criteria, and a detailed HEC-RAS/RiverCAD model. The 10, 25, 50, and 100-year flood extents were determined as part of the study.
• Grading Design – Provided analysis for the grading plan including earth balance calculations for ~64,000 cubic yards of proposed earthwork from dike removal, floodplain re-contouring, and bank stabilization operations. The final plan optimized earthwork while improving geomorphic characteristics of the river and its floodplain. Spoils from the earthmoving were used to re-level and improve drainage on existing agricultural fields adjacent to the project.
• Construction Package – Developed the construction package (specifications, drawings, engineer’s opinion of probable cost, and unit price table) for the Stormwater Pollution Prevention Plan (SWPPP), site preparation and invasive species management plan, and the earthwork plan including dike removal and floodplain re-contouring operations.
• Construction Phase Services – Led pre-bid and pre-construction meetings for grading operations, developed a staking plan for the earthmoving operations, laid out the construction using a survey grade RTK GPS system, and coordinated with the contractor on construction progress and grade checking.