Applying Channel Migration Zone Analysis to Inform Resilient Wastewater Outfall Relocation on the Tanana River

Author: Jake Ciufo, RESPEC and Kacy Grundhauser.

Video Presentation

Abstract

A Channel Migration Zone (CMZ) study was completed for an 8-mile reach of the Tanana River to evaluate long-term hydraulic feasibility at a proposed relocation site for the City of North Pole's (CNP) wastewater effluent outfall. The Tanana River is a dynamic, glacier-fed, heavily braided river that flows from eastern Alaska, forms the southern border of CNP, and flows into the Yukon River. CNP uses a passive lagoon system to treat an average of 150,000 gallons of wastewater per day for approximately 1,700 residential, commercial, and industrial customers. To meet Alaska Department of Conservation regulations, CNP uses a mixing zone which is a region where discharge is diluted with river flow to lower pollutant concentrations. Reductions in flow conveyance near the existing outfall have reduced dilution within the permitted mixing zone, leading to noncompliance with the Alaska Department of Conservation regulations. CNP contracted RESPEC to conduct a CMZ study to investigate the feasibility of a proposed outfall location. A CMZ analysis, adapted from Washington state guidance, was conducted for an 8 mile reach of the Tanana River. Historical aerial imagery from 1938-2025 was used to delineate the Active Channel, Restricted Migration Area, and Erosion Hazard Zones based on channel geometry, flow rate/distribution, sediment, vegetation, and human modifications. Particular attention was given to the hydraulic influence of the U.S. Army Corps of Engineers' Tanana River Levee and associated structures constructed from 1973-1987. Historical channel planform change was used to predict future movement and bank erosion for the proposed design life of 20 years. This presentation will summarize the CMZ process, analysis, and results, and show how CMZ analyses can inform infrastructure feasibility. Project recommendations for sustainable and resilient planning and operation will be discussed.

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