Technical Report

Retrospective: Transitioning River Geomorphology and its Impact on Habitat Management

URL: https://webapps.usgs.gov/mrgescp/documents/Harris-et-al_2023_Retrospective-Transitioning-River-Geomorphology-and-its-Impact-on-Habitat-Management.pdf

Date: 2023/01/01

Author(s): Harris, A., AuBuchon, J., Porter, M., McKay, S.K.

Publication: Prepared by U.S. Army Corps of Engineers, 15 p.

Abstract:

Since the early 1900s, the US government and state-level agencies throughout the southwest have invested ambitiously and prolifically on large-scale engineering projects to mitigate risks due to alternating conditions of drought and flood. These approaches included construction-intensive methods, particularly building dams, levees, and river channelization. The combination of these structures met design goals to reduce flood risk by reducing inundated areas and improving river conveyance. However, the impacts to sediment supply and homogenization of water discharge have generated a geomorphic response that has impacted riparian ecosystems. Channel narrowing, floodplain disconnection, and streambed erosion have been common in these heavily engineered semi-arid river systems.

Due to increased prioritization of ecological function and cost of recurring maintenance challenges, government activities have shifted from hardened river infrastructure solutions to engineering with nature, habitat restoration, and channel maintenance. However, in contrast to hard-engineering projects, habitat management faces challenges in demonstrating longevity, engineering effectiveness, and quantifying habitat quality improvement.

The purpose of this paper is to characterize the geomorphic change that has occurred in one of these highly engineered river systems, the Rio Grande, and how observed trends impact assumptions about restoration effectiveness and project scales. Based on geomorphic trends on the Rio Grande near Albuquerque, NM, we discuss an alternative framework to assess long-term restoration efficacy within the context of geomorphic change. The intention is to increase project resilience and effectiveness. We discuss challenges to innovation in over-allocated and highly engineered river systems, while also demonstrating how such alternatives have economic potential and reduce liabilities by reducing recurring maintenance and improving ecological function.