Retrospective: Transitioning River Geomorphology and Its Impact On Habitat Management

Since the 1900s, the US government and state-level agencies have invested ambitiously and prolifically throughout the southwest to mitigate risks due to alternating conditions of drought and floods by implementing large-scale engineering projects. 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 and safeguard against drought by impounding peak flow volumes and improving river conveyance. However, the impacts to sediment supply and homogenization of water discharge have generated a fluvial geomorphic response with dramatic impacts to riparian mosaics. Patterns of single channel systems, floodplain disconnection, and problematic erosion have been common trends in these heavily engineered arid river systems. Due to the increased prioritization of ecological function and recurring maintenance to control erosion affecting river-adjacent infrastructure, government activities have shifted from hardened and large-scale river infrastructure solutions to engineering with nature, habitat restoration efforts, and channel maintenance. However, in contrast to hard-engineering projects, habitat management faces challenges in demonstrating longevity, engineering effectiveness, and quantifying habitat quality improvement benefits. 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 historical and current geomorphic trends on the Rio Grande near and within U.S. Army Corps of Engineers restoration sites in the Albuquerque, NM area, an alternative framework to assess long-term project effectiveness under geomorphic change is discussed. 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. The risks associated with uncertainty and innovation are discussed relative to potential outcomes that are an improvement from the status quo.