ABSTRACT:

In arid regions with limited water supplies like the Colorado River basin of the southwestern U.S., healthy riparian ecosystems may seem in conflict with human water use. However, this is not always the case; indeed, they may be interdependent. In this paper, we use a long-term dataset of topographic, vegetation, and groundwater data collected over water years 2011–2021 to demonstrate recovery of functional connectivity between a river and its floodplain despite previous human impacts and continued human use. In the Cliff-Gila Valley of southwestern New Mexico, historical levee construction after 1940 profoundly altered the floodplain and river channel of the Gila River, a Colorado River tributary. This work ceased by the mid-1980s and over time, river anastomosis during subsequent floods reclaimed the broader floodplain, regenerating diverse native habitat. The study period spanned two high-flow events, numerous smaller floods, and seasonal dry periods. Even the lowest perennial flows (0.4–0.6 m3 s-1) sustained favorable rates of groundwater recession, supporting riparian seedling recruitment in the topographic lows created by floodplain secondary channels. Alluvial groundwater receded more sharply in a reach seasonally dewatered by irrigation diversions, but seepage through diversion structures and unlined ditches provided small yet important sources of hyporheic flow. This study demonstrates that the river’s natural flow regime (or a similar range of seasonal flows) creates conditions where human activities co-exist with robust native habitat and highlights the importance of long-term datasets for documenting ecosystem resilience, including to hydrologic drought and ongoing climate change.