A Resilience-Based Framework for Advancing Adaptive Management of Highly Regulated Rivers: A Case Study from the Middle Rio Grande, New Mexico (USA)

Abstract:

Conceptually, a degraded river-floodplain system has experienced a loss in hydrologic, geomorphic, and ecological structure and function from some baseline condition. Although there have been attempts to restore river systems to a pre-impacted condition, true restoration of highly regulated rivers is rarely a feasible goal because key hydrogeomorphic elements of the pre-disturbance system cannot be recovered. In this research, we make the case for a paradigm shift in how society thinks about and approaches rehabilitation of highly regulated river systems – one that moves away from a short-term (2- to 5-year) “build it and walk away” approach to one that involves long-term (multi-decadal) commitments to retaining ecological functional goals and objectives. To support this key point, we use the Middle Rio Grande (MRG) in central New Mexico as a case study. Along the MRG efforts to enhance spawning and rearing habitat for the federally endangered Rio Grande silvery minnow (Hybognathus amarus; RGSM) have been successful in the short term. However, the functional life of many rehabilitation sites is relatively brief due to sedimentation and ongoing encroachment by non-native vegetation. Therefore, we begin by describing the degree to which river form and functions (“system state”) have been altered to meet societal needs, but that these altered system states are incapable of sustaining imperiled species that evolved under previous system states. Second, we illustrate how active (e.g. floodplain lowering) and passive (e.g. environmental flows) rehabilitation techniques can temporarily achieve some endangered species management objectives, but that these successes are short-lived in lieu of a long-term monitoring and stewardship program. Finally, we quantify the hydrologic and biological success of recent rehabilitation designs using transdisciplinary monitoring of the sites and highlight the structured process being applied to guide adaptive stewardship of project sites. We conclude the paper by acknowledging and addressing the challenges that lie ahead, most notably regarding (1) funding long-term stewardship and (2) the importance of adaptive governance to optimize limited water supplies in the face of a changing climate.