The River Machine: A Template for Fish Movement and Habitat, Fluvial Geomorphology, Fluid Dynamics and Biogeochemical Cycling

Abstract

The dynamics of many large floodplain rivers are dominated by the flood pulse. The high kinetic energy of the erosive flows associated with the flood pulse forms and reforms the river channel. In general, the flood pulse supports the immense abundance and diversity of river life by transporting nutrients and organic matter into backwaters in spring, supporting primary and secondary production during the summer and redistributing these products to channels as water levels recede. Both North American and South American fluvial-dependent large river fishes exhibit complex, system-level longitudinal and/or lateral movements across life stages that allow them to exploit flood pulse-driven spatial heterogeneity and seasonal connectivity to feed, reproduce and avoid harsh conditions. We argue that two hydraulic variables, the magnitudes of velocity and the spatial velocity gradient, are necessary and sufficient to both understand fish 'hydro-navigation' as well as explain patterns in biogeochemistry and fluvial geomorphology and thereby create a new conceptual framework for large floodplain rivers integrating fluid dynamics, channel morphology, biogeochemical cycling and important elements of fish ecology. We illustrate the framework using summary data from the São Francisco River, Brazil that contains sub-basins possessing different levels of impact and also from the lower Paraná River (Argentina) where natural processes can still be studied. We believe the framework is an important element of large river restoration because it directly links the unique physical and chemical processes of large floodplain rivers to life requirements important to fishes and other biota.

Levee setbacks : an innovative, cost-effective, and sustainable solution for improved flood risk management

“…The application of EWN is particularly important for the Nation's rivers because almost all of them are already significantly impacted. This degraded ecological condition is particularly acute in rivers constrained by traditional levees that prevent the river from expanding into its historic floodplain during seasonal high flows (Nestler et al 2012). Nonstructural flood risk management activities, particularly watershed management, land-use planning, regulation, and floodplain evacuation, meet many underlying principles of EWN such as being holistic, sustainable, sciencebased, efficient and cost effective, socially responsive, and innovative.…”

“…The land protected by levees is often drained to become farmland or developed for other economic benefits, which permanently impairs or removes important ecological functions from the river corridor. There are a number of other effects of the seasonal flood pulse, including carbon dynamics, nutrient cycling, sediment transport, and geomorphology that are well summarized in (Nestler et al 2012, Junk et al 1989, Junk and Wantzen 2004, Welcomme and Halls 2004 and will not be summarized here.…”

“…Importantly, the designation of a levee setback as a nonstructural versus structural alternative is not clear-cut and depends on the selected baseline (or reference condition (Nestler et al 2012)), degree of setback, authority, and funding source. From an environmental perspective, the confusion occurs because the environmental conditions associated with a setback levee are intermediate between a traditional Corps mainline levee bordering the active river channel and an unleveed river.…”

Effects of whitewater parks on fish passage: a spatially explicit hydraulic analysis

“…Riverine biota have evolved to inhabit highly complex hydraulic environments formed through natural hydrologic variability and geomorphic response (Poff et al, 1997;Nestler et al, 2012;Thorp et al, 2006). Aquatic organisms exploit habitats that vary spatially and temporally across dimensions and scales, thus highlighting the need for connectivity of the river landscape (Fausch et al, 2002;Frissel et al, 1986).…”

Side Channels of the Impounded and Middle Mississippi River: Opportunities and Challenges to Maximize Restoration Potential

“…Second, habitat requirements of rare, threatened, or endangered species are often poorly known, resulting in a high uncertainty that can make distinguishing among alternative plans/actions problematic. This appears to be particularly true for large river fish species whose relationship to physical and chemical environmental characteristics is still speculative or largely unknown (Nestler et al 2011). Third, rare, threatened, or endangered species are usually relegated to a small portion of their historical range.…”