Hydraulic geometry as a physical template for the River Continuum: application to optimal flows and longitudinal trends in salmonid habitat

Abstract

The River Continuum Concept lacks a quantitative physical model to represent downstream trends in habitat. We evaluate whether hydraulic geometry relationships can be used as a physical template to predict longitudinal trends in habitat availability and optimal flows for different life-history stages of rainbow trout (Oncorhynchus mykiss). Optimal flows based on hydraulic geometry indicate that (i) optimal flows are higher for larger fish, (ii) optimal flows proportionally increase as streams became smaller and decrease downstream, and (iii) maximum predicted habitat suitabilities for fry and juveniles are in small streams, and maximum suitabilities are displaced progressively downstream for later life-history stages. These patterns are an emergent property of downstream increases in channel depth and velocity and changes in habitat suitability curves associated with increased swimming performance of larger fish. Nonlinear downstream trends in habitat imply that fixed flow percentages recommended by the Tenant method may substantially underestimate optimal flows in small streams. Despite oversimplifying complex channel structure, hydraulic geometry relationships should serve as a useful physical model for testing downstream trends in habitat-related processes along the river continuum.

High resolution, basin extent observations and implications for understanding river form and process

“…RCC starts from the premises that the physical river environment supplies energy, organic matter, and habitat space to organisms such that ecological patterns in the downstream direction are set by the DHG. Distributions of biotic communities in the downstream direction thus parallel the physical changes in the fl uvial geomorphology (Rosenfeld et al, 2007).…”

“…Although DHG is classically used to estimate morphologic characteristics at channel forming fl ows, ecologists and other river scientists are increasingly needing DHG for predictions across a range of fl ows (e.g. Rosenfeld et al, 2007). It is also notable that there is still a great deal of variability about the DHG curves for Soda Butte and Cache Creeks where the two-year fl ood and channel characteristics were used to develop the curves (Table I).…”

Causes and consequences of invertebrate drift in running waters: from individuals to populations and trophic fluxes

“…Therefore, while fish may deplete a major portion of diurnal drift in smaller streams, overall losses due to predation may be a negligible fraction of the total drift flux. Similarly, the fraction of drift consumed likely declines in larger rivers, where a much smaller proportion of physical habitat may be available to drift-foraging fishes of a given size (Rosenfeld et al 2007). …”

Long‐term simulations of the dynamics of trout populations on river reaches bypassed by hydroelectric installations—analysis of the impact of different hydrological scenarios

“…Moreover, generalization of habitat models and their extension to more species and to fish habitat guilds, as well as their biological validation, are promising avenues for enriching the gamut of methods available to study management of environmentally favourable discharge (Hatfield and Bruce, 2000;Lamouroux and Capra, 2002;Lamouroux and Souchon, 2002;Lamouroux and Jowett, 2005;Rosenfeld et al, 2007).…”