A hydrogeomorphic dynamics approach to assess in‐stream ecological functionality using the functional flows model, part 1—model characteristics

Abstract

The functional flows model integrates hydrogeomorphic processes and ecological functions for stream physical habitat evaluations. Functional flows are discharge values that serve ecological uses. Assessments of functional flows are based on evaluation of shear stress dynamics. The analysis is based on the occurrence of sediment transport regimes defined by threshold values of Shields stress estimated from discharge (Q), a parameter ( f) governing depth response to incremental discharge changes, water surface slope (S) and media grain size (D 50 ). As an example, the model was tuned for fall-run Chinook salmon spawning. Ecological functions studied were bed occupation (spawning, incubation and emergence) and bed preparation (river bed reworking periods)-both reliant on shear stress dynamics. A numerical experiment and sensitivity analysis using a wide range of realistic values of input variables indicated the effect of each variable on flow functionality.

Integrated analysis of flow, form, and function for river management and design testing

“…These results indicate that restoring or designing a pool-riffle dominated stream network to provide interspersed plane bed reaches may support higher overall ecosystem integrity by promoting distinct and complementary functions in different locations during biologically significant periods. Such findings support the emerging recognition of spatial and temporal heterogeneity as fundamental characteristics of fluvial systems and the need for a flexible framework within which natural processes, such as sediment transport and nutrient dynamics, can occur (Clarke, Bruce-Burgess, & Wharton, 2003;Gostner, Parasiewicz, et al, 2013;Vanzo et al, 2016;Escobar-Arias & Pasternack, 2010).…”

“…Five Mediterranean‐montane ecosystem functions were considered, associated with two major components of river ecosystem integrity: hydrogeomorphic processes and aquatic habitat (Table ). The performance of these functions was tested based on the following criteria: (1) a longitudinal shift in the location of peak shear stress at high flows from topographic highs to topographic lows was used to test the occurrence of flow convergence routing, a dominant geomorphic formation and maintenance process in certain channels (MacWilliams et al, ); (2) a measure of hydrogeomorphic variability was used to quantify overall habitat heterogeneity in the river corridor (Gostner, Alp, et al, ); and (3) fall‐run Chinook salmon habitat was evaluated with respect to (a) bed preparation and (b) bed occupation functions based on established shear stress thresholds and biologically significant timing thresholds (Escobar‐Arias & Pasternack, ) as well as (c) redd dewatering risk during bed occupation. These functions were evaluated using a Python script that enabled rapid evaluation of model outputs over the specific spatio‐temporal constraints.…”

Functional flows: an environmental flow regime benefits riparian cottonwoods along the Waterton River, Alberta

“…The revisions to dam operations and flow coordination across the different tributaries provided the environmental flow regime that commenced in the early 1990s and was intended to sustain the freshwater ecosystems and also support human livelihoods and well‐being (Brisbane Declaration ). As part of the environmental flow approach, specific functional flow components were implemented; these are deliberate patterns of in‐stream flow regulation that are intended to sustain and restore particular ecological functions (Escobar‐Arias & Pasternack ; Yarnell et al ). For the St. Mary and Waterton Rivers, the functional flows involved two changes to address the apparent causes of the cottonwood decline (Rood et al ).…”

Differences in river ecological functions due to rapid channel alteration processes in two California rivers using the functional flows model, part 2—model applications

“…The overall hypothesis of this paper is that differences in hydrogeomorphic conditions induce changes in ecological performance of the physical habitat, with the specific mechanism embedded into the algorithms defining the functional flow model, as outlined in the preceding article (Escobar-Arias and Pasternack, 2009). Research questions 1 to 3 listed below were formulated to test the hypothesis by comparing functional flows before and after morphologic alterations.…”

“…The overall goal of this paper was to apply the FFM, presented in the preceding article labelled as Part 1 (Escobar-Arias and Pasternack, 2009), to analyse ecological functionality under two types of rapid hydrogeomorphic change processes and under different morphologies. Consequently, the model was used in this study to advance the basic scientific understanding of stream ecological response to hydrogeomorphic change, not just report specific metrics for two rivers.…”