The ‘natural flow paradigm’ and Atlantic salmon—moving from concept to practice

Abstract

The 'natural flow paradigm' is becoming an important first principle in the setting of managed flow regimes throughout the world, including Canada. The principle states that managed flow regimes should consider the natural hydrological variability of a river system, both seasonally and interannually, to maintain its ecological integrity. While laudable, this principle is in direct conflict with hydropower development and irrigation interests. Therefore, both regulatory agencies and developers are struggling to identify the elements of hydrological variability that are critical to maintain the ecological health of rivers. In this paper, we identify flow requirements for different life stages of anadromous Atlantic salmon (Salmo salar L.). We then explore the potential effects of different flow regime scenarios on a wild Atlantic salmon population, using Harry's River in Western Newfoundland as an example. First, we link the life history patterns of Atlantic salmon to the scenario of the natural hydrological variability, incorporating the flow requirements for migration, spawning and rearing. In a second scenario, we present a flow regime managed for optimal hydropower production. Finally, we propose a conceptual model for a hypothetical managed flow regime that provides the necessary hydrological flow variations to support the life history requirements of Atlantic salmon, while permitting flow regulation and modification. This exercise identified data gaps and further research needs. Particularly, more information is needed on the amplitude of spring flooding necessary to initiate downstream migration while minimizing spill, which could potential be used for hydropower production.

Modelling Tools to Analyze and Assess the Ecological Impact of Hydropower Dams

“…Subsequently, they used the simulated water temperature as an input variable to assess the habitat suitability of fish. On the other hand, flow has also been used to predict the habitat suitability of fish [114] or macroinvertebrates [115]. In addition, biotic variables such as the biomass of invertebrates was used as an input variable in food web models to predict the changes in vertebrate communities [55].…”

“…Therefore, using one model for different life stages and for the whole-year conditions may lead to incorrect prediction results. Besides hydraulic characteristics, ecological components (e.g., riparian vegetation, present of predators, life stage of organisms), morphological characteristics (e.g., the spectrum of large river systems of the river) [26,114] and physical conditions (e.g., temperature, turbidity, substrate, seasonal variation) [32,99] are important factors that should be taken into account. The study of complex systems thus requires a multi-scale approach, in which it is necessary to consider the interactions occurring across many scales of space, time and organization [136].…”

What are the impacts of flow regime changes on fish productivity in temperate regions? A systematic map protocol

“…Flow alterations can result from many human modifications, including the construction of dams, hydroelectric facilities, water extraction for agriculture, drinking, industry, and recreation, and flood control measures [10,11]. Such changes of the natural flow regime may impact various chemical, physical, and biological attributes of rivers leading to declines in water quality, water supply, and the ecological integrity of river and stream ecosystems [12].…”

Development of an Inflow‐controlled Environmental Flow Regime for a Norwegian River

“…Recent international research shows a need for a more flexible flow regime which takes account of the variability found in the natural hydrological regime to meet the demands of the ecosystem functions (Enders et al, 2009, Poff et al, 2010. These findings are in contrast to the common practice in Norway, and the Norwegian Water Resources and Energy Directorate instigated a research programme to improve Norwegian environmental flow practices (Brittain, 2002).…”