Accounting for flow intermittency in environmental flows design

Abstract

River ecosystems world‐wide are affected by altered flow regimes, and advanced science and practice of environmental flows have been developed to understand and reduce these impacts. But most environmental flows approaches ignore flow intermittency, which is a natural feature of 30% of the global river network length. Ignoring flow intermittency when setting environmental flows in naturally intermittent rivers might lead to deleterious ecological effects. We review evidence of the ecological effects of flow intermittency and provide guidance to incorporate intermittency (non‐flow events) into existing methods judged as suitable for application in temporary waterways. To better integrate non‐flow events into hydrological methods, we propose a suite of new indicators to be used in the range of variability approach. These indicators reflect dry periods and the unpredictable nature of temporary waterways. We develop a predictability index for protecting those species adapted to temporary conditions. For hydraulic‐habitat models, we find that mesohabitat methods are particularly effective for describing complex habitat dynamics during dry phases. We present an example of the European eel to show the relationship between discharge and non‐flow days and wet area, habitat suitability and connectivity. We find that existing holistic approaches may be applied to temporary waterways without significant structural alteration to their stepwise frameworks, but new component methods are needed to address flow‐related aspects across both flow and non‐flow periods of the flow regime. Synthesis and applications. Setting environmental flow requirements for temporary waterways requires modification and enhancement of existing approaches and methodologies, most notably the explicit consideration of non‐flow events and greater integration of specific geomorphic, hydrogeologic and hydraulic elements. Temporary waterways are among the freshwater ecosystems most vulnerable to alterations in flow regimes, and they are also under great pressure. The methodological modifications recommended in this paper will aid water managers in protecting key components of temporary flow regimes, thereby preserving their unique ecology and associated services.

Habitat Preferences of Italian Freshwater Fish: A Systematic Review of Data Availability for Applications of the MesoHABSIM Model

“…The MesoHABSIM approach has already proved high potential in assessing habitat availability for freshwater species in various hydro-morphological contexts of European rivers (Vezza et al, 2014b;Acuña et al, 2020). In particular, in Italy such model is currently used for impact assessment of hydropower and e-flows design in regulated rivers (Vezza et al, 2015a;Vezza et al, 2017).…”

Disentangling the complexity of socio-cultural values of temporary rivers

“…Consistent with the temporal and geographical variability of temporary rivers and the associated socio-cultural values, in the workshop we found the research needs of elaborating environmental flow methods that preserve them. In this context, Acuña et al (2020) actually propose methodological advances for the environmental flow assessments, which include the calculation of duration, timing and frequency of both dry and wet phases. In this sense, efforts for managing environmental flows should not only preserve healthy, resilient and biodiverse ecosystems, but also protect and restore the socially valued benefits they provide for people of all cultures.…”

Mesohabitat modelling in fish ecology: A global synthesis

“…Rinaldi et al, 2015). Moreover, mapping of functional mesohabitat is more effective in complex environments where hydrodynamic models and microscale approaches struggle, such as in high-gradient Alpine streams (Vezza, Parasiewicz, Calles, et al, 2014; or intermittent rivers (Acuña et al, 2020 Farò et al, 2018) techniques represent promising approaches to circumvent subjective decision-making in the field.…”

“…Rinaldi et al., 2015). Moreover, mapping of functional mesohabitat is more effective in complex environments where hydrodynamic models and microscale approaches struggle, such as in high‐gradient Alpine streams (Vezza, Parasiewicz, Calles, et al, 2014; Vezza, Parasiewicz, Spairani, et al, 2014) or intermittent rivers (Acuña et al., 2020). Monitoring hydro‐morphological conditions in these environments is critical to evaluate potential changes in future managed and climate‐induced flow regimes.…”