Uncertainties associated with environmental flow metrics

Abstract

The demand for water withdrawal from rivers continues to increase world‐wide, and these water withdrawals can affect fish habitat and aquatic life in general. The study of river hydrology and environmental flows often require the calculation of flow metrics (e.g., mean annual flow, flow duration statistics, low flow frequency analyses, etc.); however, uncertainties in these flow metrics have not been fully studied in the literature. The present study looks at uncertainties related to four flow metrics used in environmental flow studies using bootstrapping techniques for five hydrometric stations (located in the Miramichi River basin, Canada). The objectives of the study are: (a) to calculate and compare different flow metrics, (b) to carry out bootstrap samples in order to assess uncertainties as a function of sample size and (c) to determine which flow metrics are associated with the least uncertainty when calculating environmental flows using hydrological based methods. Results showed that uncertainties rapidly decreased from a 5‐ to a 15‐year sample size for each flow metric. The uncertainties from a 15‐ to a 50‐year sample size decreased, but not as rapidly as from a 5‐ to a 15‐year sample. The mean annual flow metric showed the least variability. For monthly flow metrics, sample sizes of 25–30 years were needed to obtain similar coefficients of variation as the 5‐year sample size of the mean annual flow. Drainage area did not impact the mean annual flow metric; however, uncertainty was observed to vary more significantly for smaller rivers on a monthly basis.

Purposeful Stakeholder Engagement for Improved Environmental Flow Outcomes

“…E-flows management is complicated by the many uncertainties associated with a complex social-ecological system, including unknown flow-ecology relationships (Bunn and Arthington, 2002;Lynch et al, 2018;Watts et al, 2020), measurement uncertainty (Stewardson and Rutherfurd, 2006;Goguen et al, 2020), the dynamics of a non-stationary climate and environment (Milly et al, 2008;ThompsonLaizé et al, 2014;Poff, 2018), and ambiguous or shifting social perceptions of the water resource systems (Gleick, 2000;Hogl et al, 2012). Adaptive management seeks to reduce the uncertainties associated with ecological systems through a structured learning process (Williams, 2011;Webb et al, 2017).…”

Quantitative assessment of ecological operation effects based on flood pulses and ecology-economic coupling model: a case study of Three Gorges Reservoir, China

“…To maintain river functions (biological habitats, material exchanges, natural landscapes, etc. ), governments generally require reservoir managers to control the discharge based on the recommended environmental flow (Turgeon et al 2021), which is often determined by hydrology methods, hydraulics methods, habitat simulation methods and holistic methods (Goguen et al 2020). However, these methods ignore the importance of runoff flood pulses, because the recommended environmental flow are determined from the base flow (the minimum flow that meets the basic ecological function of the river) and the fixed value (Lobera et al 2021).…”