|Tuesday, June 01|
Inclusion of wetted perimeter in Environmental Flow Analysis in Southern Québec rivers
* Laureline Berthot, INRS, Canada
André St-Hilaire, Canada
Daniel Caissie, Canada
Nassir El-Jabi, Canada
"Faced with increasing demands for surface water and groundwater withdrawals, the Quebec Department of Environment and Fight Against Climate Change (MELCC) is revisiting its guidelines, which currently advocate the use of 7Q2 and 7Q10, as the environmental flow (e-flow) in rivers over seven consecutive days with a return period of two and ten years respectively. To sustain aquatic habitat and fish food production during low flow periods in Southern Quebec rivers, Belzile et al. (1997) suggested the use of the median monthly flow of August (AQ50) or September, or the percentage of mean annual flow (25%MAF, 35%MAF and 50%MAF), from a study of 17 fish species spread over 15 ecoregions. A first study recommended the use of regionally adapted environmental flow metrics in Southern Quebec (Berthot et al. 2020), with the AQ50 flow metric providing the highest values. In this second study, the wetted perimeter is proposed as an additional tool to assess environmental flows, thus taking into account river morphology and potential aquatic habitat. The maximum curvature point method was applied and its associated wetted perimeter value used as a riverine ecosystems protective threshold. The Tennant method (1976) was also computed for poor (10%MAF) to fair (25%MAF; 30%MAF) flow thresholds. According to Tennant (1976), 10%MAF flow values cover 60% of the substrate while 30%MAF flow values cover up to 100% of the substrate. A sample of 43 sites for 35 rivers highlighted that the 7Q10 flow metric and the maximum curvature point method low flow values were most of the time deemed weak (< 10%MAF) to protect riverine ecosystems. Considering wetted perimeter threshold values, 25%MAF, 30%MAF and summer flow metrics (like AQ50 and summer 7Q2) offer enough protection to riverine ecosystems for both flow and wetted perimeter values. "
Evaluation of a geomorphic instream flow tool for conducting hydraulic-habitat modelling
* Stefan Gronsdahl, Palmer, Canada
Dan McParland, Canada
Brett Eaton, Canada
R. Dan Moore, Canada
Jordan Rosenfeld, Canada
Reductions in streamflow associated with flow abstractions and alterations caused by human water use, agriculture, hydroelectric power production, and land-use change can negatively impact fish and aquatic habitat. When aquatic ecosystems may be compromised by anthropogenic demands for water, allocation decisions are often made within an environmental flow needs framework, which describes the timing and quantity of water necessary for these aquatic ecosystems to function. In circumstances where valued aquatic species may be affected, instream flow assessments using detailed hydraulic-habitat modelling studies are commonly used to inform resource management decisions. Conventional hydraulic-habitat modelling methods are time-consuming to implement. In response to repeated calls for more efficient and practical approaches, we have developed a Geomorphic Instream Flow Tool (GIFT) for conducting hydraulic-habitat modelling that combines a method to simulate hydraulic geometry at flows less than bankfull with empirically derived depth and velocity frequency distributions. GIFT can also easily be implemented alongside a geomorphic regime model to predict changes to stream morphology and aquatic habitat caused by environmental perturbations. This approach requires fewer resources to implement than conventional approaches; however, it has not been widely adopted by practitioners because it has been subject to minimal testing and validation. This study addresses the need to evaluate the performance of GIFT by comparing its outputs to benchmark data from eight rivers in western North America. GIFT predicted fish habitat-streamflow relationships within 20% of benchmark data, on average, in 15 of 18 situations when flows are less than 30% mean annual discharge, and in 16 of 18 situations when flows are between 30 and 100% mean annual discharge. GIFT was also used in conjunction with a geomorphic regime model for one stream, where it predicted the direction of changes in channel morphology and physical fish habitat that occurred following harvesting of 40% of the watershed forest. This evaluation indicates that GIFT can increase the efficiency of hydraulic-habitat modelling and can be used to predict how fish habitat may change under future scenarios in single-thread gravel-bed rivers with a mean annual discharge of around 15 m3/s or less. This approach provides an alternative to conventional hydraulic-habitat modelling approaches for screening-level studies, labour-intensive evaluations of multiple stream reaches, and studies in smaller streams that may be challenging for conventional hydraulic models to accurately represent. A key benefit of GIFT that differentiates it from conventional approaches is its ability to predict how future changes in climate and land-use may affect channel morphology and fish habitat. Application of this technique to large rivers, multi-thread channels, rivers without gravel beds, or in areas outside western North America should proceed with caution, as these scenarios have not been tested. Source code and a graphical user-interface that can be used to apply GIFT are available as open-source tools online.
Assessing the implications of various approaches to flow trend analysis in Western Canadian streams
* Kyle Hamilton, Hatfield Consultants, Canada
Natasha Cowie, Canada
Dan Bewley, Canada
Steven Guenther, Canada
Tim Bennett, Canada
Annual low-flow periods pose considerable stress on aquatic resources, and long-term changes in these base flows (whether climate or anthropogenic driven) can have significant impacts on environmental values and warrant changes in water management and allocation. However, the vast majority of streamflow trend analyses are simple in nature (e.g., applying the monotonic Mann-Kendall test to flow records), and may not adequately capture or represent flow changes of significance (e.g., abrupt changes, shifts in timing and frequency, or non-statistically significant gradual changes over time). Extrapolating such trends into the future potentially invites poor decision making by water and aquatic resource managers, if indeed the trends are more cyclical and poorly approximated by these simple methods. Other statistics are more rarely used (e.g., breakpoint analysis, number of thresholds exceeded) but can help to identify patterns occurring at a finer temporal scale with which to better inform future decision making. We will compare these approaches in two different study areas/flow regimes where low-flows are increasingly stressed, to determine any difference in the flow regimes detected by each approach, the validity of using simpler methods such as Mann-Kendall, and the potential implications on decision making as a result.