Abstract

Faced with increasing demands for water withdrawals and a changing climate, the Quebec Department of Environment and Fight Against Climate Change is reviewing its water withdrawal guidelines to protect riverine ecosystems. For Southern Quebec, guidelines currently limit water withdrawals to a maximum of 15% of the 7Q2 (mean 7-day low flow with a return period of two years) during low flow periods. In this context, one of the issues raised is to investigate measures that help to preserve riverine ecosystems during low flow periods by establishing cut-off flow restrictions. This study compared eight low flow metrics to investigate which can be considered useful metrics to assess environmental flow in Southern Quebec rivers. Using 98 hydrometrics stations with a minimum of 20 years of daily flow data from eight hydrological regions, those low flow metrics were compared to three thresholds based on Tennant Method for monthly and annual temporal scales. The relevance of current hydrological regions delineation was investigated by looking at results within these regions, compared to six groups of stations defined using multivariate analyses. This study emphasizes that assessing environmental flows is linked to the hydrological context of the area of interest, the temporal scale of the historical data available, and the catchment size. The results showed that (1) winter low flows were lower than summer low flows; (2) 23% to 26% of the values were under the conservative thresholds for all the metrics depending of the time scale; and (3) the 7Q2, 7Q10 (mean 7-day low flow with a return period of ten years), Q95 and Q90 (95th and 90th percentile on the flow duration curve) are the less conservative for rivers having a low regime flow. To conclude, assessing several regionally adapted environmental flow metrics is recommended rather than systematically using the 7Q2 for Southern Quebec.

摘要

面对对取水和气候变化的日益增长的需求，魁北克环境与气候变化部正在审查其取水指南，以保护河流生态系统。对于魁北克南部，目前的指导方针将低流量时段的取水量限制在7Q2的最大取水量（平均7天的低流量，回流期为两年）。在这种情况下，提出的问题之一是研究通过建立截止流量限制来帮助在低流量时期保护河流生态系统的措施。这项研究比较了八个低流量指标以进行调查，这些指标可被视为评估魁北克南部河流环境流量的有用指标。使用来自八个水文地区的98个水文站和至少20年的日流量数据，将这些低流量指标与基于Tennant方法的三个阈值进行月度和年度时间尺度的比较。通过查看这些区域内的结果，与使用多元分析定义的六组站进行了比较，研究了当前水文区域划定的相关性。这项研究强调，评估环境流量与感兴趣地​​区的水文环境，可获得的历史数据的时间尺度以及流域规模有关。结果表明：（1）冬季低流量低于夏季低流量；（2）所有指标的23％到26％低于保守阈值，具体取决于时间范围；（3）2010年第7季度，2010年第7季度（平均7天的低流量，回收期为10年），Q95和Q90（在流量持续时间曲线上分别为第95和90个百分位数）对于水位低的河流而言，保守性较差。总而言之，建议对几个区域适应性环境流量指标进行评估，而不是系统地使用魁北克南部地区的第2季度系统评估。