Various studies have helped gain a better understanding of the thermal impacts of dams on a site-specific basis, but very few studies have compared the thermal impacts of varying types of dams within ...the same region. In this study, we conducted a regional-scale assessment of the impacts of dams on the thermal regime of 13 medium-size rivers in eastern Canada. The objectives of this study were to identify features of the thermal regime of rivers that are predominantly impacted by dams and to compare the impacts associated with different types of regulation (run-of-river, storage, peaking). The thermal regime of regulated and unregulated rivers was characterized using 15 metrics that described the magnitude, frequency, duration, timing, and rate of change of water temperature. Results indicate that storage and peaking dams impounding at least 10% of the median annual runoff generally (i) reduced the magnitude of water temperature variation at seasonal, daily, and subdaily timescales and (ii) increased the monthly mean water temperature in September. This regional assessment offers important insight regarding a generalized pattern of thermal alteration by dams, and this information could be used to guide biological monitoring efforts in regulated rivers.
•A hydraulic study for environmental flows (EF) assessment in Southern Quebec.•The wetted perimeter (WP) can be a tool for local riverine ecosystems protection.•The WP associated to the maximum ...curvature point is used as a protective threshold.•The WP associated to several potential environmental flows were compared.•Water managers can provide adjusted EF for Southern Quebec rivers.
Environmental flows assessment in eastern Canada, and particularly in the province of Quebec, is mainly based on hydrological assessment of historical data during low flow periods. The mean 7-day low flow with return periods of two (7Q2) and ten years (7Q10) are two flow metrics currently used by the Quebec Department of Environment and Fight against Climate Change to prescribe minimum flow and/or maximum water abstraction while maintaining the functions and health of riverine ecosystems. This study investigated the use of the wetted perimeter as an additional environmental flows assessment method. This tool can be used by water managers to maintain the availability of river habitats during low flow periods. Twenty flow metrics were computed for inter-annual, summer and winter periods, for 43 sites from 35 rivers, and analysed to study the changes in wetted perimeter with flow. In addition, the flow associated with maximum curvature (breakpoint) of the flow-wetted perimeter function (QMC) was analyzed. Results provided a better understanding of local changes of river hydraulics and possible aquatic habitat availability associated with different flow metrics. The relevance of using a wetted perimeter threshold (WPSQMC) combined with flow thresholds (Tennant method) was also discussed. The two “fair” Tennant flow thresholds, apart from the twenty flow metrics, would provide sufficient available habitat all year long with corresponding WPSQMC thresholds of 88% and 95% of the 43 river sites. The median discharge for August flow metric for summer and the median discharge for the month with the lowest flow metric value for winter (usually February), provided the highest wetted perimeter in relative terms (72% and 79% respectively of the river sites) compared to the WPSQMC threshold. Using the 7Q2 flow metric would mean maintaining sufficient available habitat for 50%, 60% and 72% of the river sites for respectively inter-annual, summer and winter periods. Considering the single WPSQMC threshold, its associated flow provided the highest values for 16% of the river sites and the second highest one for 9% of the river sites with a single seasonal flow metric value high enough for summer or winter. This study showed that the wetted perimeter is a tool providing additional information on both river morphology and changes in potential aquatic habitat as a function of flow for river sites with small catchment size and low mean annual flow values. Indeed, the wetted perimeter can be very useful in the overall assessment of environmental flows.
Water temperature influences many physical, chemical and biological properties of rivers. It also influences the distribution of fish and many aquatic organisms within the river environment. Hence, a ...good understanding of the thermal regime of rivers is essential for effective management of fisheries and aquatic resources. This study deals with the modelling of river water temperature using a deterministic model. This model calculates the net heat flux at the water surface using meteorological conditions within the study area. The water temperature model was applied on two watercourses of different size and thermal characteristics, but within a similar meteorological region, i.e. the Little Southwest Miramichi River and Catamaran Brook (New Brunswick, Canada). Data from 1992 to 1994 were used to calibrate the model, while data from 1995 to 1999 were used for the model validation. Results showed equally good agreement between observed and predicted water temperatures during the calibration period for both rivers with a root-mean-square error (RMSE) of 1.49
°C for the Little Southwest Miramichi River compared to 1.51
°C for Catamaran brook. During the validation period, RMSEs were calculated at 1.55
°C for the Little Southwest Miramichi River and 1.61
°C for Catamaran Brook. Poorer model performances were generally observed early in the season (e.g. spring), especially for the Little Southwest Miramichi River due to the influence of snowmelt conditions, while late summer to autumn performances showed among the best results for both rivers. Late autumn performances were more variable in Catamaran Brook and presumably influenced by the groundwater, geothermal conditions and potentially riparian shading. The geothermal aspect was further investigated at Catamaran Brook (using 1998 data) and results revealed that although geothermal fluxes are present, they explained very little of the unexplained variability (<0.1
°C). Similar to previous studies, the net short-wave radiation was shown to be the dominant energy flux, while the evaporative heat flux contributed significantly to cooling rivers during warmer summers.
Environmental flows (eflows) refer to the amount of water required to sustain aquatic ecosystems. In its formal definition, three flow characteristics need to be minimally maintained: quantity, ...timing and quality. This overview paper highlights the challenges of some of the current methods used for eflow determination in the context of an evolving climate. As hydrological methods remain popular, they are first analyzed by describing some of the potential caveats associated with their usage when flow time series are non-stationarity. The timing of low-flow events will likely change within a season but will also likely shift in seasonality in some regions. Flow quality is a multi-faceted concept. It is proposed that a first simple step to partly incorporate flow quality in future analyses is to include the water temperature as a covariate. Finally, holistic approaches are also critically revisited, and simple modifications to the Ecological Limits of Flow Alteration (ELOHA) framework are proposed.
•Water potentials are higher in the east and west coasts.•Most severe low flow conditions were in the Prairies and norther territories.•Spring snowmelt is a trigger of high flows in most ...provinces.•Atlantic provinces, Ontario, and Quebec showed a second high flow period in autumn.•Flatter flow duration curves are observed in rivers with larger water potentials.
Water resources play an important role in many aspects of our daily lives, e.g. industrial food processing, irrigation, and hydropower generation, etc. The natural flow regime and water availability were studied across Canada using 167 catchments from the Water Survey of Canada dataset (Reference Hydrometric Basin Network - RHBN). We established a systematic analysis of water availability (annual and monthly runoff) to determine both the quantity and distribution of water within the year. In each province, we investigated the severity of low flow conditions namely the magnitude, seasonality, and duration of extreme low flows. There are prominent disparities in water availability at the annual and monthly time scales across Canada. The annual runoff characteristics showed a relatively abundant quantities of water on the east and west coasts (800-2300 mm/year). Annual runoff is critically low (<150 mm/year) in the prairies and northern territories. Monthly analyses revealed eminent differences in the timing and magnitude of high and low flows. The spring snowmelt is the main trigger of high flows in most provinces. However, the quantities of water during freshet period varied dramatically across provinces. British Columbia showed among the highest hydrological variability where some catchments showed relatively high flows year around. In Canada, a second high flow period was observed in some provinces (e.g., Quebec, Ontario, and the Maritimes). The underpinning hydrological processes and the precipitation regime are discussed to explain the regional hydrologic disparities. The monthly flow of the 80th percentile (Q80; monthly flow duration curve) was used as the cutoff to describe low flows both in terms of magnitude and duration. The Q80 variability across Canadian rivers was significantly large (0.3-100 mm/month). Many regions have one period of extreme low flows except in Newfoundland, New Brunswick, British Columbia, Ontario, Quebec and Saskatchewan where 2 seasons of low flows can be observed. In Newfoundland and New Brunswick the low flow period was the shortest (2.6 months). In contrast, in the prairies and north territories, the low flow period extended between 3.4 and 4 months. We further explained the disparities in water availability and low flows from analysis of the daily flow duration curve (FDC). We quantified the differences in the flow response from flow indices calculated from FDC (baseflow index, low flow index, and slope of the FDC). The results of water availability and low flows have important socio-economic impacts on water supply, reservoir operations, and far-reaching implications on the health of aquatic habitats.
Abstract
Through a case study in Southern Quebec (Canada), the assessment of environmental flows in light of the effects of climate change is investigated. Currently, the 7Q2 flow metric (7-day ...average flow with a 2-year return period) is used for water abstraction management. Several flow metrics were calculated using flow time series simulated by a deterministic hydrological model (HYDROTEL) and climate change scenarios as inputs. Results were compared within homogeneous low flow regions defined using ascendant hierarchical clustering, for the 1990, 2020 and 2050 horizons and annual, summer and winter periods. The impact of each flow metric on the potential availability of physical habitat was analyzed using the wetted perimeter as a proxy. Results indicated that: (1) the increasing non-stationarity of simulated flow data sets over time will complicate the use of frequency analysis to calculate the 7Q2 flow metric; (2) summer low flow values are expected to be lower than winter low flows; and (3) flow-duration curve metrics like the LQ50 (median discharge value of the month with the lowest flow) may become relevant environmental flow metrics by 2050. Results question current water abstraction management tools and permit us to anticipate future local and regional issues during low flow periods.
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