|Tuesday, June 01|
Improvement of hydrological ensemble predictions in a multi-model forecasting context
Patrice Dion, Canada
* Richard Arsenault, ETS, Canada
Jean-Luc Martel, Canada
"Whether it is in the context of hydroelectric reservoir management, flood management or any other operation aimed at controlling water inflows, hydrologists use hydrological forecasts to make their operational decisions. To do so, they must consider financial, environmental and, above all, public safety risks. Ensemble forecasting is a type of hydrological forecasting that allows for risk assessment by taking into account the uncertainties in these forecasts. However, hydrological ensemble forecasts are often biased, and their distribution is often undispersed when compared to observations. This problem stems mainly from the uncertainty in the meteorological ensemble forecasts used to feed hydrological models to obtain forecasts of river streamflow, and also from the model(s) used. These erroneous predictions can thus contribute to operational decisions that can endanger the public and infrastructure. This presentation introduces a new methodology that aims to improve the accuracy of ensemble hydrological forecasts used in water resource management. This methodology has been evaluated on five catchments of the industrial partner Rio Tinto in the Lac-Saint-Jean region of Quebec. ECMWF weather ensemble forecasts (50 members) from 2015 to 2019 were used to inform eight global hydrological models over a nine-day horizon. Following the calibration of the hydrological models, a data assimilation method based on Kalman ensemble filters (EnKF) is used to modify the initial conditions of each hydrological model to represent the different sources of uncertainty in the observations. Then, a post-processing of the hydrological ensembles of each model is performed using the quantile bias correction (QM) method. These same hydrological ensembles are finally grouped into a large multi-model ensemble with the objective of having a better sampling of the total uncertainty, and thus to standardize its distribution. In order to evaluate the results obtained by the methodology and its different steps, several performance criteria are used. Talagrand diagrams, two metrics for quantifying reliability and precision, as well as the Kolmogorov-Smirnov statistical test, are used to evaluate the performance of the methodology. This evaluation is performed over four distinct periods, representing different hydrological regimes over the catchments. Despite difficulties during the spring freshet period, the results obtained indicate that each step of the methodology improves the accuracy of hydrological ensemble forecasts over the five catchments under study. Finally, the use of the multi-model significantly improves the accuracy and extent of hydrological ensembles over a nine-day horizon. This research demonstrates that it is therefore possible to correct biases and improve the reliability of hydrological ensemble forecasts."
Multi-method approach to estimate the importance of groundwater inflow and outflow in a lake water budget - Example of a medium-size southern boreal lake (Quebec, Canada)
* Marie Larocque, UQAM, Canada
Simon Lavoie-Lavallée, Canada
James Harris, Canada
Sylvain Gagné, Canada
Estimating a lake water budget is most often a complicated task, especially in environments where long-term monitoring is not available. Although a variety of methods can be used to estimate lake inflows and outflows, groundwater inflow estimates are often disregarded as they are considered negligible and difficult to measure. The objective of this project was to use a multi-method approach to quantify water budget components to estimate the relative importance of groundwater inflow to a medium-size southern boreal lake. The study was performed on Lake Papineau, a 12.9 km2 lake of the Canadian Shield within the Kenauk Nature reserve in the Outaouais region of Quebec (Canada). Precipitation data (P) are available from an on-site(since 2016) and regional meteorological station (since 1980). Lake evaporation (PET) was quantified using evaporation pan data, lake water stable isotope data and a temperature-based method. Surface water inflows (QSW_i) were quantified for the four main lake tributaries using a conceptual hydrological model (2017 and 2018) and calibrated parameters were extrapolated to smaller tributaries. Surface lake outflows (QSW_o) were estimated from measured weir data at the outlet (since 2016) and estimated for past conditions using artificial neural networks (1964-2020). Groundwater inflow (QGW_i) and outflow (QGW_o) were estimated using a Darcy-based estimation of lateral inflows based on head gradients, estimation of groundwater vertical inflows (or outflows), with mini-piezometer nests and with infiltrometer measurements in lake-bed sediments. The concepts of the Budyko curve were used to estimate the resilience of the Lake Papineau watershed from observed and extrapolated data since 1981. During the 2017-2018 monitoring period, the results show that PET and QSW_o represent respectively 5% and 93% of outflows. Water out of the lake was also through storage loss (2%) while QGW_o was negligible (limited portion of the lake). P and QSW_i represented respectively 20% and 61% of total lake inflows. When considered to represent the missing inflow to the water budget, QGW_i represented 19% of the water budget, but average field-based estimates were only one third of this value. This discrepancy is explained by the large spatial variability of QGW_i and to field measurement errors. April and May are the most active months for QSW_i, QSW_o and QGW_i while July and August are those with the highest PET. Between 1981 and 2020, a large variability of QSW_i and QSW_o is observed, caused by annual temperature (3.4 to 6.5oC) and precipitation (718 and 1281 mm/yr) variations. Relatively limited groundwater level variations (average of 1-1.5 m from field observations and backwards-extrapolated groundwater levels) indicate a relative stability of QGW_i. Preliminary estimates using the Budyko framework indicate that Lake Papineau is relatively inelastic and therefore could be sensitive to changes in precipitation and temperature. This could be due to its relatively limited QGW_i. More analyses are under way to outline the implications under long-term climate change conditions.
Impacts of climate change, coastal storms, and seawater overwash on the fresh groundwater resources of Sable Island, Nova Scotia
* Julia Cantelon, Dalhousie University , Canada
Barret Kurylyk, Canada
"Coastal zones host unique ecosystems and attract dense human populations; however, they are the most vulnerable region to anthropogenic climate change. Sea-level rise and an incresing frequency of high-intensity storms is driving increased incidents of wave overwash in coastal zones. The ensuing surface flooding and erosion have severe consequences, including the contamination of fresh groundwater resources from the infiltration of seawater. Previous investigations have documented the impact of and recovery from coastal flooding events, but have been largely restricted to atoll island environments, limited in the spatial and temporal resolution of data, and have often overlooked hydrodynamic (wave and surge height) and morphodynamic drivers. This study presents data from an intensive field investigation monitoring coastal hydrodynamics, morphological change, and the associated salinization and recovery of fresh groundwater resources in response to extreme storms. Located in the Northwest Atlantic Ocean, Sable Island is a small, low-lying island designated as a Canadian National Park Reserve. This site is relatively pristine, has a long time series of environmental data, experiences strong forcing from ocean processes and changing climate and morphology, and is particularly susceptible to seawater overwash and concomitant salinization from Atlantic hurricanes. We used high-precision near-shore and offshore wave loggers, geophysical surveys, and a network of shallow monitoring wells instrumented with loggers for temperature, electrical conductivity, and pressure to capture coastal hydrodynamics and groundwater salinization in response to post-tropical storms Dorian (2019) and Teddy (2020). Results show subsurface salinization persists far beyond surface flooding in both space and time. Also, the island’s aquifer experiences prolonged recovery (flushing) in comparison to previous studies of island aquifers due to Sable Island’s high-energy beach environment. Results from this investigation are critical to enhance our understanding of freshwater resource vulnerability in coastal zones and provide valuable insights for the management of small-island, freshwater resources."
Factors for Optimized Wetlands Design for Oilsands Process Water
* Tan Vu Bui, University of Saskatchewan, Canada
Amira Abdelrasoul, Canada
Dena W. McMartin , Canada
The oilsands mining industry in Canada generates vast amounts of wastewater, known as oilsands process water (OSPW), which is acutely and chronically toxic to various aquatic biota primarily due to interactions with naphthenic acid fraction compounds (NAFCs). Furthermore, the complexity of OSPW creates challenges for treatment using conventional methods. Constructed wetlands (CW) have the benefits of harnessing an array of physical, chemical and biological treatment mechanisms that are proven effective for OSPW remediation. Along with high treatment potential, CW is a lower-cost, low-energy, ecologically friendly process requiring minimal operational attention. Two major issues of CW are temperature and climate sensitivity and the need to optimize specifically for degradation and removal of recalcitrant NAFCs. CW can be designed as site-specific engineered systems, with tailored operating and physical conditions in place to maximize its potentialities. This presentation provides an overview of the technical features and optimization methods available for enhancing CW performance in cold climate with an emphasis on removing NAFCs.
Impact of climate change in frozen soils and its effect on continental-scale hydrology of Nelson Churchill River Basin
* Ajay Bajracharya, University of Manitoba, Canada
Tricia Stadnyk, Canada
Mohamed I. Ahmed, Canada
Hervé Awoye, Canada
Masoud Asadzadeh, Canada
Hydrological models are essential tools to analyze hydrological processes in cold regions, such as permafrost, seasonally frozen soil, and snow cover. Frozen soil and permafrost processes play critical roles in runoff generation by restricting the infiltration during the frozen state and thawing during the melting phase. Therefore, an accurate representation of these processes in hydrologic models is critical for modelling the projections under climate change and reducing the uncertainty associated with estimating the freshwater runoff. In this research, the frozen soil infiltration incorporated in the HYPE model is modified by discretizing the conventional 3-soil layers scheme to a finer soil layer discretization. Each soil layer is discretized up to 5 sub-layers. This structural change allows the model to execute soil-water balance calculations at each discretized soil layer for improved simulation of such components and the runoff generation. The modified HYPE-NCRB model will be used to project climate change impacts on soil moisture, soil temperature, and implications on model uncertainty associated with streamflow projections. The model will be forced with new state-of-the-art CMIP6 GCM climate models and scenarios for future projection of water balance components for the climate change study.