Abstract:In some hydrological systems, mitigation strategies are applied based on short-range water temperature forecasts to reduce stress caused to aquatic organisms. While various uncertainty sources are known to affect thermal modeling, their impact on water temperature forecasts remain poorly understood. The objective of this paper is to characterize uncertainty induced to water temperature forecasts by meteorological inputs in two hydrological contexts. Daily ensemble water temperature forecasts were produced using the CEQUEAU model for the Nechako (regulated) and Southwest Miramichi (natural) Rivers for 1-5-day horizons. The results demonstrate that a larger uncertainty is propagated to the thermal forecast in the unregulated river (0.92-3.14 • C) than on the regulated river (0.73-2.29 • C). Better performances were observed on the Nechako with a mean continuous ranked probability score (MCRPS) <0.85 • C for all horizons compared to the Southwest Miramichi (MCRPS ≈ 1 • C). While informing the end-user on future thermal conditions, the ensemble forecasts provide an assessment of the associated uncertainty and offer an additional tool to river managers for decision-making.

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Evaporative flux is a key component of hydrological budgets. Water loss through evapotranspiration reduces volumes available for run‐off. The transition from liquid to water vapour on open water surfaces requires heat. Consequently, evaporation act as a cooling mechanism during summer. Both river discharge and water temperature simulations are thus influenced by the methods used to model evaporation. In this paper, the impact of evapotranspiration estimation methods on simulated discharge is assessed using a semidistributed model on two Canadian watersheds. The impact of evaporation estimation methods on water temperature simulations is also evaluated. Finally, the validity of using the same formulation to simulate both of these processes is verified. Five well‐known evapotranspiration models and five evaporation models with different wind functions were tested. Results show a large disparity (18–22% of mean annual total evapotranspiration) among the evapotranspiration methods, leading to important differences in simulated discharge (3–25% of observed discharge). Larger differences result from evaporation estimation methods with mean annual divergences of 34–48%. This translates into a difference in mean summer water temperature of 1–15%. Results also show that the choice of model parameter has less influence than the choice of evapotranspiration method in discharge simulations. However, the parameter values influence thermal simulations in the same order of magnitude as the choice of evaporation estimation method. Overall, the results of this study suggest that evapotranspiration and open water evaporation should be represented separately in a hydrological modelling framework, especially when water temperature simulations are required.

Sedimentation in navigable waterways and harbours is of concern for a number of water and port managers. One potential source of variability in sedimentation is the annual sediment load of the river that empties in the harbour. The main objective of this study was to use some of the regularly monitored hydro-meteorological variables to compare estimates of hourly suspended sediment concentration in the Saint John River using a sediment rating curve and a model tree (M5') with different combinations of predictors. Estimated suspended sediment concentrations were multiplied by measured flows to estimate suspended sediment loads. Best results were obtained using M5' with four predictors, returning an R 2 of 0.72 on calibration data and an R 2 of 0.46 on validation data. Total load was underestimated by 1.41% for the calibration period and overestimated by 2.38% for the validation period. Overall, the model tree approach is suggested for its relative ease of implementation and constant performance. Estimation de la concentration en sédiments en suspension dans lefleuve Saint-Jean par courbes de transport sédimentaire et à l'aide d'une approche par apprentissage machine Résumé La sédimentation dans les voies navigables et installations portuaires constitue une préoccupation importante pour les gestionnaires de l'eau. L'apport annuel qui provient du bassin versant et qui finit sa course dans le port représente l'une des sources possibles de la variabilité de cette sédimentation. Le principal objectif de la présente étude est de comparer les valeurs d'estimation horaire de la concentration en sédiments en suspension dans le fleuve Saint-Jean à partir d'une courbe de transport sédimentaire et d'un arbre de modèle (M5'). Pour ce faire, diverses combinaisons de variables hydrométéorologiques couramment utilisées ont été testées. Les concentrations estimées ont été multipliées par les débits mesurés pour obtenir des charges. Les Downloaded by [New York University] at 22:22 22 June 2015A c c e p t e d M a n u s c r i p t meilleurs résultats ont été générés à l'aide du modèle M5' à quatre prédicteurs avec un R 2 de 0,72 en période de calage et de 0,46 en période de validation. La charge totale a été sous-estimée de 1,41 % en période de calage, alors qu'elle a été surestimée de 2,38 % en période de validation. En somme, l'approche M5' est recommandée en raison de son implémentation relativement simple et de ses performances constantes.