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Ecosystem‐based management of the Laurentian Great Lakes, which spans both the United States and Canada, is hampered by the lack of consistent binational watersheds for the entire Basin. Using comparable data sources and consistent methods, we developed spatially equivalent watershed boundaries for the binational extent of the Basin to create the Great Lakes Hydrography Dataset (GLHD). The GLHD consists of 5,589 watersheds for the entire Basin, covering a total area of approximately 547,967 km2, or about twice the 247,003 km2 surface water area of the Great Lakes. The GLHD improves upon existing watershed efforts by delineating watersheds for the entire Basin using consistent methods; enhancing the precision of watershed delineation using recently developed flow direction grids that have been hydrologically enforced and vetted by provincial and federal water resource agencies; and increasing the accuracy of watershed boundaries by enforcing embayments, delineating watersheds on islands, and delineating watersheds for all tributaries draining to connecting channels. In addition, the GLHD is packaged in a publically available geodatabase that includes synthetic stream networks, reach catchments, watershed boundaries, a broad set of attribute data for each tributary, and metadata documenting methodology. The GLHD provides a common set of watersheds and associated hydrography data for the Basin that will enhance binational efforts to protect and restore the Great Lakes.

This study evaluated the capability of four spatial hydrologic models to estimate summer lowflow stream discharge, as a surrogate for baseflow, and assessed the influence of land cover/land use on these flows, in small streams across the Oak Ridges Moraine. Low-flow discharge varied predictably with area of the upstream catchment, but also with reach slope and a measure of land cover disturbance (LDI). Low-flow volumes were lowest in streams with moderate agricultural and/or urban development (LDI of eight to 12%), and high over a range of development intensities. Each of Baseflow Index (BFI×Area), Darcy Index (DI), MODFLOW (MF) and a finer resolution MODFLOW model (FMF) were about equal in their capability to estimate low-flow discharge, with MF and FMF having a somewhat stronger relationship and Darcy Index having a somewhat poorer relationship, particularly in smaller catchments. Each of the models generally predicted low-flow discharge volumes to within about 400 L/s of the actual observed low-flow discharge. The models, therefore, were generally unable to predict whether a stream was flowing during periods of low-flow when the upstream catchment was smaller than about 17,800 ha. It was found that these methods cannot be reliably applied in small catchments as there is too much natural variability in flow conditions. This paper suggests that these methods do not reflect local conditions, but rather provide generalized information about water flows. As a result, it is recommended that until spatial model predictions are improved for local applications, water managers should invest in field surveys to confirm flow conditions in small catchments. Résumé : La présente étude avait pour objectif d'une part d'évaluer quatre modèles hydrologiques spatiaux afin d'en dégager la capacité d'estimation du débit d'étiage d'été, en tant que substitut du débit de base, et, d'autre part, d'évaluer l'incidence sur ces débits de la couverture terrestre et de l'affectation des terres dans les petits cours d'eau à l'échelle de la moraine d'Oak Ridges. Les débits d'étiage variaient de manière prévisible selon la zone du bassin hydrographique en amont, mais également selon la pente du bief et selon une mesure de la perturbation de la couverture terrestre (PCT). Les volumes en période que les prédictions du modèle spatial soient améliorées pour les applications locales, les gestionnaires de l'eau auraient intérêt à investir dans les études sur le terrain afin de confirmer les conditions d'écoulement dans les petits bassins hydrographiques.

The 2007 Brisbane Declaration and the Intergovernmental Panel on Climate Change have made recommendations for assessing the water resources of a hydrologic system as an integral part of hydrologic and hydraulic modeling. Considering these recommendations, it is necessary to understand the flow regime and available water resources. This paper describes the data sources and methods used to create a water quantity vulnerability index for the Southwestern Hudson Bay and Nelson watersheds in Ontario, Canada. The index was generated for 71 gauged watersheds of the Water Survey of Canada across the project area with an impact matrix being constructed from a set of 27 scale weighted streamflow and climate impact variables. Variables were specifically selected to represent the dimensions of water quantity exposure by describing the magnitude, frequency, duration and timing of flows. Vulnerability index values ranged between 21 and 24 with hydrologic regions of Far North West being lowest at 21. A database of water quantity statistics, impact matrix variables and estimated vulnerability indices has been created to serve water policy, planning and management staff.