3.2.2 River Discharge

Information on river discharge is needed to optimize the design of various types of structures such as bridges, culverts, pipeline crossings, dams, reservoirs, hydroelectric plants, dykes and other water-related industrial structures. River discharge represents the volume of water per unit time as measured at a given location along a waterway. Historical datasets on river discharge rely mainly on in situ measurement of water level, which is converted to discharge using a rating curve (i.e. a stage-discharge relationship). River discharge measurements integrate over space and time at the catchment-scale efflux of freshwater to the coastal ocean. It also transports heat, sediments, dissolved oxygen, nutrients and contaminants to the coastal ocean. River discharge, like other hydrometeorological variables, responds to climatic change and variability. In particular, rising air temperatures and changes in precipitation patterns affect river discharge. Anthropogenic activities including fragmentation of river systems through dams, reservoirs and diversions, in addition to land use and land cover changes, also impact river discharge. As such, many data providers report whether a given site is considered regulated or “natural”. The Water Survey of Canada also maintains a series of hydrometric gauges that are part of the Reference Hydrometric Basin Network (RHBN) with minimal human influences. The RHBN sites are particularly useful to assess the impacts of climate change on river discharge.

The following table summarizes the river discharge datasets in northern Canada.

Forthcoming datasets: The Surface Water and Ocean Topography (SWOT) mission, scheduled to launch in 2022, is an international satellite program that will survey 90% of the Earth's surface water, observe the fine details of the ocean's surface topography, and measure how lakes, rivers, reservoirs and oceans are changing over time. One of the hydrology objectives is to evaluate discharge variations in rivers. SWOT will provide complete coverage of most lakes and rivers up to four times every three weeks, including northern Canada, where very few measurements are currently available. This first global inventory of Canadian waters will serve to improve our water management and assist in prediction of floods and drought (https://www.asc-csa.gc.ca/eng/satellites/swot.asp ).

Appropriate use of data: There are several options available to researchers and end users in regards to river discharge data in northern Canada. For the most part, however, there are few overlaps in terms of spatial or temporal coverage between the various datasets identified in Table 3.14. In Canada, the primary data provider for daily river discharge is the Water Survey of Canada that operates most hydrometric gauges across Northern Canada in conjunction with its territorial and provincial partners. Record lengths and continuity vary between sites, but generally good records exist starting from the 1960s onward for northern Canada’s primary waterways. Spatial coverage degrades moving northward across the three territories and is especially poor across the Canadian Arctic Archipelago. Data quality varies throughout the year, with degraded measurements during ice-on and backwater conditions or during high flows. Some hydrometric gauges remain operational only during the warm season as smaller waterways may freeze to the bottom in winter or measurements are particularly difficult underneath the ice cover. R-ArcticNet assembles all available Water Survey of Canada data, along with other international agencies, in a user-friendly, web-based portal but temporal coverage ends in 2000. This database has the advantage of providing simple graphics of river discharge time series and hydrographs of mean monthly flows, plus overall discharge statistics along with relevant site metadata.

Discharge measurements are also available for regulated waterways from several hydropower companies. These data, however, are often not available from the Water Survey of Canada’s Hydrometric Database (HYDAT), remain unpublished and/or are considered proprietary. Nevertheless, data can generally be acquired upon request from the hydropower companies. Additional discharge data are available in northern Québec/Nunavik through the provincial Centre d’Expertise Hydrique du Québec (CEHQ) and from the Yukon Government’s Water Resources Branch, which are not necessarily available on HYDAT. Experimental watersheds have also been established at several sites in the Canadian Arctic by university researchers filling key gaps in other networks. These records, however, are relatively short in duration, typically spanning no more than one to two decades.

Model-based and reanalysis gridded products provide continuous runoff datasets across all land surfaces. Distinct advantages of these datasets are their complete temporal and spatial coverage across northern Canada spanning multiple decades. However, the datasets often just provide runoff at the grid-scale rather than routed streamflow at the watershed-scale. Their relatively coarse spatial scale may impede their application for smaller watersheds. Due to model inaccuracies and the lack of robust validation studies, these datasets are to be used with caution and only when observational data are lacking.

Thus preference is given to Water Survey of Canada observational data where and when available. When insufficient or simply unavailable, other sources including from hydropower companies, experimental watersheds maintained by academic institutions and government agencies, and reconstructed streamflow data may be employed. In all cases, however, users should be aware of potential errors, biases or deficiencies in all datasets and apply them with caution.

References – Hydrology data

Muñoz-Sabater, J., E. Dutra, A. Agustí-Panareda, C. Albergel, G. Arduini, G., Balsamo, S. Boussetta, M. Choulga, S. Harrigan, H. Hersbach, B. Martens, D. G. Miralles, M. Piles, N. J. Rodríguez-Fernández, E. Zsoter, C. Buontempo, and J.-N. Thépaut, 2021: ERA5-Land: A state-of-the-art global reanalysis dataset for land applications. Earth System Science Data, 13(9), 4349-4383, https://doi.org/10.5194/essd-2021-82..