Additional information on SDAC

• The development of drainage areas
• Development work in the 2000s
• The National Scale Frameworks Hydrology -Drainage Areas, Canada, Version 5.0
• Standard Drainage Area Classification (SDAC) 2003
• Classification variant: Drainage Regions - SDAC 2003
• Future development

The development of drainage areas^{Footnote 1}

The Water Survey of Canada (WSC) developed, in 1922, a Water Resources Index Inventory as a convenient and logical system for recording and filing water resources data such as the location of waterpower sites, waterpower developments, storage reservoirs, stream measurement stations, and meteorological stations. The Water Survey of Canada delineations involved the division, sub-division and sub-sub-division of Canada into suitably sized areas based on drainage characteristics, for administrative purposes. Although the boundaries are based on drainage, the intent was to include all of Canada's land mass and waters within this drainage area hierarchy to facilitate the identification of hydrometeorological sites. Therefore, the WSC drainage areas do not necessarily define individual river basins, but can represent intervening areas along the coast or include islands.

By the 1980s, there were different digital versions of Canadian drainage areas:

1. Environment Canada produced a digital file of the paper map (1:2M scale) depicting the WSC drainage area boundaries;
2. Statistics Canada digitized the WSC boundaries separately and integrated them with a base derived from the Census files. This digital version of the WSC maps was used for the tabulation of environmental statistics by drainage area starting in the 1980s;
3. In 1985, the National Atlas of Canada produced a separate digital version tied to its 1:7.5M base and integrated this to produce paper maps for the 5th Edition of the National Atlas of Canada. This digital file depicts the drainage basins for many of the larger rivers of Canada. The National Atlas basin hierarchy has five levels (ocean drainage area, major river basin, component basin, sub-component basin, and sub-sub-component basin) and the major criterion used to define a National Atlas basin was a mean annual discharge of at least 280 m3/s at the mouth or confluence of the river;
4. Several agencies (e.g., the Prairie Farm Rehabilitation Administration), provinces, and other authorities have compiled local digital drainage area boundaries.

In addition, large hydroelectric projects (e.g., James Bay) have had a significant impact on the hydrologic base and such changes were not maintained in a uniform manner. As a result, there was not a consistent, integrated, and up-to-date set of drainage area boundaries at the national level and it became time-consuming to work with other projects based on different boundaries.

The development of drainage areas is described in the sections below. The relationship between those drainage areas is also presented in the diagram showing the Hierarchy of drainage areas.

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Development work in the 2000s

In 2000, Natural Resources Canada (NRCan), Environment Canada (EC) and Statistics Canada formed a partnership with an objective of producing one single national drainage area coverage for the country at a scale of 1:1,000,000. Each agency involved had specific requirements for the result, and certain design goals to be met. Since there were one set of drainage areas defined by Environment Canada and another by NRCan, it was agreed that a major goal for the project would be to support both definitions.The project resulted in a single national scale framework supporting the two distinct classification schemes.

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The National Scale Frameworks Hydrology - Drainage Areas, Canada, Version 5.0

The single national scale framework for drainage areas, largely based on the WSC drainage area boundaries at the sub-sub-drainage area level, contains three drainage area datasets. There are the WSC, the National Atlas and the Fundamental Drainage Area (FDA) datasets.

Even though there is a high degree of similarity between the WSC classification and the National Atlas classification - approximately 95% of the National Atlas boundaries are also WSC boundaries - meaning that, with few exceptions, the National Atlas basins can be derived from the WSC sub-sub-drainage areas, it is necessary to introduce a smaller unit in order to reconcile both classifications. That is the purpose of the FDA dataset, to allow data to be aggregated to either of the two classifications. In general, these fundamental units are the same as the WSC sub-sub-drainage areas, but some sub-sub-drainage areas have been split to accommodate the following situations:

1. Water Survey and Atlas units do not match;
2. Identifying areas of internal drainage; and
3. Inconsistencies in the flow hierarchy.

As specified above, the WSC hierarchy was designed for administrative purposes. Each level of hierarchy has its own code and name with a systematic coverage for Canada.

In contrast, the National Atlas of Canada's hierarchy defines basins whose outflow exceeds a certain criterion. At its highest level, it does divide the complete country into five ocean drainage areas but at lower levels the basins do not cover the entire country. This makes it unsuitable for use as a geographic standard for statistical reporting.

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Standard Drainage Area Classification (SDAC) 2003

Version 5.0 of the WSC dataset from the National Scale Frameworks Hydrology - Drainage Areas, Canada is used by Statistics Canada as the basis for the Standard Drainage Area Classification (SDAC) 2003. In the drainage area classification of this Frameworks dataset, Canada has eleven major drainage areas which are divided into 164 sub-drainage areas; the 164 sub-drainage areas are then further divided into 978 sub-sub-drainage areas. All drainage areas, sub-drainage areas and sub-sub-drainage areas are named and have an identifying code. This classification is used by Statistics Canada as the basis for the Standard Drainage Area Classification (SDAC) 2003. The Standard Drainage Area Classification (SDAC) 2003 also contains the major drainage areas, sub-drainage areas and sub-sub-drainage areas but with the following modifications:

• Some drainage areas in the Frameworks dataset straddle the Canada-United States border; the Standard Drainage Area Classification (SDAC) 2003 includes only the parts within Canada since this is used for reporting Canadian data. The SDAC 2003 excludes 4 of the sub-sub-drainage areas that are entirely outside the boundary of Canada. Therefore, the Standard Drainage Area Classification (SDAC) 2003 contains only the 974 sub-sub-drainage areas that are within Canada.
• The Great Lakes were not assigned a drainage area in the Frameworks dataset; Canadian islands in the Great Lakes are assigned a drainage area in the Standard Drainage Area Classification (SDAC) 2003 for the purposes of data reporting.

The Frameworks dataset as well as the SDAC classification cover all of Canada including islands and freshwater lakes; however, the classification does not cover marine water.

The concept of drainage area is used in Statistics Canada's environmental and agricultural statistics programs. Generally, the detailed level of the sub-drainage area is used for disseminating statistics. Exceptions include "A Geographical Profile of Manure Production in Canada, 2001", a research paper in which data are presented at the sub-sub-drainage area level for only those areas with livestock farming activities.

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Classification variant: Drainage Regions - SDAC 2003

The variant Drainage Regions has three levels: 5 ocean drainage areas, 25 drainage regions and 974 sub-sub-drainage areas. The drainage regions in this classification variant are based on the major river basins depicted in "Currents of Change: Final Report of the Inquiry on Federal Water Policy", Environment Canada, a report prepared in 1985 by Peter H. Pearse, Françoise Bertrand, and James W. MacLaren. The drainage regions were developed to provide a good representation of the hydrology in Canada and can be built-up from the sub-sub-drainage areas of the Standard Drainage Area Classification (SDAC) 2003. The ocean drainage areas that form a classification level in the variant are based on the ocean drainage areas in National Scale Frameworks Hydrology - Drainage Areas, Canada, Version 5. The twenty-five drainage regions are named and numbered as are the five ocean drainage areas, and the sub-sub-drainage areas.

The environmental statistics program in Statistics Canada uses drainage regions in its annual report "Human Activity and the Environment: Annual Statistics" to tabulate population and water resource characteristics. The drainage regions are also used for area sampling in environmental surveys. These regions are considered to provide a good representation of the hydrology in Canada^{Footnote 2}.

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Future development

NRCan has recently completed Version 6.0 of the National Scale Frameworks Hydrology - Drainage Areas, Canada. Statistics Canada has not participated significantly in the revision process, and has decided that there were not enough changes to justify adopting it. Statistics Canada will continue to use version 5.0 when disseminating data by drainage areas, until further notice.

In addition, NRCan is working on the National Hydro Network (NHN). The NHN is a hydrographic layer in GeoBase^{Footnote 3}, constructed using the best databases available in Canada, which improves the precision of drainage area boundaries and other hydrological components. The NHN works in cooperation with several provincial and territorial partners in the implementation of this project in their respective geographic areas. The NHN is being disseminated in progressive phases called completeness levels. The first national NHN coverage has been completed in 2008. At this point in time, Statistics Canada has begun collaborating with the NHN project.