Water Stewardship Information Sources

Citation Cole, A. 2013. Annual Unit Runoff in Canada. Agriculture and Agri-Food Canada.
Organization Agriculture and Agri-Food Canada
URL http://www.agr.gc.ca/atlas/supportdocument_documentdesupport/aafcAnnualUnitRunoff2013/en/AUR_Report_Final.pdf
Abstract/Description or Keywords Streamflow and runoff volumes are highly variable across Canada and are influenced by
local physiographic and climatic patterns. Many planning activities require the ability to
locate, evaluate, and quantify surface water supplies. This study aims to illustrate runoff
trends across the country by calculating annual unit runoff for a variety of probabilities of
exceedence commonly used by decision makers. Annual unit runoff is a measure of
runoff volume per square kilometre. This report uses units of cubic decametres (1000 m
per square kilometre (dam3
), which is equivalent to millimetres depth on the
Three previous unit runoff studies were undertaken by the Prairie Farm Rehabilitation
Administration, PFRA (which became the Agri-Environment Services Branch, AESB,
and then merged with Research Branch to become the Science and Technology Branch of
Agriculture and Agri-Food Canada):
1. “The Distribution and Variability of Runoff in Alberta, Saskatchewan, and
Manitoba”, completed in 1964 [1]
2. “Report on Median Annual Unit Runoff for the Prairie Province”, updated in
1978 [2]
3. “Annual Unit Runoff on the Canadian Prairies”, completed in 1994 [3].
The 1964 study included 230 Water Survey of Canada (WSC) hydrometric gauging
stations with effective drainage areas (EDA) smaller than 5,180 km2
and examined the
study period from 1911 to1956. The second study (1978) used 543 WSC stations without
any drainage area limit and examined the study period from 1912 to1972. The third
(1994) study included 397 stations with EDA less than 5,000 km2
and examined the
study period from 1950 to1989. The most recent two reports (1978 and 1994) included
isopleth maps of the median annual unit runoff (MAUR) – the runoff volume with 50%
probability of exceedence. The 1994 report also included isopleth maps for the 10%,
25%, 70%, 75%, 80%, and 90% probability of exceedence.
Additional hydrometric data and the availability of more sophisticated statistical and
mapping methods provide justification for the reworking and updating of these previous
reports to provide new isopleth unit runoff maps. Additional years of record also provide
an opportunity to expand the dataset that forms the basis for these maps. The Science and
Technology (S&T) Branch has also expanded its national presence and thus it is desirable
to expand the maps coverage to include as much of the country as the data will allow.
This study examines runoff measurements at hydrometric gauging stations for the period
1950 to 2006 (where possible) and reports the same seven probabilities of exceedence as
the previous 1994 report: 10%, 25%, 50%, 70%, 75%, 80%, and 90%.
Probability of exceedence refers to the chance of a unit runoff value being equaled or
exceeded in any one year. For example, an annual unit runoff of 50 dam3
at a 70%
probability of exceedence means that, in any given year, there is a 70% probability that
the annual unit runoff will be at least 50 dam3
/km2. streamflow, water yield
Information Type report
Regional Watershed Province
Sub-watershed if known
Aquifer #
Project status complete
Contact Name
Contact Email