Water quantity in Canadian Rivers indicators: data sources and methods, chapter 4


4. Methods

4.1 Categorizing Water Quantity at a Monitoring Station

Water quantity at a monitoring station is defined based on historical data recorded for Water Survey of Canada hydrometric stations. To start, frequency distributions for each day of the year were calculated using water flow data collected from 1981 to 2010 at each monitoring station. A 30-year period is used to provide a picture of the hydrologic characteristics of a station, while maximizing the number of stations included in the indicators.

Water quantity categories were defined from the frequency distributions:

Low < 25th percentile

25th percentile ≤ Normal ≤ 75th percentile

High > 75th percentile

Daily water quantity records for 2001 to 2013 were categorized as low, normal or high by comparing the measured value to the percentiles calculated for the corresponding station and day of the year over the normal period. Thus, a station described as having a low water level on, for example January 31, had a measured value ranking among the lowest 25% of values observed for each January 31 from 1981 to 2010.

A station's status for a year is the category most often observed (the mode) at a given station in a given year. Thus, a low classification does not mean that water quantity was consistently low throughout the year; it only means that low water quantity conditions were most often observed.

For the national indicator, the percentage of stations classified as low, normal and high was calculated for each year from 2001 to 2013.

Number of water quantity monitoring stations grouped by drainage region, 2013
Drainage region Number of stations
Pacific Coastal (1) 31
Fraser-Lower Mainland (2) 42
Okanagan-Similkameen (3) 19
Columbia (4) 50
Yukon (5) 18
Peace-Athabasca (6) 42
Lower Mackenzie (7) 36
Arctic Coastal-Islands (8) 6
Missouri (9) 39
North Saskatchewan (10) 16
South Saskatchewan (11) 55
Assiniboine-Red (12) 85
Winnipeg (13) 18
Lower Saskatchewan-Nelson (14) 42
Churchill (15) 18
Keewatin-Southern Baffin (16) 3
Northern Ontario (17) 17
Northern Quebec (18) 7
Great Lakes (19) 163
Ottawa (20) 28
St. Lawrence (21) 46
North Shore-Gaspé (22) 17
Saint John-St. Croix (23) 8
Maritime Coastal (24) 8
Newfoundland-Labrador (25) 52

4.2 Calculating the Regional Water Quantity in Canadian Rivers indicator

The Regional Water Quantity in Canadian Rivers indicator generalizes the water quantity classification across Canada's drainage regions.Footnote [1] For this indicator, where possible, the most downstream monitoring station of an inland drainage region was chosen to determine the water quantity category for that drainage basin. Where more than one most downstream station was identified for a drainage region, such as in coastal areas, the classification representing the greatest percentage of the drainage region was used. For example, one water quantity monitoring station at the most downstream point of the North Saskatchewan Drainage Region is sufficient to characterize water flowing out of this drainage region. In contrast, four stations were necessary to characterize water quantity in the Saint John-St. Croix drainage region (Figure 2).

Although all water flowing from a drainage basin may not be captured by this collection of long-term stations, the percentage area of the basin gauged provides an estimation of the level of certainty associated with the results.

Figure 2. Illustration of regional station selection

Drainage regions
Long description

The map on the left illustrates how one water quantity monitoring station at the most downstream point of the North Saskatchewan drainage region is used to characterize water flowing out of this drainage region. The map on the right illustrates how four stations were used to characterize water quantity in the Saint John-St. Croix drainage region.


Number of most downstream, long-term water quantity monitoring stations used to classify water quantity for each drainage region, 2013
Drainage region Regional water quantity category Number of monitoring stations used Percentage of drainage region area gauged
Pacific Coastal (1) Normal 24 25
Fraser-Lower Mainland (2) Normal 4 90
Okanagan-Similkameen (3) Normal 2 99
Columbia (4) Normal 3 100
Yukon (5) High 11 51
Peace-Athabasca (6) Normal 4 83
Lower Mackenzie (7) Normal 6 97
Arctic Coastal-Islands (8) n/a 6 4
Missouri (9) Normal 9 77
North Saskatchewan (10) High 1 87
South Saskatchewan (11) High 2 79
Assiniboine-Red (12) High 9 86
Winnipeg (13) Normal 3 94
Lower Saskatchewan-Nelson (14) High 8 88
Churchill (15) Normal 4 90
Keewatin-Southern Baffin (16) Low 3 24
Northern Ontario (17) Normal 10 37
Northern Quebec (18) High 7 19
Great Lakes (19) Normal 96 33
Ottawa (20) Normal 10 89
St. Lawrence (21) Normal 38 52
North Shore-Gaspé (22) Normal 14 21
Saint John-St. Croix (23) Normal 4 22
Maritime Coastal (24) Normal 13 11
Newfoundland-Labrador (25) Normal 46 14

Note: The percentages of the drainage regions gauged are based on the number of water quantity monitoring stations with more than 30 years of data (long-term station) used for this analysis and do not reflect the actual percentage of the drainage region gauged by Environment and Climate Change Canada's water quantity monitoring network. Values are based on the Canadian portion of the drainage basins only. Provisional data for the Maritime Coastal drainage region were used for this indicator, resulting in data for 13 stations, compared to 8 stations for the local indicator. n/a = not available.


Figure 3. Location of water quantity monitoring stations used to calculate the Regional Water Quantity in Canadian Rivers indicator, 2013

Map of Canada
Long description

The map shows the location of each of the 337 Canadian water quantity monitoring stations used to characterize water quantity in each drainage region.


Note: Natural stations are those where human activity upstream of the station has little impact on water flows. Regulated stations have water withdrawals, dams, diversions or other structures upstream that may change the water quantity in the river. Water quantity data for seasonal stations are only collected for part of the year.
Source: Environment and Climate Change Canada (2015) Water Survey of Canada.

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