what the widths mean
Licensed allocation: every current surface-water licence upstream (storage and power left out),
as an average m³/s. These are legal maxima; what is actually taken isn't published.
Reported use: what licence holders voluntarily report taking, as an average over the last 12
months, summed down the streams. Only licences someone reports for (their markers have a ring), so it is
a floor, not a total. Holders can report from "my licences" once logged in.
Measured flow: the latest daily mean discharge of a Water Survey of Canada gauge
(Oct 7), on the stretch of stream it sits on. Provisional.
Natural mean annual flow: modelled from the province's normal annual runoff (1961–1990) over the
land draining to each stretch, summed down the streams; rivers fed from beyond the map's area are scaled up by
their headwater streams; each gauge's long-term observed mean then corrects the model upstream of it.
Before that correction the model was within a factor of 2 of the observed mean at
84% of 116 gauges
(median model ÷ observed: 1.03).
It is "natural" only where nothing upstream holds or diverts water: below dams and lake outlets it is not.
Pressure: licensed allocation upstream as a share of natural mean annual flow, the measure the
province's water tools use. Low-flow months matter more than the annual mean, so a share well under 100% can
still mean little water in late summer.
Estimated flow today: natural mean flow times the nearest gauge's flow today relative to its own
natural mean. Wrong where dams, lakes or diversions shape the flow.