Evolution of the National Streamflow Monitoring Network

The first observations in the Canadian National Archive of Hydrometric data were recorded in 1850, and the first flow observations begin in 1860.

Use the slider below the timeseries plot to watch the streamflow monitoring network evolve over time. Dots in the map represent locations where streamflow monitoring observations are available at a particular point in time, where the colour of the dot is mapped to the duration of the period of record up to the selected date.

Use the timeline to examine how the streamflow monitoring network changed through time.

The plot above shows the availability of daily streamflow observations over time in terms of distinct locations. The blue line represents the mean number of locations reporting daily streamflow observations each month, and the purple line represents the mean of each year. The red dot represents the number of locations observed at the time indicated by the slider. The slider below the plot can be used to select a date, and the red dot tracks the selected date in the timeline plot. A magenta star appears when a station's period of record has expired.

Adding the time dimension turns up interesting details of the humble origins of the network's first 50 years, with the most significant expansion in the 1960s, and a major contraction in the 1990s. The precipitous drop after 2020 does not represent total abandonment of streamflow monitoring, rather it reflects the amount of work required to collect, review, and publish the vast amounts of data generated by hydrometric monitoring programs. The oscillating trend in the blue line indicates the proportion of seasonal streamflow monitoring that gets paused through winter months.

Notes

1. Water Survey of Canada sets national hydrometric standards and is responsible for publication of water data.
2. The display uses derived station locations and observation periods from HYDAT, available through the National Archive of Water Data website.