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Oak Ridges Moraine Groundwater Program

Hydrograph separation

a regional look

Spatial distribution

Hydrographs from over 200 stream gauges within our jurisdiction, all having greater than a 10 year period of record occurring sometime since the year 2000 and that is more than 75% complete, have been separated into their slow flow and quick flow components. Within our jurisdiction, it is assumed that the majority of slow flow (by volume) originates from groundwater sources, i.e., springs, seeps, losing reaches, etc.

Below are a number of pie charts, one for every gauge showing the relative proportion of slow flow (in brown) to quick flow (in blue). The diameter of the pie relates to the magnitude of total annual stream flow.

click on any pie chart to reveal station properties. Full-screen available in the top-left corner

please be patient while the map loads

The slow flow portion $(b)$ of the hydrograph is estimated as the median baseflow estimate of 14 automated hydrograph separation techniques.


Below, the results from these gauges are summarized as histograms, revealing that two thirds of observed (total) stream flow comes from groundwater sources, which amounts to roughly 220 mm/yr, a quarter of annual precipitation.