Hourly Freshwater Discharge Data of the St. Lawrence River at Quebec City Calculated by the Qmec Model

CONTEXT

Freshwater discharge data of the St. Lawrence River at Quebec City as computed by the hydrodynamic model "Qmec" developed by Bourgault and Matte [2020a, 2020b]. This represents an important update to the earlier method of Bourgault and Koutitonsky (1999) currently in use by Fisheries and Oceans Canada (DFO) to produce monthly means (see: https://ogsl.ca/en/freshwater-runoffs-quebec-city-context/). The new method is more accurate for monthly means and has a much finer temporal resolution as it produces hourly tidal values, from 1962 up until today.

The method uses water level measurements from the Neuville (station 3280) and the Saint-Francois I.O. (station 3100) tidal gauges. The discharge data time series is updated when the water level archive database is updated by DFO for these stations, that is about twice a year. See: https://www.isdm-gdsi.gc.ca/isdm-gdsi/twl-mne/maps-cartes/inventory-inventaire-eng.asp?user=isdm-gdsi&region=MEDS&tst=1&perm=0

AVAILABLE DATASETS

Two datasets are available. The first set contains the instantaneous hourly discharge and the second the daily averages. Daily averages are calculated from hourly data by applying a Godin filter of the type A24-A24-A25 in order to remove the effects of semi-diurnal and diurnal tidal modulation. See Bourgault and Matte [2020a] for more details.

Note that missing discharge values ​​correspond to missing water level data at the Neuville tide gauge or that of Saint-François.

CALIBRATION COEFFICIENTS

The method requires the following four calibration coefficients (for details, see line H-2a in Table 2 of Bourgault and Matte [2020a]):

C(1) = 1947.6881 (the equivalent width, Be)
C(2) =   20.3646   (the equivalent depth, he)
C(3) =   -1.0785    (the hydraulic slope, delta zeta)
C(4) =    0.0416    (the friction coefficient, ne)

Note that the values ​​of these parameters differ slightly from the values ​​published in Table 2 of Bourgault and Matte [2020] (line H2-a). This is because a small change with no impact on data quality was made to the Qmec code after publication. For more details, see comments to lines 92-100 in the main code (Qmec.m), version 2.0 which is available at https://doi.org/10.24433/CO.7299598.v2 (see reference below in Bourgault and Matte [2020b]).

REFERENCES:

• Bourgault D et Matte P (2020a) A physically-based method for real-time monitoring of tidal river discharges from water level observations, with an application to the St. Lawrence River Journal of Geophysical Research – Oceans 125 e2019JC015992

• Bourgault D et Matte P (2020b) Qmec : a Matlab code to compute tidal river discharge from water level [Source Code]. https://doi.org/10.24433/CO.7299598.v2

• Bourgault D et Koutitonsky V G (1999) Real-time monitoring of the freshwater discharge at the head of the St. Lawrence Estuary Atmosphere-Ocean 37 203-220

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