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](https://doi.org/10.1029/2019JC015992), [2020b](https://doi.org/10.24433/CO.7299598.v2)]. This represents an important update to the earlier method of Bourgault and Koutitonsky ([1999](https://doi.org/10.1080/07055900.1999.9649626)) 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](https://doi.org/10.1029/2019JC015992)] 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](https://doi.org/10.1029/2019JC015992)]):

    C(1) = 2058.1776  (the equivalent width, Be)
    C(2) =   19.1713  (the equivalent depth, he)
    C(3) =   -1.0897  (the hydraulic slope, delta zeta)
    C(4) =    0.0401  (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](https://doi.org/10.1029/2019JC015992)] (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](https://doi.org/10.24433/CO.7299598.v2)]).


**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](https://doi.org/10.1029/2019JC015992) 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](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](https://doi.org/10.1080/07055900.1999.9649626) Atmosphere-Ocean 37 203-220

Organization: St. Lawrence Global Observatory