Supplementary material to "Ice jam formation at river confluences: comprehensive field investigation and comparison to laboratory-derived predictive equations"

Supplements S1 : Bras-du-Nord and Sainte-Anne confluenceThe 2022 breakup at STA-BDN initiated upstream in the main river and subsequently in the tributary, concluding at all sites between April 15 and 18. Ice jams formed upstream in both rivers.The BDN cleared one day before the STA, and the tributary's discharge constricted the passage of ice from the STA, resulting in the formation of an ice jam upstream of the 5 confluence in the main river.The results of the meteorological, hydraulic and ice conditions at STA-BDN during the 2022 breakup are presented in Fig. S1.Air temperatures remained positive from March 30 onwards (Fig. S1a).The breakup sequence occurred gradually from late March to mid-April (Fig. S1e, f).Ice began to disappear from the upstream site on the STA (STA6-US) around March 30.By 10 this date, the CDDT reached 101.2°C.D. while the CDDF reached 1176.4°C.D., resulting in a CDDr of 0.09 (Fig. S1b).Based on the rapid water level rise at the upstream site on the BDN (BDN8) on April 2 nd , breakup likely initiated at this site on that day (Fig. S1h).For the other sites on the STA, breakup began following 35 mm of rainfall on April 8 to 9 (Fig. S1c).On this date, discharge began increasing, starting at 16.0 m 3 s -1 in the STA and 13.3 m 3 s -1 in the BDN for a Qr of 0.83 (Fig. S1i).The CDDT reached 180.8°C.D. and the CDDr 0.15 (Fig. S1b).Breakup downstream of the confluence began on April 14, 15 coinciding with a 14 mm of rainfall (Fig. S1c).The season's maximum discharge in the STA was reached on this date at 97.5 m 3 s -1 , while the BDN maximum was reached on April 16 at 67.1 m 3 s -1 (Fig. S1i).An ice jam formed upstream in the STA (STA14) on April 11.On April 12, an ice jam also formed upstream of the ice control structure on the STA (STA6-US).Both jams released on April 15 within hours of each other.Based on the 0.5 m water level 20 peak at the upstream site in the tributary (BDN8) on April 13, an ice jam likely formed at this site (Fig. S1h).Rising water temperature at this site on April 14 indicated the tributary was ice free from that date, i.e. before the main river (Fig. S1g).With ice releases from upstream jams and ice runs on the STA while the tributary was ice free with constricted discharge, an ice jam formed at the confluence on April 15.This jam slowed ice evacuation from the STA, causing ice jams at STA6-DS on April 15 and at STA24 on April 16.When these jams released on April 17, ice runs reached the Chute-Panet Dam (STA0), 25 where they melted in place.All sites were ice free on April 18. Figure S1: Time series of hydrometeorological conditions during the 2022 breakup at STA-BDN (March 26 to April 21, 2022) showing a) air temperature, b) CDDT, CDDF and CDDr, c) daily precipitation, d) snow on ground, e) surface ice concentration, f) ice states, g) water temperature, h) water level above the pressure probe and i) discharge and Qr.