Sedimentation dynamics within a large shallow lake and its role in sediment transport in a continental-scale watershed

Sediment sources and transport dynamics in large, regulated river systems with multiple lakes and reservoirs in the subarctic region of Canada

“…were identified as the two main sediment sources at the Lake Winnipeg outlets (Goharrokhi et al, 2021). The Red River suspended sediment samples were collected using a time-integrated suspended sediment sampler between May and November 2016.…”

“…Also, the average annual sediment accumulation rates for the cores were estimated using the depth-profiles of caesium-137 ( 137 Cs) concentrations. As these sediment cores were collected in 1997 and 1998, the chronology method based on the location of the 137 Cs fallout peak in the cores represents the average sediment accumulation rate for the period of 1963-1997/98 (for more details on the sediment dating methods using 137 Cs, see Goharrokhi et al, 2021).…”

“…Sediment source fingerprinting results at the Lake Winnipeg outlets indicate that <15% of the suspended sediment load in the outlets is from the Red River with the remainder being primarily derived from the erosion of the north shore of the lake. Approximately 600 Gg of sediment is exported from Lake Winnipeg into the UNR each year (Goharrokhi et al, 2021). Therefore, using colour and geochemical fingerprinting, $90 Gg year À1 (i.e., 15% of 600 Gg year À1 ) of the exported sediment is derived from the Red River sediment load.…”

“…With a surface area of 23 750 km 2 Lake Winnipeg is the 11 th largest freshwater lake in the world (Environment and Climate Change Canada and Manitoba Agriculture and Resource Development, 2020) and the third‐largest hydroelectric reservoir in the world (Environment Canada and Manitoba Water Stewardship, 2011). It comprises three distinct regions, the South Basin, Narrows, and North Basin with average depths of only 10, 7, and 13 m, respectively (Goharrokhi et al, 2021). It has been regulated to better match seasonal discharge to hydroelectric demand, within historical water levels, since 1976 mainly by constructing: (a) 2‐Mile and 8‐Mile Channels at the outlet and ~60 km downstream from the lake outlets, respectively; (b) the Jenpeg hydroelectric generating station (hereafter referred to as Jenpeg) ~100 km downstream of Lake Winnipeg; and (c) a control structure at Cross Lake (average depth = 4 m; surface area = 177 km 2 ; volume = 0.7 km 3 ; Coordinated Aquatic Monitoring Program [CAMP], 2008a) ~130 km downstream of Lake Winnipeg.…”

“…The UNR originates from Lake Winnipeg and, therefore, it receives a considerable amount of water from the Lake Winnipeg watershed. The outflow from the lake into the UNR passes through two outlets: (a) the relatively shallow natural outlet at Warren's Landing; and (b) the deeper 2‐Mile Channel which was constructed to improve hydraulic connectivity between the lake and the control structure at Jenpeg (Goharrokhi et al, 2021). Downstream of these outlets, the UNR splits into two channels which rejoin at Cross Lake.…”