Session K.pdf - Clarkson University

Fig. 1. Aerial view of the area from Limestone Generating Stationto Sundance Rapids and the anchor ice damWINTER OBSERVATIONS OF ANCHOR ICE FORMATIONField observations have been made by Manitoba Hydro since 1997. It has been observedthat the anchor ice dam staging effect generally starts in mid-November due to the suddenair temperature drop. The water discharge typically varies in daily cycles rangingfrom about 1,500 to 4,500 m 3 /s. Frazil ice attachment to the bed is usually the mainmechanism for anchor ice growth. Due to the daily cycling of the station outflow, theice dam is formed by a combination of anchor ice and aufeis growth. Anchor ice andborder ice upstream of the Rapids can release and contribute to the development of theice dam. The mechanisms that contributed to the ice dam formation in the SundanceRapids are considered to include: 1) anchor ice growth by frazil attachment and supercoolingeffect; 2) aufeis growth; and 3) anchor ice and border ice released from upstream.The resulting ice dam effectively closes off 80 to 90% of the channel width, restrictingflow except a few small opening slots and resulting in up to a 1.5 m increase intail water level at the station by the end of winter (Manitoba Hydro 2000).57.00056.000Elevation (m)55.00054.00053.000Observed Data onNovember 1999Open WaterRating Curve52.00051.0000.0 1000.0 2000.0 3000.0 4000.0 5000.0discharge (m 3 /s)Fig. 2. Limestone tailrace staging during November 1999324