9569 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I During Winter 2, Wick and Hawkins (1989) further investigated the relationship between stage and discharge by comparing water surface elevation change to changes in discharge in the main channel and in an embayment, with and without ice cover. The lowest main channel discharge measured was 142 cfs (4.0 ems) on December 15, 1987, and the highest was 340 cfs (9.6 ems) on March 3, 1988. Similar comparisons were made for an embayment, where ice thickness increased from 0.85 feet (25.9 cm) on December 15 to 2.12 feet (64.6 cm) on March 15. Water surface elevations increased throughout winter, compensating for a corresponding increase in ice thickness, and resulting in relatively stable effective depth. Effective depth varied only 0.1 feet (3.0 cm) between December 15 and February 17. In early March, effective depth increased 0.3 feet (9.1 cm) in response to a discharge of 340 cfs, then decreased dramatically by March 15, just prior to ice-out. This decrease in effective depth was caused by a drop in stage and bed changes resulting from increased water velocities along shorelines. These stage-discharge relationships demonstrate effects of different ice conditions on flow and river stage. As surface ice began to form, shoreline ice formed along the edge of the river, effectively reducing discharge while increasing water surface elevation (cross sectional area was reduced by ice mass controls). For example, relative stage height under . - ice-free conditions at a main channel cross section was 90.61 feet at a discharge of 236 cfs (6.7 cms). Relative stage height under ice on February 7, 1988 was 91.77 feet at 229 cfs (6.5 cms)--a change of 1.16 feet for only a 7 cfs change m discharge. Another set of measurements showing ice effect was a comparison of identical stage height at two drastically different discharges. Maximum relative stage height under ice was 92.14 feet on March 2, 12