Jan A. Derecki

Effect of Channel Changes in the St. Clair River During the Present Century

Abstract Periodic man-made changes in the outlet of Lake Huron through the St. Clair River date back to the middle of the last century. These artificial channel changes have been well documented during the present century. They consist of dredging for commercial gravel removal in the upper river during 1908–25 and uncompensated navigation improvements for the 7.6-m (25-ft) and 8.2-m (27-ft) projects completed in 1933 and 1962, respectively. The total effect of these changes on the levels of Lakes Michigan and Huron (hydraulically one lake) and on the upper St. Clair River profile was determined with dynamic flow models. The ultimate effect of the above dredging was a permanent lowering of the Lake Michigan-Huron levels 0.27 m (0.89 ft), which represents a tremendous loss of freshwater resource [32 km 3 (7.7 mi 3 )].

Stability Effects on Great Lakes Evaporation

Abstract The effects of atmospheric stability on Great Lakes evaporation computed by the modified mass transfer method have been evaluated by analysis of stability effects on the variable mass transfer coefficient, land to lake data adjustments, and ice-cover reduction of evaporation during winter. The Great Lakes which produce extreme results, Lakes Superior and Erie, and a much smaller water body within the Great Lakes chain, Lake St. Clair, were studied. Comparison of these evaporation estimates with previous studies, which excluded variable stability effects, shows that the previous studies of Lake Superior produced generally similar total annual water loss from the lake, but significantly overestimated both the seasonal high evaporation and the condensation rates. These tended to balance each other. The atmospheric conditions over Lakes Erie and St. Clair do not become as strongly stable and they normally do not exhibit large condensation. Previous evaporation studies for these lakes indicate generally higher evaporation rates, with significant overestimation of the total annual water losses (25%).

Comparison of Measured and Simulated Flows During the 15 December 1987 Detroit River Flow Reversal

Abstract Flow reversals in the Detroit River are unique hydraulic phenomena which disturb the normal flow patterns and which may cause high concentrations of waterborn pollutants by temporarily blocking their downstream transport and dilution. Until recently, flow reversals in the river have been implied from water level relationships and unsteady numerical flow models, but not directly measured. An acoustic Doppler current profiler deployed on the river bottom at Ft. Wayne, in Detroit, has provided the first opportunity to directly measure a flow reversal, which occurred for about 3 hours on 15 December 1987. The meter provided continuous measurements of the vertical velocity distribution for approximately 1-m depth segments in the overhead water column at quarter-hour intervals. These measurements provided an ideal data set to analyze river dynamics associated with flow reversals and to evaluate the importance of major factors necessary for the occurrence of flow reversals in the river. It was found that reasonably accurate simulation of flow reversals with the unsteady flow models require the inclusion of surface wind shear and the use of small time increments that are much shorter than the standard hourly water level data. Model simulation with specially obtained 5 and 15 minute water level and wind data produced generally similar model flows that are reasonably close to the measured values. Because short-period (15 minute or less) wind and water level data are not readily available, river flow reversals simulated using hourly data may be significantly underestimated.

Great Lakes Beginning-of-Month Water Levels and Monthly Rates of Change of Storage☆

Abstract Time series of beginning-of-month water levels and rates of change of lake storage were determined for each of the Great Lakes and Lake St. Clair for 1941-1975 period. The Thiessen polygon procedure was used to compute the beginning-of-month levels because it provides more representative over-all lake levels than straight averaging and requires minimum subjectivity. The effect of crustal movement on the rate of change of lake storage was investigated and found to be negligible. A gage density analysis showed good agreement between various size gage networks with the maximum deviation between networks decreasing with increasing gage density. Thiessen polygon weighting factors are presented for the current gage networks to enable future extension of the time series.

Estimates of Lake St. Clair Evaporation

Abstract Monthly evaporation from Lake St. Clair was determined for individual years of a 26-year period, 1950-75, by the mass transfer method applied to available land-based data adjusted to overwater conditions. Because of extensive ice cover on the lake, the overwater mass transfer results were adjusted for the effect of ice cover during winter. The ice-cover adjustment reduced the average annual evaporation by 100 mm to 750 mm. The mass transfer method is the only technique that permits operational evaporation estimates from this lake with presently available data and it is also the approach most amenable to future improvements.