Use of current meters for continuous measurement of flows in large rivers

Abstract

Flows in the unregulated Great Lakes connecting channels, the St. Clair and Detroit Rivers, are normally determined using mathematical flow models with calibration based on periodic discharge measurements taken during the open‐water seasons. Consequently, the calculated flows normally exhibit good accuracy during ice‐free periods, but may contain large errors during winter months with extensive ice cover. The St. Clair River is particularly prone to large ice jams because of practically unlimited ice flow supply provided by Lake Huron and an extensive river delta that retards the passage of these ice flows. This study describes the experimental results of continuous flow measurements using electro magnetic (EM) current meters and an acoustic Doppler current profiler (ADCP) meter during the 1983–1985 period. A record ice jam in the St. Clair River occurred in April 1984 and provided an excellent opportunity for testing the current meter program. Verification of current meter results was provided by flows transferred from the Detroit River, which was ice‐free and permitted accurate flow simulation. The current meter flow measurement program illustrated high consistency of exponential (logarithmic) vertical distribution of velocities. Results indicate that accurate estimates of mean river flows can be obtained with a single well‐placed current meter. However, the EM current meters are direct contact single‐point sensors that are affected by frazil ice during winter and weed effects during most of the year. The ADCP meter is a remote sensor of velocities in the overhead water column and is not affected by the frazil ice and weed problems.