Dam69, Grand Rapids, Michigan


On Wednesday afternoon in Grand Rapids, Michigan, a three-person boat became stuck at a dam on the Grand River near 6th Street Dam – all three people managed to safely escape and swim away before it sank completely.

The concentration pattern at the study site appears to correlate more closely with sediment supply than with water velocity; however, seasonal differences can be detected in terms of delivery and transport of sediment delivery and transport. For instance, during spring freshet of 2003 there was an unexpectedly large increase in sediment delivery that took weeks to arrive at the study site, while more modest freshet events in 2004 and an extreme freshet event in 2005 both contributed sediments that contributed significantly to long transport lanes during this timeframe.

An intuitive model where sediment enters and passes through a freshwater reach on a weekly timescale appears accurate when considering normal hydrologic conditions in adjoining watersheds; however, attenuation or storage during extreme tributary high-flow events could significantly reduce exports predicted by this approach. It is therefore possible that previous estimates of annual or seasonal sediment delivery from tributaries and Federal Dam to ETM and harbor may have been considerably overstated, particularly for years with extremely high tributary flows toward or even after flushing season.

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