Low water offers a better look at the Grand River
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EmailThe Grand River is Michigan’s longest river, and like most large rivers, its water often runs brown. The dry summer has left water clear and low in the Grand this year, providing a glimpse at habitat that is normally hidden from view.
Nothing in a river stays the same. Water washes endlessly downstream, so the water you see in a Michigan river today will likely be part of a Great Lake in a few hours to a few days. Rain, melting snow, and groundwater provide the majority of water for most rivers and the runoff from precipitation washes in particulate and dissolved matter from the land. This might include sand, soil, nutrients, or toxic pollutants, but the muddy-brown color of most large rivers does not necessarily mean they are full of toxins.
The Grand River flows north from Jackson through Lansing and then hooks west toward Grand Rapids and its eventual destination in Lake Michigan at Grand Haven. In a journey of 248 miles, give or take, it accumulates a load of sediment that typically colors its water brown. During dry seasons, the amount of water flowing in the river drops and water clarity increases.
A river’s discharge can be measured in cubic feet per second (cfs). Discharge is highly variable, but the Grand River’s median daily discharge is around 7,000 cfs in late March and drops below 2,000 cfs from early July through the end of October, according to 85 years of data collected by the U.S. Geological Survey. This means we can expect relatively low water in September, but this year’s dry summer resulted in even lower discharge than usual for this time of year.
On September 26, discharge in the Grand River at Grand Rapids was 25 percent below the daily median and water clarity was exceptional. Visibility (as measured by Secchi disk) was greater than nine feet in locations where visibility is measured in inches during springtime. This provided a rare opportunity to view the bottom of the river in deep waters that are normally hidden from view.
A series of four videos from September 26 are now available on the Michigan Sea Grant YouTube channel. These videos depict the bottom of the river (substrate) above Sixth Street Dam. Recent discussions regarding the possibility of dam removal and rapidsrestoration have included questions regarding the accumulation of sediment above the dam and the presence of a limestone bedrock shelf on the east side of the river. The videos show soft sediments that have accumulated on the bottom along with the edge of a bedrock shelf and a deep channel that carries substantial current even during low water periods.
While videos do not answer questions regarding sediment contamination, the total amount of fine sediment accumulated above the dam, or the total amount of shallow bedrock habitat available, they do provide a unique opportunity to visualize the habitat available above the dam.
