Flushing the mighty Mississippi | clintonherald.com

The prolonged period of high water has chronicled a miserable summer for river enthusiasts along Clinton’s Mississippi River paradise. The raging river currents of muddy water have carried many floating logs that have torpedoed unsuspecting boaters. Fortunately, record flood levels haven’t been reached but it may set records for seasonal high water events. The unseen impacts of prolonged high water are hidden below the murky depths of the river.

Prior to the 1930s construction of locks and dams that impounded the Upper Mississippi River, there was seasonal flooding that was representative of a natural river system. After the Great Flood of 1965 many communities, like Clinton, built levees to control flooding and minimize property damage. Extensive development within the historic flood plain followed. The miles of additional concrete and other structures now push river flows higher and into areas that are far from the historic flood plain.

Clinton is geographically situated in a transition zone where the Upper Mississippi River changes its environmental character. The river north of Clinton extending to Minnesota contains extensive flowing side channels, islands, braided backwaters and a myriad of wetlands. The river south of Clinton down to St. Louis is more constricted with few side channels, backwaters and wetland complexes. The open Lower Mississippi River (no locks and dams) below St. Louis is a fast flowing channel mostly bordered by levees.

A major effect of high water is increased sedimentation in our backwaters. In a typical year, there is less than an inch of mud added to the backwaters by sediment deposition. We can potentially expect several inches of mud to be deposited this year due to the high flows of sediment laden currents.

Beaver Island is a prime example of the impacts of sedimentation. An aerial photo shows that water flowing from Beaver Channel into Upper Cut is the prime contributor of sediment being trapped within the island’s interior. These formerly deep backwater lakes are now filled with several feet of mud. During normal water levels, the majority of these lakes are only a few inches deep. The planned Beaver Island habitat restoration project’s goal is to restore these lakes to deep water and to improve forest diversity.

High water flows also carry increased amounts of nutrients that run off from agricultural fields and urban areas. These nutrients accumulate along the 2,300 mile Mississippi River length and are ultimately dumped into the Gulf of Mexico. The result is a nearly 6,000 square mile Dead Zone where low levels of oxygen make it uninhabitable for marine life.

Fish and other aquatic species take advantage of high water events to expand their range. Asian carp migrated north during the 1993 flood, leaving the Lower Mississippi River and venturing into the Illinois River and Upper Mississippi River, a journey of many hundreds of miles. These unwelcome invaders are now silently moving upriver through open dams and will undoubtedly be established in our area within a few years.

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