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Slip off Slope

By Ranger Steve Mueller

By Ranger Steve Mueller

Rivers slip off slopes and create cut banks. Rivers, streams and brooks move from side to side to create cut banks and slip-off-slopes that become important habitats for wildlife and plants. The movement of stream channels creates unique nature niche environments.

Belted Kingfishers use cut banks for excavating deep tunnels where they nests. Marsh marigolds flower on slip-off-slopes. Slip-off-slopes floodplains retain water that reduces flooding of homes downstream.

A stream or river channel is the trough filled with flowing water. It cuts deeper every season, decade, century, and millennium. The work is slow but not steady. In spring after heavy rains or snowmelt, channel cutting increases. Once the river valley did not exist and the land was nearly level with the surrounding landscape. Following glacial retreat, water flowed to lower areas and began moving particles. Continued flow cut deeper into the landscape creating river valleys.

When water meets an obstacle like a tree or rock, it is diverted sideways and cuts into the opposite bank of the channel creating a cut bank. What was a straight flowing stream forms a meander. Bank undercutting creates hidden hollows where fish hide. Meanders become larger loops but the stream channel width normally remains about the same size. If it was 3-foot wide or 30-foot wide, the size does not change significantly.

Where the stream cuts into a bank along the outer edge of a meander, water flows faster with greater force. On the inside of the channel’s meander, water moves more slowly and drops sediment. It creates shallower water in the process of filling the channel on that side. As the cut bank is eroded on one side, a new wetland known as a slip-off-slope floodplain is formed on the other. The slip-off-slope is named because the river channel is actually slipping off the streambed as it creates new land. The opposite shore can have a nearly vertical bank. It might only be a foot or two high or almost 100 feet. Over time the river moves back and forth across the river valley.

This can be observed along the Grand River, Rogue River, and even Little Cedar Creek. At Ody Brook, the stream valley is about as wide as a football field is long. In Grand Rapids, roads climb slopes of the Grand River’s cut bank toward the Medical Mile to the east and to the west on I-196 west from US 131. Where the Grand River channel flows through town, we have worked to stop the sideway meandering by constructing concrete walls.

To protect businesses and homes on the slip-off-slope floodplain, it was necessary to prevent stream movement back and forth. One can observe more natural slip-off-slope wetland communities at places like Millennium Park. Ody Brook is a headwater for Little Cedar Creek that feeds Cedar Creek, Rogue River, and Grand River. Upstream from Ody Brook, the channel is dry in August but water flows year around at Ody Brook because springs seep from the cut bank maintaining continuous flow.

Even this small watercourse channel that is 4 to 5 feet wide and usually a few inches deep has cut a valley about 12 feet deep and about 300 feet wide. During flooding as water flows through the wetland forest, the current is slowed and drops rich fertile sediment nourishing floodplain communities.

Mouse “houses” and low bird nests get washed away during high water and minks visit more frequently. Failed nests require adults to rebuild, bare new young or lay replacement eggs. Mice trapped on floodplain islands swim to higher ground. It is not just people that construct homes in locations prone to flooding.

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at odybrook@chartermi.net Ody Brook, 13010 Northland Dr, Cedar Springs, MI 49319-8433, or call 616-696-1753.

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