This lesson focuses on the importance of excess sediment as a major type of nonpoint source pollution affecting the Lower Grand River Watershed. Students explore excess sediment as illustrated by the 2013 Grand River flood event. They create a concept map about the effects of excess sediment in streams and rivers. After observing the characteristics of sediment and soils, students create a physical model of a stream noting how sediment moves. They research the sediment patterns in the Lower Grand River Watershed and explore how to reduce excess sediment loads. Outdoor explorations include looking for erosion in their schoolyard and stream monitoring.
Students answer these essential questions in the context of the Lower Grand River Watershed:
What is sediment?
What are the sources and effects of excess sediment?
What are some methods of monitoring excess sediment and its effects?
How can the sediment load in a stream or river be reduced?
The U.S. Environmental Protection Agency (U.S. EPA) lists sediment as the most common pollutant in rivers, streams, lakes, and reservoirs. It also is listed as a major pollutant in the Lower Grand River Watershed Management Plan (LGRWMP), the document used by watershed managers to restore and protect our local water resources.
Sediment refers to the organic and inorganic materials that can be carried away by water, wind, or ice. These materials eventually can be deposited and accumulate on the bed or bottom of a body of water. While the term is often used to indicate mineral-based soil particles (e.g. clay, silt and sand), decomposing organic substances and inorganic material from organisms are also considered sediment. In aquatic environments, sediment can be dissolved, suspended (floating in the water column), or bedded (settled on the bottom of a body of water).
While natural erosion produces nearly 30 percent of the total sediment in the United States, accelerated erosion from human use of land accounts for the remaining 70 percent. The most concentrated sources of excess sediment come from construction activities, including relatively minor home-building projects such as room additions and swimming pools. Other sources of sediment include cropland, urban landscapes, stream bank erosion, rill and gully erosion, and lakeshore erosion.
The Lower Grand River Watershed drains into Lake Michigan. A distinct river plume of sediment is usually evident at the mouth of the Grand River, where it enters Lake Michigan. Gravity moves the water from the headwaters near Jackson, Michigan to the Lake. As it moves, the water mixes with sediment. At the Grand River’s headwaters, the smallest sediments (silts and clays) are quickly swept away, leaving behind the sand, gravel, and larger rocks. As the slope of the landscape lessens, the river slows and the energy of the flowing water decreases. The river has less energy to carry the heavier sand, and sandbars can accumulate along the curves and twists of the riverbed. Finally, as the slope becomes nearly flat as it reaches Lake Michigan, the velocity of the current is reduced to a crawl and even the smallest sediments are deposited, which can lead to silt-covered deltas and clay-like mud deposits.
Understanding land use and the effects of urbanization are key to understanding the sediment load in the Grand River. Excessive erosion and runoff contribute to increased volumes of runoff and high velocities of flow. This results in more rapid rises and falls in water level, as well as stream bank erosion. When the stream flow returns to its dry weather condition, the water will slow down, have less energy to carry sediment, and the excess sediment from erosion will accumulate in the stream channel and cover desirable habitat.
For more detailed background information and references, click on Lesson 2: Managing Excess Sediment, in the For Teachers section below.
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The Michigan Department of Environmental Quality’s Nonpoint Source Program assists numerous non-profit entities and other local, state, and federal partners to reduce nonpoint source pollution (NPS) statewide. NPS pollution comes from all over the watershed – anywhere rain falls. There is no specific source like a pipe or smoke stack. As such, the basis for this program is watershed management.
The Lower Grand River Watershed Management Plan (LGRWMP) is a document developed to provide a description of the watershed, identification of impairments, and goals and objectives for management and improvement of the watershed. The WMP’s Information and Education (I&E) Strategy calls for educating stakeholders about the watershed and the impacts that stakeholders have on the watershed. The strategy has three steps: (1) awareness, (2) education, and (3) action.
With funding from the Michigan Department of Environmental Quality (MDEQ) Nonpoint Source Program, four lessons that draw upon information from the Lower Grand River Watershed Management Plan (WMP) have been developed for teachers. The purpose of these lessons is to further the I&E objectives that reach students as outlined in the WMP.
The three main nonpoint source pollutants of concern in the Lower Grand River Watershed Management Plan include sediment, pathogens, and nutrients. The lesson titles, which reflect this, are: