The U.S. Environmental Protection Agency lists sediment as the most common pollutant in bodies of water and although sediment transport occurs naturally, as much as 70% is due to human use of land accelerating the rate of erosion. Any solid material moved by wind, ice, or water and deposited in a new location is considered sediment and this includes everything from a particle of clay, a grain of sand, or a boulder.
Transportation of sediment by rivers has played an important role throughout history in the development of culture and society. Areas rich in sedimentary soils are also rich in biodiversity and entire civilizations have formed along deltas and river banks where high levels of sediment are deposited, creating the most fertile agricultural areas of a region. Rivers exist in a dynamic state, a constantly changing combination of water, vegetation, sediment, and aquatic life. Variations in this state occur naturally and are within the ecosystem's capability to maintain balance.
Problems arise when natural changes are exacerbated (usually accelerated) by human behavior and the amount of sediment entering a river is beyond nature's ability for adaptation.
An abundance of dirt in a river does not just create visually unappealing muddy water, it also blocks sunlight from reaching aquatic plants, increases the cost of treating drinking water, clogs the gills of fish, and covers crucial habitat such as shoals and cobble beds. Plants growing in the water, same as those on land, require sunlight to produce the nutrients they need to grow. When sediment stops sunlight from penetrating the water to the plants below, aquatic plants die, increasing the amount of potentially harmful nutrients in the water and reducing habitat for aquatic organisms. After native aquatic plants are dead and gone, invasive species such as hydrilla may replace them and then grow out of control.
Similarly, emergent vegetation such as shoal spider lilies, river willow, cattails, the like can be inundated with too much mud and sand to the point that new and older shoots and stalks cannot outgrow the rate of sediment deposition. This sort of pollution literally leads to the elimination of important riverine vegetation and fundamentally changes the nature of the river.
In areas where submerged and emergent aquatic vegetation are not as important, other problems remain. Riverside communities draw their water from their river. River water high in sediment speeds up wear-and-tear to filtration and treatment equipment, increasing costs for the water utility which will then transfer those costs to consumers via their monthly water bill. And, even in the Lower Flint where farms, industry, and communities typically (but not always) draw groundwater rather than surface water, excess sediment can show up there due to backflow from the river into the aquifer.
But the Piedmont and Pine Mountain regions of the Flint are especially vulnerable due to the ongoing expansion of Atlanta at the river's headwaters combined with the growth of the exburbs and development of the riverbank for homes, cabins, and private boat ramps. Saved in the 1970s from dam construction, and again in 2008 and 2009, this region of rapidly changing elevation and rocky shoals could have been saved from dams only to be buried by silt.
As part of Flint Riverkeeper's mission to restore and preserve the habitat, water quality, and flow of the Flint River, construction projects in tributary creeks plus near and along the river, both large and small in scale, are closely monitored for failures in sediment control measures. When a problem is found, Flint Riverkeeper works quickly with the property owner, and if necessary a governing government body, to stop excess sediment entering the river. A necessary element to the work is citizen-reporting of potential problems. Flint Riverkeeper staff rely strongly on citizens who care for the Flint River to notify the organization when a potential problem is observed.
