Erosion is the removal of soil particles from a site due to the forces of water, wind, and ice. Over time, these forces will slowly wear away or disintegrate the soil. In the case of a stream, erosion may occur in several ways.
Stream erosion in agricultural areas normally occurs as a result of one of three factors: change in stream flow, water flowing over or through the streambank, and the discharge of concentrated runoff from other sources. Streams are subject to wide fluctuations in both flow depth and velocity over a period of years, due to normal seasonal changes in rainfall and large single-storm events. As flow depths and velocities increase, the force of the water flowing against the streambank removes soil particles from the banks, and in many cases erosion causes banks to slump and fall into the flowing water. In extreme situations where high flows persist over long periods, banks may erode several feet annually. Rain falling on streambanks or runoff from adjacent fields that enters a stream by flowing over the streambanks can also erode soil from streambanks, particularly if banks are inadequately protected.
Finally, water discharged into a stream from tributary drainage systems (such as waterways or tile lines) can also erode streambanks, particularly if the water is discharged in an area where the bank is unstable and highly erodible. In many cases, moving the outlet to a point where the steam is less erodible or stabilizing the outlet area with rock can alleviate this problem.
Although a stream channel may appear to be stable, when viewed over a period of decades or centuries most streams exhibit a tendency to adjust or shift location. In some instances, changes result from single events, such as a tree falling into a stream and deflecting the flow of the water. In other instances, these changes are due to differences in soil type and structure within the stream channel or are the result of erosion occurring from catastrophic storm events. Any straight stream channel will eventually erode on portions of each bank and begin to bend or meander. As the stream bends become longer and more sharply curved, more soil is eroded from one side of the channel and deposited on the other side of the channel. Description from HOW TO CONTROL STREAMBANK EROSION. (2006) Iowa Department of Natural Resources.
Agricultural drainage channel designs have a simplified form, disconnected floodplains, little diversity and dynamism, and management regimes that prevent system recovery through natural processes. According to the Census of Agriculture, government agencies reported over 77,500 total miles of streams had been converted to agricultural ditches in Indiana, Michigan, Minnesota, and Ohio alone through official legal mechanisms.
Experiences with agricultural drainage in the Midwest suggests that many of the modifications made to streams and regular maintenance activities are done by private landowners. These activities are not captured in Census estimates. Therefore, the Census estimates are likely an underestimation of the true extent of modified agricultural ditches in the region. In some watersheds, ditches may account for 80% or more of the entire length of the drainage network (Blann et al., 2009).
While ditches successfully drain the soil profile, their deviation from natural conditions drives the loss of ecological function and services, such as water purification, downstream flood control, and the provision of habitat and biodiversity. Reconnecting the channel to its original floodplain is not always practical since the adjacent land use is dependent upon the drainage functions the channel provides. However, water quality problems associated with agriculture and the deleterious ecological, fluvial, and economic impacts of ditch maintenance have forced a collective rethinking of drainage management strategies in the North Central Region that provide drainage, but also enhances other important ecological services.
For more information including case studies on agricultural ditches see agditches.osu.edu
|Example of bank erosion taken 3/17 Hardin Co. LaBarge||Example of bank erosion taken 3/17 Hardin Co. LaBarge|
|Cleaned ditch taken 10/14 Henry Co. LaBarge||Same cleaned ditch taken 4/17 Henry Co LaBarge|
Best Management Practices