Ohio State University's Natural Channel Design (which two-stage ditches are also known as) site includes info best agricultural management practices.
Article by Andy Ward & Dan Mecklenburg on the two-stage ditch design
By observing natural processes of stable streams and rivers, researchers have designed a drainage channel that will benefit both agriculture and the environment. Known as the two-stage ditch, its a conservation tool that truly works.
Understanding the Two-Stage Ditch Design
Drainage has long been an important component in Indiana agriculture and property management. Land with flat, poorly drained soils require intensive draining for seedbed preparation and planting in order to minimize plant stress and subsequent yield reduction resulting from poor soil aeration due to waterlogging.
Yet what we have done to gain proper drainage has dramatically influenced the landscape in the Midwest over the last 200 years. Draining of wetlands, tillage practices and deepening streams or ditches are just a few ways that we have changed the land, and with it, allowed water to become an unintentional threat.
Water, when confined to a channel such as a stream or ditch, has the potential to cause great destruction. If there is too much water moving through an undersized area of land, then there is nowhere for it to go but to rush out of its barriers. Bank erosion, scouring, and flooding are good indicators that there is problem with how the water is drained from the soil. Researchers have been working on a type of in-stream restoration called the two-stage ditch that may help relieve these problems.
The concept of the two-stage ditch is quite simple. It was developed by observing natural processes that form stable streams and rivers. The design incorporates a floodplain zone, called benches, into the ditch by removing the ditch banks roughly 2-3 feet about the bottom for a width of about 10 feet on each side. This allows the water to have more area to spread out on and decreases the velocity - or energy - of the water. The flow of that water is a function of the velocity and area of the water. And since flow can be considered as the amount of water moving through the ditch, the design has actually increased the amount of water that the ditch can process by constructing the benches, or floodplain area. This not only improves the water quality, but also improves the biological conditions of the ditches where this is located.
The Benefits of Two-Stage Ditches
The benefits of a two-stage ditch over the typical agricultural ditch include both improved drainage function and ecological function. The two-stage design improves ditch stability by reducing water flow and the need for maintenance, saving both labor and money. It also has the potential to create and maintain better habitat conditions here in Indiana and elsewhere (see Gulf Hypoxia).
Better habitats for both terrestrial and marine species is a great plus when it comes to the two-stage ditch design. This is done by minimizing the amount of sediment and nutrients (such as phosphorus and nitrogen) that are transported from ditch to stream to river to sea. The transportation of sediment and nutrients is decreased considerably because the design allows the sorting of sediment, with finer silt depositing on the benches and courser material forming the bed. Two-stage ditches may also be useful in improving water quality by the possibility that the design may encourage nutrient assimilation.
What The Nature Conservancy is Doing with Two-stage Ditches
Since August of 2003, the Indiana Chapter of the Nature Conservancy has been working on two-stage ditch designs in headwater areas of rivers in our aquatic portfolio sites. Headwater areas are located in the upstream most parts of the watershed where there are many small streams and man-made ditches that drain the landscape. These areas allow the greatest potential to improve the condition of the downstream, larger rivers.
In 2007, The Joyce Foundation provided $5 million in grants to The Nature Conservancy and three other conservation organizations that would pay for projects in Indiana, Michigan and Ohio that would offer tangible and lasting improvements to both water quality and wildlife habitat in the Maumee River - one of the largest sources of pollution to Lake Erie.
The Conservancy will use these funds to fuel projects around St. Joseph River, found in northeastern Indiana. Our chapter will enlist Hoosier farmers to test the two-stage design with the goal of 2-4 miles of these ditches in the Fish Creek watershed ( a St. Joseph tributary) to reduce sediment and nutrients from leaving farm fields. We also plan on restoring 1,500 acres of wetlands and riparian corridors along St. Joe to filter water for nutrients and to reduce soil erosion. The construction of more two-stage ditches are set to begin this fall.