Two Stage Ditch

Two stage ditch demonstrating 1st and 2nd stage land setup
A two stage channel has a 1st stage or low flow area where water flows during non rain events. It also has the 2nd stage which acts as a floodplain. During high rainfall events, the water rises in the channel and spreads out on the 2nd stage. This slows the water down allowing sediment to drop out and deposit on the bench area.

What it is:

Two stage ditches are an alternative design for open channel systems, which are typically constructed and maintained as a trapezoidal shape. The two stage design is a more sustainable approach to surface and subsurface drainage management.

Two stage ditch diagram
This diagram shows the difference in shape between a traditional agricultural drainage channel and the two stage channel.

How it helps:

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 slowing down water flow and reducing the need for maintenance, saving both labor and money. It also has the potential to create and maintain better habitat and water quality conditions for the waters into which our drains flow into such as the Gulf of Mexico or Lake Erie. 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 overall Return on Investment should consider the long term benefits of the conversion of a typical drainage channel into a two stage channel.

Two stage ditch on the Kurt Demonstration Farm
Standing in the Kurt Demonstration Farm two stage channel, the 1st stage is located in the center of the picture (where the dark green vegetation is). The 2nd stage is on either side of the 1st stage.

Planning ahead:

Like many conservation practices, a two-stage design is better suited in certain locations. Consulting a knowledgeable professional such as your county engineer, local Soil and Water Conservation District, and/or a professional engineering company is a must before any earthwork is performed. Having an accurate survey and engineering design will help you determine the costs associated with constructing a two stage ditch.

Two stage ditch after large rainfall event
During a large rainfall event, water is seen rising in the two stage channel. Note that tile drainage is still free flowing.

Management:

A significant amount of the work/resources goes into the proper design and construction of the two-stage channel. Special consideration should be given to the size and elevation of the constructed benches, transitions into and out of the two-stage section, and areas near culverts or crossings Rock chutes can be installed where concentrated surface flows enter the channel from the field or from drain tiles. After construction, care should be taken to establish and maintain vegetation on disturbed areas to prevent erosion. If designed and installed properly, sediment clean out from the bottom of the ditch should be much less than a typical drainage channel.

Additional Resources:

  • Ohio State University Two-stage Ditch Cost Estimator Tool
  • Building Better Ditches
  • Economics of Implementing Two-stage Channels
  • Sizing Two-stage Channels in an Agricultural Landscape
  • Two-stage Ditch Case Study-Chris Kurt Farm