Promoting Naturalized Drainage Channel Design
Upper St. Joseph River in MI /,
The Nature Conservancy
Basin Program Funds:
In the Upper St. Joseph River watershed a major problem is hydrologic alteration and sedimentation (stream bank erosion) resulting from the intensive tiling and drainage of agricultural lands, which poses a significant threat to aquatic biodiversity.
Laird Creek is one of many agricultural drainage ditches found within the watershed that is representative of the traditional channel design: straight, narrow channels with trapezoidal cross sections that have been deepened to accommodate the flow from drainage pipe outlets and to promote runoff near the channel. The result is a system of incised channels that are over-sized for small flows and generally lacking a floodplain to accommodate larger flows. While effective in moving water away from fields, this design is prone to flashiness, resulting in bank instability, scouring, and excessive stream channel erosion during periods of high flow. Recent research suggests that a significant fraction of the sediment discharge from headwater systems is due to bank instability and in-stream processes.
Increased soil erosion and subsequent runoff into the streams reduces water quality and increases the transport of soil particles and chemical pollutants (insecticides, herbicides, and fertilizers). Mussels and their host fish are especially vulnerable to these non-point source pollutants. The Upper St. Joseph River system supports what is probably the most diverse community of naiad mussels, fish and associate fauna in the Great Lakes Basin.
This project demonstrates the economic and environmental benefits of a naturalized channel design on low-gradient agricultural drainage ditches. The traditional drainage channel design usually has a trapezoidal cross section. Drainage channel capacity and shape must be continually maintained at considerable cost to counties, soil and water conservation districts and landowners. This project transforms a traditional ditch that has been deepened and straightened through periodic maintenance activities, to an alternative “two-stage” design that incorporates naturalized fluvial features.
The modified two-stage ditch will have a primary channel sized to handle bank-full flows, and a new low-level vegetated bench that will accommodate higher flows. It might be visualized as “a stream within a ditch,” where the primary channel is allowed to meander slightly within the constructed floodplain corridor.
A channel naturalization demonstration site on a 2,600-foot section of Laird Creek, immediately north of Territorial Road was developed. The newly formed berms, banks, and benches were seeded and fertilized. Sampling equipment was installed in order to obtain data on the performance of the ditch. After implementation, we conducted a field day and educational workshop on two-stage ditch design and stream geomorphology to promote the benefits of channel naturalization.
At 19 months after construction, the benches have been vegetated and there is only one small area that shows evidence of erosion. All materials associated with construction were chosen for long-life characteristics (straw blankets, seed mixes, etc.). Native vegetation was not used for this project due to the fact that this is not an established, proven practice. The project team did not want to have a serious erosion event occur because of choosing the wrong vegetation. The local drainage official is contracted to maintain this practice for a period of 5 years, although no additional maintenance is expected.
The bank erosion has virtually been eliminated by increasing the floodplain area. The area with erosion has slumped down to the bench area and is currently resting there. This appears to be the only area that has had this issue and we have corrected the problem by reseeding this. It is calculated that there was 10.5 tons of bank that was lost due to this. There is no evidence that this will be a chronic issue throughout the entire newly constructed area.
The field day was a great success. There were over 80 attendees, representing various State and Federal Agencies from Ohio, Indiana, and Michigan, private consulting firms, and interested landowners. This was a targeted audience for this initial event. Volunteers from the University of Michigan and OSU led group discussions during the event.
Contact: Mr. Joe Draper, 260-665-9141