Sustainable Ditch Stabilization

SUMMARY

This project was a study in how to restore and stabilize a high-flow seasonal drainage ditch that transects grass seed production fields in Oregon’s Upper Willamette Valley. This type of ditch poses unique challenges as any plants growing in it can easily contaminate the adjoining grass seed fields and interfere with seasonal field burning used for sanitation.

Over the past four decades, seed certification agencies and field burning authorities have required and emphasized the importance of clean field borders, including adjacent drainage ditches and roadside ditches to ensure seed purity and expedite field burning. While most of the actual grass seed fields are protected from erosion by the crop itself, many field borders and seasonal drainage channels are currently kept bare with chemical sterilization. Keeping the banks of high-flow seasonal drainage ditches bare can lead to extensive erosion with the resulting silt going directly into the local streams and rivers.

A secondary problem is the development of a weed complex that is immune to the current chemical mix used to sterilize ditch banks and flourishes in the absence of competition. One of the main plants in this weed complex is wild carrot, which moves into and contaminates the adjacent grass seed crops.

The drainage ditch chosen for this project had been highly eroded over many years. We planned to reshape a 1,200- to 1,500-foot section of the ditch, then establish creeping red fescue on the sides to provide bank stability and competition for weeds without posing a major contamination risk to the adjacent grass seed crops. The creeping red fescue should allow the use of the lower application rates of varying herbicides, which keep undesirable weeds/grasses from establishing while reducing the potential chemical movement into the waterways downstream. We used coir erosion matting underlain with straw to keep the soil in place while the creeping red fescue established.

OBJECTIVES

1) Address water quality, soil erosion and weed problems associated with high flow seasonal drainage ditches in commercial grass seed fields in Oregon’s Upper Willamette Valley.
2) Enhance water quality by preventing and/or reducing soil erosion from to runoff following rainstorms.
3) Determine the most economic and efficient method to stabilize high-flow seasonal drainage ditch banks in grass fields while suppressing weeds.
4) Verify that erosion control blankets are effective in helping establish fine fescue and stabilize ditch banks during grass establishment.

RESULTS

The major accomplishment of this project was the establishment of a grass-protected waterway after restoration and reshaping of a highly eroded, weed-infested, high-flow seasonal drainage ditch. This project was a successful research and demonstration effort, which has lead to several subsequent ditch restoration projects in this conservation district. Ditch restoration is considered cost prohibitive for use on local farms.

For an accurate cost of earthmoving and ditch reshaping, it would have been much easier (though more expensive) had we hired a contractor. The equipment I had at my disposal was more representative of a normal local farm operator than that of an earthmoving contractor, so I did have some limitations. We had some weather challenges. Rain came in sooner than normal and hindered our ability to get the ditch shaped as desired, delaying us considerably.

The cost of moving earth and ditch shaping varies considerably from project to project. We were not able to get the ditch as perfect as we wanted, but it was a vast improvement. The local extension service and conservation agency staff, however, felt the result was a very functional grass waterway ditch and an excellent demonstration of what can be done on a Willamette Valley farm.

In this project, we were trying to establish the best method, for the least cost for permanent stabilization of reshaped ditch banks. Our work proved that the coir mat was necessary in our circumstances, but there were no real apparent differences in performance between the various mats used for underlayment. One of the problems we encountered with some of the “weed free” straw erosion mats was that they did include some exotic weeds. For this part of the project, the goal was to see how inexpensively we could anchor the banks and cure the imported weed problem. We used two types of local straw, wheat and annual ryegrass. We hydro-seeded the entire ditch with a commercial hydro mulch fiber made from recycled newspaper. We included Pennlawn creeping red fescue seed at a rate of 80 pounds per acre, Gulf annual ryegrass seed at a rate of 10 pounds per acre and 80 pounds per acre of 20-20-20 fertilizer. We also included a little PAM to help stick the soil in place. Then we spread the straw loose across the entire ditch with the coir mat anchoring the straw in the center. Where the 13½-foot coir mat was not wide enough in a curve, we supplemented with a 4-foot section of Geo jute on the backside of the curve. We found the wheat straw easier to work with and spread than the annual ryegrass straw. It also doesn’t present the seed contamination problems that often come with annual ryegrass.

Fine fescue does not persist in the bottom of the ditch where it is underwater for any extended period. Because lack of an established sod at the bottom of the ditch could lead to renewed erosion, we decided to establish Seaside creeping bentgrass in the bottom portion of the ditch, which will survive extended flooding. We should be able to keep it in the bottom of the ditch and out of the creeping red fescue and the adjacent seed field through the judicious use of selective herbicides.

The winter of 2004-2005 did not supply the normal rainfall, so we did not get the extended high flows of water that are normal during the winter in this ditch. For much of the time, when the ditch would normally be running full, there was not enough flow to pull water samples. While based on limited sampling, analysis indicated that sediment, nitrogen and phosphorous concentrations were below levels considered problematic for fish or invertebrate populations.

BENEFITS OR IMPACTS ON AGRICULTURE

This approach gives producers a chance to repair and reshape eroded ditches and have them hold that shape. It should cut down on sediment entering streams and rivers fed by the ditches while at the same time helping to alleviate some of the weed problems. An added benefit is it should also lead to a reduction in the use of herbicides on the ditch edges.

A couple of drawbacks are that the producer will likely need to get a “side arm” mower or flail of some type to clip the grass in the ditch. Initially, the annual ryegrass needs mowing to keep it from smothering the fine fescue and then after the fine fescue is established to keep it from heading out, lodging and smothering itself. The other drawback is that the vegetated ditch banks provide a much better cover for field mice or voles than the bare ditch banks. This provides a source of rodent “seed stock” to infest the adjacent fields and their burrows or holes could undermine the whole ditch-bank stabilization process.

PRODUCER ADOPTION

There were at least five to six projects of various sizes done in my conservation district this fall, which are spin-offs of my project.

REACTIONS FROM PRODUCERS

A number of other producers are interested in this project, especially considering there were five or six similar projects this fall in the same conservation district. One of the main concerns expressed by producers is the cost of such a project on any sizable scale.

RECOMMENDATIONS OR NEW HYPOTHESIS

Start early. If you will not have enough time or the right equipment to get the job done well and in a timely fashion, hire a contractor for the earthmoving and ditch shaping. If using loose straw, don’t apply it too thick and don’t plant too much annual ryegrass with the fine fescue; either one of these can smother or at least reduce the stand emergence of the fine fescue. Try to mow or clip the ditch banks before the annual ryegrass heads out. If the annual ryegrass gets too mature or lodges before mowing, it will be tough on the fine fescue.

If dealing with high flow ditches, you should use the wide (13½ ft) coir mat. The coir mat is more expensive but should last longer than Geo jute. The coir can be underlain with commercial erosion mats or local straw. Using local straw, you simply spread it uniformly in the ditch and don’t need to staple it; so it can be applied considerably faster than the mats, though it may not hold as well under flow where not held down by the coir mat. We prefer wheat straw to ryegrass straw; it spreads easier and more uniformly and does not present the seed contamination potential when used adjacent to other species.

Additional research should be conducted to see if broadcast seeding could be used in place of hydro-seeding, to reduce costs, where straw and mats are being used. Small plots included in this project indicated that broadcast seeding may work, but testing is needed on a larger scale. In addition, more research is needed to find and evaluate acceptable additional water-tolerant species for ditch bottoms.

OUTREACH
Numerous groups were given tours of this project including: more than 60 FFA students who were on site for the regional FFA soil judging contest in 2004, members of the Linn County SWCD board along with some Linn County Commissioners and NRCS staff, personnel from the USDA-ARS National Forage SEED production Research Center in Corvallis, OR, the erosion team from the USDA-ARS National Sedimentation Laboratory in Oxford, MS, and interested local producers on the Linn County Extension Service spring tour.

Posters were developed and displayed in the Linn County Extension Office in Albany for several months and at the 2004 Willamette Valley AG Show in Albany and at the Linn County Extension Association annual meeting.

Articles on the project were published in the “UPDATE,” the Linn County Extension Service’s monthly publication with a circulation of about 7,000, and in the Linn County SWCD annual report. This was also included in a supplement in the Albany “Democrat Herald,” the local daily newspaper with a circulation of around 15,000 to 20,000.

An Oregon State University Extension publication, EM 8876, “Vegetative Filter Strips Near Surface Water in the Pacific Northwest” by Jed Colquhoun was based in part on this project and includes pictures from my farm.