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Wetland Treatment Project Completed
OID equipment operator Jon Ash places rip-rap 18-inch minus angular rock around a new structure to prevent erosion on the south berm of the wetland treatment project at the Union Slough. - photo by Photo Courtesy Of Jason Jones


A new wetland treatment system, the first project of its kind in the Oakdale Irrigation District, is in its final stage and getting the finishing touches at the Union Slough on V.A. Rodden land between Crow Road and Ellenwood, south of Claribel.

The Union Slough Wetlands and Water Quality Enhancement Project cleans drain water for irrigation. Water from the Union Slough eventually goes into Dry Creek, a tributary to the Tuolumne River. OID engineer John Davids reported that this project was specifically not for (required environmental) mitigation – it was an opportunity for OID to work with the landowner and to produce a variety of benefits to the area.

“The Union Slough collects a tremendous amount of tail water,” Davids said. “The real benefit of this project is removal of chloroform bacteria, nitrate/nitrogen, and phosphorus all before it gets to Dry Creek and then the Tuolumne River.”

The benefit to the landowner is that when he takes drain water out downstream to water orchards, it’ll be free of those contaminants. For the district, it’s a good neighbor policy.

“We recognize the importance of doing things in our watershed to help water quality,” Davids said. “…Dry Creek is a hot button because there’s a lot of irrigated Ag along it. Anything we can do to clean drain water before it leaves the district is good.”

He said there’s also a benefit to wildlife. There are a lot of waterfowl there year-‘round including ducks, geese, other migratory birds, and nesting birds.

He reported that a new central berm was constructed to raise the water surface so that there would be more flood area on the property. This project is comprised of 6.8 acres of wetlands and 1.2 acres of riparian buffer that includes native bushes, shrubs, and trees that are all non-irrigated, native species. There will be California bulrush, tule, and cattail in the north and south cells of the wetland, which are divided by the central berm. The buffer area will contain cottonwood and willow tree cuttings, mule-fat, coyote brush, and mugwort. Davids also noted that River Partners of Modesto will do the plantings in the area. They will gather seed, do transplants, and deal with that part of the environmental restoration.

The idea, Davids said, is to keep all 6.8 acres inundated, which shouldn’t be a problem because there’s a significant amount of acreage upstream that contributes greatly to drain water. He explained that the wetland project area was previously a small, defined stream course with a series of old, small dams for irrigation. He added that the district is seeing a lot of land use conversion to trees annually and that they’ve taken that into consideration for the long-term sustainability of this wetlands enhancement project.

All the project construction was done by OID at an estimated cost of $464,000 and designed by CH2M Hill, Davids said. OID support services manager Jason Jones reported that the project got started Oct. 18.

Jones added that the OID workforce excavated the area and replaced what they removed with suitable material, which was then compacted to construct the new central berm. They placed rip-rap on the existing south berm to prevent erosion. Then they excavated material prior to constructing the central berm’s concrete spillway so that in times when storm water flows are greater than the pipe’s capacity, the water can spill over the spillway and not erode the berm.

“The dry winter has allowed us to do some work in an otherwise nasty situation,” Davids said. “It’s usually a swamp.”

Further, OID was able to get the permits done in four to five months, which was unusual since most other projects take at least a year or more for permits.