19 March 2013

Mitigation Details Indicated for Saddle Creek Project

Impacted wetlands and stream channel alterations associated with the lower Saddle Creek area CSO! project will be replaced to a greater extent, because of government regulations.

The City of Omaha is required, through provisions of Section 404 of the Clean Water Act, to replace .017 acres of wetland and 417 linear feet of stream, according to the just available mitigation plan. The impacts will occur because of a street runoff/sewer flow separation project — associated with Clean Solutions Omaha — now underway on the east side of Westlawn-Hillcrest Memorial Park cemetary, in the 55th and Center Streets area within the river city.

Site plans for mitigation areas. Both images from the Army Corps of Engineers mitigation/restoration plan.

Wetland mitigation will occur on the east side of cemetery. It will include a 50-foot "permanent, native herbaceous and woody buffer" around the site, as well as a 20-foot buffer along the stream channel, according to the official plan.

Seeds and saplings of a large variety of plant species will be sown. The wetland seed mix will include red top, bristly sedge, dark green bulrush, fowl manna grass, fox sedge, prairie cordgrass, soft rush, Virginia wildrye, water plantain, arrowhead, blue flag iris, blue vervain, joe pye weed, monkey flower, swamp milkweed and sweet flag. Each of these species were listed in the mitigation plan.

Of these species, red top is not a native species, according to David M. Sutherland, professor emeritus at the University of Nebraska at Omaha.

Impacts on trees were also considered and any removed tree will be mitigated. The official plan, indicates that 684 trees need to be replaced, so there will be plantings of native willow species, dogwood, spring birch, maple, hackberry, red mulberry, paper birch, butter-nut hickory, black cherry and American Basswood.

For the tree species mix, Sutherland said: "The tree list looks okay except for paper birch, which is not native to this area. I wonder where they are getting the red mulberry, a native, but rather uncommon tree. It would be good to plant, but I wonder if it won't turn out to be just white mulberry."

Although there was an indicated loss of some few cottonwood trees, they are not, apparently, going to be replaced.

Channel mitigation — to replace "R4SB channel" — will occur closer to Little Papillion Creek, lower in the basin area, and also within the urban confines south of Center Street, especially westward from 60th Street. The property where this mitigation will occur has purchased from private land owners.

Basics of the locale include a requisite flow channel of particular extent and slope, with adjacent 9-12 foot terraces, and having an overall twenty foot width, according to the mitigation plan. "A series of 3 pools and rifles are also planned as part of the proposed stream channel."

On the upland buffer portions of both mitigation sites, the species indicated in the expansive list of species to be seeded include little bluestem, buffalo grass, sideoats grama, blue grama, black-eyed susan, blanket flower, blue flax, butterfly milkweed, dwarf red coreopsis, grayhead coneflower, Illinois bundleflower, lance-leafed coreopsis, leadplant, lemon mint, Mexican red hat coneflower, New England aster, pale purple cone flower, perennial lupine, pitcher sage, plains coreopsis, purple coneflower, purple prairie clover, showy partridge pea, thickspike gay feather, upright coneflower, white prairie clover and white bergamont.

This apparently matches a seed mix available from a local seed company.

"On the upland list," Sutherland commented, "there are a few odd choices: Blanket flower, lemon mint, perennial lupine, and white bergamot are not native to this area. Blue flax is not native and does not persist for long. Showy partridge pea is a somewhat weedy native annual that will be showy the first year or two but will not persist."

The mitigation plan indicates that the created features will be monitored for several years, following their completion, and be the responsibility of the City of Omaha.

Nine separate criteria are listed in the mitigation plan, and are, as summarized:

  1. assessment of vegetation
  2. soils evaluation
  3. vegetation, which includes field sampling
  4. hydrology, including identification of surface water and/or saturation indicators
  5. photographs taken at a minimum of eight "photo station points" at both localities
  6. fauna, which includes "any fauna found to be using the east wetland mitigation site or west stream site will be recorded by species and, if possible, documented by photograph; indicators include actual sighting, scat, nests, feathers, fur, bird calls/song are examples of faunal evidence.
  7. sight inspection
  8. inlets/outlets, or a visual inspection of conditions at the diversion pipes
  9. cross sections - "three cross sections ... will be taken of each of the restored channel, existing channel and created channel; this measurement, according to the permit requirements, will be measured after final grading, then for five more years.

Monitoring will start in the fall of 2014, after cover vegetation is established, and be done by a hired firm, according to Public Works staff. This information, once gathered would need to be submitted to the Corps of Engineers for evaluation.

There is a deed restriction on the project site, and according to city officials "is an agreement between the West Lawn Cemetery, the City of Omaha and the U.S. Army Corps of Engineers, which has regulatory jurisdiction over the said wetlands area(s). The West Lawn Cemetery and the City of Omaha agree that the area shall be for perpetual use as a conservancy area in accordance with the terms and condition of the Department of the Army permit regarding fill material in the wetland area."

Initial construction associated with this project are currently underway.

The multi-page mitigation/restoration plan, which included color versions of map graphics, was received — free of charge — through a Freedom of Information Act request to the Army Corps of Engineers, office of counsel at Omaha.