A new methodology is now being used to create emergent sandbar along the Missouri National Recreation River in northeast Nebraska.
Due to high water flow conditions, geotextile tubes are being placed into the river channel to promote an accumulation of sand down-river, with the intent to create sandbars which the Least Tern and Piping Plover could use for nesting next season.
The project is just getting underway, with worked expected to be completed by mid-April, 2011.
About 75 acres of emergent sandbar habitat is expected to be created at three locations along the MNRR:
- River mile 757, just upriver from Ponca State Park
- River mile 759, roughly four miles upriver from Ponca State park
- River mile 789.6 near Wynot, Nebraska
- River mile 759, roughly four miles upriver from Ponca State park
These sites were selected for two reasons, according to Corps officials: historic use by both species, and "natural sand accumulation" within the area. There are already large, submerged sand deposits in each of the three" locations.
Habitat is usually created using a dredge to move and pile sand which is then formed into a barren sandbar, suitable for the nesting birds. An unusually high release of water from Gavins Point Dam, has required that an alternative method be used.
"Water releases are so high that it is next to impossible to get onto the river to create habitat using the dredging process," said Matt Krajewski, a project manager with the Corps of Engineers. There is currently about 50,000 cubic feet per second of water being released from the dam.
Using the geotube method to promote habitat creation is much less expensive, Krajewski said, as fuel costs are significantly reduced. "Each site will require 4000 to 6000 cubic yards of fill to be dredged from the river bottom, compared to over 200,000 c.y. of fill for a typical emergent sandbar habitat constructed sandbar."
The contract cost of the projects are, according to Corps figures: river mile 757 - $890,000; river mile 759 - $922,500, and river mile 789.6 - $710,000.
"This is, generally, 20% - 40% of a typical dredging project," Krajewski said.
Picture showing an installed geotube. Image courtesy of the Corps of Engineers. |
Geotubes are made of a "specially engineered textile" which can be filled with sand, and allow water to permeate the heavy-duty fabric, according to a fact sheet issued by the Corps. Each tubes will be filled with a dredge, and then put in place. The tubes slow the water flow and are expected to "induce" the river to naturally deposit sand. The geotubes - filled to heights ranging from 3 to 8 feet - will be placed in a chevron configuration, perpendicular to the flow of the water. A "scour mattress" will also be used to prevent the river from undercutting the geotubes.
"The effectiveness of using geotubes is uncertain, as they have not been used previously on the Missouri River, with its high flows," Krajewski said. "We have a monitoring plan in place to determine the effectiveness of this operation. It commenced with a pre-construction survey and will continue until the geotubes are removed."
Once the sand has accumulated in the coming months, the geotubes will be removed next spring, prior to the arrival of the terns or plovers. The sandbar areas may then need to be "dressed," to optimize the habitat area, Krajewski added.
The 2003 Biological Opinion released by the U.S. Fish and Wildlife Service in 2003, requires that the Corps of Engineers provide tern and plover habitat along the Missouri River. The current project is the latest effort, developed by the agency partners involved in the planning and implementation process involved with sandbar construction. These agencies involved are the Corps, National Park Service, Fish and Wildlife Service, Nebraska Game and Parks Commission and South Dakota Fish and Game.