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Title: Upper Mississippi River System Environmental Management Program Definite Project Report (SL-3) with Integrated Environmental Assessment : Pharrs Island Wetland Habitat Rehabilitation, Pool 24, Mississippi River, Pike County, Missouri
Authors: United States. Army. Corps of Engineers. St. Louis District.
Keywords: Restoration ecology
Environmental protection
Environmental management
Mississippi River
Publisher: United States. Army. Corps of Engineers. St. Louis District.
Abstract: The Pharrs Island wetland complex is located in Mississippi River Pool 24, about three miles upstream from Lock and Dam 24. It consists of approximately 525 acres of Federal lands and water. The area is managed for fish and wildlife purposes by the Missouri Department of Conservation under cooperative agreements between the state and the Department of Interior, and between the Department of Interior and the Corps of Engineers. Pool 24 is located within a major flight corridor for millions of migrating waterfowl. The most abundant duck in the Mississippi flyway is the mallard, and within the Upper Mississippi River, Pool 24 is one of the most important areas for this species. The importance of this area is highlighted by the North American Waterfowl Management Plan's designation of the Upper Mississippi River as one of the waterfowl habitat areas of major concern in the U.S. The plan notes that on-going habitat loss is of concern in areas used by waterfowl for rest stops during migration and for wintering. Commercial and sport fishing are important activities on the UMRS, including the Pool 24 area. Both commercial and sport fish have specific life requirements, and extensive backwaters are needed for their optimum feeding and reproduction. Biologists are concerned that the continuing loss of Upper Mississippi River System backwater habitat could result in a future reduction in the numbers and diversity of these fishes. The Comprehensive Master Plan for the Management of the Upper Mississippi River System identified sedimentation as the most significant resource problem affecting the river system. The Great River Environmental Action Team estimated that most off-channel habitats within the Pools 20-25 reach of river would be completely filled with sediments within the next century. Compared to other UMRS pools, Pool 24 has little existing off-channel water habitat. The Pharrs Island complex illustrates well the ongoing conversion process in Pool 24 from water-to-land habitat. As the lower (growing) end of Pharrs Island achieves a more stable configuration, it is anticipated that the island's non-forested wetlands habitat will eventually disappear. During the 15-year period between 1972 and 1987, the conversion of water-to-land within the complex proceeded at a rate of 3 acres per year. At this rate, all interior non-forested wetlands habitat would be expected to disappear from the project area during the next 50 years. The Pharrs wetland complex is also affected by fluctuations in pool stage. These water elevations can fluctuate by a number of feet above and below normal pool stage, and for extended periods of time. A drop in water elevation can cause a drawdown action (with a resulting loss of young fish and eggs) that lowers the utility of the island's shallow interior wetlands for fish spawning and rearing. Water level fluctuations can also impact the production of aquatic plants, and the availability of these plants as a food source to waterfowl. In addition to acreage shifts, evidence of habitat degradation at the Pharrs Island site exists in the form of hunter blind counts. The number of blinds in the project area decreased from 51 in 1957 to 24 in 1987, a rate of nearly 1 blind per year. To retard the deposition of sediment into the project area, and to provide additional backwater habitat, a 10,200-foot long rock dike would be constructed. The upstream end of the dike would be bull-nose shaped, (crown elevation 453 NGVD) and would then trail in a southeasterly direction to the downstream end of the project (tapering from 453 NGVD to 449 NGVD). The dike would be constructed entirely of graded stone "A" along the trail dike segment, but along the bull-nose portion it would consist of an A-stone exterior covering with a gravelly-red clay interior. The A-stone providing protection from river currents, ice and debris, the gravelly-red clay providing protection against sediment thru seepage. The trail dike being parallel rather than perpendicular to the river flow was not judged to need special seepage control. To provide a means for controlling water levels on the island, about 8,255 feet of levee would be constructed. This levee would supplement existing segments of natural levee along the island's perimeter. This construction would bring the entire island perimeter to a minimum grade of 452 NGVD. In addition to water control, the levee system would also help provide sediment protection to the island. The new levee would consist of a long lower island segment (3,950 feet long), two intermediate length mid-island segments adjacent to the navigation channel (an upstream segment 1,760 feet long, and a downstream segment 1,495 feet long), and a number of smaller slough closure segments (totaling 1,050 feet) along the upper island. A 100-foot wide vegetative buffer would be included between the longer levee segments and the island's shoreline to safeguard eagle perch sites. About 43 acres of borrow area would be required just landward of the levee construction zones. These borrow areas would serve as future non forested wetland management sites. Forty-six acres of younger-aged tree vegetation would be cleared from lower elevation (449 to 450 NGVD) areas to further expand non-forested wetland habitat. In addition to the levee, a 36-inch culvert drain with a gatewell protected sluice gate, and a 15,000 GPM portable pump would be provided for water control on the island. Installation of the gated drain would be accomplished using a cofferdam; this drain would be used primarily for the discharge of interior waters, and for the input of water up to the elevation of normal pool (449 NGVD). The pump would enable the raising of water levels from normal pool to 451 NGVD. To facilitate the input and output of water, 5 segments of interior island slough would be dredged for a combined total length of 12,000 feet, a width of 25 feet, and a bottom elevation of 446 NGVD. Three 500-foot segments along this ditch system would be opened to a bottom width of 50 feet, with depth to 443 NGVD to serve as summer fish refuges. Approximately 10 acres of forest, distributed between two interior island locations, would be cleared and the site perimeter bermed. These areas would be used to contain the slough dredged material. To improve aquatic habitat cover within the new backwater area, 200 clumps of cedar trees would be weighted and suitably anchored to the shore to prevent movement. To permit the access of MDOC service boats (and at MDOC's discretion, recreational craft) to the island's interior, a boat pullover device would be provided. The two goals of the project are to enhance migratory waterfowl habitat, and to enhance habitat for slackwater fishes. Specific objectives for attaining the waterfowl goal are (1) decreasing sedimentation into the island's wetlands, (2) providing a means to control water levels on the island independent of river stage, (3) increasing reliable food production for waterfowl (particularly moist soil plant species), and (4) increasing total wetland values (i.e., habitat units) for migratory waterfowl. Objectives for the fisheries goal are (1) increasing the quantity of river slackwater habitat, (2) reducing the potential for backwater sedimentation, (3) increasing the photic zone, (4) increasing the available cover, and (5) increasing the total habitat values for slackwater fishes.
Description: Definite Project Report with Integrated Environmental Assessment
Rights: Approved for Public Release; Distribution is Unlimited
Size: 295 pages / 16.05 MB
Types of Materials: PDF/A
Appears in Collections:Environmental Documents

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