FINAL - ENVIRONMENTAL IMPACT STATEMENT CHENA RIVER LAKES PROJECT FAIRBANKS, ALASKA PREPARED BY ALASKA DISTRICT, CORPS OF ENGINEERS ANCHORAGE, ALASKA 7 SEPTEMBER 1971 CHENA RIVER LAKES FLOOI} CONTROL PROJECT Fairbanks, Alaska ( ) Draft (X) Final Environmental Statement Responsible Office; Alaska District, Corps of Engineers, Anchorage, Alaska 1. Name of Action; (X) Administrative ( ) Legislative 2. Description of Action; The project, authorized by the Flood Control Act of 1968, is a multiple-purpose project located in Interior Alaska, near the City of Fairbanks. The recommended project is designed to protect the City of Fairbanks and surrounding community from damaging floods originating on the Tanana and Chena Rivers by a combination of two methods; two earthfill dams to regulate and restrict the Chena and Little Chena Rivers, respectively, and a Tanana River levee system. Construction is scheduled to commence in April of 1973. 3. a. Environmental Impacts: The project will provide flood protection; dislocate 32 families and/or businesses; impound 2200 acres of terrestrial habitats and 2 miles of natural stream section; accelerate development of the protected flood plain; provide recreational opportunities, and may provide habitat for fish and wildlife species. b. Adverse Environmental Effects; Loss of plants and animals in 2200 acres of terrestrial habitats to be impounded; loss of plants and animals in 1000 acres of habitats to be occupied by flood control structures; possibility of water quality problems in reservoir and dis­ charge water; and termination of periodic downstream flooding will be adverse to those plant communities dependent on such inundation. 4. Alternatives; "No development;" alternative dam site; floodway; levees; relocation; and flood plain management. 5. Comments Received: State of Ak., Dept, of Natural USDA, U. S. Forest Service Resources, Div. of Parks USDI, Alaska Power Administration Dept, of Interior, Bureau of Sport Alaska Conservation Society Fisheries & Wildlife Environmental Protection Agency, Dept, of Interior, Nat. Park Ser. Water Quality Office Dept, of Interior, Bureau of USDI, Geological Survey, Water Land Management Resources Division Dept, of Interior, Bureau of USDI, Soil Conservation Service Outdoor Recreation 6 . Draft Statement to CEQ: 23 July 1971: Final Stateme to CEQ: 2 7 OCT ^71 FINAL ENVIRONMENTAL STATEMENT CHENA RIVER LAKES FLOOD CONTROL PROJECT FAIRBANKS, ALASKA Prepared by ALASKA DISTRICT, CORPS OF ENGINEERS ANCHORAGE, ALASKA 7 September 1971 FINAL ENVIRONMENTAL STATEMENT CHENA RIVER LAXES FLOOD CONTROL PROJECT Fairbanks, Alaska Project Description. The Chena River Lakes project is located near Fairbanks, Alaska. Fairbanks, the second largest city in Alaska (45,000 population), is located 400 road miles northeast of Anchorage and 100 miles south of the Arctic Circle. The project was authorized by the Flood Control Act of 1968 for flood control, recreation, and fish and wildlife enhancement. This multiple-purpose project is designed to protect approximately 72,000 acres of the city of Fairbanks and adjacent Chena Rivers Valley from damaging floods originating from the Tanana and Chena Rivers by a combination of two methods; two dams to regulate and restrict the Chena and Little Chena Rivers, respectively, and a levee system along the Tanana River. Characteristics of the project features" are given below in tabulated form; TABLE I. DIMENSIONAL DATA, CHENA RIVER FLOOD CONTROL PROJECT Moose Creek Little Chena-Tana'na Dam Chena Dam River Levee Length 7 .1 miles 4,675 feet 27 miles Average Height 30 feet 60 feet 12.5 feet Top Width 24 feet 30 feet 12 feet • T°P Elevation +525 m.s.l +655 m.s.l. Variable Embankment 5 million 1.9 million 4.0 million Volume cubic yards cubic yards cubic yards Freeboard 3 feet 6 feet 3 feet Recreation Pool Elevation +500 m.s.l. p° o1 North 700 acres Surface Maximum 2,500 Area South 1500 acres cres p° o1 North 1 mile x 1 mile 6 miles x Dimension South 2 miles x 3 mis. 2 miles long Mean North 10 feet Depth South 5 feet _ Moose Creek Dam and Reservoir. The Moose' Creek Dam is located about 17 air miles cast of Fairbanks. This dan will divert fiocd 2 *. ,\:r. fro m the Chena River into the Tanana River to prevent flooding in the vicinity of Fairbanks. The accompanying storage reservoir, which will be formed by the annual spring runoff, will be divided into two pools by a low, im­ pervious rockfaced overflow sill. This sill will be located about mid­ way along the dam and will extend eastward (about 2,500 feet) from the dam until the top intersects natural ground at elevation plus 500 feet v mean sea level (m.s.l.). The maximum probable flood stage (elevation plus 522 feet) could inundate up to 10,000 surface acres (behind the dam). Moose Creek reser­ voir level will range between 500 and 522 feet, remaining at 500 feet except during flood control operation. The reservoir level will be above the permanent pool elevation of 500 feet from several hours to several v/eeks depending upon the magnitude of the flood event. Vertical fluctuation will normally be about 2 to 3 feet with the maximum probable flood creating a 22-foot (plus 522 feet m.s.l.) vertical pool fluctuation. Flexibility will be stressed in project design so that operation schemes may be revised and adjusted according to further recommendations from environmental agencies. Although an operation plan is pending further research studies, a preliminary reservoir operation schema is conceived as a three-phase seasonal plan. a. Phase one: As spring flood flows subside, the south pool will either be drained into the Chena River or free passage will be provided allowing salmon snolts, which are migrating downriver at this time, to continue their downstream movement. Draining will be accomplished by constructing a drainage channel connecting the south pool with the Chena River. This channel will also facilitate seepage•collection and the passage of the south pool fish population to the Chena River. If drained the south pool will then be filled again for summer recreation purposes. b. Phase two: At other than flood stages the plan provides for a summer-season reservoir pool (at elevation 500 feet) of-about 2,200 acres. c. Phase three: The third phase of yearly operation will consist of draining the south reservoir before freezeup due to the relatively shallow condition of tie south pool and its questionable capability for sustaining a fish population during the winter. This will leave the 700- acre north reservoir as a permanent body of water throughout the year. The north pool, with deeper water and better circulation may be able to sustain a year-round fishery population. A fish passage facility will be located on the Chena River to enable resident and anadromous fish passage over the dam during flood or low flow stages. A fish passage facility is not anticipated for the Moose Creek spillway. The spillway and channel are designed'with the capability of allowing passage of migrating salmon. This spillway works (1,200 feet wide) will be located at ground elevation (+502 m.s.l.) and will lead into an 8,000-foot long channel (500-foot bottom width), directing Chena River flood flows into the Tar.ar.a River. 2 Diverting Chena River water into the Tanana River during fail high flow periods nay mislead migrating salmon. They could migrate past the mouth of the Chena River and proceed up the Tanana to the spillway works; therefore, the spillway will be designed to pass fish. The outlet works on the Chena River will include debris racks, control gates, and energy dissipators. The project will be accessible from the north or south. A public access road about 5 miles long will connect the project area with the Chena Hot Springs road on the north and the road on top of the dam will connect with the Richardson Highway on the south. Relocation of one mile of the Eielson spur of the Alaska Railroad, elevating 1/2 mile of the Richardson (Alaska) Highway to coincide with the elevation of the reconstructed Moose Creek dike, and associated new bridges to accommodate the relocated railroad and highway, respectively, are also an integral part of the project. The bridges, intended to span the Moose Creek spillway, will be 1,200 feet long. The ground in the v icinity of the bridges will be riprapped to withstand increased water velocities through the spillway section. In order to protect the area between the Moose Creek Bluff and Eielson Air Force Base from peak flood flows, a training dike, extending eastward from Moose Creek Bluff for about three miles, will also be constructed. Examination of the present alignment of the proposed 48-inch Trans - Alaska pipeline indicates it will cross the southern portion of the Chena River Dam and Reservoir. The Corps of Engineers is maintaining close liaison with the Alyeska Pipeline Service Company to assure project compatibility. It is presently recommended that the pipeline be realigned to avoid any conflict with the project. Little Chena Detention Dam. The Little Chena Dam and detention reser­ voir will provide only flood protection as high water flows will only be temporarily restricted (about a 1- to 2-week period) and not permanently impounded. The dam design incorporates an uncontrolled outlet works con­ sisting of two concrete conduits for downstream water release. Because little is known of the Little Chena fisheries resource, a passage facility will not be recommended until further studies indicate a demonstrated need exists. Chena-Tanana River Levee. The levee system will be located along the north b -»k of the Tanana River from the reconstructed Moose Creek dike to the con'luer.ce of the Chena River and extending upstream on the Chena for approximately four miles.