Illinois River Habitat Enhancement Project

 

Tailraces often lack suitable fish habitat due to reduced inputs of sediment and woody debris coupled with frequent scouring flows. These habitat deficiencies have significant impacts on fish populations and subsequent management of tailrace fisheries. For example, reductions in usable area limits the amount of productive stream for anglers because fish are concentrated in few suitable areas. Fish movement and dispersion is also limited because necessary habitat is not available throughout the stream continuum. The absence of overhead cover increases fish susceptibility to predation and warming of stream water. Further, the lack of hydraulic checks limit flow dynamics and flow-related habitat alternatives necessary for fish feeding, resting and moving.

Similar to other tailrace fisheries, the lower Illinois River is characterized by the habitat limitations described above. Significant habitat improvements within this stream are necessary to improve physical and hydraulic habitat conditions and the angling potential of the system.

ODWC began to enhance stream habitat in the lower Illinois River in 2002 by identifying areas that lack quality habitat. Many hours of survey work indicated that a cross vane would be a beneficial structure for a particularly degraded reach of stream located just below the island, downstream of the powerhouse.

After the project location was determined the Department staff began designing the enhancement structure. A detailed budget was also developed such that funding could be solicited. Once again, anglers went above and beyond to provide assistance necessary to make the project happen. The Tulsa Chapter of Trout Unlimited, the Federation of Fly-Fishers, the Northeast Oklahoma Fly-Fishers and Nature Works collectively donated 25-percent of the money needed to complete the work. These donations were then matched with Sportfish Restoration dollars to fund the project.

ODWC personnel completed the cross vane in March 2004. The structure is U-shaped and extends across the stream with the bottom of the U pointing upstream (see pictures). It was constructed using large rock placed into the river with heavy equipment. The sides of the structure are attached to the stream bank at an elevation equal to the water level when two power turbines are being operated to produce electricity. The sides of the structure extend upstream at a 20 – 30-degree angle until reaching 1/3 of the way across the channel (two thirds total). The sides the structure slope downwards at a 2 – 7 degree angle from the bank toward the channel center. The tip of the U, which composes the middle third of the structure, is slightly below the water level during base-flow periods.

There are two main purposes of the cross vane structure. First, bank stabilization is obtained as flow is diverted to the middle of the stream. This reduces stress to the banks as stream energy is forced to the center of the channel. Secondly, in-stream habitat is created by this energy as it cuts deeper pool habitat below the structure. Deepening also results above the structure as flow is impounded upstream. Both of these areas create resting/ambush sites for trout, out of the current, behind the rocks.

ODWC biologist plan to continue habitat improvements at the lower Illinois River over the coming years. Several other projects are possible and, given adequate funding and resources, this stream should continue to benefit from new enhancement initiatives. *(Click on pictures to view larger image)