Arkansas River Division 2 Design Report

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Design Report for Canon City Whitewater Kayak and Recreation Park in the Arkansas River • is in equilibrium with the upstream and downstream reaches. No changes to channel form downstream of the project area are expected. No long-term impacts from the project are expected. The project may have temporary construction impacts with track equipment driving on and excavating the bed material in the wet channel. Construction activity may have isolated increases in turbidity. Best management practices (as described in Plate C-5 attached) such as turbidity curtains, silt fences, construction sequencing and care of water shall be utilized to minimize potential turbid conditions and locations. The environmental effects of the proposed hydraulic structures could prove beneficial to the over wintering habitat for fish. The proposed project would improve the riparian zone, which may reduce local water temperatures. X. Hydraulic Analysis There are two proposed recreation enhancement structures within the reach. Each of the two structures creates what is known as a"control section," in which flows pass through a"critical"state. In the CWCB's 2003 Technical Criteria,the CWCB defined control as: "A section across the stream where a manmade structure causes the flow to pass through critical depth when flow changes from sub-critical to super-critical." Each of the two structures enhances a hydraulic jump for recreation;this hydraulic jump happens at a section across the river where flows pass from a sub-critical state to a super- critical state. The proposed structures "control"the flow to create the desired hydraulic jump. The"critical" state of flow is measured by a Froude Number. When a Froude Number is greater than 1.0 the flow is super-critical,when less than 1.0 the flow is sub- critical, and when equal to 1.0 the flow is considered critical. Below,table 3 shows the Froude Numbers for the structures. For each structure, these Froude Numbers were calculated at three sections: at the structure,upstream of the structure, and downstream of the structure,to reveal the control section and the hydraulic jump. This table includes the hydraulic parameters of depth,velocity and Froude Numbers for each of the three sections for each structure(based on 1 dimensional hydraulic modeling with mixed flow regime). The upstream structure, Flytrap,would be modified into a control section resulting in a hydraulic jump. The feature would have wings that extend from the main channel to both the left and right banks. The Flytrap would have two flatter profile precast structures to form a hole. The hole would form at all flows;however, above 250 cfs the downstream pool deepens to greater than 3 feet. Depths of 3 feet and greater are generally considered adequate for rolling. Therefore, 250cfs is the minimal flow rate for the proposed Flytrap • IVE ��%� 11 of 16