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<br />Concentrated flow structures may take a variety of forms ranging from structures <br />composed entirely of fill materials to those which are completely incised into the <br />ground, or some combination thereof. Various channel configurations and lining <br />materials may be used to provide stability for various flow volumes and velocities. The <br />shape of the channel used to convey runoff may be triangular, parabolic or trapezoidal, <br />and will be specified to fit the environmental conditions and flow characteristics of the <br />location in which they are used. Structures will be sized and capable of passing the <br />predicted flows for the type and duration of use. Permanent and critical structures will <br />be capable of passing larger volumes of runoff than temporary ones. During <br />construction all trees, brush, stumps, obstructions, and other objectionable materials <br />will be removed to avoid interference. Sediments accumulated against berms will be <br />periodically cleaned. Maintenance activities will ensure that breaching hazards are <br />corrected immediately. <br />Flow structures may be unlined or lined for erosion protection. When lining materials <br />are specified they may be vegetative, reinforced substrate matrix materials with <br />vegetation, netting, various erosion control fabrics, riprap, or some combination of these <br />materials. Reconstructed channels may use biotechnical stabilization measures for <br />stabilization. Normally these structures will be constructed from materials readily <br />available onsite. If local materials are inadequate, special construction materials will be <br />imported from outside the area for specific applications. Adequate compaction is <br />critical to structure function and appropriate linings are required to protect the <br />structures from erosion. Particular attention will be paid to allowable velocities for <br />specific lining materials. <br />In reclaimed areas, reconstructed drainage channels will be placed as necessary to route <br />runoff through disturbed and restored areas and into undisturbed channels. <br />Stabilization measures will be judiciously employed to ensure long-term stability of <br />reconstructed channels and transition zones to undisturbed features. To the extent <br />practicable, smooth channel transitions will be made between reconstructed and <br />undisturbed areas. <br />Adequate construction procedures and material quality control are critical to <br />concentrated flow structure performance. Construction inspections will be performed <br />to ensure the integrity of flow structures. Materials used on the project will meet or <br />exceed structure specifications. <br />2.1.1.1 Unlined Channels <br />Unlined channels will be used as temporary structures. Permanent channels will have <br />at a minimum a vegetation lining. Concentrated flow structures will be maintained as <br />necessary to ensure function. Permissible velocity will be used to establish channel- <br />lining requirements. Channel erosion control linings or gradient control structures will <br />be used where necessary to ensure stability and to protect against excessive erosion of <br />Prel~minarv Response Plan A-6 <br />Yankee Gulch Sodium Minerals Project <br />American Soda. L.L.P. <br />