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included in the application, existing dams will need to be removed <br />(prior to seeding and installation of fiber blankets in those <br />segments to be seeded), and cobble dams in accordance with an <br />approved design will need to be replaced.in appropriate locations <br />as specified in tYie amended application. <br />Cobble dams using the river rock could be used in temporary <br />ditches, or as interim treatments in permanent ditches, while rock <br />check dams of similar design but constructed with graded angular <br />riprap are recommended as additional stabilization measures to <br />complement revegetation on permanent perimeter ditches. In either <br />case, rock should :be placed such that dam faces are no steeper than <br />2:1, and the dam bases should be excavated such that channel <br />capacity is not compromised. Appropriate gravel filter blanket <br />and/or filter cloth underliner should be utilized. The dams should <br />also be keyed into the sides of the ditch. The top of the dam <br />should be configured such that the center is lower than the sides, <br />and large rock should placed in the high energy area at the <br />downstream toe of the dam to prevent scour and undercutting. <br />Temporary stabilization measures to be utilized as needed to <br />` control flow veloc:ities and minimize erosion until the piles are <br />reclaimed and vegetation cover is established should be discussed <br />in the text of the application. Acceptable approaches as discussed <br />in the inspection report include the use of various structures in <br />temporary "in pit" ditches, including dugout sediment traps used <br />singly or in combination with riprap, straw bale check dams, rock <br />check dams, or similar structures. Design, installation, <br />monitoring, and maintenance of such structures should be specified <br />in the application. Sediment which accumulates behind check dams <br />or within sediment traps will need to be cleaned out regularly to <br />maintain the effectiveness of the structures. A good management <br />practice would be to initiate cleanout when sediment level reaches <br />1/2 the height of the check dam or 1/2 the depth of the sediment <br />trap. Traps should be designed to allow for easy access and <br />cleanout. <br />High velocity channel segments at the lower end of RP-2/3 east side <br />ditch, and the lower segment of the RP-4 east side ditch have been <br />lined with river rock as a temporary measure. The river rock will <br />probably need to be replaced by graded riprap as described in Item <br />3, even though the ditch segments may not be at final design <br />location or elevation, due to the high erosion potential of these <br />segments. <br />6. The erosion control ditches as depicted on amended Map 77 may <br />need to be more closely spaced (i.e. 15' vertical spacing rather <br />than 30') for maximum effectiveness, and it would appear that the <br />ditches need to be extended further to the south on RP-2/3 than <br />depicted on the ma:p. Use of such ditches should be considered for <br />5 <br />