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Build a temporary dike, if necessary, to the down slope side of the • <br />structure to prevent bypass flow. <br />Block and Gravel Filter - A barrier formed around the storm drain inlet <br />with standard concrete blocks and gravel. See Figure 4.2.8. <br />Provide a height of 1 to 2 feet above inlet. <br />• Recess the first row 2-inches into the ground for stability. <br />• Support subsequent courses by placing a 2x4 through the block <br />opening. <br />• Do not use mortar. <br />• Lay some blocks in the bottom row on their side for dewatering the <br />pool. <br />• Place hardware cloth or comparable wire mesh with %2-inch openings <br />over all block openings. <br />• Place gravel just below the top of blocks on slopes of 2H:1 V or flatter. <br />• An alternative design is a gravel donut. <br />• Provide an inlet slope of 3H:1V. <br />• Provide an outlet slope of 2H:1 V. <br />• Provide al -foot wide level stone area between the structure and the • <br />inlet. <br />• Use inlet slope stones 3 inches in diameter or larger. <br />• Use gravel'/2- to 3/4-inch at a minimum thickness of 1-foot for the <br />outlet slope. <br />• <br />Volume II — Construction Stormwater Pollution Prevention - August 2012 <br />4-81 <br />