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1 <br />2 <br />chapters 6115.0215, subpart 4, item E, and 6115.0216, subpart 2. Work must not <br />proceed until approved by the commissioner. See Figure 8. <br />Figure 8. Riprap Guidelines <br />Regulatory <br />flood <br />protection <br />elevation <br />Riprap Guidelines <br />Above OHWL get local <br />government unit permit <br />Below OH-WL: get GNR <br />permit or permission <br />OHM.. <br />River. <br />Fitter <br />3 <br />Finished slope below OHM, must <br />be less than a l:3 ratio <br />3 <br />4 b. Construction or replacement of rock riprap, retaining walls, and other erosion control <br />5 structures within the bluff impact zone and the water quality impact zone are allowed with a <br />6 permit consistent with provisions of scction 117 148(j)(6) (conditions of land alteratie-n <br />7 -permit approval) provided that: <br />8 1. If the project includes work at or below the OHWL, the commissioner has already <br />9 approved or permitted the project. <br />10 2. The structures are used only to correct an established erosion problem as determined <br />11 by the City of Ramsey. <br />12 3. The size and extent of the structures are the minimum necessary to correct the erosion <br />13 problem and are not larger than the following, unless a professional engineer <br />14 determines that a larger structure is needed to correct the erosion problem: <br />15 (i) Retaining walls must not exceed five feet in height and must be placed a minimum <br />16 horizontal distance of ten feet apart; and <br />17 (ii) Riprap must not exceed the height of the regulatory flood protection elevation. <br />18 c. Repair of existing rock riprap, retaining walls, and other erosion control structures above the <br />19 OHWL does not require a permit provided it does not involve any land alteration undcr <br />20 scction 117 148(j)(2) (land alteration permit). <br />21 (4) Stormwater management. <br />22 a. In the bluff impact zone, storm water management facilities are prohibited except by <br />23 permit if: <br />24 1. There are no alternatives for storm water treatment outside the bluff impact zone <br />25 on the subject site; <br />26 2. The site generating runoff is designed so that the amount of runoff reaching the <br />27 bluff impact zone is reduced to the greatest extent practicable; <br />28 3. The construction and operation of the facility does not affect slope stability on <br />29 the subject property or adjacent properties; and <br />30 4. Mitigation based on the best available engineering and geological practices is <br />31 required and applied to eliminate or minimize the risk of slope failure. <br />32 b. In the water quality impact zone, development that creates new impervious surface, a-s <br />33 allowed by exemption in scction 117 148(1) (exemptions), or fully reconstructs existing <br />34 impervious surface of more than 10,000 square feet requires a storm water permit or <br />35 approved storm water plan. Multipurpose trails and sidewalks are exempt if there is <br />36 down gradient vegetation or a filter strip that is at least five feet wide. <br />Page 113 of 160 <br />