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Horita Acres Review Comments <br />December 7, 2017 <br />Page 2 <br /> <br />K:\03455-000\Admin\Docs\Plan Reviews\2017-12-07 Horita Acres\3455-000 Horita Acres Review Submittal 171207.docx <br /> <br />4. Stormwater, Grading, and Drainage <br />a. We recommend that the outlet control structures be revised to use larger orifices. The <br />proposed outlet control structures will likely clog with debris at the 1” and 1.5” orifices <br />without sufficient protection, especially when the orifice is located at the pond invert. A <br />trash grate should be installed. Efforts should be made to protect the low orifices from <br />ice formation. If clogging of the small orifices occurs the ponds will fill with stormwater <br />which will degrade the aesthetics of the pond and attract mosquitos and other insects. <br />The MPCA stormwater manual highly recommends a minimum orifice of 3” when in <br />tandem using an external trash rack and minimum of 1” when using an internal orifice <br />protection. If a small orifice is utilized, the basin should be modeled assuming this orifice <br />is clogged to verify that the stormwater basin still meets freeboard and peak rate <br />discharge requirements. <br />b. We recommend installing a type of trash rack, grate, or end treatment over the top of the <br />8” riser to prevent clogging of the outlet device from debris and floatables. <br />c. We recommend sloping the stormwater basins to provide adequate overland drainage to <br />the outlet device. This will prevent the creation of small ponding depressions which will <br />degrade the aesthetics of the ponds. <br /> <br />5. Storm Sewer <br />a. Culvert analysis in HydroCAD shows the same drainage area parameters for both <br />drainage areas routed to the culvert. Please verify drainage areas are correct, revise as <br />necessary, and verify culvert is still sized appropriately. <br />Please let me know if you have any questions. <br />Sincerely, <br /> <br />WSB & Associates, Inc. <br /> <br />Matt Schulz <br />Highway Drainage Engineer <br />(612) 322-2124 <br />mschulz@wsbeng.com