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MnDOT Drainage Permits Checklist <br />Purpose of the MnDOT Drainage Permit <br />MnDOT Metro District regulates activities that impact its drainage systems and its MS4 <br />regulated area. The purpose of the Drainage Permit is to protect State of Minnesota <br />investment in infrastructure including but not limited to roadways, storm water treatment <br />basins, ditches and storm sewer systems. Excess storm water and/or sediment laden storm <br />water added to MnDOT's drainage systems leads to degradation of these assets. Negative <br />impacts include but are not limited to: sediment deposition, loss of flood storage capacity <br />and also loss of hydraulic conveyance capacity. These impacts may cause premature <br />flooding of the road surface and/or erosion damage on State right-of-way. <br />Technical Requirements of the MnDOT Drainage Permit <br />The permit applicant shall demonstrate that offsite runoff coming to MnDOT drainage <br />system and/or right-of-way will not increase as a result of the proposed project. This is <br />quantified as a "no increase in discharge" criteria for the 2 -year, 10 -year and 100 -year <br />storm events. Compliance is demonstrated by applying hydraulic/hydrologic software <br />models. HydroCAD and XPSWMM are the approved models to compare the pre and post <br />project discharge values. Typically, HydroCAD is sufficient to model most proposed <br />projects. However, XPSWMM may be required if the project contains extensive storm <br />water pipe systems connected to MnDOT storm sewer or if HydroCAD cannot in <br />MnDOT's judgment effectively model pressure flow, complex junctions and/or <br />backwater effects that are present. The 2 -year, 10 -year and 100 -year storm events shall be <br />based upon Atlas 14 runoff amounts per the NOAA website. <br />In addition, Drainage Permit Applicants shall meet all applicable water quality treatment <br />requirements established by the local Watershed District(s) and the MPCA. <br />Permit applicants should anticipate that specific projects that seek to divert runoff to <br />another sub -watershed or watershed will be denied. It is MnDOT practice to avoid such <br />watershed diversions whenever practicable. <br />Submittal Requirements: <br />• Readable/legible watershed maps that show pre and post project drainage <br />conditions. These two separate contour maps shall be large enough in scale so that <br />approximate flow paths can be determined for verifying the Time of <br />Concentrations used in the models. The drainage/watershed maps shall include <br />enough detail so that Curve Numbers used in the hydraulic models may be <br />verified by MnDOT. <br />April 2014 <br />