04-27-2022 Council Packet - Laserfiche WebLink

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