A.   Soil Erosion And Sediment Control Required: No land shall be developed and no use shall be permitted that results in water runoff causing flooding, erosion, or deposit of minerals on adjacent properties. Such runoff shall be properly channeled into a storm drain, watercourse, ponding area, or other public facilities in compliance with title 8, chapter 4 of this Code, subject to the review and approval of the City Engineer.
   B.   Permit Required To Disturb Land: No person shall initiate any land disturbing activity without first obtaining a permit from the City as may be required by title 9, chapters 6 and 7 of this Code, subject to review and approval of the City Engineer.
   C.   Drainage Plans: In the case of all residential subdivisions, multiple-family, business and industrial developments, the drainage plans with appropriate spot site elevations shall be submitted to the City Engineer for review, and the final drainage plan shall be subject to written approval. In the case of such uses, no modifications in grade and drainage flow through fill, erection of retaining walls or other such actions shall be permitted until such plans have been reviewed and received written approval from the City Engineer.
   D.   Standards: The following standards shall apply to all development and activity that necessitates the grading, stripping, cutting, filling, or exposure of soils:
      1.   General Standards:
         a.   The development shall conform to the natural limitations presented by topography and soil so as to create the least potential for soil erosion.
         b.   Erosion and siltation control measures shall be coordinated with the different stages of development. Appropriate control measures shall be installed prior to development when necessary to control erosion.
         c.   Land shall be developed in increments of workable size such that adequate erosion and siltation controls can be provided as construction progresses. The smallest practical area of land shall be exposed at any one period of time.
         d.   The drainage system shall be constructed and operational as quickly as possible during construction.
         e.   Whenever possible, natural vegetation shall be retained and protected.
         f.   Where the topsoil is removed, sufficient arable soil shall be set aside for respreading over the developed area. The soil shall be restored to a depth of four inches (4") and shall be of a quality at least equal to the soil quality prior to development.
         g.   When soil is exposed, the exposure shall be for the shortest feasible period of time. No exposure shall be planned to exceed sixty (60) days. Said time period shall be extended only if the Zoning Administrator is satisfied that adequate measures have been established and will remain in place.
         h.   The natural drainage system shall be used as far as is feasible for the storage and flow of runoff. Stormwater drainage shall be discharged to marshlands, swamps, retention basins or other treatment facilities. Diversion of stormwater to marshlands or swamps shall be considered for existing or planned surface drainage. Marshlands and swamps used for stormwater shall provide for natural or artificial water level control. Temporary storage areas or retention basins scattered throughout developed areas shall be encouraged to reduce peak flows, erosion damage, and construction costs.
      2.   Exposed Slopes: The following control measures shall be taken to control erosion during any activity where soils are exposed:
         a.   Grading and erosion control plans for exposed slopes shall comply with section 9-6-5 of this Code and are subject to review and approval of the City Engineer.
         b.   At the foot of each exposed slope, a channel and berm should be constructed to control runoff. The channelized water should be diverted to a sedimentation basin (debris basin, silt basin or silt trap) before being allowed to enter the natural drainage system.
         c.   Along the top of each exposed slope, a berm should be constructed to prevent runoff from flowing over the edge of the slope. Where runoff collecting behind said berm cannot be diverted elsewhere and must be directed down the slope, appropriate measures shall be taken to prevent erosion. Such measures should consist of either an asphalt paved flow apron and drop chute laid down the slope or a flexible slope drain. At the base of the slope drain or flow apron, a gravel energy dissipator should be installed to prevent erosion at the discharge end.
         d.   Exposed slopes shall be protected by whatever means will effectively prevent erosion considering the degree of slope, soils material, and expected length of exposure. Slope protection shall consist of mulch, sheets of plastic, burlap or jute netting, sod blankets, fast growing grasses or temporary seedings of annual grasses. Mulch consists of hay, straw, wood chips, corn stalks, bark or other protective material to be anchored by means as approved by the City Engineer.
         e.   Alternate control measures, other than those specifically stated above or provided in title 9, chapter 6 of this Code, may be used in place of the above measures if it can be demonstrated that they will as effectively protect exposed slopes, subject to review and approval of the City Engineer.
      3.   Design Standards:
         a.   Waterways:
            (1)   The use of the natural aboveground drainage system to dispose of runoff is strongly encouraged. Storm sewers are only to be used where it can be demonstrated that the use of the aboveground natural drainage system will not adequately dispose of runoff. Aboveground runoff disposal waterways may be constructed to augment the natural drainage system. To the extent possible, the natural and constructed waterways shall be coordinated with an open space trail system.
            (2)   The widths of a constructed waterway shall be sufficiently large to adequately channel runoff from a 10-year storm. Adequacy shall be determined by the expected runoff when full development of the drainage area is reached.
            (3)   No fences or structures shall be constructed across the waterway that will reduce or restrict the flow of water.
            (4)   The banks of the waterway shall be protected with a permanent turf vegetation.
            (5)   The banks of the waterway shall not exceed five feet (5') horizontal to one foot (1') vertical in gradient.
            (6)   The gradient of the waterway bed shall not exceed a grade that will result in a velocity that will cause erosion of the banks of the waterway.
            (7)   The bed of the waterway shall be protected with turf, sod, or concrete. If turf or sod will not function properly, rip rap may be used. Rip rap shall consist of quarried limestone, fieldstone (if random rip rap is used) or construction materials, provided said construction materials are limited to asphalt cement and concrete. The rip rap shall be no smaller than two inches (2") square nor no larger than two feet (2') square. Construction materials shall be used only in those areas where the waterway is not used as part of a recreation trail system.
            (8)   If the flow velocity in the waterway is such that erosion of the turf sidewall will occur and said velocity cannot be decreased via velocity control structures, then other materials may replace turf on the sidewalls. Either gravel or rip rap may be allowed to prevent erosion at these points.
         b.   Water Velocity:
            (1)   The flow velocity of runoff in waterways shall be controlled to a velocity that will minimize erosion of the waterway.
            (2)   Flow velocity shall be controlled through the installation of diversions, berms, slope drains, and other similarly effective velocity control structures.
         c.   Sediment Control:
            (1)   To prevent sedimentation of waterways, pervious and impervious sediment traps and other sediment control structures shall be incorporated throughout the contributing watershed.
            (2)   Temporary pervious sediment traps could consist of a construction of bales of hay with a low spillway embankment section of sand and gravel that permits a slow movement of water while filtering sediment. Such structures may serve as temporary sediment control features during the construction stage of a development.
            (3)   Permanent impervious sediment control structures consist of sediment basins (debris basins, desilting basins, or silt traps) and shall be utilized to remove sediment from runoff prior to its disposal in any permanent body of water.
         d.   Maintenance Of Erosion Control System:
            (1)   The erosion and velocity control structures shall be maintained in a condition that will ensure continuous functioning according to the provisions of this title.
            (2)   Sediment basins shall be maintained as the need occurs to ensure continuous desilting action.
            (3)   The areas utilized for runoff waterways and sediment basins shall not be allowed to exist in an unsightly condition. The banks of the sediment basins and waterways shall be landscaped.
            (4)   Prior to the approval of any development, the developer shall make provision for continued maintenance of the erosion and sediment control system.
   E.   Building Elevations:
      1.   The top of the foundation and the garage floor of all structures shall be eighteen inches (18") above the grade of the crown of the street upon which the property fronts.
      2.   The lowest floor, including basement floor, of all structures constructed on lots preliminarily platted or established after January 24, 2016, shall be at a level at least three feet (3') above the highest known groundwater table elevation. If requested by the building official, the groundwater table elevation shall be determined by a licensed soils engineer using soil borings, piezometers, or the observation of mottled soils.
      3.   Exceptions to this standard may be approved by administrative permit upon consultation with the City Engineer for special circumstances such as increased setback, site topography, septic system operation and the like; provided, that proper site and area drainage is maintained and the elevation of the structure is in keeping with the character of the area.
   F.   Wetlands: In addition to the requirements of chapter 93 of this title, the following shall be the minimum protection for natural wetlands:
      1.   Runoff must not be discharged directly into wetlands without appropriate quality and quantity runoff control, depending on the individual wetland's vegetation sensitivity, subject to approval of the City Engineer. (Prior Code § 20-16-5)
      2.   Wetlands must not be drained or filled, wholly or partially, unless replaced by either restoring or creating wetland areas of at least equal public value. Compensation, including the replacement ratio and quality of replacement, should be consistent with the requirements outlined in the rules adopted by the Board of Water and Soil Resources to implement the Wetland Conservation Act of 1991, as amended. (Prior Code § 20-16-5; amd. 2018 Code)
      3.   Work in and around wetlands must be guided by the following principles in descending order of priority:
         a.   Avoid both the direct and indirect impact of the activity that may destroy or diminish the wetland.
         b.   Minimize the impact by limiting the degree or magnitude of the wetland related activity and its implementation.
         c.   Rectify the impact by repairing, rehabilitating, or restoring the affected wetland environment with one of at least equal public value.
         d.   Reduce or eliminate the adverse impact over time by preservation and maintenance operations during the life of the activity.
         e.   Compensate for the impact by replacing or providing approved substitute wetland resources or environments.
      4.   a. A protective buffer of natural vegetation at least twenty feet (20') wide from the delineated edge at the time of development shall surround all wetlands within parcels preliminarily platted, developed, or redeveloped after October 14, 2002. The City Engineer may require a larger buffer than the minimum based upon site specific design issues. The design criteria should follow common principles and the example of nearby natural areas. The site should be examined for existing buffer zones and mimic the slope structure and vegetation as much as possible.
         b.   A principal building setback of forty feet (40') from the delineated edge of all wetlands or twenty feet (20') from the edge of a buffer easement, whichever is greater, shall be provided within parcels preliminarily platted, developed, or redeveloped after October 14, 2002.
         c.   Grading, construction, or vegetation alteration/disturbance within this buffer is prohibited. Buffer design and protection during construction shall accomplish any or all of the following:
            (1)   Slow water runoff.
            (2)   Enhance water infiltration.
            (3)   Trap sediment, fertilizers, pathogens, heavy metals, blowing snow and soil, and act as corridors for wildlife.
            (4)   Drain tiles shall be identified and rendered inoperable.
         d.   The wetland and buffer shall be platted as an outlot if established as part of a subdivision application. All other applications shall require dedication of a perpetual conservation easement.
      5.   Ponding areas established for stormwater drainage purposes are exempt from the provisions of this section.
   G.   Security:
      1.   The developer shall provide the City financial security in the form of a cash escrow or letter of credit for required grading, landscape, and driveway improvements required by this title as a condition of subdivision approval and/or issuance of a building permit; letters of credit must be from a State or Federally chartered bank or savings and loan association, insured by the Federal Deposit Insurance Corporation that has an office in the State of Minnesota, or a subsidiary of such bank or savings association with an office in the State of Minnesota.
      2.   An as built certificate of survey shall be submitted to verify that the final as built grades and elevations of the lot and building setbacks are consistent with the approved grading plan for the development and amendments as approved by the City Engineer, that all required property monuments are in place, and verify that all required landscaping and driveway improvements are completed.
      3.   If the developer fails to perform required grading, landscape, or driveway improvements, or submit an as built certificate of survey as required by this title within one year from the date of occupancy, the security is forfeited to the City and may be used by the City to cure any default. The property owner shall further agree to be responsible for all costs incurred by the City that exceed the amount of the security forfeited. (Prior Code § 20-16-5)