§ 55.07  DESIGN STANDARDS.
   (A)   The City Manager shall cause to be prepared, by a licensed professional engineer, standards and specifications for facilities to collect, store, detain, retain, and/or transport water/run-off generated by rainfall, snow melt and/or foundation drains. These standards and specifications shall be made effective by resolution of the City Commission and may be the same as previously adopted pursuant to the subdivision regulations (Chapter 154 of this code) and shall apply equally to the development and/or redevelopment of all other property within the boundaries of the city. The City Manager may cause these standards and specifications to be revised from time to time and said revisions may be adopted by resolution of the City Commission.
   (B)   No person, firm, or corporation shall construct any drainage system of piping, ditches, catch basins, detention or retention ponds, or storage areas of any kind, requiring approved plans or a permit from the city, or required to be built by city ordinance without conforming to the specifications set out in the city drainage standards.
   (C)   Requirements.
      (1)   General requirements.
         (a)   Stormwater detention requirements for any new construction development, redevelopment, or land use change must be in compliance with the stormwater management plan and construction must be in compliance with the stormwater permit.
         (b)   The peak runoff rate during a ten-year storm event from a developed or improved site shall not exceed the allowable discharge rate. This rate is determined as outlined in § 55.06 of this chapter.
         (c)   Engineering calculations must be submitted with the stormwater discharge permit application. The calculations shall follow the procedures outlined in this chapter.
         (d)   Roof drains shall not be connected directly to the city storm sewer system. Unrestricted runoff from the roof drain will not be accepted.
         (e)   All proposed developments shall provide sump pump discharge outlets for each lot. These leads shall not be connected to rear lot drainage systems. A storm sewer lead extended to the right-of-way/property line of each lot (minimum four inches diameter pipe) shall be provided for rear lot drainage.
         (f)   The owner/developer and city shall make a determination as to whether any or all of the facilities proposed are to become privately or publicly maintained as part of the city drainage system, Clinton County Drain Commissioner drainage system, Clinton County Road Commission drainage system, or the Michigan Department of Transportation drainage system. After that determination is made, the owner/developer shall pursue any and all necessary permitting through the receiving agency.
         (g)   The City Manager shall, in the case of a proposed subdivision, make a determination as to those control elevations that shall be entered on the final plat or make a determinations as to the necessity for deed restrictions on any particular lot in the proposed subdivision requiring the preservation of mandatory drainage facilities. Where a non-subdivided parcel of land is proposed for development, the City Manager shall make a determination as to the need for covenants to maintain responsibility for mandatory drainage facilities. All said facilities shall be located in easements dedicated to the public and shall be subject to continual inspection during the construction period.
         (h)   Soil erosion and sedimentation control measures must be implemented both during construction and permanent measures after the construction of the proposed development is complete.
      (2)   Storm sewer piping.
         (a)   Proposed storm sewer shall be designed to have capacity to pass ten-year design storm runoff rate. The five-year storm and one-year storm shall also be included in the calculations and submitted to the City Manager for reference.
         (b)   Pipe material shall be in conformance with the City of St. Johns standards and adhere to the Michigan Department of Transportation specifications.
         (c)   A minimum cover of 2.5 feet from the top of the pipe to the surface above shall be provided anywhere that pipe is constructed with public rights-of-way.
         (d)   A minimum sand bedding of four inches compacted depth is required under the bottom of the storm sewer pipe and a minimum of 12 inches compacted depth of sand backfill is required over the top of the storm sewer pipe.
         (e)   Drainage structures (manholes and/or catch basins) shall be placed at a maximum distance of 400 feet from the next in-line drainage structure for access and maintenance purposes.
      (3)   Detention and off-lot drainage. For developments in the following districts: MC, O, GC, CBD, I1, I2, MU, lot coverage limits require engineered systems. Coordinate with Chapter 155 of this code for lot coverage as it relates to aesthetics and other environmental consideration.
      (4)   Rear lot drainage.
         (a)   All lots within a condominium or platted development shall require that a lead be constructed to the edge of the city right-of-way for future rear lot drainage.
         (b)   Minimum rear lot drainage lead shall be four inch diameter pipe minimum at a minimum slope of 0.50%.
         (c)   Sand backfill and bedding shall be required wherever a pipe is to be buried under vehicle travel areas.
         (d)   Rear lot drainage leads shall be constructed at a depth such that there is a minimum of two feet of cover from the top of the any pipe to the ground surface.
         (e)   A ten feet wide easement shall be provided to the city on each lot adjacent to rear lot drainage systems for the purpose of maintenance access to the system by the city and by neighboring lot or condominium owners.
         (f)   Existing rear lot drainage systems abutting a proposed development may be used for the development provided the following are true:
            1.   The existing rear lot drainage system has the capacity to convey stormwater runoff from the proposed rear lot drainage areas; and
            2.   A signed agreement is obtained from property owners located within the existing development allowing the proposed development's rear lot stormwater runoff to pass through their existing system.
         (g)   Phased developments owned by the same proprietor may utilize proposed rear lot drainage for a current development phase on future phases provided that appropriate deed restrictions/covenants are recorded with the affected properties allowing for future phases of the development to drain into or through the existing rear lot drainage system.
         (h)   Rear lot drainage shall be included on preliminary plat documents or site plan documents.
         (i)   All rear lot drains shall connect to an approved stormwater drainage system. They cannot connect to road underdrains.
         (j)   Rear lot drainage systems in platted developments are the responsibility of the landowners and homeowners' association. An easement is to provide for maintenance work on rear lot drainage systems. The property must be returned to its pre-maintenance conditions after repairs or maintenance has been completed. The homeowners' association should develop and keep a preventative maintenance plan for the rear lot system to assure continuing proper function of the system.
   (D)   Variances from requirements. The City Manager may issue a stormwater discharge permit that waives detention requirements. This action requires the following conditions:
      (1)   A petition shall be submitted describing in detail the rationale for the proposed design changes including hydraulics and hydrology computations;
      (2)   Special circumstances or conditions exist which will affect the property under consideration such that strict compliance with the provisions of the stormwater discharge permit would deprive the applicant of the reasonable use of their land;
      (3)   A variance is necessary for the preservation and enjoyment of a substantial property right of the proprietor;
      (4)   Granting of the variance will not be detrimental to the public health, safety of general welfare, or injurious to other property in the area; and
      (5)   The City Manager has sought and received an affirmative recommendation from a qualified professional engineer.
   (E)   Stormwater system maintenance plans. It is recommended that a maintenance plan be developed for sites with a stormwater management plan. The owner or lease holder should be informed how the stormwater system operates and what maintenance work will be required to keep good operation in perpetuity.
(Ord. 644, passed 6-25-2018)