§ 55.06  DESIGN CALCULATIONS.
   (A)   All drainage plans shall be prepared under the direct supervision of a licensed professional engineer and shall conform to the adopted drainage standards of the City of St. Johns.
   (B)   Applicants for building permits must certify that the finished topography of the site will not have any adverse effects on adjoining properties because of any change in the flow of surface water.
   (C)   A drainage plan shall consist of narrative text, engineering drawings, contour maps, and all supporting engineering calculations, as applicable to the land area covered by the plan, which are required to demonstrate full compliance with the requirements of this chapter and the city drainage standards.
   (D)   In general, surface water and roof water shall be collected onsite and transported underground to an approved drainage system. This provision does not apply to one and two-family dwellings unless special site circumstances exist, as determined by the City Manager. No site run-off will be directed to adjacent property.
   (E)   Allowable discharge rate. The discharge rate for site drainage following the completion of a proposed construction shall not exceed the discharge rate of the site before construction, and also limited by the maximum coverages as listed in division (F).
   (F)   Stormwater detention requirements.
      (1)   Detention requirements shall be based on the following lot coverages within zoning districts.
 
Zoning District
Lot Coverage
R1 Low Density Residential
40%
R2 Medium Density Residential
45%
R3 High Density Residential
55%
MC Municipal Center
55%
O Office
60%
GC General Commercial
70%
CBD Central Business District
100%
I1 Industrial High Performance
70%
I2 Industrial Liberal Performance
70%
MU Mixed Use
60%
 
      (2)   Additional lot coverage shall require detention facilities calculated to the difference between allowable lot coverages listed above and the actual lot coverage proposed. Districts R1, R2, and R3 are excluded from allowable additional coverage and therefore shall maintain the maximum coverage listed above.
   (G)   Stormwater quality principals.
      (1)   Additional consideration may be given by the City Manager for calculated discharge rate limits if the applicant incorporates Low Impact Design practices within the proposed project. Examples of such practices include, but are not limited to:
         (a)   First flush basin;
         (b)   Rain garden;
         (c)   Bio-filtration; and
         (d)   Bio-swale.
      (2)   These practices may result in up to a 30% detention volume requirement as determined by the City Manager.
(Ord. 644, passed 6-25-2018)