§ 151.049  STORMWATER MANAGEMENT SYSTEM DESIGN AND EVALUATION.
   The following criteria should be used in evaluating and designing the stormwater management system. The underlying objective is to provide capacity to pass the ten-year peak flow in the minor drainage system and to provide an overland flow path for flows in excess of the design capacity.
   (A)   Design methodologies.
      (1)   Minor drainage systems may be designed using the rational formula.
      (2)   Major drainage system for areas up to ten acres may be designed using the rational formula.
      (3)   Major drainage systems for areas larger than ten acres and all detention basins must be designed using an approved hydrograph-producing runoff calculation method.
   (B)   Positive drainage.
      (1)   All areas of the property must be provided with an overland flow route that will pass the 100-year flow at a stage at least two feet below the lowest adjacent grade of structures hydraulically connected to the flow route.
      (2)   Overland flow routes up to the 100-year frequency flow level shall be placed in drainage easements. Drainage easement language shall strictly prohibit the placement or construction of fill or other obstructions that would impede stormwater runoff flow.
      (3)   Wherever possible, storm sewers should be used as minor drainage systems in lieu of drainage swales for rear and side yard drainage.
(Ord. 07-02, passed 4-16-2007)