1117.07 DETENTION/RETENTION OF STORM WATER.

   Detention/retention of storm water shall be required for each subdivision unless specifically exempted by the Planning Commission.

   The objective of a detention/retention facility is to regulate the run-off from a rainfall and to control discharges to downstream areas in order to reduce the impact on downstream drainage systems.

   (a)    Definitions. Unless the context specifically indicates otherwise, the meaning of the terms used in this section shall be as follows:

      (1)    "Storm water detention/retention facility" means any structure or facility used to detain storm water run-off, and gradually release the stored run-off at an acceptable rate.

      (2)    "Detention basin" means dry surface areas created by constructing an excavated or embankment basin.

      (3)    "Retention basin" means permanent ponds where additional storage capacity is provided above the normal water level.

      (4)    "Storm water run-off' means that portion of rainfall that is not lost to infiltration, surface storage or evaporation.

   (b)    Exemptions to Detention/Retention Requirements. The developer may apply to the Planning Commission for exemption from construction of detention/retention facilities. Each request will be reviewed on its own merit and as it affects the entire drainage area in which it lies and into which it flows.

   (c)    Design.

      (1)   Quantity of run-off. The peak rate of run-off during the 100 year post development storm cannot exceed the peak rate of run-off during the two year pre-development storm. For those areas where a study of the downstream area indicates the extended time of high discharge and/or velocity due to restricted release rate and storage may cause flooding and/or excessive erosion, the City Engineer may require additional controls.

   (d)    Submission Requirements. Plans and supporting data to verify storage volumes, release dates, etc., shall be submitted to the City Engineer. The submission shall include, but is not limited to, the following:

      (1)    A plan prepared by a registered professional engineer which may be the improvement plan, drainage and grading plan or similar plan at a scale of one inch to 100 feet or larger, shall be submitted and contain at least the following information:

         A.    All existing and proposed drainage facilities.

         B.    Existing and proposed contours.

         C.    Existing structures.

         D.    The detention/retention facility with outlet structures.

         E.    Cross section through detention/retention facility.

         F.    Pertinent elevations, e.g., water surface, flowline of flow control devices, etc.

         G.    Emergency spillway designed to pass a 100 year storm and with a minimum depth of one foot.

         H.    Any other information required by the City Engineer to clarify intent or design features.

      (2)    All calculations, outlines and designation of drainage areas, and other supporting data in sufficient detail and form to facilitate an expedient and accurate review.

   (e)    Fees. Review work performed by professional consultants and other costs incurred by the City may be charged to the applicant at their billed cost plus ten percent (10%). The fee must be paid in full prior to approval of the plans by the Planning Director.

      (Ord. 25-14. Passed 4-14-14.)