(A) The city understands that many streams and drainage channels serving the city may not have sufficient capacity to receive and convey stormwater runoff resulting from existing and continued urbanization. Accordingly, the storage and controlled release rate of excess stormwater runoff shall be generally required for any development, redevelopment and new construction located within the city.
(B) The release rate of stormwater from development, redevelopment, and new construction shall not exceed the stormwater runoff rate from the land area in its pre-developed condition. The developer must submit to the city, detailed computations of runoff before and after development, redevelopment or new construction that demonstrate that the runoff rate will not be increased.
(C) These computations must show that the peak runoff release rate after development for the 100-year return period storm must not exceed the ten-year return period pre-development peak runoff rate. Furthermore, the peak runoff rate after development for the ten-year return period storm of critical duration must not exceed the two-year return period pre-development peak runoff rate.
(D) Special cases may exist where the detention of runoff from a development would be detrimental to the overall watershed and drainage outfall. The Board, after thorough investigation and evaluation, may waive or reduce the requirement of controlled runoff for a specific development site if hydrologic modeling of the watershed and receiving stream prove that controlled runoff is not needed. It shall be the responsibility of the developer to have such modeling prepared and submitted to the city for approval.
(E) Special cases may also exist where the downstream drainage capacity may be limited in such a way that strict adherence to this policy may result in undue property damage. In these cases, the Board may further restrict the peak runoff release rate for storms up to and including the 100-year return period storm.
(Ord. 7-2006, passed 6-12-06)