(A) It is recognized that the smaller streams and drainage channels serving the city may not have sufficient capacity to receive and convey stormwater runoff resulting from continued urbanization. Accordingly, the storage and controlled release rate of excess stormwater runoff shall be required for any development, redevelopment and new construction located within the city which requires development plan approval under Chapter 158 of the City Code of Ordinances, or which requires subdivision plat approval under Chapter 156 of the City Code of Ordinances.
(B) The release rate of stormwater from development, redevelopments, and new construction may not exceed the stormwater runoff from the land area in its present state of development. The developer must submit to the city detailed computations of runoff before and after development, redevelopment or new construction, which demonstrate that runoff will not be increased.
(C) These computations must show that the control devices will limit the discharge to a rate such that the release rate from the site is no greater than the two-year predeveloped rate for 0-10 year return interval storms and the ten-year predeveloped rate for 11-100 year return interval storms. That is, all storms up to and including the ten-year return period storm must be detained at a release rate below the predeveloped peak two-year return period stormwater runoff rate. The release rate for developments and redevelopments for the 11-100 year return period storms shall not exceed the predeveloped peak ten-year return period rate. Note: The allowable release rates may be reduced from these levels if downstream restrictions exist.
(D) Computations for areas up to and including 200 acres may be based on the Rational Method; typical runoff coefficients are listed herein. For areas larger than 200 acres, hydrography techniques and/or computer drainage modeling methods may be used. Hydrograph techniques and computer modeling methods used to determine stormwater runoff shall be proven methods subject to approval of the Commission.
(Ord. 16-C-98, passed 6-9-98; Am. Ord. 22-C-98, passed 8-11-98; Am. Ord. 22-C-04, passed 11-9-04; Am. Ord. 3-C-05, passed 3-15-05)