(A) Runoff rate. The peak runoff rate from the development area shall not be greater after development than it was before development. The applicant shall provide engineer certified calculations proving no increase in the runoff rates from the two, ten, 25, and 100-year storms. Peak runoff rates for the post-developed 100-year storm event shall be limited to the pre-developed ten-year peak rate. Where appropriate in the city's opinion, design shall also limit peak runoff rates for the post-developed ten-year storm to the pre-developed two-year storm peak discharge rate. All stormwater calculations shall be certified by a professional engineer registered in the State of Indiana. Complete calculations and logic for all portions of the runoff calculations shall be submitted in a clear and orderly format.
(B) Runoff volume. When determined by the city due to downstream stormwater facility limitations, increases in the runoff volume shall be offset by further restricting runoff rates. Increased stormwater discharge to combination sewers, if approved by the city, shall be offset by a factor of 2:1 by developer funded combined sewer system (CSS) mitigation projects downstream of or immediately upstream of the development.
(C) Where the city determines that site constraints exist in a manner that compromises the intent of this chapter to improve the management of stormwater runoff as established in this section, practical alternatives may be used to result in an improvement of water quality and/or a reduction of stormwater runoff. Such alternatives must be in keeping with the intent and likely cost of those measures that would otherwise be required to meet the objectives of this section. When possible, all practical alternatives shall be implemented within the drainage area of the proposed development project. Practical alternatives can include, but are not limited to:
(1) Fees shall be paid in an amount specified by the city. These fees shall be applied by the city to stormwater management practices that reduce existing stormwater runoff in the drainage basin impacted by the owner;
(2) Implementation of off-site stormwater management practices;
(3) Watershed or stream restoration;
(4) Retrofitting of an existing stormwater management practice; or
(5) Other practices approved by the city in keeping with the intent of this section.
(Ord. 3436, passed 9-6-05) Penalty, see § 156.99