3.18 Detention Facilities
a. Where Required.
1) Peak storm water runoff shall be controlled by detention facilities for all developments, including:
a) Parking lots with 2,500 square feet or more of impervious area
b) All other developments where such control is needed to prevent the capacity of the downstream system from being exceeded.
c) All subdivisions with four (4) or more units.
2) Developers shall be responsible for demonstrating to the satisfaction of the City Engineer that the downstream system has capacity for the proposed flows.
3) Developers proposing to not provide detention or control shall, on a case by case basis, be responsible for demonstrating to the satisfaction of the City Engineer that such control is not beneficial to the City Stormwater System.
b. Allowable Runoff Rate (Outflow}.
1) Peak runoff rate shall be limited to that which would occur in a 5-year frequency storm with pre-development conditions as defined above, or the remaining available downstream capacity for the site being developed, whichever is more stringent.
2) Remaining available downstream capacity is defined as the downstream capacity unused during the design storm event. The remaining available downstream capacity for the site being developed is that portion of the remaining available downstream capacity equivalent to the ratio of the site being developed to the total undeveloped land in the basin.
c. Detention Facility Siting.