(A) Stormwater drainage facilities. The developer shall submit a stormwater management plan to the city. Stormwater drainage facilities shall comply with all federal, state and local requirements and be designed to convey the flow of surface waters without damage to persons or property. The system shall ensure drainage at all points along streets, and provide positive drainage away from building as well as on-site waste disposal to accommodate frequent floods. Drainage plans shall be consistent with local and regional drainage plans. The facilities shall be designed to protect against surface erosion and siltation of surface water and to prevent the discharge of excess runoff onto adjacent properties. The natural drainage shall be used as far as is feasible for the storage and flow of runoff. The following requirements shall also apply.
(1) No existing ditch, stream, drain or drainage channel shall be deepened, widened, re-routed or filled without written permission from the City Engineer and other appropriate governmental agencies.
(2) Where drainage channels must be constructed to augment the natural drainage system, the channels, as well as natural drainageways, may be planned as a part of a recreational trail system. When this is done, channels shall be designed to be aesthetically compatible for recreational trail use.
(B) Stormwater drainage standards.
(1) All developments are responsible for control of surface or stormwater to equal or improve pre-development conditions.
(2) The developer shall complete all water quality improvements.
(3) Development drainage systems shall be provided that:
(a) Accept flow from upstream areas;
(b) Control, convey and pond development runoff;
(c) Limit outflow to the natural pre-development rate; and
(d) Do not have detrimental impacts on downstream properties.
(4) All pipe conveyance shall be of ten-year design return frequency. Flood protection shall be provided for 100 years. All ponding, detention or retention shall be designed for 100-year frequency storm condition with a positive outlet. Flood protection for public and personal property shall be one foot plus any encroachment above the floodplain. All storm runoff shall be calculated by the Soil Conservation Service Method TR55.
(C) City Engineer. The City Engineer shall approve all subdivision grading, drainage and wetland mitigation plans.
(Prior Code, § 12-7-9) (Ord. 259, passed 5-4-2006)