(A) Purpose. The purpose of these regulations is to diminish threats to public health, safety and welfare caused by runoff of excessive stormwater from new development and redevelopment. This excessive stormwater could result in flooding of damageable properties. The cause of increase in stormwater runoff quantity is the development and improvement of land and, as such, this section regulates these activities to reduce adverse impacts.
(B) Applicability. No building permit shall be issued for the construction, reconstruction or structural alteration of a building and/or its parking area nor shall a certificate of occupancy be granted for a use nor shall a preliminary plat, final plat or site plan be approved without conformity with the provisions of the stormwater detention regulations.
(C) Stormwater detention criteria.
(1) All stormwater storage areas must be designed to contain and safely pass stormwater runoff. When platting, the land extending to the centerline of any adjacent right-of-way shall be considered part of the development for purposes of determining the runoff rate. Adequate spillway provisions shall be provided to transport peak runoff from a 100-year storm assuming the outlet to be plugged. All stormwater facilities shall be designed in accordance with the design standards established by the city engineer.
(2) For the release for drainage, the combined capacity of these storage areas shall be sufficient to contain the stormwater runoff from a 100-year storm from the development with a peak release rate less than or equal to the predevelopment release of the one-hundred year storm using the Iowa Statewide Urban Design and Specifications Manual for design guidelines.
(3) For the release for drainage, the combined capacity of these storage areas shall be sufficient to contain the stormwater runoff from a two-year storm from the development with a peak release rate less than or equal to the predevelopment release of the two-year using the Iowa Statewide Urban Design and Specifications Manual for design guidelines.
(4) For the release for drainage, the combined capacity of these storage areas shall be sufficient to contain the stormwater runoff from a one-year storm from the development with a peak release rate less than or equal to the predevelopment release of one-year storm using the Iowa Statewide Urban Design and Specifications Manual for design guidelines.
(5) For the release for drainage, the combined capacity of these storage areas shall be sufficient to contain the stormwater run off from a five-year storm from the development with a peak release rate less than or equal to the predevelopment release of the five-year storm, using the Iowa Statewide Urban Design and Specifications Manual for design guidelines.
(D) Exemptions. The following shall be exempt from these regulations.
(1) Any final plat approved within three years of October 28, 2008, and based upon a preliminary plat which was approved prior to the October 28, 2008, subject to the development not being required to provide detention facilities by any other ordinances of the city.
(a) Any preliminary or final plat of a single-family or two-family development consisting of no more than two acres in total area;
(b) A preliminary or final plat of single-family development consisting of lots, all of which are one acre or larger; and
(c) Any developed lot zoned commercial, industrial or multi-family which existed on October 28, 2008, where the sum of modifications or additions:
1. Does not increase the stormwater runoff more than 25% for any storm, as determined, using the rational formula; and
2. Does not increase the impervious area more than 10,000 square feet.
(2) (a) Any developed lot zoned commercial, industrial or multi-family which existed on October 28, 2008, which does not qualify for these exemptions shall provide stormwater detention sufficient to store the increased runoff resulting from the alterations and additions; and
(b) Any single-family and two-family developed and undeveloped lots which existed on October 28, 2008.
(E) Stormwater detention plan review. Stormwater detention plans shall be submitted to the City Engineer for review.
(1) For new or expanding commercial, industrial and multi-family developments, a stormwater detention plan shall be submitted as part of the site plan review.
(2) For new single-family and two-family residential developments, a stormwater detention plan shall be submitted as part of the plat review.
(3) If no plat or site plan review is required, a stormwater detention plan must be approved by the City Engineer before a building permit is issued.
(F) Stormwater detention plan requirements. Each applicant shall submit all calculations and other information as deemed necessary to demonstrate to the City Engineer the stormwater runoff rate and capacity of stormwater storage facilities. Required information may vary according to the size of development but shall include, but not be limited to, the following:
(1) Map of the property and immediate vicinity showing elevation or contours (based on city datum);
(2) Mapping and description of existing and proposed drainage system features of the property and immediate vicinity;
(3) Physical features of the property and immediate vicinity; and
(4) If the development is to be staged, a plan of how the stormwater detention requirement will be met for each stage.
(G) Common detention facilities. The city may, in lieu of on-site detention facilities, accept the furnishing of off-site facilities which, when added to on-site detention facilities shall provide sufficient storage capacity to provide the stormwater detention required to meet this regulation. Until the time as the permanent off-site stormwater detention facilities are available, temporary on-site detention shall be provided. An acceptable legal contract between the developer and the off-site land owner shall be approved by the City Council.
(H) Completion of facilities. The stormwater detention facilities shall be constructed and in use according to the following criteria.
(1) For commercial, industrial and multi-family developments, the facilities shall be constructed concurrent with site grading. A certificate of completion shall be furnished by the developer’s engineer certifying that they have been constructed according to the approved plans before an occupancy permit is issued by the city.
(2) For single-family and two-family residential buildings, the developer’s engineer shall certify that the structural improvements have been substantially complete and the detention facility rough graded before a building permit is issued. A certificate of completion shall be furnished by the engineer certifying that the facilities into which the lot(s) drain have been constructed according to the approved plans before an occupancy permit is issued by the city. These requirements may be delayed for six months when the developer provides to the city a performance bond, by cash or certified check, guaranteeing construction of the detention facility in an amount equal to 150% of the estimated cost. The city shall assume its maintenance responsibilities upon the receipt of the engineer’s certificate of completion.
(I) Responsibilities.
(1) Industrial, commercial, condominiums and multi-family developments and single-family or two-family lots or development with individual detention facilities or single-family or two-family lots or development when the developer elects that the maintenance of the stormwater detention facility shall be the responsibility of parties other than the city.
(a) The developer shall be responsible for providing a plan of ownership of the detention facilities involving a single owner, an association or another plan of ownership approved by the city.
(b) The owner shall be responsible to ensure the continuing functioning of the facility as originally designed and intended.
(c) The owner(s) shall be responsible for the continued functioning and adequate maintenance and repairs of the detention facility.
(d) The developer shall dedicate an easement to the city reserving the land for use as a stormwater detention facility providing the city with the right to inspect the facility and the necessary easements for ingress and egress.
(e) The Public Works Director, or his or her designee, shall provide inspection of the detention facilities at the schedule established by Council resolution. If the Director finds any maintenance work is necessary, the Director shall serve a written order to the owner of the facilities specifying therein the work necessary to be done and providing for a reasonable time for its completion. Any property owner to whom an order is directed shall have the right, within three days from service of the order, to appeal to the City Administrator who shall review the order within five working days and file his or her decision. Unless the order is revoked or modified, it shall remain in full force and be obeyed by the owner as directed within the time established by the Director’s written order or the time as modified by the City Administrator’s decision. When an owner to whom an order has been issued fails to comply within the time specified, the Director shall remedy the condition, or contract with others for the purpose, and charge all costs, including administration, to whom the order is directed. If the cost of remedying a condition is not paid within 30 days after the mailing of a statement therefore from the Public Works Director, the cost shall be assessed against the property for collection in the same manner as a property tax. In the event the association fails or is unable to pay the costs associated with detention facility maintenance, these costs shall be assessed against those users of the facility based upon their percentage of use.
(2) Single-family and two-family development with common detention facilities where maintenance or the stormwater detention facility shall be the responsibility of the city.
(a) Common detention facilities, for the purpose of this section, shall be defined as a facility which serves two or more lots which has outlet pipes and structures in conformance with city design and construction standards.
(b) The developer shall dedicate an easement to the city reserving the land for use as a stormwater detention facility; the right to enter upon the lands to inspect, reconstruct, regrade, maintain and repair the facility including the levee and detention structures and the necessary easements for ingress and egress.
(c) The owner of the land upon which the detention easement is located shall mow and maintain the grass, trees and other vegetation, but shall not plant or allow to grow trees, shrubs or bushes on or within ten feet of the detention levee or berm. The owner may place nonfloatable benches or other nonfloatable amenities within the easement area but same shall be maintained by the owner.
(d) The city shall be responsible for the continued functioning maintenance and repair or the detention levee or berms, storm sewer, inlet structures or similar appurtenances.
(J) Appeal. The City Council may, in the resolution approving the preliminary plat of any subdivision and upon appeal of the developer or the recommendation of the Director of Community Development, waive or change the requirements of this chapter for a particular development whenever the developer demonstrates either:
(1) Due to the location of the property, strict compliance would provide no discernible benefit for reduction of flooding on any plat adjacent or downstream property;
(2) Due to the nature of the property, strict compliance would create unusual hardship out of proportion to any foreseeable benefit and that the requested change or reduction in requirements will not increase the risk of flooding of any building or the buildable portion of any lot on any adjacent or downstream property; or
(3) The developer, in lieu of a detention facility, provides stormwater management sufficient to achieve the purpose of this chapter by keeping stormwater runoff from the property in accordance with division (C) above.
(Ord. 2390, passed 10-28-2008; Ord. 2543, passed 9-27-2016; Ord. 2748, passed 6-11-2024) Penalty, see § 53.99