(A) Each applicant who is required to have coverage under general permit #2 for a site or is required to have final plat, a site plan, or a new construction building permit, except as noted below under division (I), shall install post-construction stormwater management facilities as set forth herein and as approved by the city during site plan, platting or construction plans.
(B) Each applicant or its successor person(s) or entity shall be responsible for maintaining all stormwater management facilities as approved by the city.
(C) Each applicant must provide to the city as-built plans detailing dimensions and elevations as well as a certification that stormwater management facilities were built as part of the approved development that includes the site, in addition to as-built plans as required by Chapters 150 and 159 of this code of ordinances.
(D) The city hereby adopts the Iowa Stormwater Management Manual (ISWMM) and City of Urbandale Design Criteria supplemental for management of stormwater. In cases where ISWMM does not speak to a stormwater issue, such as sizing or installation of pipes, the design shall follow SUDAS and City of Urbandale Supplemental Specifications and Design Manual Addendums, or streambank stabilization in the Iowa River Restoration Toolbox, as applicable.
(E) For sites with existing stormwater facilities, those facilities shall be brought into compliance with the previously approved stormwater management plan.
(F) Each applicant must include, in their site design, those stormwater management facilities that will convey drainage through the property to one or more detention and/or treatment areas so that no development shall cause downstream property owners, water courses, channels or conduits to receive stormwater runoff from the proposed development site at a peak flow rate greater than that allowed by the policy or standard in effect at the time of approval of the development unless those requirements are waived by the city. Nothing contained herein shall prohibit the city from changing the policies or standards in the future, nor from requiring the site to comply with the new requirements.
(G) Each applicant shall comply with all other applicable city, state or federal permit requirements as they apply to the city or to the property.
(H) At the discretion of the city, the applicant may satisfy the post-construction stormwater management requirements by ensuring the conveyance of the stormwater discharge from the property to a regional detention facility. For purposes of this chapter, a REGIONAL DETENTION FACILITY shall be wet or dry detention basins, which are designed to accept stormwater runoff from two or more sites and that otherwise complies with all city, state or federal permit requirements as they apply to stormwater management requirements for those sites.
(I) Applicability. The requirements for post-construction stormwater management shall apply as follows:
(1) New development. Any development of currently undeveloped land adding more than 10,000 square feet of new impervious surface shall provide stormwater management as required in this chapter. This threshold is a cumulative amount of new square footage and may be reached over time in increments. At such time that a development site exceeds 10,000 cumulative square feet of new impervious surface, the entire site will be required to come into compliance with this chapter.
(2) Redevelopment.
(a) Any expansion or redevelopment of an existing developed site adding more than 10,000 square feet of new impervious surface or building area but disturbing less than 50% of the site shall provide stormwater management at the ISWMM Water Quality standard, and shall also meet the ISWMM Channel Protection standard or demonstrate why doing so is infeasible.
(b) Any expansion or redevelopment of an existing developed site disturbing more than one acre and less than 50% of the site shall also meet, in addition to the above, the ISWMM Overbank protection standard and ISWMM Extreme Flood protection for the disturbed area, or demonstrate why doing so is infeasible.
(c) Any redevelopment disturbing 50% or more of a site shall require the entire site to meet the same stormwater management standards as new development.
(d) The thresholds noted above are a cumulative amount of site work after January 1, 2021, and may be reached over time in increments.
(3) City projects. Stormwater management standards shall apply to all city projects except as noted below.
(4) Exemptions. The following activities shall be exempted from meeting the ISWMM stormwater management standards of this chapter:
(a) New development of less than 10,000 square feet of impervious surface;
(b) Expansion of previous development adding less than 10,000 cumulative square feet of new impervious surface or new building area from the original design and disturbing less than 50% of the total site. Site shall still be required to show compliance with any previously approved stormwater management plan;
(c) Pavement repairs involving the removal and replacement of impervious surface exactly matching location and area;
(d) Logging or agricultural activity that is consistent with an approved soil conservation plan or timber management plan prepared or approved by the appropriate agency, as applicable;
(e) Additions or modifications to single-family structures;
(f) Repairs to any stormwater management BMP deemed necessary by the city;
(g) Linear projects such as road and trail construction.
(J) It is intended that this chapter be construed to be consistent with this code of ordinances as well as any other applicable local, state or federal regulation. In particular, Chapters 53, 54, 150, 157, 159, and 160 should be consulted for additional requirements.
(K) The requirements of this chapter should be considered minimum requirements, and where any provision of this chapter imposes restrictions different from those imposed by any other chapter, rule or regulation, or other provision of law, whichever provisions are more restrictive shall take precedence.
(Ord. 2007-18, passed 9-25-2007; Ord. 2021-04, passed 3-9-2021)
Cross-reference:
Building Regulations, see Chapter 150
Construction Site Erosion and Sediment Control, see Chapter 54
Illicit Discharge to Stormwater System, see Chapter 53
Site Planning, see Chapter 157
Subdivisions, see Chapter 159
Zoning, see Chapter 160