[Amended 8-14-2024 by Ord. No. 2024-367; 8-23-2023 by Ord. No. 2023-357; 10-23-2019 by Ord. No. 2019-446]
The provisions of Sections 13.34.220 through 13.34.250, inclusive, shall apply to the following areas under development:
A. 
There is no statute of limitations that would exempt multiple impervious area additions that cumulatively create over 5,000 square feet, unless granted a waiver per Section 13.34.100.
B. 
Any development which, in the opinion of the City Engineer, lacks an adequate external or internal system for the passage of stormwaters as to not exceed the capacity of the receiving storm sewer system.
C. 
The following activities are exempt from this chapter:
1. 
Development or redevelopment projects that do not create more than 5,000 square feet of impervious area, regardless of previous condition, provided they are not part of a larger common development plan that does create more than 5,000 square feet of impervious area, or that do not meet the requirement of Subsection 13.34.300B.
2. 
The subdivision of a property with the intent of removing excess land from a homestead.
3. 
The replatting of one or more properties with the intent of constructing one single-family residence.
D. 
When a site development or redevelopment plan is submitted that qualifies as a development or redevelopment as defined in Section 13.34.030 of this chapter, appropriate on-site management practices will be required and shall be guided by the latest editions of the Iowa Stormwater Management Manual, the Iowa Rain Garden Manual, the Davenport Stormwater Manual, or approved equal. Final authorization of all development and redevelopment projects will be determined after review and approval by the City of Davenport.
E. 
Any development or redevelopment within the floodplain must comply with Chapter 15.44, Flood Damage Prevention. Stormwater detention is not permitted within the floodway or within special flood hazard (100-year floodplain) areas as delineated as areas of special flood hazard identified by the Federal Insurance Administration through a scientific and engineering report entitled "The Flood Insurance Study for Scott County, Iowa, No. 19163CV000A, dated February 18, 2011," with accompanying Flood Insurance Rate Maps, and any revision thereto are adopted by reference as part of Chapter 15.44.
[Amended 8-14-2024 by Ord. No. 2024-367; 8-23-2023 by Ord. No. 2023-357; 10-23-2019 by Ord. No. 2019-446]
A. 
The release rate of stormwater from any detention basin required under this chapter for new development and redevelopment shall not exceed the stormwater runoff rate from the drainage area from a five-year frequency storm using a runoff coefficient commensurate with actual existing conditions. The Modified rational method may be used for areas under twenty acres. Utilize the S.C.S. TR-55 "Urban Hydrology for Small Watersheds" and the "Iowa Users Guide and Supplement" for said TR-55 for areas over twenty acres
B. 
All release rates shall not exceed permissible velocities per the ISWMM Design Standards Chapter for Open Channel Flow or the Iowa SUDAS Design Chapter for Grass Channels. Information pertaining to the maximum permissible velocities for channels must be included in the submitted SWMP.
C. 
The planning and design of drainage systems should be such that problems are not transferred from one location to another. Outfall points and velocities should be designed in such a manner that will not create flooding hazards downstream; or deterioration of existing structures; or degradation of biological functions or habitat; or increased stream bank erosion.
D. 
The single-stage outlet (i.e., one culvert pipe) is not recommended because of its inability to detain post-developed runoff from storms less that the five-year interval (i.e., channel protection volume storm event). In many cases, runoff from storm events less than the five-year recurrence interval has created erosion and sedimentation problems downstream of a detention basin.
E. 
Reserved.
[Deleted 8-23-2023 by Ord. No. 2023-357]
F. 
The minimum orifice size shall be 4 inches in diameter when located on the outside wall of a structure, where one side of the orifice is not accessible. Otherwise, the minimum orifice size may be smaller. In both cases of a 4 inch or smaller orifice to meet release rate requirements, the orifice shall possess protections to minimize plugging.
[Amended 8-14-2024 by Ord. No. 2024-367; 8-23-2023 by Ord. No. 2023-357; 10-23-2019 by Ord. No. 2019-446]
A. 
Utilize the Unified Sizing Criteria (USC) from the Recharge Volume (Rev) up to Extreme Flood Protection (Qf) for the required volume of stormwater detention. The Recharge Volume can be used to help meet the WQv. The WQv shall provide 100% retention, infiltration or abstraction (where soils do not allow full infiltration) of the 1.25-inch-in-a-twenty-four-hour rainfall event per Section 13.34.310.
B. 
City standards that are to be used in conjunction with the USC are:
1. 
The Modified Rational method may only be used for small catchments less than twenty acres.
2. 
The recharge volume (Rev) need not be included in detention calculations.
3. 
The Modified Rational Method may only be used for small catchments < 20 acres.
C. 
For sites greater than twenty acres, the method of sizing of the detention storage volume must be approved by the City engineer. The TR-55 method is an approved method.
1. 
For drainage areas larger than 2,000 acres, or for situations where the methods described above are not appropriate, TR-20, HEC-1, HEC-HMS, or other approved alternatives may be used.
D. 
For redevelopment sites, utilize the USC detention requirements from the WQv up to Qf unless a partial waiver or general waiver has been granted per Section 13.34.100, Waivers.
E. 
Detention storage may be provided as a dry bottom or wet bottom storage area.
1. 
Dry bottom stormwater storage areas may be designed to serve a secondary purpose for recreation, open space, parking, or other types of uses that will not be adversely affected by intermittent flooding.
a. 
A method of carrying the low flow or a system of drains to prevent soggy areas shall be provided.
b. 
Concrete or otherwise paved swales to carry low flow shall only be permitted if stormwater has already been passed through a water quality treatment facility.
c. 
Outlet control structures shall be designed as simply as possible and shall require little or no attention for proper operation. Utilize the Unified Sizing Criteria for staged outlet design. Each stormwater storage area shall be provided with a method of emergency overflow in the event that a storm in excess of the one-hundred-year frequency storm occurs. This emergency overflow facility shall be designed to function without attention and shall become part of the excess stormwater passageway described in Section 13.34.140. Hydraulic calculations shall be submitted to substantiate all design features and shall comply with ISWMM design standards.
d. 
Paved surfaces thatare to serve as stormwater storage areas and rooftop storage shall be designed with permanent-type control outlets. Emergency overflow areas shall be provided.
e. 
Outlet control structures shall not direct flows over sidewalks, through curb sections or onto the roadway; nor shall they be constructed or put in a location that will cause icing issues within the right of way.
2. 
Wet bottom stormwater storage areas shall be designed with all of the items required for dry bottom stormwater storage areas, except that the provisions of Subsection E1a of this Section shall not be required. Utilize the Iowa Storm Water Management Manual.
a. 
Restrictor (orifice) plates to control release rates placed within a pipe section or at the outlet of a pipe will not be accepted. Only orifice plates integrated into a staged release design structure that cannot be removed will be accepted.
[10-23-2019 by Ord. No. 2019-446]
A. 
Detention facilities for stormwater runoff control shall be constructed as part of the first phase of construction of a project unless alternate construction phasing is agreed upon, in writing, by the Natural Resources Manager or City Engineer.
B. 
The construction of the stormwater management systems shall be accomplished as part of the cost of land development. If the amount of storage capacity can be increased to provide benefit to the City, negotiations for public participation in the cost of development shall be initiated.
C. 
All flood-control items, such as earthen embankments, conduits, outlet structures, flood-control structures, spillways, excess stormwater passageway channels, etc., shall be built as permanent facilities, and all materials and their manner of construction shall be assembled to accomplish as much permanency as is possible.
D. 
Water quality practices may be constructed within detention areas to allow owners to conserve space. However, below-grade volume for infiltration in a detention basin shall not be counted as required detention storage area unless detailed plans and calculations are submitted, reviewed and approved, in writing, by the Natural Resources Manager or City Engineer.
[Amended 8-14-2024 by Ord. No. 2024-367; 10-23-2019 by Ord. No. 2019-446]
A. 
Plans, specifications, and all calculations for stormwater runoff control(s) shall be submitted in accordance with the Davenport Stormwater Manual for review and approval, prior to the approval of a final plat (in the case of a subdivision or planned unit development), approval of a final development plan, or issuance of a building permit (in the case of commercial or industrial construction).
B. 
Comply with 13.34.080, Inspections.
C. 
No certificate of occupancy for any building in the development will be issued until the stormwater facilities are constructed, inspected and approved.
D. 
In the event weather prohibits the completion of stormwater management facilities or any associated landscape at the time subdivision acceptance or certificate of occupancy is applied for, a security bond for 125% in favor of the city of the estimated amount of construction and landscape materials with installation cost may be submitted. The cost of construction and landscape materials with installation must be determined by a landscape architect, construction estimator or other landscape business professional.