[Amended 8-14-2024 by Ord. No. 2024-367; 10-23-2019 by Ord. No. 2019-446]
A. 
The provisions of Sections 13.34.300 through 13.34.320, inclusive, shall apply to the following areas under development:
1. 
Any development or redevelopment which cumulatively creates 5,000 square feet or more of impervious surface area, regardless of previous condition, unless granted a waiver under Section 13.34.320 of this chapter.
2. 
Development and redevelopment projects located within 50 feet of a natural waterway, modified natural waterway, or constructed channel or which include a new storm drain outfall to such waterway, regardless of project size or impervious surface. This requirement is intended to protect environmentally sensitive areas.
B. 
The following activities are exempt from this chapter:
1. 
Additions or modifications to existing single-family structures that do not meet the requirement of Section 13.34.300A2.
2. 
Interior remodels and routine maintenance or repair, including roof or exterior surface replacement and resurfacing.
3. 
Development or redevelopment projects that do not create more than 5,000 square feet of impervious area, 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 Section 13.34.300A2.
C. 
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.
D. 
Any development or redevelopment within the floodplain must comply with Chapter 15.44, Flood Damage Prevention. Stormwater quality treatment is not permitted within the floodway. Stormwater quality treatment may be considered within special flood hazard (100- or 500-year floodplain) areas, provided that the treatment practice provides a net ecological benefit and is able to be maintained per Section 13.34.060, Requirements for stormwater management plans.
[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]
Unless judged by the City of Davenport to be exempt or granted a waiver, the following performance criteria shall be addressed for stormwater management at all sites:
A. 
All site designs shall establish stormwater management practices to control the peak flow rates of stormwater discharge associated with specified design storms and reduce the generation of stormwater runoff.
B. 
The City of Davenport reserves the right to require superseding and additional treatment criteria or objectives for specific pollutant(s) as necessary to meet overall stormwater quality management program objectives or directives under a watershed improvement or total maximum daily load (TMDL) program, as may be directed by the State of Iowa or United States Environmental Protection Agency.
C. 
For new development and redevelopment, structural best management practices shall be designed to provide 80% bacteria reduction, based on current research accepted by the Natural Resources Division of Public Works, and 100% retention or infiltration of the 1.25-inch-in-twenty-four-hour rainfall event. A best management practice complies with this standard if it is:
1. 
Sized to capture the prescribed water quality volume (WQv);
2. 
Designed according to the specific performance criteria outlined in the Iowa Stormwater Management Manual, Iowa Rain Garden Manual, or approved equal;
3. 
Constructed properly; and
4. 
Maintained regularly.
D. 
Stormwater discharges from land uses or activities with higher potential pollutant loadings may require the use of specific structural treatment and pollution prevention practices.
E. 
Prior to design, applicants are encouraged to consult with the Natural Resources Division of Public Works to determine if they are subject to additional stormwater design requirements.
F. 
The calculations for determining small storm flows as found in the Iowa Stormwater Management Manual shall be used for sizing all stormwater quality management practices.
G. 
If utilizing infiltration -based practices to comply with water quality management, soil boring information will need to be provided to ensure the practice will function. Additional information can be found in the Davenport Stormwater Management Manual.
[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]
Healthy soil provides important stormwater management functions, including efficient water infiltration and storage, adsorption of excess nutrients, filtration of sediments, biological decomposition of pollutants, and moderation of peak stream flows and temperatures. In addition, healthy soils support vigorous plant growth which intercepts rainfall, reducing runoff by increasing evaporation and transpiration. Urbanization and development severely diminish a soil's capacity to absorb, filter and store rainwater. Common development practices, including clearing and removal of topsoil during grading, compaction of remaining soil, and planting into unimproved soil or poor quality imported topsoil, produce unhealthy plants and lawns that require excessive fertilizers and pesticides, which can lead to polluted stormwater runoff. All areas subject to clearing and grading that have not been covered by impervious surfaces, incorporated into a stormwater management practice, or engineered as structural fill or slopes shall, at project completion, use one or more of the following practices to improve soil structure and water quality:
A. 
Soil retention. Soil shall be retained on site per requirements of the NPDES GP# 2 and as outlined in the Davenport Stormwater Manual. Topsoil verification measures pre and post-construction are described more fully in the Davenport Stormwater Manual.
B. 
Soil quality restoration. Amend existing site topsoil or subsoil to a minimum rate of 5% organic matter content and a pH from 6.0 to 8.0 or matching the pH of the original undisturbed soil using methods specified in the Iowa Storm Water Management Manual. Soil that already meets the depth and organic matter quality standards, and is not compacted, does not need to be amended. Upon completion of the project the soil restoration layer shall have a minimum depth of eight inches, per the method utilized in the Iowa Stormwater Management Manual except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at least four inches with some incorporation of the upper material to avoid stratified layers.
C. 
Maintenance. Soil quality and depth should be established toward the end of construction and, once established, shall be protected from compaction and erosion. The Davenport Stormwater Manual and Iowa Storm Water Management Manual contain additional recommendations for maintenance of soil quality restoration areas.
D. 
Inspection. Areas where soil retention or soil quality restoration are implemented must meet the inspection requirements of Section 13.34.080 and the Davenport Stormwater Manual and be inspected prior to seeding or turf placement.
E. 
The City Engineer or their designee will approve the source of off-site topsoil or compost, if utilized. Surface soils from ditch bottoms, drained ponds, and eroded areas, or soils that are supporting growth of noxious weeds or other undesirable vegetation, will not be accepted. The Engineer will determine if testing is necessary. The Contractor will be responsible for payment of the testing if the off-site topsoil does not meet the above requirements, regardless of testing outcome.
[10-23-2019 by Ord. No. 2019-446]
A. 
The construction of water quality BMPs shall not commence until upstream areas which discharge runoff to the proposed system(s) have been stabilized with suitable ground cover or suitable protection has been installed to prevent sediment-laden water from entering the system.
B. 
The construction of the stormwater management systems shall be accomplished as part of the cost of land development. If the amount of treatment capacity can be increased to provide benefit to the City, negotiations for public participation in the cost of development may be initiated.
C. 
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.
1. 
In-basin water quality treatment may require additional maintenance measures, which must be clearly outlined in the maintenance and repair agreement.
[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. 
Plans, specifications, and all calculations for stormwater quality management features shall be submitted in accordance with the most recent versions of the Iowa Storm Water Management Manual, SUDAS and 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 Section 13.34.080, Inspections.
C. 
No certificate of final 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.