[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.
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.
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 8-23-2023 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:
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 peak flows as found in the Iowa
Stormwater Management Manual shall be used for sizing all stormwater
quality management practices.
[Amended 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. Native topsoil shall be retained in an undisturbed
state to the maximum extent practicable. In any areas requiring grading,
remove and stockpile the topsoil on site in a designated controlled
area where it will not be compacted, and not adjacent to stormwater
management areas. Before stockpiled topsoil can be reapplied to other
portions of the site, it must be tested, and amended if needed, to
meet the organic matter or depth requirements specified in the Davenport
Stormwater Manual. When topsoil is replaced, it shall be uncompacted
to a depth of four inches. Subsoils below the topsoil layer should
be scarified with some incorporation of the upper material to avoid
stratified layers.
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. 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 8-23-2023 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.
