[10-23-2019 by Ord. No.
2019-446]
The provisions of Sections 13.34.120 through 13.34.160 shall
apply to the following areas under development:
A.
All residential development of two acres or more and all commercial
and industrial developments in excess of one acre;
B.
Any development where the percentage of the impervious area of the
lot is 50% or greater;
C.
Any development which, in the opinion of the City Engineer, lacks
an adequate internal or external passage of stormwaters as to not
exceed the capacity of the receiving storm sewer system.
[Amended 8-23-2023 by Ord. No. 2023-357; 10-23-2019 by Ord. No. 2019-446]
A.
Design
flows shall normally be calculated using the procedures outlined in
the Soil Conservation Services, Technical Release No. 55 "Urban Hydrology
for Small Watersheds" and the "Iowa Users Guide and Supplement" for
said Technical Release No. 55. For drainage basins of twenty acres
or less, the Modified Rational Method may be used. 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.
B.
Stormwater
management documents shall be submitted following the format of ISWMM
9.03-3 Storm Water Management Plan formatting.
[10-23-2019 by Ord. No.
2019-446]
A.
Storm sewers and intakes shall be designed for a ten-year frequency
storm in such a manner that the flooded street width shall not exceed:
|
Street Width
(feet)
|
Allowable Flooded Width Each Side
(feet)
|
Required Nonflood Lanes
|
|---|---|---|
|
27
|
8
|
1 10-foot lane
|
|
31
|
10
|
1 10-foot lane
|
|
35
|
9
|
2 8-foot lanes
|
|
41
|
10
|
2 10-foot lanes
|
|
45
|
11
|
2 11-foot lanes
|
|
49 and wider
|
12
|
2 12-foot lanes
|
B.
An acceptable method of determining the flooded width of the street
shall be the use of width-discharge curves provided by the City.
C.
An acceptable method of determining catch basin capacity for various
conditions shall be the use of capacity charts provided by the City.
D.
Prior to acceptance of storm sewers installed by a private contractor,
the City of Davenport Sewer Division must televise the lines to ensure
that they meet acceptable City standards. Fees for this service shall
be set from time to time by City Council resolution and will be billed
to the developer or property owner and must be paid before the system
will be accepted and released for further development.
[Amended 8-23-2023 by Ord. No. 2023-357; 10-23-2019 by Ord. No. 2019-446]
A.
An excess stormwater passageway easement shall be provided for all
developments. Such passage shall have the capacity to convey through
the proposed development the excess stormwater from the tributary
watershed. The capacity of such excess stormwater passage shall be
constructed in such a manner as to transport the peak rate of runoff
from a 100-year return frequency storm, assuming all storm sewers
are inoperative, all upstream areas are fully developed in accordance
with the City's current land use plan, and that antecedent rainfall
has saturated the tributary watershed.
B.
No buildings or structures shall be constructed within such passage;
however, streets, parking lots, playgrounds, park areas, pedestrian
walkways, utility easements and other open space uses shall be considered
compatible uses. In the event such passageway is reshaped or its capacity
to transport excess stormwater otherwise restricted, the City Engineer
shall notify the agency, party or parties causing said restriction
to remove the same and set a reasonable time for its removal. If said
persons refuse to or are unable to comply with said order, the City
Engineer shall cause said restrictions to be removed at the expense
of said persons.
C.
Where specifically approved by the City Engineer, the excess stormwater
passageway may consist of a conduit. In such cases, the inlet capacity
shall be twice the capacity necessary to convey the 100-year stormwater
flow.
D.
Where a proposed development contains existing natural drainage,
appropriate land planning shall be undertaken to preserve said natural
drainage as part of the excess stormwater passage.
E.
Individual lot grading in a subdivision or other larger common plan
of development must comply with the City approved final grading plan
and the lowest entry elevation of the approved plat or construction
plans. Final grading shall maintain the original intent and function
of final grading plan, drainage areas, stormwater overland flow design
and storm sewer system design. Lot drainage slopes will not be less
than 1.5% to minimize ponding, and not excessive to cause uncontrollable
erosion. Final grading shall also maintain positive drainage away
from structures; must not direct water directly toward any down-grade
structure foundations; and must comply with Chapter 12.28 Driveway
and Approaches, SUDAS Section 7030, International Residential Code
(IRC) for frost protection of footing, and the City of Davenport SUDAS
Supplemental Specifications;
F.
Water entry levels for structures adjacent to the excess stormwater
passageway shall be established one foot above the 100-year flood
elevation.
G.
Spot elevations should be listed at each rear lot corner, at the
mid-point of the side yard line, and along the proposed drainage ways
and easements.
[10-23-2019 by Ord. No.
2019-446]
A.
The size and shape of open channels shall be designed to meet the
requirements of runoff, depth, side slopes, gradient, and velocity
limitations in accordance with the site conditions. Runoff shall be
based on the 100-year storm frequency. Manning's Formula, as cited
in most civil engineering handbooks, shall be used in hydraulic design
of open channels. Channel banks shall be protected by use of low vegetation,
rip-rap, or paving as design velocity dictates, subject to the approval
of the City Engineer.
