[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 8-14-2024 by Ord. No. 2024-367; 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 basins greater than twenty acres, TR-55 may be used, or other method approved by the City Engineer. 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.
C. 
For those storm sewers that will handle footing drains, added Q values per house per ISWMM Chapter 2 must be used.
D. 
For culvert and ditch conveyance frequencies, guidance per ISWMM Chapter 2 must be used.
[Amended 8-14-2024 by Ord. No. 2024-367; 4-10-2024 by Ord. No. 2024-178; 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.
C. 
An acceptable method of determining catch basin capacity for various conditions shall be the use of capacity charts.
D. 
For culvert and ditch conveyance frequencies, guidance per ISWMM Chapter 2 must be used.
E. 
Prior to acceptance of storm sewer installed by private contractor, all storm sewers and structures must be cleaned and televised to ensure that they meet acceptable City standards. Televising will be completed as detailed by the City standards, and inspection files shall be provided to the City Engineer or their representative for review and acceptance. 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 8-14-2024 by Ord. No. 2024-367; 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. 
Where specifically approved by the City Engineer, the excess stormwater passageway may consist of a conduit. In such cases, the capacity of the conduit shall be twice the capacity necessary to convey the one-hundred-year stormwater flow.
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 on the final grading plan at each rear lot corner, at the mid-point of the side yard line, and along the proposed drainage ways and easements.
[Amended 8-14-2024 by Ord. No. 2024-367; 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. Channel capacity shall be based on one-hundred-year storm frequency. Manning's Formula as cited in most civil engineering handbooks, shall be used in hydraulic design of open channels. A minimum cleaning velocity of 3 ft/s should be used for the design storm per the ISWMM Chapter 2, Design Frequencies for Conveyance Facilities. 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.