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94-276 Storm Drainage And Flood Hazard Areas
94-277 Responsibility For Drainage
94-278 Flood Hazard Areas Designated
94-279 Areas Not Designated Floodway; Drainage Assessment
94-280 Flowage Easements
94-281 Floodway-Fringe Areas
94-282 Runoff
94-283 Tributary And Surface Drainage Channels
94-284 Storm Sewers
94-285 Drainage Channel Location
94-286 Site Grading
94-287 Surface Water Collection
94-288 Drainage Easement Widths
94-289 Closed Storm Sewer Construction Requirement
94-290 Bridges Or Culverts; Size
94-291 Open Paved Storm Drainage Channels; Specifications
94-292 Improvements, Drainage Easements, Agreements Beyond Boundaries
94-293 Property Owner Agreements
94-294 Retention Reservoirs
Cross reference- Utilities, Ch. 110.
A. All subdivisions of land shall comply with the design and improvement requirements established in this division for the protection of flood hazard areas and the prevention of erosion.
B. For the purposes of these regulations, drainage shall be classified as follows:
1. Major tributary. Any channel having a drainage basin of not less than one (1) square mile or greater than twenty-five (25) square miles.
2. Minor tributary. Any drainage channel having a drainage basin of six hundred forty (640) acres (one (1) square mile) or less in area.
3. River. Any channel having a drainage basin of greater than twenty-five (25) square miles.
4. Surface drainage. The runoff of such a limited quantity or slow rate that it does not cause erosion of a defined channel.
(Code 1991, § 12-495)
Responsibility for drainage shall be allocated as follows, unless otherwise specifically designated:
A. The developer of a subdivision is responsible for the following:
1. All surface drainage on the subdivision;
2. All increase in surface drainage outside the subdivision which results from the development of the subdivision;
3. The improvement of all minor tributaries lying within the subdivision;
4. Any significant increase in the rate or quantity of runoff in any minor or major tributary or river which results from the development of the subdivision; and
5. Provision for the maintenance of all floodway and floodway-fringe areas of major tributaries and rivers which have not been dedicated to the public.
B. The City and other levels of government will be responsible for the following:
1. The improvement of floodways of major tributaries;
2. The improvement of river floodways; and
3. The maintenance of floodway and floodway-fringe areas dedicated to the public.
(Code 1991, § 12-496)
For all areas not otherwise designated in a floodway or floodway-fringe area, the developer shall be responsible for having an engineer, registered in the State, prepare a drainage assessment of all of the area of the proposed subdivision and all areas affected by runoff resulting from development of the proposed subdivision in accordance with the following provisions:
A. The one hundred (100) year maximum flood shall be used as the basis for the sizing of all drainage channels, bridges, and other structures, unless otherwise specified in this section;
B. The calculation of all runoff shall be based on saturated urbanization of the drainage basin for minor tributaries and surface drainage, as reflected in the comprehensive plan, and shall be based on the maximum degree of urbanization, as reflected in the comprehensive plan, for the drainage basin of a major tributary or river; and
C. The calculation of stream flow and runoff characteristics of the subdivision shall be carried out in consultation with the City Engineer, and the methodology and formulas used shall result in quantities which would be not less than those derived from the application of the following formulas and values:
1. Runoff from all drainage areas shall be not less than that determined by the Rational Formula:
Q = AIR
Q Cubic feet per second.
A Area to be drained, in acres, determined by field surveys for areas less than six hundred forty (640) acres and by latest government quadrangle maps for larger areas.
I Percent of imperviousness of the area. This may vary between forty percent (40%) and ninety-five percent (95%), but no value of less than fifty percent (50%) may be used for saturated urban development.
R Rate of rainfall over entire drainage area in inches per hour, based on time of concentration and latest government records for the area.
2. The size of closed storm sewers, open channels, culverts, and bridges shall be not less than that determined by using the Manning Formula:
Q Discharge in cubic feet per second.
A Cross-sectional area of water in conduit in square feet.
r Hydraulic radius of water in conduit.
s Mean slope of hydraulic gradient in feet of vertical rise per foot of horizontal distance.
n Roughness coefficient, based on condition and type of material of conduit lining, but not less than 0.013.
(Code 1991, § 12-498)
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