[Ord. No. 5.000 § III, 9-9-1991]
Runoff rate computations shall be by the Rational Method, or
Unit Hydrograph Method. The use of the Rational Method should generally
follow the criteria set forth by the American Public Works Association,
Kansas City Metropolitan Chapter. The use of the Unit Hydrograph Method
should generally follow criteria set forth by the Soil Conservation
Service.
[Ord. No. 5.000 § III, 9-9-1991]
Storm drainage facilities shall be designed for flows generated
by storm probabilities as follows:
A.
Enclosed Systems.
|
Residential
|
-
|
10%
|
|
Commercial
|
-
|
4%
|
|
Industrial
|
-
|
4%
|
|
Street Crossings
|
-
|
2%
|
|
(Open channel capacity must be provided above enclosed systems
run on back or side property lines)
|
B.
Open Systems.
|
Residential
|
-
|
4% (in channel)
|
|
-
|
1% (total waterway)
| |
|
Commercial
|
-
|
4% (in channel)
|
|
-
|
1% (total waterway)
| |
|
Industrial
|
-
|
4% (in channel)
|
|
-
|
1% (total waterway)
| |
|
Bridge waterways
|
-
|
2% (below lowest structure)
|
|
-
|
1% (including structure)
|
[Ord. No. 5.000 § III, 9-9-1991]
When multiple land use occurs in a design area, a composite
return frequency shall be developed based on weighted areas. Design
flow shall be the sum of flows from each weighted area, calculated
for each runoff co-efficient and corresponding return frequency.
[Ord. No. 5.000 § III, 9-9-1991]
Detention facilities shall be sized utilizing inflow hydrographs.
Hydrographs shall be developed using Soil Conservation Service methods,
or appropriate computer methods such as modified-puls. Where controlled
areas discharge into a proposed system, the regulated flow rate shall
be used.
[Ord. No. 5.000 § III, 9-9-1991]
A.
Values for the runoff co-efficient, "C", shall be selected from the
following table. For areas not specifically listed, a composite co-efficient
shall be developed based on percentages of various surface types.
Antecedent precipitation multipliers are not required.
|
Runoff
| ||
|---|---|---|
|
Values of Runoff Co-Efficient "C"
| ||
|
Type of drainage area
|
Runoff Co-efficient, "C"
| |
|
Lawns:
| ||
|
Sandy soil, flat, 2%
|
0.50-0.10
| |
|
Sandy soil, average, 2-7%
|
0.10-0.15
| |
|
Sandy soil, steep, 7%
|
0.15-0.20
| |
|
Heavy soil, flat 7%
|
0.13-0.17
| |
|
Heavy soil, average, 2-7%
|
0.18-0.22
| |
|
Heavy soil, steep, 7%
|
0.25-0.35
| |
|
Business:
| ||
|
Downtown areas
|
0.70-0.95
| |
|
Neighborhood areas
|
0.50-0.70
| |
|
Residential:
| ||
|
Single-family areas
|
0.30-0.50
| |
|
Multi units, detached
|
0.40-0.60
| |
|
Multi units, attached
|
0.60-0.75
| |
|
Suburban
|
0.25-0.40
| |
|
Apartment dwelling areas
|
0.50-0.70
| |
|
Industrial:
| ||
|
Light areas
|
0.50-0.80
| |
|
Heavy areas
|
0.60-0.90
| |
|
Parks, cemeteries
|
0.10-0.25
| |
|
Playgrounds
|
0.20-0.35
| |
|
Railroad yard areas
|
0.20-0.40
| |
|
Unimproved areas
|
0.10-0.30
| |
|
Streets:
| ||
|
Asphaltic
|
0.70-0.95
| |
|
Concrete
|
0.80-0.95
| |
|
Brick
|
0.70-0.85
| |
|
Drives and walks
|
0.75-0.85
| |
|
Roofs
|
0.75-0.95
| |
B.
Rainfall intensity shall be calculated using the Steel Formula. Time
of concentrations shall be the overland flow time to the proposed
system, plus the system travel time if necessary to the point under
construction. Time of concentration shall be determined using APWA
methods for systems and watersheds under two hundred (200) acres,
and Kirpich's Nomograph for watersheds over two hundred (200) acres.
