Q = CIA
| ||||
---|---|---|---|---|
Where:
| ||||
Q
|
=
|
maximum expected discharge in cubic feet per second
| ||
C
|
=
|
runoff factor expressed as a percent of the total water falling
on an area
| ||
I
|
=
|
the rate of rainfall for the time of concentration of the drainage
area in inches per hour for a given storm frequency
| ||
A
|
=
|
the drainage area expressed in acres
|
Description of Area
|
Runoff Coefficient (C)
| ||
---|---|---|---|
Residential
| |||
2-acre lots
|
0.40
| ||
1-acre lots
|
0.46
| ||
1/2-acre lots
|
0.50
| ||
1/4-acre lots
|
0.56
| ||
Townhouses, multifamily
|
0.70
| ||
Commercial
|
0.75
| ||
Industrial
|
0.80
| ||
Parks, cemeteries
|
0.38
| ||
Unimproved
|
0.35
| ||
Where the above table is not applicable, the following factors
may be used:
| |||
Roofs and all impervious surfaces
|
0.90
| ||
All other surfaces except forest
|
0.40
| ||
Forest
|
0.30
|
Storm Frequency
(years)
|
Factors
| |
---|---|---|
10 and less
|
1.0
| |
25
|
1.1
| |
50
|
1.2
|
Table 1
| |||||||
---|---|---|---|---|---|---|---|
Recommended Average Velocities of Runoff Flow for Determining
Time of Concentration
| |||||||
Description of Course of Runoff Water
|
Slope in Percent
| ||||||
0-3
|
4-7
|
8-10
|
11-15
|
16-20
|
21-25
|
26-30
| |
Velocities in Feet/Second
| |||||||
Forest
|
0.5
|
1.0
|
1.5
|
1.7
|
2.0
|
2.7
|
3.5
|
Meadow
|
0.8
|
1.5
|
2.2
|
2.6
|
3.0
|
4.1
|
4.5
|
Cultivated (row crop)
|
1.0
|
2.0
|
3.0
|
3.5
|
4.0
|
4.5
|
5.0
|
Pavement
|
5.0
|
12.0
|
15.5
|
18.0
|
—
|
—
|
—
|
Natural draw not well defined
|
0.8
|
2.5
|
4.0
|
6.0
|
—
|
—
|
—
|
Lawn
|
1.0
|
1.8
|
3.2
|
4.9
|
—
|
—
|
—
|
Q = AV
| ||||
Where:
| ||||
Q
|
=
|
discharge of water in cubic feet per second
| ||
The discharge capacity for a drainage facility at a particular
location shall be equal to or greater than the maximum expected discharge
(MED) for the location.
| ||||
A
|
=
|
the net effective area in square feet provided by the drainage
facility
| ||
By "net effective area" is meant that cross-sectional area of
the facility which may be used to carry water. It may not be desirable
that the entire cross-sectional area of the drainage facility be utilized
to carry water.
| ||||
V
|
=
|
the velocity of the water in feet per second
The velocity shall be determined by Manning's equation.
| ||
Manning's equation is as follows:
| ||||
V = 1.486/n R2/3S1/2
| ||||
Where:
| ||||
V
|
=
|
velocity in feet per second
| ||
R
|
=
|
hydraulic radius is equal to the net effective area (A) divided
by the wetted perimeter (WP)
| ||
R
|
=
|
A/WP
| ||
The wetted perimeter is the lineal feet of the drainage facility
cross section which is wetted by the water.
| ||||
S
|
=
|
slope of energy line (for approximation, use water surface slope
in wetted stream and streambed slope in dry stream)
| ||
n
|
=
|
the roughness coefficient
Acceptable roughness coefficients are presented in Table 2.
|
Table 2
| |||
---|---|---|---|
Roughness Coefficient "n" for Manning's Equation
| |||
Description
|
"n"
| ||
Concrete pipe
|
0.012
| ||
Corrugated metal pipe or pipe arch
| |||
a.
|
Plain or coated
|
0.024
| |
Vitrified clay pipe
|
0.012
| ||
Cast iron pipe
|
0.013
| ||
Asphalt pavement
|
0.015
| ||
Concrete pavement
|
0.014
| ||
Grass medians
|
0.05
| ||
Earth
|
0.02
| ||
Gravel
|
0.02
| ||
Rock
|
0.035
| ||
Cultivated areas
|
0.03 to 0.05
| ||
Dense brush
|
0.07 to 0.14
| ||
Heavy timber—little undergrowth
|
0.10 to 0.15
| ||
Streams
| |||
a.
|
Some grass and weeds—little or no brush
|
0.03 to 0.035
| |
b.
|
Dense growth of weeds
|
0.035 to 0.05
| |
c.
|
Some weeds—heavy brush on banks
|
0.05 to 0.07
|
NOTE: In considering each factor, more critical
judgment will be exercised if it is kept in mind that any condition
that causes turbulence and retards flow results in a greater value
of "n."
|
Roughness Coefficient "n" for Helical Corrugated
Metal Pipe
| ||||||||||
---|---|---|---|---|---|---|---|---|---|---|
Corrugations
| ||||||||||
2 2/3 x 1/2
(inches)
|
3 x 1
(inches)
| |||||||||
Diameters
(inches)
| ||||||||||
18
|
24
|
36
|
48
|
60
|
72
|
84
|
96
|
All
| ||
Plain or coated
|
0.014
|
0.016
|
0.019
|
0.020
|
0.021
|
0.021
|
0.021
|
0.021
|
0.024
|
Table 3
| |||
---|---|---|---|
Allowable Water Velocities
| |||
Material
|
Allowable Velocity Feet per Second
| ||
1. Well-established grass on good soil
| |||
Short pliant bladed grass
|
5 to 6
| ||
Bunch grass—soil exposed
|
2 to 4
| ||
Stiff stemmed grass
|
2 to 3
| ||
2 Earth without vegetation
| |||
Fine sand or silt
|
1 to 2
| ||
Ordinary firm loam
|
2 to 3
| ||
Stiff clay
|
3 to 5
| ||
Clay and gravel
|
4 to 5
| ||
Coarse gravel
|
4 to 5
| ||
Soft shale
|
5 to 6
| ||
3. Shoulders
| |||
Earth
|
See 2 above.
| ||
Stabilized
|
6
| ||
Paved
|
10 to 15
|
Table 4
| ||||||
---|---|---|---|---|---|---|
Type M or S Inlet Capacities (In Swale)
| ||||||
Back Slope
| ||||||
Grade
|
2:1
|
4:1
|
6:1
|
12:1
|
Dike
| |
1.0
|
3.2
|
3.6
|
3.9
|
4.1
|
9.1
| |
2.0
|
3.0
|
3.3
|
3.5
|
3.7
|
8.3
| |
3.0
|
2.5
|
2.8
|
3.2
|
3.5
|
7.4
| |
4.0
|
1.6
|
2.0
|
3.0
|
3.2
|
6.4
| |
5.0
|
1.6
|
2.0
|
2.5
|
3.0
|
6.3
| |
6.0
|
1.6
|
2.0
|
2.5
|
2.8
|
6.1
| |
7.0
|
1.5
|
2.0
|
2.4
|
2.6
|
6.0
| |
8.0
|
1.5
|
2.0
|
2.2
|
2.4
|
5.8
|
Pavement Width
(feet)
| |||||
---|---|---|---|---|---|
Classification
|
Traffic Volume
|
R.O.W.
(feet)
|
No Street Parking
|
Parking One Side
|
Parking Both Sides
|
Arterial*
|
3,001+
|
—
|
—
|
—
|
—
|
Collector
|
1,001 to 3,000
|
60
|
24
|
34
|
44
|
Primary
|
501 to 1,000
|
50
|
24
|
32
|
40
|
Secondary
|
200 to 500
|
50
|
22
|
30
|
36
|
Local access
|
0 to 200
|
40
|
20
|
28
|
30
|
NOTE:
|
---|
* As required by state or federal requirements.
|
Housing Type
|
Average Weekday Trip Generation Rates
(trips per dwelling unit)
| |
---|---|---|
Single-family detached
|
10
| |
Duplex (twin), multiplex, townhouse, etc.
|
8.1
| |
Apartment
|
5.4
| |
Retirement village
|
3.3
|
Criteria
|
Primary
|
Secondary
|
Local Access
| ||
---|---|---|---|---|---|
Vertical alignment
| |||||
Minimum grade
|
1.0%
|
1.0%
|
1.0%
| ||
Maximum grade
|
7.0%
|
7.0%
|
10.0%
| ||
Typical within 50 feet of intersection
|
3.0%
|
4.0%
|
4.0%
| ||
Horizontal alignment
| |||||
Minimum center-line radius
|
350 feet
|
140 feet
|
100 feet
| ||
Minimum tangent between curves
|
150 feet
|
100 feet
|
50 feet
| ||
Minimum stopping sight distance
|
275 feet
|
200 feet
|
175 feet
|
Y
|
=
|
corner sight distance, measured from point a to c and c to d
| |
---|---|---|---|
a and d
|
=
|
a point of 3.5 feet above the center line of the major roadway
| |
b
|
=
|
eye level from a car stopped at the intersection on the minor
road; for this chapter, b is situated 3.5 feet above the roadway,
20 feet from the edge of paving of the major road.
| |
c
|
=
|
approximate center of intersection of two streets
|
Minimum Corner Sight Distance (Y)
| ||
---|---|---|
Major Road Type/Design Speed
|
Y
(feet)
| |
Existing street/50 mph
|
500
| |
Existing street/40 mph
|
400
| |
Primary street/35 mph
|
350
| |
Secondary street/30 mph
|
300
| |
Local access/25 mph
|
250
|
Minimum Intersection Spacing
| ||
---|---|---|
Major Road Type
|
Spacing
(feet)
| |
Existing streets
|
1,600
| |
Primary streets
|
300
| |
Secondary streets
|
125
| |
Local access
|
N/A
|
Design Speed of Road
(miles per hour)
|
Minimum Deceleration Lane Length
(feet)
| |
---|---|---|
30
|
165
| |
40
|
230
| |
60
|
310
|
Preserved Tree Caliper
(inches)
|
Credited Trees
| |
---|---|---|
3 to 7
|
1
| |
8 to 12
|
2
| |
13 to 19
|
3
| |
20 to 29
|
5
| |
30 or greater
|
7
|
Base Course
| |||||
---|---|---|---|---|---|
Street
|
Subbase
(inches)
|
C.A.B.C.
(inches)
|
Bit. Con.
(inches)
|
Surface Course
(ID-2)
(inches)
| |
Arterial
|
6
|
10
|
2 1/2
| ||
6
|
6
|
1 1/2
| |||
Collector
|
6
|
10
|
2 1/2
| ||
6
|
5
|
1 1/2
| |||
Primary
|
6
|
8
|
2 1/2
| ||
6
|
5
|
1 1/2
| |||
Secondary
|
6
|
8
|
2 1/2
| ||
6
|
5
|
1 1/2
| |||
Local access
|
6
|
6
|
2 1/2
| ||
6
|
4
|
1 1/2
| |||
Single access
|
6
|
6
|
2 1/2
| ||
6
|
4
|
1 1/2
| |||
Industrial/ commercial
|
6
|
10
|
2 1/2
| ||
6
|
6
|
1 1/2
| |||
Marginal access
|
6
|
6
|
2 1/2
| ||
6
|
4
|
1 1/2
|
LEGEND:
|
C.A.B.C.
|
=
|
crushed aggregate base course
| |
Bit. Con.
|
=
|
bituminous concrete base course
| ||
ID-2 (1 1/2)
|
=
|
1 1/2-inch-depth wearing course
| ||
ID-2 (2 1/2)
|
=
|
1 1/2-inch-depth binder course, plus 1-inch wearing course
|
Parking Area Dimensions
| ||||
---|---|---|---|---|
(Minimum parking area dimensions shall be as listed in
the following table.)
| ||||
Angle of Parking
(degrees)
|
Parking Stall Width
(feet)
|
Parking Stall Depth
(feet)
|
Driveway One-Way
(feet)
|
Driveway Two-Way
(feet)
|
90
|
9
|
19
|
24
|
24
|
60
|
9
|
19
|
18
|
21
|
45
|
9
|
19
|
15
|
18
|
30
|
9
|
19
|
12
|
18
|
Parallel
|
8
|
22
|
12
|
18
|
Handicapped
|
12.5
|
19
| ||
Oversized*
|
(As determined by Borough)
|
NOTE:
|
---|
* Depth indicated in chart is for all vehicles except recreational
vehicles, tandem trailers, trucks and buses.
|
Total Nonresidential Parking
|
Required Handicapped Parking
| |
---|---|---|
0 to 9
|
None
| |
10 to 50
|
1 space
| |
51 or more
|
1 space per 50 spaces
|