Route Analysis

Constraints
1. Horizontal

a. Minimum recommended distance from top of stream bank

i. 35’ stream buffer plus
ii. 5’ construction room plus
iii. Half of sewer easement width

1. 8” – 12” pipe diameter requires 15’ total easement width
2. 15” – 18” pipe diameter requires 20’ total easement width
3. 21” – 36” pipe diameter requires 25’ total easement width

b. Absolute minimum distance from top of stream bank

i. 10’ stream buffer plus
ii. Half of sewer easement width

c. Maximum length between manholes

i. 8-12” pipe – 500’
ii. 15-27” pipe – 550’
iii. 30-42” pipe – 700’

d. Intersection angles must be 90 degrees or greater
e. Minimize stream crossings
f. Maintain access for properties across creek
g. Minimize manhole depth (desirable maximum design depth < 16’)
h. Minimize number of parcels
i. Parallel property lines where possible
j. Highway 485 / 51 interchange constraints
k. Perpendicular road and stream crossings

2. Vertical alignment

a. Top of pipe 4’ below natural ground
b. Top of pipe 1’ below stream bed, minimum
c. MH rims at grade in street right of way and lawns
d. MH rims 2’ above natural ground except as noted above
e. Vents spaced every 1000’
f. Vent height 2’ above 100 year floodplain elevation
g. No vertical drops in manholes for pipes 18” and larger
h. Minimize hydraulic jumps

3. Stream crossings

a. Require anchorage to prevent wash out or floatation
b. Ductile or RCP only
c. Aerial crossings must be above 25 year event
d. No pipe joints in the crossing or within 2’ of stream bank