HomeMy WebLinkAboutCattail Sewer Report_ REV 12162021Synergy Engineering
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Cattail Duplexes
Sewer Design Report
Project Background:
• 11-unit duplex
• Residential single-family use
• 2.11 people per dwelling unit
• Population = 11 units * 2.11 people per unit = 23.21 people
• 64.4-gallons per capita per day
• Infiltration rate: 150 gallons/acre/day *0.708 acres = 106.2 gallons/day
• 11units*2.11 people per unit*64.4 GPD = 1494.72 GPD + 106.2 GPD infiltration =
1600.92 GPD
• Qmax = 18 + (0.02321)^½ = 18.1523
• Qavg = 4 + (0.02321)^½ = 4.1523
• Peaking Factor = Qmax/Qavg = 4.4
• 1601 Gallons per day * 1 day/24 hours * 1hour/60 minutes = 1.11 gpm average
• Peak Hour = 1.11 gpm * 4.4 = 4.9 gpm
Sewer Main Specifications:
• 8-inch PVC pipe
• Slope 2% or greater
• Minimum cover is four feet
• Cleanout installed within 3 feet of foundation wall
COB Standard Drawings:
• COB 02720-4 Standard Straight Manhole
• COB 02720-6 Precast Manhole Bases
• COB 02720-7 Typical Manhole Channel Details
• MPW 02730-1 Nomograph for Air Testing
• COB 02730-2 Sanitary Sewer Service Line
• COB 02730-3 Deep Sanitary Sewer Service Line
• COB 02730-4 Sanitary Sewer Cleanout
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Wastewater Collection: 8’’ sanitary sewer main, 135 feet of PVC pipe, connecting to existing
city sewer main with a proposed manhole terminating with a second proposed manhole. A
slope of no less than 2.0% and minimum cover of four feet. New sewer is sized to flow at no
more than 75% full.
Manhole: Two manholes are required for this sewer main extension. One the connection with
the existing sewer main and one at the end of the sewer main extension. Barrel size shall be
48’’. Manholes shall have full-depth channels. When a smaller main is being connected to a
larger main at a manhole, the manhole inverts shall be set so that the 8/10 depth of flow of
each main is equal in elevation. The minimum drop across a manhole is 0.2 feet.
Sanitary Sewer Services: Diameter is 4-inches. Services shall connect to the main with in-line
gasketed wyes. Max slope of ½ inch per foot. Minimum slope is ¼ inch per foot. Installed
perpendicular to the main. Each townhouse shall have a separate service line.
Manning’s Formula: 𝑉𝑉=𝑘𝑘𝑛𝑛𝑅𝑅ℎ2/3𝑆𝑆1/2
V = average velocity in ft/s
n = 0.013
Rh = hydraulic radius = d/4 = 0.1997
S = slope = 0.02
k = 1.49
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Manning Formula Uniform Pipe Flow at Given Slope and Depth
Inputs:
Pipe Diameter, dₒ 7.9420 in
Manning Roughness, n 0.0130
Pressure slope (possibly equal to pipe slope), S₀ 2.0000 % slope
Percent of (or ratio to) full depth (100% or 1 if flowing full) 75.0000 %
Results:
Flow, Q 685.9606 gal/min
Velocity, v 5.5221 ft/s
Velocity head, hv 0.4739 ft
Flow Area, A 0.2768 ft^2
Wetted Perimeter, P 1.3861 ft
Hydraulic Radius 0.1997 ft
Top Width, T 0.5732 ft
Froude Number, F 1.40
Shear Stress (tractive force), τ 0.6197 psf
Version 2.0 (20 June 2017)
HawsEDC Calculators
12/16/2021