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CTC 450 Review. WW Characteristics. Objectives. Understand the basics of storm drainage systems Understand the basics of sewer systems. Storm Sewer System. Surface waters enter system through inlets Water is then conveyed through pipes and manholes

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ctc 450 review
CTC 450 Review
  • WW Characteristics
objectives
Objectives
  • Understand the basics of storm drainage systems
  • Understand the basics of sewer systems
storm sewer system
Storm Sewer System
  • Surface waters enter system through inlets
  • Water is then conveyed through pipes and manholes
  • Quantity of runoff is determined using the rational method (Q=CIA)
  • Velocities designed for 3-10 fps
sanitary sewer system
Sanitary Sewer System
  • Laterals collect wastewaters to branch lines which are conveyed to large mains (also called trunks or outfall sewer)
  • Force main has WW conveyed under pressure via pumps
  • Sanitary sewers are placed deep enough to prevent freezing
differences between storm sewer
Differences between Storm/Sewer
  • Storm systems are designed to overflow periodically (frequency)
  • Sewer systems are designed to contain all the wastewater; if surcharging occurs it’s usually a result of infiltration of stormwater
  • Stormwater pipes are much bigger than sewer pipes
example 10 1
Example 10-1
  • What is the maximum population that can be served by an 8” sanitary sewer laid at minimum grade using a design flow of 400 gpcd & a flowing full velocity=2 ft/sec?
  • From Table 10-1 Q=310 gpm @ min. slope (full-flow)
  • 310 gpm / 400 gpcd (and adjust for units)
    • =1100 people (approx. 275 houses)
example 10 1 continued
Example 10-1 (Continued)

7

Compute the diameter of storm drain to serve the same population based on the following:

30 people/acre; C=0.4, 10-yr frequency w/ IDF curve on page 123, tc=20 min, vel=5 ft/sec

Area=37 acres

Intensity=4.2”

Q=62 cfs

Assuming full-flow; Area=12.4 square ft

Diameter=4 ft

manholes
Usually circular with an inside diameter of 4 feet

Placed at all changes in sewer grade, pipe size, or alignments changes (horiz. & vertical)

Also placed at all intersections, at the end of each line, and at distances not greater than 400 ft (<=15”) or 500 ft (>15”)

Manholes
other decorative manholes
Other Decorative Manholes
  • http://www.therawfeed.com/2006/04/nyc-manholes-turned-into-coffee-for.html
  • http://damncoolpics.blogspot.com/2006/12/japanese-manhole-cover-art.html
surcharged manholes
Surcharged Manholes
  • http://www.youtube.com/watch?v=SBPd0WOW70o
  • http://www.youtube.com/watch?v=4BkFp5CL4q0
  • http://www.youtube.com/watch?v=xwar6VbgY-M&feature=related
service connections
Service Connections
  • House service pipe is connected to the collecting sewer
  • Traps prevent backup of sewer gases into the building interior
  • Building vents prevent traps from being siphoned dry
sewer pipes and jointing
Sewer Pipes and Jointing
  • Vitrified clay, PVC, or precast concrete may be used
  • DIP (ductile iron pipe) is used for force mains
ductile iron pipe http img alibaba com photo 50364371 ductile iron pipe jpg
Ductile Iron Pipe (http://img.alibaba.com/photo/50364371/Ductile_Iron_Pipe.jpg)
load on buried pipe
Load on Buried Pipe
  • Loading on pipe must be considered
  • Common types of bedding are shown on page 345
sewer testing
Sewer Testing
  • Monitor infiltration (before connections)
    • Only works if pipe is below water line
  • Monitor exfiltration
    • Used if pipe above water line
  • Air testing
lift pump stations
Lift (Pump) Stations
  • Pumping stations used when gravity flow not feasible
  • Avoid if possible because a nonfunctional lift station means that sewage water can back up into houses/businesses
  • Pumps can be installed in the wet well or kept separate from the wet well