Storm Drainage Systems (D-3)

Question 1

What is a Roof Drain?

Answer 1

• A fitting device that is installed in the roof
• Permits stormwater to drain into a Leader

Question 2

What is the purpose of a Flow-Control Roof Drain?

Answer 2

• Used to drain the roof at a controlled rate (usually flows at a slower rate)
• The roof must be structurally designed to hold the excess rain water

Question 3

What is a Siphonic Roof Drain?

Answer 3

• A drain that is designed to drain water faster which in turn creates a Siphonic condition.
• Because it drains water faster, minimal roof drains are required.
• can be connected into a single rain leader

Question 4

What are Rainwater Leaders (RWL)?

Answer 4

• Located either inside or outside a building.
• Can be made from: sheet metal, non-circular tubing, or pipe

Question 5

What is a Deck Drain?

Answer 5

• Same idea as a roof drain
• Has a flat strainer (instead of a dome shape)
• Located in areas like walkways

Question 6

What is a Roof Gutter…

Answer 6

• Collection device
• Located at the lower side of pitched roof
• Made from: aluminum or steel w/ corrosion-resistant coating.
• Terminates at external leader

Question 7

What is a Roof Scrupper?

Answer 7

• Boxlike collection device
• Located on exterior building
• Receives storm water on one side

Question 8

What does an Emergency Roof Scrupper do?

Answer 8

• Are overflow protection for flat roofs
• Usually installed with flow control roof drains + parapet walls

Question 9

What is a Catch Basin?

Answer 9

• Used to drain areas such as parking lots
• CB lead to storm sewars.
• Is designed ti trap debris to prevent it from entering the drainage pipe.

Question 10

Storm drainage piping system….

Answer 10

• Designed for gravity or pumped flow to point of discharge

Question 11

Who regulates the discharge rate for stormwater systems?

Answer 11

-Authority Having Jurisdiction

Question 12

Lets talk aboot Combined Drainage Piping Systems

Answer 12

• Designed to collect storm drainage AND wastewater
• This is not an ideal set up as a heavy rainfall or snowmelt can overload the sewer system.
• These systems may employ combined sewer overflows (CSOs)

Question 13

What is a Combined Sewer Overflow?

Answer 13

• Installed (sometimes) in Combined drainage pipiing systems)
• They are designed to overflow / discharge excess flow directly to a predetermined disposal area (ex: river) w/o reaching the sewage treatment plant.

Question 14

When couplings for corrugated steel pipe are used what needs to be kept in mind?

Answer 14

• Maintaining pipe alignment
• Pipe separation doesn’t occur
• Root penetration doesn’t occur
• Keeps other material out

Question 15

Where is corrugated steel galvanized pipe used?

Answer 15

For building sewers

Question 16

Where are sheet metal leaders ued?

Answer 16

• Above ground outside only

Question 17

What is all included in the storm drainage system?

Answer 17

• Rainwater leaders
• Storm / combined building drains
• storm / combined building sewers

Question 18

What unit is used when measuring loads for the storm drainage system?

Answer 18

• Litres

Question 19

How does the load of litres have a relationship with flow rate?

Answer 19

• A time frame is needed?

Question 20

What time frame is used to calculate flow rate?

Answer 20

• 15 min
• Lires/ 15 min

Question 21

How do you calculate the load in L/15 min from a roof or paved surface?

This is for Drainage Load for a Flat Surface

Answer 21

• Have to find the area that is being drained
• Multiply the area in metres squared (m2) by the rainfall intensity in mm/15 min

m2 x mm = 1L

Example on page 21

Question 22

How do you solve Hydraulic load for a flat roof with an adjoining wall?

Drainage Load for a Flat surface with an Adjoining Wall

Answer 22

• Flat roof calculation = roof area (via area) x rainfall intensity.
• When calculating the wall, only one half of the wall has to be considered (as per code)
• wall calculation: Area = L x W, then divide by 2

m2 x mm = 1L –> L/15min = rainfall intensity

Question 23

What happens when there are 2 or more adjoining walls?

Answer 23

Code states that only one-half of the largest adjoining wall area be considered.

Question 24

How do you determine Loads from appliances that produce semi or continuous flow?

Answer 24

• Only fixtures or appliances that discharge clearwater waste may drain to a storm drainage system
• The flow rate of a fixture expressed in L/sec is multiplied by 31.7 to find the hydraulic load expressed in fixture units imposed on the sanitary system by that fixture.