What is the slope ratio for a 150 mm storm drain?

What is the slope ratio for a 150 mm storm drain?

• A. 1:50
• B. 1:200
• C. 1:100
• D. 1:20

Answer: (C)

Slope ratio in gravity drainage expresses the gradient of the pipe — how much vertical drop occurs over a given horizontal length. For a 150 mm storm drain, the minimum practical slope used to keep the flow moving and avoid deposits is 1:100. That means about 1 centimeter of drop per meter of pipe, or a 1% gradient. So the correct choice corresponds to a moderate, self-cleansing gradient: 1:50 would be much steeper (about 20 mm per meter), 1:200 would be quite flat (about 5 mm per meter), and 1:20 would be very steep (about 50 mm per meter).

Slope ratio in gravity drainage expresses the gradient of the pipe — how much vertical drop occurs over a given horizontal length. For a 150 mm storm drain, the minimum practical slope used to keep the flow moving and avoid deposits is 1:100. That means about 1 centimeter of drop per meter of pipe, or a 1% gradient.

So the correct choice corresponds to a moderate, self-cleansing gradient: 1:50 would be much steeper (about 20 mm per meter), 1:200 would be quite flat (about 5 mm per meter), and 1:20 would be very steep (about 50 mm per meter).