Open-channel flow (Manning) worksheet with answers

Free printable Open-channel flow (Manning) worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

Water flows uniformly 0.9 m deep in a rectangular gravel channel 4.5 m wide (Manning n = 0.025). The bed slope is S = 0.002. Use Manning’s equation in SI units to find the mean velocity V.

b = 4.5 my = 0.9 mn = 0.025S = 0.002

V = m/s

2.Easy

Water flows uniformly 2 m deep in a rectangular gravel channel 5 m wide (Manning n = 0.025). The bed drops 1 m per kilometre. Use Manning’s equation in SI units to find the mean velocity V.

b = 5 my = 2 mn = 0.025drop = 1 m/km

V = m/s

3.Medium

A concrete storm sewer with an inside diameter of 900 mm flows half full. Manning n = 0.013 and the slope is S = 0.0005. Find the flow rate Q in m³/s.

D = 900 mmn = 0.013S = 0.0005

Q = m³/s

4.Medium

A concrete storm sewer with an inside diameter of 600 mm flows half full. Manning n = 0.013 and the slope is S = 0.0008. Find the flow rate Q in m³/s.

D = 600 mmn = 0.013S = 0.0008

Q = m³/s

5.Hard

A concrete sewer with an inside diameter of 375 mm (Manning n = 0.013) must reach a self-cleansing velocity of 0.6 m/s when flowing just full. Find the minimum slope S (in m/m).

D = 375 mmn = 0.013V = 0.6 m/s

S = m/m

6.Hard

A concrete sewer with an inside diameter of 375 mm (Manning n = 0.013) must reach a self-cleansing velocity of 1 m/s when flowing just full. Find the minimum slope S (in m/m).

D = 375 mmn = 0.013V = 1 m/s

S = m/m

Answer key

1. V = 1.332 m/s
2. V = 1.357 m/s
3. Q = 0.2024 m³/s
4. Q = 0.08683 m³/s
5. S = 0.001429 m/m
6. S = 0.003968 m/m

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