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 1 m deep in a rectangular gravel channel 1 m wide (Manning n = 0.025). The bed slope is S = 0.003. Use Manning’s equation in SI units to find the mean velocity V.

b = 1 my = 1 mn = 0.025S = 0.003

V = m/s

2.Easy

Water flows uniformly 1.2 m deep in a rectangular gravel channel 1.5 m wide (Manning n = 0.025). The bed slope is S = 0.003. Use Manning’s equation in SI units to find the mean velocity V.

b = 1.5 my = 1.2 mn = 0.025S = 0.003

V = m/s

3.Medium

A rectangular unfinished concrete channel is 1 m wide. Water flows uniformly 0.5 m deep. Manning n = 0.014 and the bed slope is S = 0.0015. Find the flow rate Q in m³/s.

b = 1 my = 0.5 mn = 0.014S = 0.0015

Q = m³/s

4.Medium

A concrete storm sewer with an inside diameter of 750 mm flows half full. Manning n = 0.013 and the slope is S = 0.004. Find the flow rate Q in m³/s.

D = 750 mmn = 0.013S = 0.004

Q = m³/s

5.Hard

A concrete sewer with an inside diameter of 300 mm (Manning n = 0.013) must reach a self-cleansing velocity of 0.75 m/s when flowing just full. Find the minimum slope S (in m/m).

D = 300 mmn = 0.013V = 0.75 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 1.2 m/s when flowing just full. Find the minimum slope S (in m/m).

D = 375 mmn = 0.013V = 1.2 m/s

S = m/m

Answer key

1. V = 1.053 m/s
2. V = 1.308 m/s
3. Q = 0.5489 m³/s
4. Q = 0.352 m³/s
5. S = 0.003006 m/m
6. S = 0.005714 m/m

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