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
b = 3 my = 1.9 mn = 0.014

Water flows uniformly 1.9 m deep in a rectangular unfinished concrete channel 3 m wide (Manning n = 0.014). The bed slope is S = 0.003. Use Manning’s equation in SI units to find the mean velocity V.

b = 3 my = 1.9 mn = 0.014S = 0.003
V = m/s
2.Easy
b = 3.5 my = 0.4 mn = 0.012

Water flows uniformly 0.4 m deep in a rectangular finished concrete channel 3.5 m wide (Manning n = 0.012). The bed slope is S = 0.003. Use Manning’s equation in SI units to find the mean velocity V.

b = 3.5 my = 0.4 mn = 0.012S = 0.003
V = m/s
3.Medium
b = 4 my = 0.7 mn = 0.03, S = 0.003

A rectangular grass-lined earth channel is 4 m wide. Water flows uniformly 0.7 m deep. Manning n = 0.03 and the bed slope is S = 0.003. Find the flow rate Q in m³/s.

b = 4 my = 0.7 mn = 0.03S = 0.003
Q = m³/s
4.Medium
b = 4 my = 1.3 m1 : 1n = 0.014, S = 0.002

A trapezoidal unfinished concrete channel has a bottom width of 4 m and side slopes of 1:1 (horizontal:vertical). Water flows uniformly 1.3 m deep. Manning n = 0.014 and the bed slope is S = 0.002. Find the flow rate Q in m³/s.

b = 4 my = 1.3 mz = 1n = 0.014S = 0.002
Q = m³/s
5.Hard
b = 1 my = 0.6 mn = 0.012, Q = 1.3 m³/s

A rectangular finished concrete channel 1 m wide must carry 1.3 m³/s in uniform flow at a depth of 0.6 m. Manning n = 0.012. Find the required bed slope S (in m/m).

Q = 1.3 m³/sb = 1 my = 0.6 mn = 0.012
S = m/m
6.Hard
b = 1.5 my = 2.2 mn = 0.015, Q = 6.7 m³/s

A rectangular brickwork channel 1.5 m wide must carry 6.7 m³/s in uniform flow at a depth of 2.2 m. Manning n = 0.015. Find the required bed slope S (in m/m).

Q = 6.7 m³/sb = 1.5 my = 2.2 mn = 0.015
S = m/m

Answer key

  1. 1. V = 3.478 m/s
  2. 2. V = 2.16 m/s
  3. 3. Q = 3.299 m³/s
  4. 4. Q = 20.48 m³/s
  5. 5. S = 0.003822 m/m
  6. 6. S = 0.002013 m/m

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