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.

New worksheetPractise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
b = 6 my = 1.5 mn = 0.025

Water flows uniformly 1.5 m deep in a rectangular gravel channel 6 m wide (Manning n = 0.025). The bed drops 5 m per kilometre. Use Manning’s equation in SI units to find the mean velocity V.

b = 6 my = 1.5 mn = 0.025drop = 5 m/km
V = m/s
2.Easy
b = 6 my = 1.8 mn = 0.014

Water flows uniformly 1.8 m deep in a rectangular unfinished concrete channel 6 m wide (Manning n = 0.014). The bed slope is S = 0.002. Use Manning’s equation in SI units to find the mean velocity V.

b = 6 my = 1.8 mn = 0.014S = 0.002
V = m/s
3.Medium
b = 2.5 my = 0.6 m3 : 1n = 0.014, S = 0.0015

A trapezoidal unfinished concrete channel has a bottom width of 2.5 m and side slopes of 3:1 (horizontal:vertical). Water flows uniformly 0.6 m deep. Manning n = 0.014 and the bed slope is S = 0.0015. Find the flow rate Q in m³/s.

b = 2.5 my = 0.6 mz = 3n = 0.014S = 0.0015
Q = m³/s
4.Medium
b = 2.5 my = 1.1 mn = 0.015, S = 0.001

A rectangular brickwork channel is 2.5 m wide. Water flows uniformly 1.1 m deep. Manning n = 0.015 and the bed slope is S = 0.001. Find the flow rate Q in m³/s.

b = 2.5 my = 1.1 mn = 0.015S = 0.001
Q = m³/s
5.Hard
b = 3 my = 1.2 m1.5 : 1n = 0.022, Q = 5 m³/s

A trapezoidal clean earth channel with a bottom width of 3 m and side slopes of 1.5:1 (horizontal:vertical) must carry 5 m³/s in uniform flow at a depth of 1.2 m. Manning n = 0.022. Find the required bed slope S (in m/m).

Q = 5 m³/sb = 3 my = 1.2 mz = 1.5n = 0.022
S = m/m
6.Hard
b = 5 my = 2.1 m1 : 1n = 0.03, Q = 39 m³/s

A trapezoidal grass-lined earth channel with a bottom width of 5 m and side slopes of 1:1 (horizontal:vertical) must carry 39 m³/s in uniform flow at a depth of 2.1 m. Manning n = 0.03. Find the required bed slope S (in m/m).

Q = 39 m³/sb = 5 my = 2.1 mz = 1n = 0.03
S = m/m

Answer key

  1. 1. V = 2.828 m/s
  2. 2. V = 3.455 m/s
  3. 3. Q = 3.938 m³/s
  4. 4. Q = 4.056 m³/s
  5. 5. S = 0.0005026 m/m
  6. 6. S = 0.004075 m/m

Full step-by-step solutions: practise this topic on examproblems.com.