1. Exercise 1
Clean and straight natural channel
Bed slope 1:2000, Length = 1000 m
Assuming steady uniform flow
1. Calculate the velocity and discharge using
Manning , assume n = 0,02 s/m1/3
2. Calculate the mean boundary shear stress
3. Is the flow turbulent?
4. Value specific energy?

2. Open channel, with bed slope >0
2211 AuAuQ 
Head loss
Reference line
𝑦1 + 𝑧1 +
𝑢1
2
2𝑔
= 𝑦2 + 𝑧2 +
𝑢2
2
2𝑔
+ ∆𝐻1−2
4

3. Manning’s formula
𝑉 =
𝑅
2
3 ∙ 𝑆𝑓
1
2
𝑛
𝑉 = Mean Fluid Velocity [m/s]
R = Hydraulic Radius [m]
𝑆𝑓 = Slope Total head [1]
𝐴 = Wetted Area [m2]
𝑃 = Wetter Perimeter [m]
𝑛 = Mannings roughness coefficient [s/m1/3]
6

6. Exercise 2
Clean and straight natural channel
Bed slope = 0 (horizontal), Length = 1000 m,
Water level downstream = +1,0 m N.A.P. ,
water depth downstream = 0,70 m.
Q = 1,5 m3/s, Assuming steady flow
1. Calculate water level upstream using Manning, ,
assume n = 0,02 s/m1/3
2. Calculate the mean boundary shear stress
3. Is the flow turbulent?
4. Uniform or non-uniform flow?
5. Value specific energy?

7. u1
Reference [m]
Surfacelevel y +z [m]
Total Head H [m]
P1
z1
y1
u1
2/2g
P2
z2
y2
u2
2/2g
u2
21
2
2
22
2
1
11
22
 H
g
u
zy
g
u
zy
Head loss [m]
ΔH
Velocity Head [m]
Open channel, with bed slope <= 0
4

10. Little errors or inaccuracies with calculation by hand.
1. Length between the calculation points.
2. Assume that between the calculation points ∆H = ∆y
+1,31 m

11. Model in sobek
Waterdepth
Distance (m) Sobek (m) By Hand (m)
0 0.7 0.7
200 0.78 0.81
600 0.89 0.94
1000 0.96 1.01
+1 m NAP
+1,26 m NAP