Combined sewer / gemengd rioolstelsel

50 m

Ø300 PVC

Ø500 concrete

Ø250 PVC

pump

P4 P3 P2

GL (ground level) +6.00 m

IL +4,00 m IL +3,90 m

IL +3,73 m

Rain water

Waste water

Rain

Waste

+5,5 m

IL (Invert level) +3,53 m

P1

1

Length

Chezy formula

Chezy formula describes the mean velocity of uniform, turbulent flow

ΔH

𝑉 = 𝐶 ∙ 𝑅 ∙ 𝑆𝑓

𝑉 = Mean Fluid Velocity [m/s]

R = Hydraulic Radius [m]

𝑆𝑓 = Hydraulic gradient [1]

𝐶 =8𝑔

𝜆 Chezy coefficient [m1/2/s]

𝑆𝑓 =ΔH

𝐿

3

Total Head

Pressure Head

Head loss sewer pipe

𝑉 = 𝐶 ∙ 𝑅 ∙ 𝑆𝑓 𝑄 = 𝑉 ∙ 𝐴 𝑆𝑓 = 𝑖 =∆𝐻

𝐿 Combine

∆𝐻 = 𝐿𝑄2

𝐶2 ∙ 𝑅ℎ ∙ 𝐴𝑠2

∆𝐻 = Head Loss, energy loss [m]

Q = discharge pipe [m3/s]

L = length of the pipe [m]

C = Chezy coefficient [m1/2/s]

R = Hydraulic Radius [m]

A = Wetted Area, flow surface [m2]

Sf ,i = slope of hydraulic gradient [-] 3

Question 1

50 m

Ø300 PVC

Ø500 concrete

Ø250 PVC

Pump

P4 P3 P2

GL +6.00 m

IL +4,00 m IL +3,90 m

IL +3,73 m

Rain

Waste

Rain

Waste

+5,5 m

IL +3,53 m

P1

5

Question 2

50 m

Ø300 PVC

Ø500 concrete

Ø250 PVC

Pump

P4 P3 P2

GL +6.00 m

IL +4,00 m IL +3,90 m

IL +3,73 m

Rain=0

Waste=10l/s

Rain=0

Waste=10l/s

+5,5 m

IL +3,53 m

Q=20 l/s

Q=10 l/s

P1

5

Partially filled pipe

𝐼𝑛𝑝𝑢𝑡: 𝑄𝑝𝑎𝑟𝑡

𝑄𝑓𝑢𝑙𝑙= 0,17

𝑂𝑢𝑡𝑝𝑢𝑡: ℎ

𝐷= 0,27

𝑂𝑢𝑡𝑝𝑢𝑡: 𝑢𝑝𝑎𝑟𝑡

𝑢𝑓𝑢𝑙𝑙= 0,75

5

Table

5

Question 3

50 m

Ø300 PVC

Ø500 concrete

Ø250 PVC

Pump

P4 P3 P2

GL +6.00 m

IL +4,00 m IL +3,90 m

IL +3,73 m

Rain=1,1 ha

Waste=10 l/s

Rain=3,75 ha

Waste=10 l/s

+5,5 m

IL +3,53 m

P1

5

Question 3c

50 m

Ø300 PVC

Ø500 beton

Ø250 PVC

Pump

P4 P3 P2

GL +6.00 m

Rain=66 l/s

Waste=10 l/s

Rain=225 l/s

Waste=10 l/s

+5,5 m

Q=66 l/s

Q=291 l/s

P1

In example m = 1,8 5

Q=0 l/s

s/m1/3

Strategy [situation with overflow]

Preparation

Information available for each pipe

- Diameter, R, L, k, C

- Discharge and Velocity

Information Overflow / weir

- Width, m

- Discharge

- Level crest in m N.A.P.

𝐶 = 18 ∙ 𝑙𝑜𝑔12𝑅

𝑘

5

1. Calculate H at weir

2. Calculate ∆H each pipe

3. Water level at weir (P1) = level crest weir + H at weir

4. Water level at P2 = Water level at weir + ∆Hweir(p1) – p2

5. Water level at P3 = Water level at P2 + ∆H p2– p3

6. Water level at P4 = Water level at P3 + ∆H p3– p4

Strategy [situation with overflow]

Steps

All levels in m N.A.P.

𝑄 = 𝑚 ∙ 𝐵 ∙ 𝐻32 ∆𝐻 = 𝐿

𝑄2

𝐶2 ∙ 𝑅ℎ ∙ 𝐴𝑠2

5

Little error or inaccuracy:

Distance between H en y is velocity head. At manhole

(bigger than sewer pipe) we assume velocity head is = 0