Slides course Rural Water Management, Delta Academy

1. Water drainage
Darcy’s law
Groundwater flow
Design water drainage Pipelines
1

2. Flow through a dike
Seepage (kwel) flows through dam
Pressure line
1

3. Piping erosion
Water pressure
Seepage (kwel) beneath structure
civil structure
Flushing of particles
1

4. Dewatering
(verlagen grondwaterstand)
Maximum capacitity
Well point system
Size filters
Original ground
water level
1

5. Groundwater level
New groundwater level because of rain
percipitation
Ditch or drainage
Drainage
2

6. Landuse / Grondgebruik
Percipitation
Neerslag
(mm/dag)
Groundwater level below
surface
Grondwaterstandsdiepte
(m)
grassland / grasland 7 (10) 0,30 (0,20)
farm land / bouwland 7 (10) 0,50 (0,30)
horticulture / vollegronds tuinbouw 7 (10) 0,50 (0,30)
flower bulbs on clay soil / bloembollen op
klei 7 0,50
flower bulbs on sand soil / bloembollen op
zand 10 0,30
fruit / fruitteelt 7 (10) 0,70 (0,60)
forest / bos 5-7 0,50 - 0,30
military training area / militair oefenterrein 7 0,70
athletic fields, camping areas, play grounds /
sportvelden, kampeerterreinen, speel- en
ligweiden 15 0,50
building sites / bouwterreinen 10 0,50
urban area / woongebieden (50% verhard) 5 0,70
industrial area / industrieterreinen 7 0,50 2

7. 3
Groundwater flow

8. Darcy’s law
3

9. 3
Soil / grondsoort
conductivity
doorlatendheid
(m/day)
heavy clay /zware klei 0.0001
potklei 0.001
Moderate heavy clay / matig zware klei 0.01
sandy clay / zandige klei 0,05
bolder clay / keileem 0,05
peat / veen 0.001 - 0.1
clay peat / kleiig veen 0,005
sandy peat / sterk zandig veen 0,05
loam /leem/löss 0,05
sandy loam / zandige leem 0,3
silt / lichte zavel 0,5
humus / teelaarde 5
shells / schelpen 30
fine sand / fijn zand 1 - 10
dune sand / duinzand 7
coarse sand / grof zand 30
very coarse sand / zeer grof zand 80
very coarse sand / uiterst grof zand 200
fine gravel / fijn grind 1.000 - 10.000
coarse gravel / grof grind 10.000 - 100.000

10. Darcy’s law
IAkq  Ikv 
Laminar flow
q = discharge [m3/s]
k = hydraulic conductivity [m/s]
A = area [m2]
I = S = slope pressure line
3

11. ]1[Re

dv
w


If Rew < 5 Laminar flow
Rew = Reynolds number [1]
v = Average velocity [m/s]
d = Average grain size [m]
ν = Kinematic viscosity [m2/s] = 10 -6
3
Reynolds number

12. Groundwater level rise
New groundwater level because of rain
percipitation
Ditch or drainage
Drainage
4

13. Drainage agriculture parcel
2
2
max/ amiddle H
K
aW
H 


4
HaHmiddle/max
W
a
K

14. Drainage agriculture parcel
2
2
max/ amiddle H
K
aW
H 


W = vertical velocity rainfall [m/s]
a = horizontal distance from stream channel to highest ground water
level [m]
K = hydraulic conductivity [m/s]
Ha = vertical distance from impereable layer to water level stream
channel [m]
Hmiddle= vertical distance from impereable layer to highest ground
water level[m]
4

15. Design criteria drainage pipeline
• Manning’s formula
• n=0,013 s/m1/3
• Sbed =1/1000
• Pipe 50% filled with water
• Outflow 10 cm above surface water
u = mean velocity [m/s]
R = hydraulic radius [m]
S = slope energy line [1]
assumed is that Sf = Sbed
n = manning’s roughness coefficient [s/m1/3]n
SR
u
2
1
3
2


5

16. m
4
4/1 2
D
D
D
O
A
R 





m
4)(5,0
)4/1(5,0 2
D
D
D
O
A
R 





R and circle’s
5