Fundamentals of Infiltration and Analyses - ASCE OC American Society of Civil Engineers - Orange County Branch - Geo Institute - Civil Engineering - Dinner Presentation - August 15 2017

1. Presented by:
David Albus, RCE, GE

2. Definitions
Infiltration Rate-
The “straight-path” velocity at which water enters into soil
Is dependent on the water pressure
More pressure= higher infiltration
Permeability Rate-
Also known as Hydraulic Conductivity
Is an intrinsic value - does not vary due to pressure
Percolation Rate-
Rate that water falls in a percolation test
Dependent on water pressure and geometry of test
All three have units of length/time- leads to confusion

3. Flow of water through Soil

4. Flow of water through Soil
Hydraulic Gradient
TOTAL HEAD=
PORE PRESSURE +
ELEVATION
SATURATED FLOW

5. Flow of water through Soil
Adjacent
Elements
Element
K·i
(X-direction)
K·i
(Y-direction)
Boundary
Flux
Change in Water
Content

6. Infiltration in a Basin

7. Infiltration in a Basin
Impounding layer caused by soil
with lower permeability

8. Infiltration in a Basin

9. Other “Basin” Systems
Arched Chamber Systems Stackable Block Systems

10. Dry Well System

11. Types of Percolation Testing

12. Shallow Percolation Pit - Falling Head

13. Deep Percolation Pit - Falling Head

14. Deep Percolation Pit - Falling Head

15. Deep Percolation Pit - Falling Head

16. Deep Percolation Pit - Falling Head

17. Single-Ring Infiltrometer – Constant Head

18. Single-Ring Infiltrometer – Constant Head

19. Double-Ring Infiltrometer – Constant Head

20. Double-Ring Infiltrometer – Constant Head

21. Double-Ring Infiltrometer – Constant Head

22. Well Permeameter - Constant Head
USBR 7300-89

23. Well Permeameter - Constant Head

24. Laboratory Testing for Comparison

25. Laboratory Testing for Comparison

26. Laboratory Testing for Comparison

27. Laboratory Testing for Comparison
Kozeny-Carmen Equ. from Chapuis & Aubertin (2003)
A2 a constant in the range of 0.29-0.51;
commonly 0.29 is used.
Gs the specific gravity of solids, 2.65.
S the specific surface (m2/kg)
e void ratio
k hydraulic conductivity in m/s

28. Design of Chamber or Basin

29. Design of Chamber or Basin

30. Design of Chamber or Basin

31. Design of Chamber or Basin
Ratio of Clearance to
Aquitard/width of BMP
Effective Infiltration Rate
2.25 0.75U + 0.25L
1.5 0.5U + 0.5L
0.75 0.25U + 0.75L
U= Upper Permeability
L= Lower Permeability

32. Design of Chamber or Basin
Depth of Ponding
(in)
Percent of Infiltration for
12 inches of ponding
9 75%
6 50%
3 25%

33. Design of Chamber or Basin

34. Design of Chamber or Basin

35. Design of Dry Well

36. Well Permeameter Equations

37. Well Permeameter Equations

38. Well Permeameter Equations

39. Well Permeameter Equations

40. Well Permeameter Equations

41. Well Permeameter Equations

42. Well Permeameter Equations
Find Q at ave. water
level and Volume of
segment
T1=V1/Q1
Find Q2 and V2 T2=V2/Q2
Find Q3 and V3
T3=V3/Q3
Find Q4 and V4 T4=V4/Q4
Find Q5 and V5 T5=V5/Q5
Find Q6 and V6 T6=V6/Q6
Add up for Total
Time
Ave. water level
of segment

43. Well Permeameter Equations
K=saturated permeability
T1 & t2= Times of interest
H1 & H2= height of water in well at t1 & t2
L= Length of well screen
r= Well radius

44. Computer Model of Dry Well
Water Surface
More permeable
layer
Less permeable
layer
Impermeable
Layer (fill)
Radial Distance
of Saturation
Upper
Chamber
Lower
Well

45. Computer Model of Dry Well
Chamber Section
Gravel Section
95’ Invert
80’
60’

46. Computer Model of Dry Well
TIME= 0 HR
Groundwater

47. Computer Model of Dry Well
TIME= 1.7 HR

48. Computer Model of Dry Well
TIME= 5.5 HR

49. Computer Model of Dry Well
TIME= 9.7 HR

50. Computer Model of Dry Well
TIME=13.6 HR

51. Computer Model of Dry Well
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18 20
HeightofWaterinWell(ft)
Time (hrs)
40-foot deep, 4-foot diameter: Height of Water in
Dry Well

52. Design Parameters
Infiltration Basin/Chamber-
Infiltration rate = permeability if ponding is 12” or more
Reduce infiltration rate for ponding less than 12” using linear reduction
Adjust rate in consideration of impeding layers or GW
If impeding layer or GW more than 3X width, minimal effect
If shallower than 3X Width, roughly weighted to proportion of distance
Provide a second infiltration rate for down draw determination
Use ½ of the value appropriate to the max ponding depth
Dry Well-
Infiltration rate ≠ permeability
Need Q value for specific well configuration
Use computer software or closed-form equation if suitable
Effective Infiltration rate = Q/wetted area
Effective Infiltration Rate will be much greater than permeability
Don’t be surprised to get rate that is 5X to 20X of permeability
Use finite step method or Horslev equation for explicit draw down
Or use computer model to determine drawdown time

53. Questions & Answers