Presented by: David Albus, RCE, GE

Transcription

1 Presented by: David Albus, RCE, GE

2 Definitions Percolation Rate- Rate that water falls in a percolation test Dependent on water pressure and geometry of test 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 All three have units of length/time- leads to confusion

3 Flow of water through Soil

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

5 Flow of water through Soil Element Adjacent Elements 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

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 ; commonly 0.29 is used. Gs the specific gravity of solids, S e k the specific surface (m2/kg) void ratio 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 U L U + 0.5L U L 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 Ave. water level of segment Find Q at ave. water level and Volume of segment T 1 =V 1 /Q 1 Find Q 2 and V 2 T 2 =V 2 /Q 2 Find Q 3 and V 3 T 3 =V 3 /Q 3 Find Q 4 and V 4 T 4 =V 4 /Q 4 Find Q 5 and V 5 T 5 =V 5 /Q 5 Find Q 6 and V 6 T 6 =V 6 /Q 6 Add up for Total Time

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 Upper Chamber Impermeable Layer (fill) More permeable layer Lower Well Less permeable layer Radial Distance of Saturation

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

46 Computer Model of Dry Well TIME= 0 HR Groundwater

47 TIME= 1.7 HR Computer Model of Dry Well

48 TIME= 5.5 HR Computer Model of Dry Well

49 TIME= 9.7 HR Computer Model of Dry Well

50 TIME=13.6 HR Computer Model of Dry Well

51 Computer Model of Dry Well foot deep, 4-foot diameter: Height of Water in Dry Well Height of Water in Well (ft) Time (hrs)

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