How do we Quantify Hydraulic Conductivity in an Urban Setting?

0

Great Lakes and St. Lawrence Green Infrastructure Conference

May 31, 2017

Christian Braneon, PhD Georgia Institute of Technology

Outline

1

• Fundamentals of Hydraulic Conductivity

• Infiltration vs. Drainage

• Measurement Methods

• Concluding Remarks

Fundamentals of Hydraulic Conductivity

2

• Has dimensions of velocity [L/T] • A combined property of the medium and the fluid • Ease with which fluid moves through the medium

k = cd2 intrinsic permeability ρ = density µ = dynamic viscosity g = specific weight

𝐾𝐾 = 𝑘𝑘 𝛾𝛾𝜇𝜇

Source: Dingman

Fundamentals of Hydraulic Conductivity (2)

3

Source: Dingman

Fundamentals of Hydraulic Conductivity (3)

4

• Homogeneous –Properties same at every

point • Heterogeneous

–Properties different at every point

• Isotropic –Properties same in every

direction • Anisotropic

–Properties different in different directions

• Stratification during sedimentation

verticalhorizontal KK >

Source: USGS

Hydrology

5

Above – infiltration is the process of moving water from the surface into the soil (tension infiltrometer, double-ring unit) Left - If the water moves into the subsurface, does it drain or just sit? (Amoozemeter; CCHP)

Infiltration vs Drainage

Source: USEPA

6

• The mini disk infiltrometer measures the hydraulic conductivity of the medium it is placed upon.

• Hydraulic conductivity is useful to scientists, land managers, and growers, in knowing how quickly water will infiltrate when applied to a given field or soil type.

• Infiltration is also relevant in fields of study such as contaminant transport, ground water recharge and ecosystem sustainability

Mini disk Infiltrometer

Source: Decagon Devices

7

• For most soils, a suction rate of 2 cm should be adequate.

• To adjust the suction rate, move the suction tube up or down so the water level is even with the desired suction rate marked on the side of the tube.

• For the calculation of hydraulic conductivity to be accurate at least 15 to 20 mL of water needs to be infiltrated into the soil during each measurement.

Mini disk Infiltrometer (2)

Source: Decagon Devices

8

Sample Infiltrometer Data

Source: Decagon Devices

9

• The double-ring infiltrometer consists of two thin-walled metal cylinders. The two cylinders are concentrically placed and driven into the soil to a depth of 5 to 10 cm.

• Water is ponded to the same shallow depth in both the inner and outer rings.

• The flow in the inner ring is presumed to be one dimensional with vertical streamlines.

Double-Ring Infiltrometer

Source: Univ. of Conn.

10

• Water flow rate vs. time from the inner ring is monitored until it reaches a constant value.

• The assumption is that the soil layer immediately below the ponded area is fully saturated and presumably renders the final infiltration rate (final flux) equal to the soil's saturated hydraulic conductivity, Ks.

Double-Ring Infiltrometer (2)

Source: Royal Eijkelkamp, Univ of Conn.

Amoozemeter / CCHP

11

• Constant head permeameter method (also known as the shallow well pump-in method). In this method, a hole of known diameter (usually 2.25 inches) is bored to a known soil depth.

• The hole is filled with water to a desired level and, as the water flows into the soil, more water is added to maintain a constant water level

• The Amoozemeter is placed next to an augered hole and the water supply tube and water dissipating unit are lowered into the hole.

Source: Purdue Univ

Amoozemeter / CCHP (2)

12

• The Amoozemeter is placed next to an augered hole and the water supply tube and water dissipating unit are lowered into the hole.

• When the water in the hole reaches a constant level and the rate of water flow into the soil reaches a constant, steady-state conditions are assumed and the rate of water flow into the soil can be used to determine the soil’s hydraulic conductivity at the measured depth (for more detailed information on this method, see Amoozegar and Warrick, 1986). Source: Purdue Univ.

Detroit, East side, Findlay

13

Infiltration: 0.2±0.2 cm/hr, silty clay loam Drainage: 0.4, 0 cm/hr at 24, 58 cm depth Red light

Maine St.

14

0.4±0.2 cm/hr, silt loam 2.5, 0.2 cm/hr at 22, 57 cm depth Too much soil, uneven packing Could save 3+ yards of material per lot Red light…

Convex, though we’d rather have concave

Dwyer 1

15

• 0.7±0.3 cm/hr, sandy clay loam • 193, 0.1 cm/hr at 30, 75 cm depth • Uneven packing, works both ways Yellow Light

Dwyer 2

16

4.3±0.8 cm/hr, sandy loam (thin layer) 0.2, 0.1 cm/hr at 25, 19 cm depth Yellow light

17

1.8±0.5 cm/hr, sandy loam 2.2, 3.2 cm/hr at 20, 59 cm depth Could be concave

Dwyer 3

Thank you for your time

18

Concluding Remarks

• For most soils, a suction rate of 2 cm should be adequate when using a mini-disk infiltrometer

• The mini-disk infiltrometer has the advantage of being easy to use and avoids macropore challenges

• The double-ring infiltrometer maintains a small constant head to estimate saturated K over a larger area

• The amoozemeter allows measurements of steady-state drainage rate at varying depths under constant head

• All these techniques are relatively inexpensive but dependent on the experience of the user

Thank you for your time

19

Christian Braneon, Water Resources Engineer, Georgia Institute of Technology BraneonCV@gatech.edu Thank you to: Bill Shuster (USEPA-ORD), Robert Ford (USEPA-ORD), Mike Borst (USEPA-ORD), Tami Thomas-Burton (USEPA-Region 4), David Egetter (USEPA-Region 4)

mailto:BraneonCV@gatech.edu

How do we Quantify Hydraulic �Conductivity in an Urban Setting?  Outline Fundamentals of Hydraulic ConductivityFundamentals of Hydraulic Conductivity (2)Fundamentals of Hydraulic Conductivity (3)HydrologyMini disk InfiltrometerMini disk Infiltrometer (2)Sample Infiltrometer DataDouble-Ring InfiltrometerDouble-Ring Infiltrometer (2)Amoozemeter / CCHPAmoozemeter / CCHP (2)Detroit, East side, FindlayMaine St.Dwyer 1Dwyer 2Dwyer 3Thank you for your timeThank you for your time