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METHODS TO ESTIMATE HYDRAULIC CONDUCTIVITY

METHODS TO ESTIMATE HYDRAULIC CONDUCTIVITY. Saturated Hydraulic Conductivity- K h *. Parameter that describes a soil or rock’s resistance or conductivity to water flow (also called K SAT or K S ). More permeable, higher K h *. Table 6-1 Dingman (Physical Hydrology).

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METHODS TO ESTIMATE HYDRAULIC CONDUCTIVITY

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  1. METHODS TO ESTIMATE HYDRAULIC CONDUCTIVITY

  2. Saturated Hydraulic Conductivity- Kh* Parameter that describes a soil or rock’s resistance or conductivity to water flow (also called KSAT or KS). More permeable, higher Kh* Table 6-1 Dingman (Physical Hydrology)

  3. More Realistic Range K (cm/sec)From Freeze and Cherry (1989)

  4. Particle Size Estimation Methods for Ksat Rosetta Neural Network Prediction (Hydrus-1D)

  5. Grain-Size Distribution to Estimate KSat These methods often have grain size range limitations The Breyer is valid for poorly sorted grains, with 0.06mm< D10<.6mm, while the Hazen is valid for sediments with 0.1mm< D10< 3 mm

  6. Particle-Size Analysis Hydrometer Method Sieve Method

  7. Particle-Size Analysis ** Later used to estimate saturated and unsaturated hydraulic conductivity.

  8. Soil Classification Triangle • Soil classification is typically made based on the relative proportions of silt, sand and clay. Follow any two component percentages to find the nominal name for the soil type. For example, 30% sand, 30% clay and 40% silt: • Find 30% along the bottom (sand) line, and follow the slanted line up and to the left. Stop at the horizontal line for 30% clay, and find the soil type: clay loam.

  9. Soil Classification to Estimate Kh Unsat K Parameters Computer program called Rossetta. Based on measured values for K and capillary parameters from thousands of soils (primarily USDA database). Correlate soil classification to these measured values using a pedo-transfer function approach http://www.ars.usda.gov/Services/docs.htm?docid=8953

  10. Rosetta Class Averages

  11. Rosetta Neural Network Prediction(this one in Hydrus-1D)

  12. Darcy Apparatus to Measure KS

  13. Need Soil Samples • Trench • Particle size analysis: ~ $60 • Ksat from Darcy column ~ $250 (lab) $ 400 buy your own • Geoprobe • ~$1200 /day • 100 feet total

  14. Field Methods • Double ring infiltrometer • Guelph Permeameter • Slug Test • Tension-disc Infiltrometer On-site Monitoring Well

  15. Costs • Double ring infiltrometer ($300-$700) • Guelph Permeameter ~$ 2100 • Slug Test (Need wells) • Tension-disc Infiltrometer $3000 • Darcy falling-head apparatus

  16. Average infiltration rate over time is calculated by either: • Measuring rate of decline of water level inside inner ring over the time. • Measuring the volume of water added to maintain a constant level and dividing by the time of the experiment. Double Ring Infiltrometer Because the inner- as well as the outer ring are filled with water, the water flows virtually vertically through the inner ring into the soil.

  17. Infiltration Rate Changes over Time Common Sense Observations Initial rate is high because soil is dry (capillarity) Ponding occurs when infiltration rate < w Long-term, if w > K*h, ponding occurs Theoretically i reaches steady rate ~ K*h Dingman Fig 6-19

  18. Factors Affecting Infiltration Rate • Rate at which water arrives w(t), or depth of ponding H(t) • Saturated K • Antecedent water content of near-surface soil • Inclination and roughness of the soil • Chemical characteristics of the soil surface • Physical and chemical properties of water Dingman Pages 247-248

  19. Guelph Permeameter – Ksat & Kunsat Well Diameter Water Height Outflow Rate (Ř)

  20. Slug Test - Ksat Water Level h0 Add a “slug” of water to the monitoring well Measure h with time as the water level falls t37 = time it takes for the water level to fall to 37% of the initial change Water Level at t0

  21. Slug Test (Ksat) Log Scale! 0.37 t37 = 314 hrs

  22. Slug Test (Ksat)

  23. Tension-disc Infiltrometer –Ksat & Kunsat • Directly measures Kunsat 20 cm Tension Disc Tensions = -15, -6, -3 cm Obtain infiltration rates (qx) at each tension Eliminate certain pores from the flow process (* Macropores) Effects of pore-size distribution Water Level Bubble Tower Water Reservoir Porous Disc

  24. Tension-disc Infiltrometer (Ksat) • Wooding’s equation:

  25. Measured vs. Estimated (Ksat) Log Scale! Percent Difference ~60%

  26. Unsaturated Hydraulic Conductivity • Based on porous-media properties (permeability, k) • And on fluid properties (, ) • And on the distribution of fluid in the pore spaces • K = k krw  g/ = Kh*krw • K and krw are functions of  Relative Permeability • 0< krw < 1 • K() takes on similar shape kr For water-air system, wetting phase is water, non-wetting is air

  27. Rosetta Method • Used data obtained from the Rosetta neural network (uses particle-size distribution) and van Genuchten-Mualem transform:

  28. Guelph Permeameter (Kunsat)

  29. Tension-disc Infiltrometer (Kunsat)

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