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2013 PE Review: Soil & Water Management

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  1. 2013 PE Review:Soil & Water Management Michael C. Hirschi, PhD, PE, CPESC, D.WRE Senior Engineer Waterborne Environmental, Inc. hirschim@waterborne-env.com also Professor Emeritus University of Illinois

  2. Acknowledgements: Chris Henry, I-C PE Review (2006-2009) Rod Huffman, past PE Review coordinator

  3. Session Topics • Soil & Water Basics Review • Evapotranspiration • Subsurface Drainage • Irrigation • Nutrient Management

  4. S&W Basics Review • Soil makeup • Infiltration & soil-water • Soil-Water-Plant Relations

  5. Subsurface Drainage • Basic issues • Design considerations • System sizing • System installation

  6. Irrigation • Plant water use • Types of irrigation • Sprinkler • Flood • Drip • Design considerations

  7. Nutrient Management • Soil loadings • Application issues

  8. A few comments • Material outlined is about 3 weeks or more in a 3-semester hour class. I’m compressing at least 6 hours of lecture and 3 laboratories into 2 hours, so I will: • Review highlights and critical points • Do example problems • You need to: • Review and tab references • Do additional example problems, or at least thoroughly review examples in references

  9. Basics – Soil Make Up • Mineral • Water • Air • Organic Matter

  10. Infiltration & soil-water • Infiltration is the passage of water through the soil-air interface into pores within the soil matrix • Movement once infiltrated can be capillary flow or macropore flow. The latter is a direct connection from the soil surface to lower portions of the soil profile because of root holes, worm burrows, or other continuous opening • Infiltrated water can reappear as surface runoff via “interflow” and subsurface drainage

  11. Soil, water, air The inter-particle space (voids) is filled with either water or air. The amount of voids depends upon the soil texture and the condition (ie. tilled, compacted, etc.).

  12. Water (moisture) content • Special terms reflect the fraction of voids filled with water (all vary by texture and condition): • Saturation: All voids are filled with water • Field Saturation: Natural “saturated” moisture content which is lower than full saturation due to air that is trapped. • Field capacity: Water that can leave pores by gravity has done so (0.1 to 0.33 bars) • Wilting point: Water that is extractable by plant roots is gone (15 bars) • Hygroscopic point: Water that can be removed by all usual means is gone (but some remains, 30 bars)

  13. Saturated (all pores filled) Field Capacity (Some air, some water) Wilting point (water too tightly held for plant use)

  14. Water States by Soil Texture Gravitational Plant Available Unavailable

  15. Any questions on general soil and water basics?

  16. Evapotranspiration (ET) • Evaporation • Crop water use • Reference Crops • Pan Evaporation • Crop Coefficients

  17. Evaporation • Transfer of water from liquid to vapor state • Tabulated as “lake evaporation” across the US. Generally, evaporation exceeds precipitation west of the Mississippi River.

  18. Example • The mean annual lake evaporation in inches in Amarillo, TX (panhandle), is most nearly: • 50 • 65 • 75 • 85

  19. Evaporation Fangmeier et al. (2006), pg 56

  20. Evaporation The mean annual lake evaporation in inches in Amarillo, TX (panhandle), is most nearly: • 50 • 65 • 75 • 85 = 1900mm/25.4 mm/in = 75 in, so answer is C

  21. Evapotranspiration (ET) • Combined Evaporation and Transpiration • Also called “consumptive use” • Useful to predict soil water deficit • Estimation methods (predict ETo, which is for Reference Crop) • Evaporation Pan • Penman-Monteith (see example in Fangmeier et al., 2006, pages 64-66)

  22. ET vs. Precipitation

  23. Reference Crops • Alfalfa (comparable to field crops) • Grass (easy to maintain under weather station, data can be related to alfalfa data)

  24. Crop Coefficients • Relate crops at various stages of growth to reference crops • ETc = Kc x ETref

  25. Crop Coefficients Both figures: Fangmeier et al. (2006) page 70

  26. Crop Coefficients, by crop & stage Fangmeier et al. (2006) page 71

  27. Crop growth stages Fangmeier et al. (2006) page 71

  28. Example Estimate ETc for corn (maize) in Sioux City, Iowa if the ETref is 8mm/day on July 1. Planting date was April 15. A: 8mm B: 9mm C: 10mm D: 11mm

  29. Solution ETc = Kc x ETref Initial growth stage is 20 days, to May 5 Development stage is 40 days, to June 9 Mid stage is 50 days, to July 29 So, on July 15, in Mid-stage, so Kc is 1.2 ETc = Kc x ETref = 1.2 x 9 = 10.8mm, or 11mm (D) Hint: Follow Fangmeier example 4.4

  30. Any questions on ET?

  31. Drainage • Removal of excess water • Benefits include • More days to work in field • Less crop stress due to high moisture • Early germination because of warmer soil • Liabilities include • Expense • Potential water quality issues • Outlet required, may need pump

  32. Objective of Drainage is Financial Benefit • Optimize crop growth • Increase yield • Reduce wetness-based disease • Reduce variability within fields and from year to year • Improve timeliness of field work • May use smaller equipment • May increase acreage • May reduce labor costs • Increase value of land

  33. Drainage types • Surface • Basic enhancement of flow patterns • Surface grading/planing • Surface ditching • Subsurface • Irregular • Regular • Watertable Management

  34. Subsurface Drainage • Removes gravitational water only • Degree of drainage specified as depth/day • System design dictated by crop, soil, location, topography and more… • Can be used to manage watertable down or up • Changes hydrologic response of field and if widely installed, the watershed

  35. HYDROLOGIC CYCLE (with tiles)

  36. Design Considerations • Soil type • Crop to be grown • Outlet • Topography

  37. Cost/Acre Crop Yield Rate of Return 100 Profitability CostorYieldRatio (%) Tile Density Spacing

  38. Drainage system design • Capacity to remove water is expressed as depth/day (eg. 3/8 in/day) • Spacing, maximum and minimum depth (absolute minimum of 24” without special protection), and maximum and minimum slope are dictated by soil and topography

  39. Depth/Spacing Choices

  40. Excellent Reference:ASABE Standards The material that follows is directly from ASABE EP480, issued MAR1998 (R2008), “Design of Subsurface Drains in Humid Areas”

  41. Drain Spacing

  42. Diagram for Hooghoudt Eq.

  43. Drain Spacing by Hooghoudt Eq

  44. Area Drained

  45. CPT Capacity

  46. Example A subsurface drainage system is to be installed on a square 160 acres (1/4 section) in East Central Illinois. The Drainage Coefficient is 3/8”/day and the Illinois Drainage Guide indicates a 120’ spacing at 4’ depth. The proposed slope is 0.1%. What diameter CPT is needed for each lateral? A: 3” B: 4” C: 5” D: 6”

  47. Solution A square 160 acres is a ½ mile on each side, or 2640’. A spacing of 120’ gives an area for each lateral of 120x2640 or 316800 sq.ft. If the system removes 0.375”/day, the flow rate needs to be 316800ft2*0.375in/day/12in/ft/24hr/day/3600s/hr or 0.115 cfs. Enter the chart

  48. Answer: D, 6”