Chapter 6 Fetter Soil moisture and groundwater recharge

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Chapter 6 Fetter Soil moisture and groundwater recharge

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Chapter 6 Fetter Soil moisture and groundwater recharge

  1. 1. Al-Azhar University-Gaza Master Program of Water and Environmental Science Soil Moisture and Groundwater Recharge prepared by Safaa A. EL Derawi
  2. 2.  Introduction The uppermost layer of the earth may contain a three phase system of material:  solid  liquid  gaseous
  3. 3. The earth layer that contain the three phase system is called the: vadose zone also know as zone of aeration, and unsaturated zone .
  4. 4. Porosity and water content of soil
  5. 5.  Porosity
  6. 6.  The void ratio of the soil is the ratio of volume of the voids to the volume of the solids.
  7. 7. V= Vv + Vs , n= Vv/V n= Vv / Vv +Vs divide by Vs V= Vv + Vs , e= Vv/Vs e= Vv / V - Vv divide by V
  8. 8.  The gravimetric water content  The volumetric water content  The saturation ratio
  9. 9. Bulk Soil = Particle volume + pore volume  The dry bulk density :  The particle density:
  10. 10.  Porosity can be calculated in practice:
  11. 11. Soil Water Measurement Measures mass water content  Take field samples  weigh(Wm)  oven dry at 105 C  weigh ( Ws) until a constant mass is obtained Ww=Wm-Ws Gravimetric water content = Wm-Ws / Ws and Vw = (Wm - Ws / w )/V Volumatric water content =Vw/V
  12. 12. Electrical Resistance Blocks & Meters
  13. 13.  Capillarity and the capillary fringe Capillary forces : The forces acting on soil moisture in the unsaturated zone, attributable to molecular attraction between soil particles and water.
  14. 14. The capillary rise in cm is : Capillary Rise
  15. 15. Capillary fringe :
  16. 16. The zone of aeration is best defined as the zone where the soil moisture is under tension
  17. 17.  Pore-water tension in the vadoes zone  Fluid pressures in the vadose zone are negative  The negative pressure head is measured in the field with a tensiometer
  18. 18. Tensiometer for Measuring Soil Water Potential Water Reservoir Variable Tube Length (12 in- 48 in) Based on Root Zone Depth Porous Ceramic Tip Vacuum Gauge (0-100 centibar)
  19. 19.  soil water is the water in the vadoes zone, that is available to growing plants.
  20. 20. Soil moisture depend on: 1. Change in the amount of precipitation. 2. Change in the amount of evapotranspiration
  21. 21. Types of soil water
  22. 22. Field Capacity - Wilting Point
  23. 23.  Theory of Unsaturated Flow The infiltration of water into the unsaturated can be considered in terms of:  Gravity potential, Z  Moisture potential, ψ
  24. 24. Darcy’s law is valid for flow in the unsaturated zone. Is not constant , content is a function of the volumetric water
  25. 25. Idealized curves showing relationships of volumetric water content, hydraulic conductivity, and soil-moisture head
  26. 26.  Water-Table Recharge When the front of infiltrating water reaches the capillary fringe, it displaces air in the pore spaces and cause the water table to rise.
  27. 27. Rate of Recharge The rate of water-table recharge depends on: 1. Thickness of the unsaturated zone (The thinner zone, the faster rise of water table) 2. The vertical unsaturated hydraulic conductivity 3. The permeability . May generate a localized ground-water mound

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