Soil Moisture Characteristic Curve.pptx

Soil Moisture Characteristic Curve.pptx

• 1.
  Soil Moisture Characteristic Curve
• 2.
  • Soil moisturecharacteristic curve is the relationship between the water content and the soil water potential, ψ. • It describes the functional relationship between soil water content and its energy status in terms of its matric potential under equilibrium conditions. • This curve is characteristic for different types of soil. • It is also called the Water retention curve.
• 3.
  • A soilwater characteristic (SWC) curve describes the amount of water retained in a soil (expressed as mass or volume water content, θm or θv) under equilibrium at a given matric potential. • A SWC is an important hydraulic property related to size and connectedness of pore spaces. • It is strongly affected by soil texture and structure, and by other constituents including organic matter.
• 4.
  • Modeling waterdistribution and flow in partially-saturated soils requires knowledge of the SWC. • It plays a critical role in water management and in prediction of solute and contaminant transport in the environment.
• 5.
  • The SWCfunction is highly nonlinear and relatively difficult to obtain accurately. • The matric potential extends over several orders of magnitude for the range of water contents commonly encountered in practical applications, it is often plotted on a logarithmic scale.
• 6.
  Typical soil watercharacteristic curves for soils of different texture
• 9.
  • The SWCis a primary hydraulic property required for modeling water flow in porous materials. • It is used to predict the soil water storage, water supply to the plants (field capacity) and soil aggregate stability. • Due to the hysteretic effect of water filling and draining the pores, different wetting and drying curves may be distinguished.
• 10.
  • At potentialsclose to zero, a soil is close to saturation, and water is held in the soil primarily by capillary forces. • As θ decreases, binding of the water becomes stronger, and at small potentials (more negative, approaching wilting point) water is strongly bound in the smallest of pores, at contact points between grains and as films bound by adsorptive forces around particles.
• 11.
  Factors influencing soilwater retention – Soil structure (b, aggregate size distribution) • important at low suctions, 0 to 50 kPa • Capillary effects – Clay content • Positively related to surface area of soil particles • Positively related to water adsorption • Dominant factors at high suctions
• 12.
  • Early conceptualmodels for SWC curve were based on the "bundle of cylindrical capillaries" (BCC) representation of pore space geometry (Millington and Quirk, 1961). • The BCC representation postulates that at a given matric potential a portion of interconnected cylindrical pores is completely liquid filled, whereas larger pores are completely empty. Soil sample actual pore equivalent capillary
• 13.
  SWC measurement ranges