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Soil Water. Topics Soils Soil water properties Soil water balance Reading: Applied Hydrology Sections 4.3 and 4.4 (Green- Ampt method). Soil Map of the United States. USDA Soil Classes. Developed from SSURGO – Soil Survey Geographic Database. - PowerPoint PPT Presentation

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Energy fluxes

Soil WaterTopicsSoilsSoil water propertiesSoil water balanceReading: Applied Hydrology Sections 4.3 and 4.4 (Green-Ampt method)

Soil Map of the United States

Developed from SSURGO Soil Survey Geographic DatabaseUSDA Soil Classeshttp://www.arcgis.com/home/webmap/viewer.html?webmap=0edea1c7bbb84ba5842d20483af11679 Soil Map of Texas

Developed from SSURGO Soil Survey Geographic Database

Soil Map of Central Texas

Soils in the Brushy Creek Watershed

Brushy Bend DrDam 7MollisolsMollisols have deep, high organic matter, nutrient-enriched surface soil (A horizon), typically between 6080cm in depthFormed under grasslands (the liveoak savannah that originally covered much of south and central Texas)

VertisolsSoils that have a high content of expanding clay and that have at some time of the year deep wide cracks. They shrink when drying and swell when they become wetter

Soil Sieves

http://www.rtg.wa.edu.au/loanpool/belmont/sieves.jpg

http://www.uga.edu/srel/kidsdoscience/soils-planets/soil-particle-size.pdf

Soil Texture TriangleSource: USDA SoilSurvey Manual Chapter 3

Soil Texture is defined by % of silt, sand, clay

Silty Clay Loam ~ 55% silt, 10% sand, 35% claySoil Water Content

Soil Water ContentSoil Water Flux, q

q = Q/ASoil Water Tension, yMeasures the suction head of the soil water Like p/g in fluid mechanics but its always a suction (negative head)Three key variables in soil water movementFlux, qWater content, qTension, y

Total energy head = h

z=0z1z2

q12TensiometersMeasure soil water potential (tension)Practical operating range is about 0 to 0.75 bar of tension (this can be a limitation on medium- and fine-textured soils)Electrical resistance blocksMeasure soil water potential (tension)Tend to work better at higher tensions (lower water contents)Thermal dissipation blocksMeasure soil water potential (tension)Require individual calibrationSoil Water Measurement

Tensiometer for Measuring Soil Water Potential, Porous Ceramic TipVacuum Gauge (0-100 centibar)Water ReservoirVariable Tube Length (12 in- 48 in) Based on Root Zone Depth

Electrical Resistance Blocks & MetersSoil Water Tension, yMeasures the suction head of the soil water Like p/g in fluid mechanics but its always a suction (negative head)Three key variables in soil water movementFlux, qWater content, qTension, y

Total energy head = h

z=0z1z2

q12

40 cm80 cmDarcys LawK = hydraulic conductivityq = specific discharge V = q/n = average velocity through the area

Definitions

solidPore withairPore withwaterElement of soil, V(Saturated)Element of soil, V(Unsaturated)

Continuity Equation

yzxdydzdx

Continuity (Cont.)

ContinuityEquationRichards EquationRecall Darcys LawTotal headSo Darcy becomes

Richards eqn is:

Soil water diffusivity