408U/508
HYDROLOGIC GEOLOGY CYCLE
CHAPTER 6 Brady & Weil, 13th ed.
AND THE
SOIL
THE HYDROLOGIC CYCLE
(FIGURE 6.2)
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WATER BALANCE EQUATION
Watershed - an area of land drained by a single stream system and is separated from adjacent areas by ridges An important ecological concept; activities in one area may affect entire watershed Water-balance equation: P = ET + SS + D P = precipitation ET - evapotranspiration SS - soil storage D - discharge
FATE OF PRECIPITATION & IRRIGATION WATER Interception - catchment of precipitation by canopy vegetation - may prevent 30-50% rainfall from reaching soil Water impacting soil: - infiltration - soil storage - drainage from profile - surface runoff - may cause erosion
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FATE OF PRECIPITATION & IRRIGATION WATER
Effects of Vegetation & Soil Properties on Infiltration Type of vegetation - grasslands - dense vs sparse cover - forests - dense vs sparse cover Stem flow - slows and captures rainfall - varies with vegetation type Soil management - enhance surface retention in cultivated fields - cover crops Soil porosity
SOIL-PLANT-ATMOSPHERE CONTINUUM
(SPAC)
Water movement through various media
(FIGURE 6.10)
3
WATER BALANCE
SPAC = Soil - Plant - Atmosphere Continuum -major component of hydrologic cycle Water movement - two major points of resistance - root-soil water interface - leaf cell - atmosphere interface Component Moisture potential Atmosphere -20,000 kPa Leaf surface -500 kPa Upper plant (internal) -85 kPa Lower plant (internal) -75 kPa Soil water -50 kPa
SOIL-PLANT-ATMOSPHERE CONTINUUM
Evaporation (E) - loss of water from soil surface Transpiration (T) - loss of water from plant leaves Evapotranspiration (ET) - combined loss of water - most commonly measured Potential evapotranspiration (PET) - useful info Water deficit = (PET) - (ET) ET losses vary greatly with plant type
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CONTROL OF EVAPOTRANSPIRATION
In most areas, it is desirable to limit ET: limit nutrient supply to plants to limit growth decrease plant density (partially effective) limits leaf area index eliminate undesirable plants (weeds) fallow cropping (use in semiarid lands)
LIQUID AND VAPOR LOSSES
Partitioning of liquid water losses (discharge) and vapor losses (evaporation and Transpiration) in regions varying from low (arid) to high (humid) levels of annual precipitation. (FIGURE 6.18)
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CONTROL OF SURFACE EVAPORATION
Vegetative mulches: sawdust, manure, leaves, straw, crop residue Paper & plastic mulches: - generally use specially prepared material - can use newspapers, etc Crop residues & conservation tillage: - leaves a high percentage of previous crop - leaves stubble mulch - plants next crop without tillage
LIQUID LOSSES OF WATER FROM THE SOIL
Percolation & leaching: Loss of water/chemicals to the groundwater Study with tile drains or lysimeters High percolation rates give a high potential for leaching losses Percolation losses influenced by: amount & distribution of rainfall
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LIQUID LOSSES OF WATER FROM THE SOIL
Generalized curves for precipitation & evapotranspiration for three temperate zone regions Max. supply is not generally during max. need
(FIGURE 6.22)
PERCOLATION AND GROUNDWATERS
Groundwater resources: significant water source for domestic, industrial & agricultural uses about 50% of people use some groundwater local versus regional aquifers - Ogallala aquifer supply versus withdrawl overpumping aids contaminant influx coastal areas: potential saltwater
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SUBSURFACE WATER MOVEMENT
Relationship of the water table and groundwater to water movement into and out the of soil. (FIGURE 6.25)
PERCOLATION AND GROUNDWATERS
Shallow groundwater: most dynamic portion of groundwater may supply growing plants via capillary fringe Chemicals in drainage water: chemicals may leach into groundwater - nutrients - loss from plant use (lost $$) - cause eutrophication (NO3-) - contaminants - pesticides - pathogens
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PERCOLATION AND GROUNDWATERS
Chemical movement through macropores: preferential or bypass flow - chemicals merely applied to surface do not contact bulk of soil high intensity rain or irrigation increases bypass flow need to control irrigation rates and manage soil properties (macropore properties)
BYPASS FLOW IN MACROPORES
Preferential or bypass flow in macropores transports soluble chemicals downward through a soil profile. Note that if the pore is not open to the surface, the bypass flow will NOT occur. (FIGURE 6.27)
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ENHANCING SOIL DRAINAGE
Reasons for enhancing drainage: engineering problems: soil stability for roadbeds, building foundations plant Production: tillage restrictions, oxygen limitations, low temps in springtime, limited rooting depth in springtime Surface drainage systems: - drainage ditches - land forming
ENHANCING SOIL DRAINAGE
Subsurface (internal) drainage: deep open-ditch drainage - best for coarse textured soils - barriers for eqiopment buried perforated pipes (drain tiles) - can last for many years - do not disrupt surface operations building foundation drains - Figure 6.32c mole drainage - inexpensive; use in clay soils
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REGIONAL AND PERCHED WATER TABLES
(FIGURE 6.28)
UNDRAINED AND TILEDRAINED LAND
Illustration of water levels of undrained and tile-drained land in the spring and summer.
(FIGURE 6.29)
tile
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OPEN DITCH & TILE DRAINS IN FIELDS
(FIGURE 6.32a,b)
FOOTER DRAIN AROUND FOUNDATION
(FIGURE 6.32c)
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SEPTIC TANK AND DRAIN FIELD
Wastewater stimulation of lawn grass from poorly functioning system
Utility of perc test
Standard system
(Figure 6.38)
IRRIGATION PRINCIPLES & PRACTICES-1
Importance of irrigation today: landscaping - use is increasing - used to grow non-native species - large amounts used in semi-arid regions food p...