groundwater Flashcards
Hydrologic horizons in order
root zone
intermediate zone
capillary fringe
water table
groundwater zone
impermeable layer
2 main zone of hydrologic soil horizons
Vadose (unsaturated) = water fills some pores
Phreatic (saturated) = water fills all pores
Capillary fringe
Belt of variable thickness presenting wet envr in saturated zone due to capillary rise
Process affecting water in subsurface
Infilitration
percolation
recharge
capillary rise
interflow/ subsurface flow
GW flow
Infiltration
movement of water from soil surface downwards
Percolation
downward movement of water in unsaturated zone
recharge
addition of water to saturated zone
capillary rise
movement of water from saturated zone upwards into unsaturated zone
Interflow/ subsurface flow
flow occuring in unsaturated zone in lateral direction
GW flow
flow in saturated zone
Soil texture
describes grain size distribution for particles below 2mm -> influence infilitration, runoff, etc.
total porosity (n) equation
n = V voids/ V total
Void ratio (e)
V voids/ V solids
soil water content volumetric
V water / V total
soil water content gravimetric
(Mass wet - mass dry )/ mass dry
Relating gravimetric to volumetric
(Bulk density soil/ bulk density water) x mass
Degree of Saturation (S)
S = V water / (V water + V gas)
soil water storage type
Gravitational: excess drained under gravity at saturation
Capillary: held in soil pore in intermediate/wet conditions
Hygroscopic: thin films holding onto soil grains in dry conditions
Soil moisture critical values
Field capacity
permanent wilting point
plant available water
Field capacity
max amount of water soil holds after gravitation drainage
PWP
Minimum soil moisture content after gravity drainage AND plant evapotranspi
Plant available water
difference between FC and PWP
hydro horizon and critical moisture value:
root: PWP < moisture < n
intermediate: FC < moisture < n
capillary : moisture = n
saturated: moisture = n
Water migration caused by
water pressure difference:
-from higher to lower pressure
hydro horizon and water pressure
unsaturated soil: negative P
saturated : positive P
water table: P = 0
water table
fluctuates up and down with precipi
usually parallel to soil surface
measuring soil water tension
Tensiometer -> tube partially filled with water with low-permeability porous cup at bottom that balance with soil pressure
Hydraulic conductivity (K)
ease at which water can move through pore spaces/ soil fractures
-larger for sand VS smaller for clay
Rainfall rate (i)
rainfall intensity = amount per time
infiltration capacity (fc)
max rate soil can absorb water through surface
infiltration fate f(t)
time-variable rate of water entering soil via surface
how does f(t) vary throughout rainfall event
at first, decrease rapidly
then plateau near fc
Wetting front
sharp discontinuity in soil profile with dry below and wet above -> created by change of soil moisture with depth due to top-down infiltration
BUT not always at constant depth -> preferential flow
Cumulative infiltration F(t)
accumulated depth of infiltration from beginning of rainfall to given time -> area under curve of f(t)
Time of ponding H(t)
time a which surface layer is saturated with rainfall rate exceeding hydraulic conductivity
2 conditions:
fully saturated soil OR higher rainfall rate than infiltration rate
Horton & Philip models
Both measure f(t) , F(t) and H(t)
Horton -> include f0 and fc
Philip -> use suction and K
what controls infiltration
soil surface condition
subsurface conditions
influencing factors
flow influence
hydrophobicity
Subsurface conditiond
soil characteristics (porosity, depth, etc.)
root system
water table depth
subsurface drainage
hydraulic conductivity
soil surface conditions
land use
vegetation cover
roughness and slope
cracking/ crusting
surface sealing
factor influencing surface/ subsurface conditions
mechanical process
freeze-thaw cycle
litter layer
compaction
antecedent soil water conditions
chem activity
bio activtiy
microbial activity
hydrophobicity
dryness
heat
plant chem
aromatic oils
fire
other chem
Flow influence
ponding
soil and water temperature
Saturated flow
movement of water via saturated pores & fractures
-relatively slow BUT higher in limestone
Flow velocity depends on:
slope of water table
permeability of rock/ sediment of aquifer
aquifer
saturated, permeable, geologic unit transmitting significant amount of GW under ordinary gradient
aquiclude
saturated, geologic unit doesnt transmit significant amount of GW under ordinary gradient
Aquifer types
unconfined
confined
perched
unconfined aquifer
aquifer with lower barrier bc of aquiclude below BUT not upper barrier -> water fluctuates upwards
-partially filled and rapidly recharged
confined aquifer
aquifer with lower and higher barrier bc aquiclude above and below
-completely filled and slow to recharge
perched aquifer
unconfined water zone sitting on top of clay and separated from main aquifer below
