Soil water and Groundwater I Flashcards
what is infiltration?
water that moves from above-ground to the subsurface
what is a water table?
subsurface boundary below which the ground is completely saturated with water
what is percolation?
water that moves vertically through the soil toward the water table -> movement after infiltration
what is recharge?
water that is added to the water table
what is groundwater flow?
water that is flowing below the water table
what is capillary fringe?
saturated zone above the water table, in which groundwater seeps upward due to capillary forces
where is the subsurface?
under the surface, above water table
what happens to water after infiltration?
- storage in shallow soil layers (stored as soil moisture)
- redistribution (vertically through perculation - groundwater recharge OR laterally through unsaturated flow or groundwater flow)
what are pedologic horizons?
distinct layers of soil profile. Differentiated by color, texture, organic matter, degree of deposition or removal of material by physical and chemical processes.
what are hydrologic horizons? and name them
defined by soil moisture.
Root zone - Intermediate zone - capillary fringe - groundwater
Why is soil referred to as porous?
Within soil there is an interconnected network of pores (voids) filled with fluids (liquid or gas)
what is soil texture?
term used to describe grain size distribution by weight for particles of less than 2 mm
what is the equation for total porosity?
n= V(voids)/ V(total)
what is the void ratio equation?
e= V (voids)/ V (solids)
what is the volumetric soil moisture content equation?
omega = V (water)/ V (total)
what is the degree of saturation equation?
S= Vwater/ (Vwater+Vgas)
What is the equation for gravimetric soil moisture?
G= (Mwet soil - Mdrysoil)/ Mdrysoil
what is the name for an unsaturated zone in the soil profile?
vadose zone
what is the name for the saturated zone in the soil profile?
phreatic zone
what does the capillary fringe look like?
- just above water table
- belt of variable thickness
what is capillary action?
process of a liquid moving in a narrow space without the assistance of gravity. made possible through the forces of cohesion and adhesion, occurs when the adhesion forces of water to a solid material > cohesive forces between liquid water molecules
how does water storage change based on different soil moisture?
at saturation: excess water drains under the influence of gravity
-> field capacity
intermediate to wet conditions: water held in soil pores (capillary water)
-> permanent wilting point
dry conditions: only thin films of water hold onto soil grains (hydroscopic water)
what is the field capacity of a soil?
tension below which water cannot be drained by gravity. for subsurface flow to occur, soil moisture has to exceed field capacity
what is the permanent wilting point of a soil?
WPW is soil moisture content produced after gravitational drainage + plant evapotranspiration losses
–> tension below which plant root systems cannot extract water from the soil
what is plant available water?
PAW is the difference between field capacity and permanent wilting point
what is soil water pressure?
force per unit area applied by water in all directions, measured relative to atmospheric pressure
* at water table, water pressure = atmospheric pressure
what is soil water tension?
measure of how tightly water is held to soil particles
- expressed as negative pressure
- miminum pressure that must be exerted to extract water from soil
what path does soil water pressure follow in the soil profile?
unsaturated soils: negative (tension/suction)
at water table: 0
saturated soils: positive
what instrument is used to measure soil water tension?
tensiometer: a tube partically filled with water and a low-permeability porous cup at bottom that allows pressure equilibration with the soil
how does water move in the subsurface?
- from high pressure (water less tightly bound to soil grains) to low pressure
- from low tension to high tension
what is hydraulic conductivity?
K describes the ease with which water can move through pore spaces or fractures in the soil
rate sand, gravel, silt, clay from highest to lowest K?
gravel > sand > silt > clay
