GEOG 408 QUIZ 4

groundwater

water beneath the surface that fully saturates the pores in the ground

porosity

the fraction of rock/soil which is composed of “void space” , water may occupy those spaces

measuring porosity

weigh, dry and reweigh core samples

permeability

the ability of rocks/soil to transmit water (allow flow)

effective porosity n_e

is the volume fraction of a rock, sediment, or soil that participates in water flow

aquifer

an underground layer of water-bearing rock, or unconsolidated material (soil, sediment)

Hydraulic head

height of water in a piezometer above an arbitrary line beneath the surface (datum)

elevation head

distance from the datum to the base of the piezometer , represents the potential energy from gravity

pressure head

distance from the base of the piezometer to the water level, represents the pressure energy in the system

hydraulic gradient

the difference in hydraulic head between two points, divided by the distance between the points

hydraulic conductivity

encompasses both the ability of the medium to transmit fluid and the ability if the fluid to flow (ie permeability and viscosity)

saturation

the proportion of pores that contain water

unsaturated hydraulic head

in the unsaturated zone pressure head is less than atmospheric pressure and negative

field capacity

the wtaer content at which gravity drainage rate becomes “negligible”

permanent wilting point

point where plant suction cannot overcome the adhesive forces holding water to the soil grains

Leidenfrost effect

is the formation of a gas barrier between a hot surface and a boiling liquid if the temperature difference is great enough

infiltration

the process by which water arriving at the surface as rain or snowmelt enters the soil

water input rate

rate at which water arrives at the soil surface

Inflitration rate

rate at which water enters the soil

inflitration capacity

maximum infiltration rate

No ponding

infiltration rate equals input rate and is less than infiltration capacity

Ponding (saturation from above)

water input rate exceeds infiltration capacity

Ponding (saturation from below)

water table has risen to the surface, infiltration stops

Infiltration rate decreases over time

pores saturate, decreasing pressure head gradient; clay particles swell when wet, reducing pore space; raindrops can wash soil down, clogging pores

wetting front

the downwards movement of water

Groundwater recharge

natural process whereby water enters the saturated zone

without recharge

the natural discharge of groundwater would result in a steadily decreasing water table

equipotential

an imaginary line (usually drawn on a cross-section or plan view) where all points have the same flow potential (hydraulic head)

we can only reliably draw stremnlines between equipotentials if

the aquifer is isotropic and homogeneous

medium is homeogeneous

if hydraulic conductivity (K) is the same at all points

medium is isotropic

if Hydraulic conduictivity (K) is the same in all directions