Hydrology Flashcards
evapotranspiration
Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere
transpiration
Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers
percolation
the downward movement of water through soil layers due to gravity and capillary forces
interflow (subsurface runoff)
relatively rapid flow toward the stream channel that occurs below the surface. It occurs more rapidly than baseflow, but typically more slowly than surface runoff.
interception
relatively rapid flow toward the stream channel that occurs below the surface. It occurs more rapidly than baseflow, but typically more slowly than surface runoff through evaporation
ground water recharge
a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer.
base flow
the portion of the streamflow that is sustained between precipitation events, fed to streams by delayed pathways
vadose zone (unsaturated zone)
zone that extends from the top of the ground surface to the water table.
-includes the soil, intermediate and capillary zones
phreatic zone
(zone of saturation) The soil or rock zone below the level of the water-table, where all voids are saturated.
intermediate zone
zone that separates the saturated phreatic zone from soil water
lies above the capillary fringe and consists of water in
the form of thin films adhering to the pore lining. This water is free to drain
downward under the forces of gravity.
interstitial water
subterranean water in the pores of rocks, soils, and bottom sediments of oceans, seas, and lakes
What is Vt?
the total volume of water in both solids (Vs) and voids (Vv). Only voids are able to hold both air and water.
degree of saturation
ratio of the water volume to the void volume expressed as a percentage (Vs/Vv X 100)
degree of saturation less than 100%
indicates that air occupies some of the voids
moisture content
the volume of water divided by the total volume (Vw/VT X100) expressed as a percent
capillary water zone
t the contact between the lower part of a dry porous material and a saturated
material, the water rises to a certain height above the top of the saturated material. The driving force for this is surface tension which can be compared to a stretched membrane
surface tension
a force acting parallel to the surface of
the water in all directions because of an unbalanced molecular attraction of the
water at the boundary
water table
the underground water surface at
which the pressure is exactly equal to atmospheric
water above this table is at a
pressure below atmospheric while water below this table is at a pressure
greater than atmospheric
evaporation
the process of liquid turning into gas without boiling, such as water becoming water vapor and is powered by heat
-can take place in both soil and free water surfaces
plants=evapotranspiration
-evapotranspiration= both plants and soil (combination of the two)
potential evapotranspiration
the amount of water that
would evaporate or transpire from a surface if water was available to that surface
in unlimited supply
-is a temperature dependent quantity, and is a measure of the moisture
demand for a region
- The
vegetation (or lack thereof) in a region is thus a reflection of the precipitation-potential evapotranspiration ratio
rules that govern the hydrologic cycle
-when precipitation is equal to potential evapotranspiration, the surplus = 0
-when the rate of precipitation exceeds the rate of infiltration, there will be some water available for overland runoff
-when the temperature drops sufficiently so that precipitation exceeds potential evapotranspiration, a water surplus is realized
-soil zone serves as a buffer- taking in moisture during surplus periods and releasing moisture during deficit periods
maximum permissible infiltration ___ with increasing time
decreases
infiltration capacity
the maximum rate by which water on the ground surface enters the soil
field capacity
used to denote
an upper limit of moisture content in soils. This is when the soil is holding all
the water it can under the pull of gravity
-both interflow and ground water recharge can commence when the moisture content exceeds this capacity.
-dependent on the nature of the soil zone. Thinner soils with impervious rocks = interflow may be dominant. Thicker pervious soils = downward migration may dominate
base flow
component of streams represents the withdrawal of ground water from storage and is termed ground water recession
hydrograph
consists of overland flow, interflow, and base flow
effluent or gaining streams
Streams that receive water from the ground water reservoir by the base flow component
influent or losing streams
Streams
that lose water to the ground water reservoir. This occurs when the ground water table
is well below the base of the stream.
