Definitions Flashcards
Isotopes
Have the same number of protons in nucleus, but different number of neutrons.
Cohesion
Liquid-liquid molecular attraction
Adhesion
Liquid-solid molecular attraction
Vapour Density
Mass of water in a unit volume of air.
Vapour Pressure
Partial pressure exerted by water vapour.
Streamflow
Rate at which water leaves a catchment via the stream channel, discharge.
Runoff
Total quantity of water leaving a catchment in a specific time interval; usually expressed as average depth of water over catchment are, water yield.
Stage
Elevation of water surface above some reference, locally or absolute(datum).
Daily Flow
Streamflow average over a one day interval.
Annual Flow
Maximum streamflow in a given year.
Hydrograph
Plot of water level or discharge against time.
Systematic error
Acts consistently in one direction; either over- or underestimated; accumulate through time.
Random error
Acts unpredictably in either direction; tend to cancel out over time.
Spurious Change
Changes in instruments used for measuring, changes to site characteristics, change in station location.
Double mass curve
Plots mass curves for two locations to compute the slope before and after some change in measurement procedure.
Exceedence Probability
The probability that a specific rainfall intensity or depth would be equalled or exceeded in a given year.
Return Period
Mean length of time between occurrences of that event.
Gross rainfall
Above-canopy rainfall (usually measured in the open)
Throughfall
Rainfall that reached the ground either as canopy drip or by falling directly through gaps (direct through fall)
Stemflow
Water that reaches the ground by running down trunks and stems.
Interception loss
Water that evaporates (or sublimates) form the canopy, stems of trees, understory and leaf littler on the soil surface.
Net Rainfall
Throughfall + rainfall
Porosity
Volume of fluid/ Volume total
Volumetric water content
Volume water/Volume total
Total Head
Pressure head + gravitational head
Pressure head
Results from the forces exerted by adjacent water molecules, including hydrostatic pressure and capillary forces.
Gravitational head
Equal to the work done in raising a mass of water by a vertical distance.
Water Table
Surface within a soil along which pressure head = 0 (or, equivalently, water pressure = ambient atmospheric pressure)
Hydrostatic
Wate not moving, h does not vary with location.
Vadose Zone
Unsaturated zone, between land surface and zone of saturation
Phreatic Zone
Saturated zone, below the water table
Capillary Fringe
Subsurface layer where groundwater seeps up from a water table by capillary action to fill pores.
Field Capacity
The water content at which the rate of drainage by gravity exhibits a marked decrease. Nominally defined as the water content corresponding to pressure head = -33m
Drainable Porosity
The difference between the total porosity and field capacity. Analogous to “specific yield” in hydrogeology.
Homogeneity
Properties do not vary in space (K(x), K(y), K(z))
Isotropy
Hydraulic conductivity does not vary with the direction flow (K(x)=K(y)=K(z))
Infiltration-excess overland flow
Water enters a soil system faster then the soil can absorb it.
Saturation-excess overland flow
Return flow + direct precipitation on saturated source ares. Soil becomes saturated, and any additional precipitation or irrigation cause runoff.
Throughflow
Downslope flow in a saturated layer within soil.
Infiltration rate
The rate at which water enters a soil at the surface.
Infiltration capacity/infiltrability
The maximum rate at which water can enter a soil.
Hydrophobicity
Organic matter volatiles, diffuses downwards to cooler soil layers and condenses, coating mineral soil particles and rendering them water repellant.
Honeycomb Frost
Low soil moisture content at time of freezing, relatively permeable.
Concrete Frost
High soil moisture content at time of freezing, limited permeability and low infiltration capacity
Zero Flux Plane
Location where upwards and downwards groundwater flow meet.
Aquifer
Saturated geological unit that is sufficiently permeable that water flows through it faster than through adjacent, less permeable geological units.
Aquiclude
Saturated geological unit that has sufficiently low permeability that water flow is restricted, relative to adjacent, more permeable, geological units
Unconfined Aquifer
Aquifer that is not confined above by an aquiclude; the water table may rise and fall in response to changes in groundwater storage.
Confined Aquifer
Aquifer that is confined above by an aquiclude.
Specific Yield
Ratio volume of water that a saturated soil will yield by gravity to the volume of the body itself.
Specific Retention
Ration of the volume of water that a given body of soil will hold against the pull of gravity to the volume of the body itself.
E
Evapotranspiration. Net loss of water vapour form some specified portion of the earth’s surface. Controlling factors: availability of water and energy, transport of vapour water form surface.
Potential Evapotranspiration
Rate at which evapotranspiration would occur under a given set of meteorological conditions if availability of water is not limiting, and thus is a function of available energy and transport for surface, sometimes referred to as “atmospheric demand”
Firn
Snow on a glacier that has survived at least one summer (density around 500 km/m3)
Accumulation
Processes that add mass to a glacier (snowfall, avalanches, freezing of rain or meltwater)
Ablation
Processes that remove mass form a glacier (melting, wind scouring, sublimation, evaporation, clawing of ice bergs)
Summer balance (b(s))
Net difference between accumulation and ablation form approx. May-October (northern hemisphere)
Winter balance (b(w))
Net difference between accumulation and ablation from approx. November-May (northern hemisphere)
Net balance
Net difference between accumulation and ablation during an accumulation season and the following ablation season. bw + bs
Accumulation Zone
Areas on glacier where the winter balance is greater than the summer balance or the net balance is above zero.
Ablation Zone
Areas on glacier where the summer balance is greater than the winter balance or the net balance is less than zero.
Equilibrium Line Altitude (ELA)
Line along which the winter and summer balances are equal or net balance is zero. Altitude of end-of-summer snowline (for temperate glaciers)
