geob 305

fresh snow density

100 kg/m3

water density

999.97 kg/m3

Causes of spurious changes to precipitation records

Changes in site characteristics, changes in instruments for measurement, changes in station location.

matrix

solid framework of a porous system. solid phase of soil, formed by mineral particles and solid organic materials.

free surface

surface of fluid subject to both zero perpendicular normal stress and parallel shear stress, such as boundary between 2 homogenous fluids, like liquid water and air in atmosphere.

nipher snow gauge

used to capture snow and measure its water content in millimetres. It's much bigger than either the standard rain gauge or the tipping bucket. The nipher snow gauge is mounted on a sliding metal pipe so that, as snow accumulates over the winter, the whole gauge can be raised to keep the top edge 5 feet above the surface of the snow. Why? So that snow from the ground doesn't drift into the gauge and give us false readings!

Well

water level in well indicates depth of water table

interflow (subsurface storm flow)

water that travels laterally or horizontally through the zone of aeration (vadose zone) during or immediately after a precipitation event and discharges into a stream or other body of water. water that infiltrates the soil surface and travels by means of gravity toward a stream channel (always above the main groundwater level) and eventually empties into the channel. Interflow occurs when water infiltrates into the subsurface, hydraulic conductivity decreases with depth, and lateral flow proceeds downslope. As water accumulates in the subsurface, saturation may occur, and interflow may exfiltrate as return flows, becoming overland flow. In hydrologic terms, the lateral motion of water through the upper layers until it enters a stream channel. This usually takes longer to reach stream channels than runoff. This also called subsurface storm flow.

hypsographic/hyspometric curve

% area below/above certain altitudes for selected area

Green Ampt theory of infiltrability - key points

1. infiltrability of a soil is greater than or equal to the saturated hydraulic conductivity (unless the soil has become compacted by land use or heated by a forest fire and rendered water repellent), 2. Infiltration is initially dominated by the pressure head gradient between the wetting front and the soil surface, leading to high rates of infiltrability early in a rain event 3. As wetting front progresses deeper into the soil, the pressure head gradient gets weaker, & gravity becomes dominant force causing downward percolation of water in the soil 4. As pressure head gradient weakens, infiltrability asymptotically declines to a value equal to the saturated hydraulic conductivity (regardless of the initial soil moisture content) 5. pressure head gradient will be stronger in an initially dry soil than in an initially wet soil; initial infiltrability will be higher in a dry soil than a wet soil.

hectopascal (hPa)

100 times a pascal. same as a millibar (mb or mbar). Standard atmospheric pressure is 1013.25 hPa (= 1 atmosphere)

1 meter = ? millimeters

1000 millimeters are in a meter.

Oxygen-18

8 protons, 10 neutrons. 0.204% of oxygen.

Oxygen-16

8 protons, 8 neutrons. 99.76% of oxygen.

Oxygen-17

8 protons, 9 neutrons. 0.037% of oxygen

Acceleration due to gravity at sea level

9.8 m/s2

Hydraulic head (h)

= pressure head + gravitational head (gravitational potential energy [work done in raising mass of water by vertical distance] per unit weight of water) Total pressure potential energy. Water always moves from high to low hydraulic head.

water potential (Ψ)

=Energy required, per quanitity of water, to transport an infinitesimal quantity of water from sample to reference pool of pure water. Classical physics recognises kinetic (i.e. movement) and potential (i.e. position) energy. In soil, water does not move rapidly so kinetic energy is negligible. Therefore, water moves constantly in direction of potential energy (i.e. wet to dry soil), where the gradient of potential energy with distance is the moving force causing flow. Ψ is defined as the work water can do as it moves from its present state to the reference state (reference state is the energy of a pool of pure water at an elevation defined to be zero). In soil, the reference state is the energy level of water in the soil at saturation. That is, when all pores are filled with water. At this point soil water potential (Ψ) is nominally zero (~0). In most cases, however, soil water potential (Ψ)is less than zero. As the soil dries out soil water potential (Ψ)decreases. Total water potential = matric potential (adsorption to surfaces) + gravitational potential (position), + osmotic potential (solutes), + pressure potential (hydrostatic/pneumatic)

humus

A brown or black organic substance consisting of partially or wholly decayed vegetable or animal matter that provides nutrients for plants and increases the ability of soil to retain water.

pressure potential

A component of water potential that consists of the physical pressure on a solution, which can be positive, zero, or negative. Using units of energy per unit weight provides a simple and practical definition of ψp as the vertical distance from the point of interest to the free water surface (unconfined water table elevation). The convention used here is that ψp is always positive below a water table, or zero if the point of interest is at or above the water table. In saturated soil, the pressure potential is sometimes called the piezometric potential; it can be measured with a piezometer.

Differential equation

A differential equation is a mathematical equation that relates some function with its derivatives. In applications, the functions usually represent physical quantities, the derivatives represent their rates of change, and the equation defines a relationship between the two.

Confined aquifer

A groundwater storage area trapped between two impermeable layers of rock, aquitards. An aquifer overlaid by an aquitard is less susceptible to contamination than one that is not because contaminated water has difficulty percolating through the aquitard.

Zero flux plane

A zero-flux plane exists in a soil when there is upward flow in the upper part of the soil column and downward flow in the lower part. The boundary between upward and downward flow is the zero-flux plane. It is commonly found after a rain event, when water in deeper soil layers is draining downward under the force of gravity, but there is upward flow in the near-surface soil caused by drying of the soil surface by evaporation, which creates a more negative pressure head (as soil moisture content decreases, pressure head becomes more negative), and the resulting upward pressure gradient force is stronger than the downward force of gravity.

Unconfined aquifer

Aquifer in which there is no impermeable layer restricting the upper surface of the zone of saturation. Unconfined aquifers are sometimes also called water table or phreatic aquifers, because their upper boundary is the water table or phreatic surface.

Soil water potential: Osmotic/solute potential (ψs)

Arises from dilution effects of solutes dissolved in water. This is always negative. ψs is the solute or osmotic potential determined by the presence of solutes in soil water, which lower its potential energy and its vapour pressure. The effects of ψs are important when: (i) there are appreciable amounts of solutes in the soil; and (ii) in the presence of a selectively permeable membrane or a diffusion barrier which transmits water more readily than salts. The effects of ψs are otherwise generally negligible when only liquid water flow is considered and no diffusion barrier exists. The two most important diffusion barriers in the soil are: (i) soil-plant root interfaces (cell membranes are selectively permeable); and (ii) air-water interfaces (when water evaporates, salts are left behind).

surface tension: liquid-air

At liquid-air interfaces, surface tension results from the greater attraction of water molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). The net effect is an inward force at its surface that causes water to behave as if its surface were covered with a stretched elastic membrane. Because of the relatively high attraction of water molecules for each other, water has a high surface tension (72.8 millinewtons per meter at 20 °C) compared to that of most other liquids.

Clay vs silt

Clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. Clay: <.002 mm Silt: .002 mm - .05 mm (USDA)

matric potential (Ψm)

Component of water potential due to adhesion of water molecules to nondissolved structures of system, i.e. the matrix, such as soil particles. Hydrogen bonding of water to surfaces. It is always negative and is significant in relatively dry systems, like in soils, where much of water is tightly bound to soil particles. In other words, matric potential is energy required to extract water from a porous medium, overcoming the capillary and adsorptive forces. adhesion (attraction) of water to the soil matrix represents a matric force (i.e. adsorption and capillarity) which reduces energy of water particles near surfaces. In saturated soil, water free to flow; Ψm not a factor and its value is 0. As volumetric water content increases, matric potential decreases.

Specific humidity

Concentration, by mass, of water vapour in a sample of moist air.

Darcy's Law

Darcy's Law is a generalized relationship for flow in porous media. It shows the volumetric flow rate is a function of the flow area, elevation, fluid pressure and a proportionality constant. It may be stated in several different forms depending on the flow conditions. Since its discovery, it has been found valid for any Newtonian fluid. Likewise, while it was established under saturated flow conditions, it may be adjusted to account for unsaturated and multiphase flow. describes the flow of a fluid through a porous medium. Darcy's law at constant elevation is a simple proportional relationship between the instantaneous discharge rate through a porous medium, the viscosity of the fluid and the pressure drop over a given distance. Darcy's law is a simple mathematical statement which neatly summarizes several familiar properties that groundwater flowing in aquifers exhibits, including: if there is no pressure gradient over a distance, no flow occurs (these are hydrostatic conditions), if there is a pressure gradient, flow will occur from high pressure towards low pressure (opposite the direction of increasing gradient - hence the negative sign in Darcy's law), the greater the pressure gradient (through the same formation material), the greater the discharge rate, and the discharge rate of fluid will often be different — through different formation materials (or even through the same material, in a different direction) — even if the same pressure gradient exists in both cases. Darcy's law is only valid for slow, viscous flow; fortunately, most groundwater flow cases fall in this category. Typically any flow with a Reynolds number less than one is clearly laminar, and it would be valid to apply Darcy's law. Reynolds numbers up to 10 may still be Darcian, as in the case of groundwater flow

Reynolds number

Defined as the ratio of inertial forces to viscous forces. Used to help predict similar flow patterns in different fluid flow situations. Also used to characterize different flow regimes within a similar fluid, such as laminar or turbulent flow: Laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion. Turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow instabilities.

Pressure head gradient

Difference in pressure head between the surface and the wetting front divided by the depth to the wetting front. After a rain event, when water in deeper soil layers is draining downward under the force of gravity, but there is upward flow in the near-surface soil caused by drying of the soil surface by evaporation, which creates a more negative pressure head (as soil moisture content decreases, pressure head becomes more negative), and the resulting upward pressure gradient force is stronger than the downward force of gravity.

Baroclinic

Distinct air mass regions exist. Fronts separate warmer from colder air. In a synoptic scale baroclinic environment you will find the polar jet in the vicinity, troughs of low pressure (mid-latitude cyclones) and frontal boundaries. There are clear density gradients in a baroclinic environment caused by the fronts. Any time you are near a mid-latitude cyclone you are in a baroclinic environment. Part of the word baroclinic is clinic. If the atmosphere is out of balance, it is baroclinic, just as if a person felt out of balance they would need to go to a clinic.

Gravitational potential energy

Equals work done in raising mass of water by vertical distance

Gravitational head (z)

Gravitational potential energy per unit weight of water

Bad vs good wetting

Greater than 90 degree angle: bad wetting. Less than 90 degree angle: good wetting.

run-in

In certain geologic settings, water can be transported directly to groundwater by a process called run-in. Run-in occurs where there are karst-carbonate aquifers—fractured and/or solution-riddled limestone or dolomite at or near the land surface. In areas where such aquifers exist, there maybe sinkholes, cavities in the bedrock that are open to the atmosphere. Water containing contaminants can enter a sinkhole and then reach groundwater either directly or after some percolation through the soil.

Potentiometric surface (groundwater)

In groundwater "potentiometric surface" is a synonym of "piezometric surface" which is an imaginary surface that defines the level to which water in a confined aquifer would rise were it completely pierced with wells. If the potentiometric surface lies above the ground surface, a flowing well or artesian well results. an imaginary surface that represents the level to which water rises in wells in a confined aquifer; (similar to the water table of an unconfined aquifer)

Macropore

In soil, macropores are defined as cavities that are larger than 75 μm (micrometre - 1 millionth of metre). Functionally, pores of this size host preferential soil solution flow and rapid transport of solutes and colloids.

Chemical potential

In thermodynamics, chemical potential, also known as partial molar free energy, is a form of potential energy that can be absorbed or released during a chemical reaction. It may also change during a phase transition.

Infiltration-excess overland flow

Infiltration-excess overland flow occurs when the intensity of rainfall (and/or snowmelt) exceeds the infiltrability (also known as infiltration capacity) of a soil.

Intensive vs extensive properties

Intensive properties: don't depend on system size or amt. of material in system. Temp, density (mass/volume), hardness are examples. Extensive properties: additive; proportional to amt. of material in system. Mass, and volume are examples.

Loam

Loam is soil composed mostly of sand and silt, and a smaller amount of clay (about 40%-40%-20% concentration, respectively

Viscosity, tensile stress

Measure of resistance to gradual deformation by shear stress or tensile stress. Tensile stress: Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. The volume of the material stays constant. When equal and opposite forces are applied on a body, then the stress due to this force is called tensile stress.

Hydraulic conductivity

Measure of the soil's ability to transmit water when submitted to a hydraulic gradient. Defined by Darcy's Law.

Tensiometer

Measure water pressure and provide an indirect measure of soil water changes. In the unsaturated zone, the pore pressure is determined by capillarity and is also referred to as tension, suction, or matric pressure. Pore water pressures under unsaturated conditions (vadose zone) are measured in with tensiometers.

Pressure head

Pressure potential energy per unit weight. Zero at free water surface.

Tritium

Radioactive isotope (same proton #, diff. # of neutrons) of hydrogen. Has 1 proton (like protium and deuterium), but 2 neutrons.

Barotropic

Region of uniform temperature distribution; A lack of fronts. A perfect example of a barotropic environment is the southeast U.S. in the summer or the tropics. Everyday being about the same (hot and humid with no cold fronts to cool things off) would be a barotropic type atmosphere. Part of the word barotropic is tropic. The tropical latitudes are barotropic. There are no fronts in the tropics.

relative density (aka specific gravity)

Relative density, or specific gravity, is ratio of density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water.

Pressure potential energy

Results from forces exerted by adjacent water molecules, including hydrostatic pressure and capillary forces.

Saturation-excess overland flow

Saturation-excess overland flow occurs when the water table rises to the soil surface and the soil column is completely saturated. Because the soil is completely saturated, any rain or snowmelt occurring over the saturated area cannot infiltrate and continues downslope as overland flow. In addition, subsurface water will often be discharging out of the soil, and this "return flow" (so called because it is water that has infiltrated the water upslope, flowed downslope as subsurface flow, and is returning to the surface) also becomes overland flow. Thus, saturation-excess overland flow has two components: (1) direct precipitation onto the saturated source area and (2) return flow.

soil colloid

Soil colloids are extremely small particles of soil with particle sizes of 2 um (micrometers) in diameter or smaller suspended in a soil with larger particles. Soil colloids are typically found in clay or humus soils.

Deuterium

Stable isotope of hydrogen. One proton and one neutron.

Protium

Stable isotope of hydrogen. hydrogen-1. Makes up 99.98% of hydrogen. One proton, no neutrons.

Stress and strain

Stress: internal forces that neighbouring particles of a continuous material exert on each other. Strain: measure of deformation of material. Mechanical stress: includes viscous stress (opposes change) and elastic stress (any strain [deformation] of a solid material generates an internal elastic stress, that tends to restore material to its original [non-deformed] state).

Supercooling

Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid. A liquid crossing its standard freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form creating a solid. Lacking any such nuclei, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs. Homogeneous nucleation can occur above the glass transition temperature, but if homogeneous nucleation has not occurred above that temperature an amorphous (non-crystalline) solid will form. Water normally freezes at 273.15 K (0 °C or 32 °F) but it can be "supercooled" at standard pressure down to its crystal homogeneous nucleation at almost 224.8 K (−48.3 °C/−55 °F), so long as water is pure and free of nucleation sites (which can be achieved by processes like reverse osmosis). Droplets of supercooled water often exist in stratiform and cumulus clouds. Aircraft flying through these clouds seed an abrupt crystallization of these droplets, which can result in the formation of ice on the aircraft's wings or blockage of its instruments and probes, unless the aircraft are equipped with an appropriate de-icing system. Freezing rain is also caused by supercooled droplets.

base flow

That part of the stream discharge that is not attributable to direct runoff from precipitation or melting snow; it is usually sustained by groundwater discharge. Delayed flow or 'indirect' runoff. Water moves within the saturated zone under the influence of gravity from areas where the water table is high toward areas where the water table is lower. As it does, groundwater may flow into surface water, such as a lake or river. In fact, this process, known as baseflow, accounts for most of the water that recharges perennial streams, rivers, and lakes. streamflow generated from relatively slow, long-term drainage of groundwater and delayed subsurface flow, which sustains streamflow between storms

Bergeron Process

The Wegener-Bergeron-Findeisen process (after Alfred Wegener, Tor Bergeron and W. Findeisen), (or "cold-rain process") is a process of ice crystal growth that occurs in mixed phase clouds (containing a mixture of supercooled water and ice) in regions where the ambient vapor pressure falls between the saturation vapor pressure over water and the lower saturation vapor pressure over ice. This is a subsaturated environment for liquid water but a supersaturated environment for ice resulting in rapid evaporation of liquid water and rapid ice crystal growth through vapor deposition. If the number density of ice is small compared to liquid water, the ice crystals can grow large enough to fall out of the cloud, melting into rain drops if lower level temperatures are warm enough. The Bergeron process, if occurring at all, is much more efficient in producing large particles than is the growth of larger droplets at the expense of smaller ones, since the difference in saturation pressure between liquid water and ice is larger than the enhancement of saturation pressure over small droplets (for droplets large enough to considerably contribute to the total mass).

Collision/Coalescence process

The collision-coalescence process is an important mechanism in forming raindrops in warmer clouds (those with tops warmer than -15°C = 5°F). In these warm clouds raindrops form exclusively by this process. Most tropical rain is formed in this way. The collision- coalescence process is of relatively little importance in middle and high latitudes where, even in the summer, most precipitation begins high in the clouds where temperatures are well below freezing and the dominant precipitation-producing mechanism is the so-called ice-crystal or Bergeron process. However falling raindrops in these clouds do grow by the collision-coalescence process.

Gauge pressure

The difference between total pressure and atmospheric pressure. In essence, is the pressure caused by the substance itself.

saturation vapour pressure

The partial pressure of water vapour molecules when air is saturated with water vapour, and thus when air holds maximum amt of water vapour molecules at that temp (the maximum vapour pressure), and the vapour is in equilibrium with the liquid phase. The vapour in it condenses as quickly as it evaporates.

hydrostatic pressure

The pressure exerted by the weight of water at any given point in a body of water at rest. Pressure which results from the weight of the fluid from above in a column. Related to the height of the column, the density of the fluid and gravity. Force per unit area on an object within a static fluid associated with the weight of the fluid above it.

Tipping bucket rain gauge

The tipping bucket rain gauge consists of a funnel that collects and channels the precipitation into a small seesaw-like container. After a pre-set amount of precipitation falls (.25 mm), the lever tips, dumping the collected water and sending an electrical signal. The tipping bucket rain gauge is not as accurate as the standard rain gauge because the rainfall may stop before the lever has tipped. When the next period of rain begins it may take no more than one or two drops to tip the lever. This would then indicate that pre-set amount has fallen when in fact only a fraction of that amount has actually fallen. Tipping buckets also tend to underestimate the amount of rainfall, particularly in snowfall and heavy rainfall events.[11][12] The advantage of the tipping bucket rain gauge is that the character of the rain (light, medium, or heavy) may be easily obtained.

Absolute pressure

The total pressure exerted on a system, including atmospheric pressure.

Piezometer

Water inside piezometer has the same hydraulic head (total pressure potential energy per unit weight of water) as water in soils surrounding the screen at equilibrium. Assume hydrostatic equilibrium in piezometer. Measures pore water pressure in phreatic zone. A piezometer is either a device used to measure liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity, or a device which measures the piezometric/hydraulic head of groundwater at a specific point. A device used to measure groundwater pressure head at a point in the subsurface.

specific weight (γ)

Weight per unit volume of material.

Dew point temperature and dew point depression

When air is cooled, at constant pressure and water vapor content, to the saturation (or condensation) point, the resulting air temperature is the dew point temperature. The difference between the actual temperature and the dew point is called the dew point depression.

Hydrostatic head

When generating hydropower, the head is the distance that a given water source has to fall before the point where power is generated. Ultimately the force responsible for hydropower is gravity, so a hydroelectricity plant[1] with a tall/high head can produce more power than a similar plant with a short/low head. In short, for a given water flow, a larger head will be converted into greater kinetic energy. That energy is then harnessed by a water wheel or water turbine to create usable hydropower.

work

a force does work if, when acting on a body, there is a displacement in point of application in the direction of the force. when a ball is held above the ground and then dropped, the work done on the ball as it falls is equal to the weight of the ball (a force) multiplied by the distance to the ground (a displacement). SI unit: joule or newton-metre.

Well

a vertical bore hole in which a pipe-like structure is inserted into the ground in order to discharge (pump) water from an aquifer

Artesian well

a vertical bore hole in which a pipe-like structure is inserted into the ground so that it withdraws water from a confined aquifer (artesian aquifer)

capillary action

ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to, external forces like gravity. Due to intermolecular forces between the liquid and surrounding solid surfaces. If diameter of the tube is small enough, combo of surface tension (caused by cohesion within the liquid) and adhesive forces between the liquid & container act to lift the liquid. In short, the capillary action is due to the pressure of cohesion and adhesion which cause the liquid to work against gravity.

Moraine

an accumulation of earth and stones carried by a glacier and usually deposited into a high point like a ridge

Plume

an underground pattern of contaminant concentrations created by the movement of groundwater beneath a contaminant source. Contaminants spread mostly laterally in the direction of groundwater movement. The spill/source site is the highest concentration, and the concentration decreases away from the source.

Phreatic zone / zone of saturation

area in an aquifer, below water table, in which all pores & fractures are saturated with water.

viscous stress

arises when shape of a fluid element is changed in a flow

aquifer

below water table, in phreatic zone. any geological formation containing or conducting ground water, especially one that supplies the water for wells, springs. permeable, geologic material through which significant quantities of water can move. Geologic materials that serve as aquifers include unconsolidated material, such as sand and gravel; permeable sedimentary bedrock, such as sandstone, limestone, and dolomite; and fractured crystalline bedrock

meniscus

curve in the upper surface of a liquid close to the surface of the container or another object, caused by surface tension. It can be either convex or concave, depending on the liquid and the surface.

double mass analysis

data analysis approach for investigating the behaviour of records made of hydrological or meteorological data at a number of locations. It is used to determine whether there is a need for corrections to the data to account for changes in data collection procedures or other local conditions. Such changes may result from a variety of things including changes in instrumentation, changes in observation procedures, or changes in gauge location or surrounding conditions.

Snow pack water equivalent

depth of water would get if melt snow. ps(snow density)/pw(water density)

Soil water potential: gravitational potential (ψz)

determined solely by the elevation of a point relative to some arbitrary reference point, and is equal to the work needed to raise a body against the earth's gravitational pull from a reference level to its present position. When expressed as energy per unit weight, the gravitational potential is simply the vertical distance from a reference level to the point of interest. The numerical value of ψz itself is thus not important (it is defined with respect to an arbitrary reference level) - what is important is the difference (or gradient) in ψz between any two points of interest. This value is invariant of the reference level location. In a soil profile the gravitational potential (Ψg) of water near the soil surface is always higher thanΨg in the subsoil. As a result of heavy precipitation or irrigation, therefore, the difference inΨg causes downward flow of water deeper into the soil profile.

Sand

finer than gravel and coarser than silt. .05 mm - 2 mm (USDA)

Till

glacier deposits composed primarily of unsorted sand, silt, clay, and boulders laid down directly by the melting ice

Hydrograph

graph showing the rate of flow (discharge) versus time past a specific point in a river, or other channel or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs).

acquiclude, aquitard

hydrogeologic unit which, although porous and capable of storing water, doesn't transmit it at rates sufficient to furnish an appreciable supply to a well or spring. An aquitard is a zone within the earth that restricts the flow of groundwater from one aquifer to another. Aquitards comprise layers of either clay or non-porous rock with low hydraulic conductivity.

partial pressure

hypothetical pressure of that gas if it alone occupied the volume of the mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of each individual gas in the mixture.

Runoff-total

includes the sum of surface runoff (overland flow), baseflow, and interflow (subsurface stormflow) that moves across or through the land and enters a stream or other body of water.

Density

mass divided by volume

Vapour density

mass of H2Ov in a unit volume of air (kg m-3)

Weight

mass x local gravitational acceleration (g). W = mg.

Vadose zone / unsaturated zone

part of Earth between the land surface and the top of the phreatic zone i.e. position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the Latin for "shallow"). Hence the vadose zone extends from the top of the ground surface to the water table. Water in the vadose zone has a pressure head less than atmospheric pressure, and is retained by a combination of adhesion and capillary action. If the vadose zone envelops soil, the water contained therein is termed soil moisture. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the capillary fringe. The unsaturated zone is the portion of the subsurface above the groundwater table. Unlike the aquifers of the saturated zone below, the unsaturated zone is not a source of readily available water for human consumption.

actual vapour pressure

partial pressure of water vapour molecules in air at a temp, above a surface of water. *vapour pressure is often presented in kilopascals (kPa = 1000 Pa) or hPa. Vapor pressure rises with temperature.

Interception loss

precipitation that is intercepted by trees, vegetation, and/or buildings and evaporates quickly back into the atmosphere before reaching the ground.

Velocity

rate of change of displacement. difference between final and initial position of an object. equivalent to a specification of speed and direction.

Acceleration

rate of change of velocity of an object

relative humidity

ratio of actual vapour pressure (kPa) to saturation vapour pressure (kPa) at same temperature. The relative humidity is the percent of saturation humidity, generally calculated in relation to saturated vapour density. Air which is at 100% relative humidity (RH) contains water vapour whose VP is its SVP at the given temperature. This corresponds to air which is in equilibrium with liquid water.

Capillary fringe

saturated zone immediately above the water table where saturation is maintain by capillary tension exerted by soil pores

Bedrock

solid or fractured rock usually underlying unconsolidated geologic materials; bedrock may be exposed at the land surface

throughflow

subcomponent of interflow. sporadic horizontal flow of water within the soil layer (Figure 8m-1). It normally takes place when the soil is completely saturated with water. This water then flows underground until it reaches a river, lake, or ocean.

Runoff-direct

the sum of surface runoff and interflow

Cone of depression

the zone (around a well in an unconfined aquifer) that is normally saturated, but becomes unsaturated as a well is pumped; an area where the water table dips down forming a "V" or cone shape due to a pumping well

throughfall

throughfall is the process which describes how wet leaves shed excess water onto the ground surface. These drops have erosive power because they are larger than rain drops, however, if they travel a shorter distance their erosive power is reduced.

water table

water table is the surface where the water pressure head (Pressure potential energy per unit weight) is equal to the atmospheric pressure (where gauge pressure = 0). It may be conveniently visualized as the "surface" of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as surface tension holds water in some pores below atmospheric pressure. Individual points on the water table are typically measured as the elevation that the water rises to in a well screened in the shallow groundwater. The groundwater may be from infiltrating precipitation or from groundwater flowing into the aquifer. In areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths water fills in more of the pore spaces in the soils, until the zone of saturation is reached. In permeable or porous materials, such as sands and well fractured bedrock, the water table forms a relatively horizontal plane. Below the water table, in the phreatic zone, permeable units that yield groundwater are called aquifers. The ability of the aquifer to store groundwater is dependent on the primary and secondary porosity and permeability of the rock or soil. In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table may be more difficult to define.

Hydrostatic conditions

you have a body of fluid, and it tells you it's not moving. Sum of forces = 0. there isn't any flow. No viscous effect. hydro=fluid, stat=not moving. if there is no pressure gradient over a distance, no flow occurs (these are hydrostatic conditions).