Water Quality

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The absolute nearness to the truth. In physical measurements it is the degree of agreement between the quantity measured and the actual quantity. Not to be confused with precision, which denotes the reproducibility of the measurement.

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accuracy

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(1) Transfer by horizontal motion. (2) In meteorology, predominantly horizontal atmospheric motions resulting in horizontal transport and mixing of atmospheric properties.

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advection

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A general term for all detrital material deposited by a stream where it emerges from an upland onto a plain.

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alluvium

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An instrument for measuring the force or velocity of wind; a wind gage.

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anemometer

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The angle with the horizontal which the sloping face of a bank of loose material assumes.

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angle of repose

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The degree of wetness of the soil at the beginning of a runoff period, frequently expressed as an index determined by summation of weighted daily rainfalls for a period preceding the runoff in question.

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antecedent moisture

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A geologic formation or structure that transmits water in sufficient quantity to supply the needs for a water development.

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aquifer

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The direction that a slope faces, measured at right angles to the contour. It is a physiographic feature.

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aspect

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A flow condition where streamflow completely fills the stream channel up to the top of the bank.

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bankfull discharge

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Sustained or dry-weather runoff. It includes water draining from natural storage in groundwater bodies, lakes or swamps, and delayed subsurface runoff.

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base flow

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Sediment that moves by sliding, rolling or skipping on or very near the stream bed; sediment that is moved by tractive or gravitational forces, or both, but at velocities less than that of adjacent flow.

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bed load

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Structural devices that temporarily store or treat urban stormwater runoff to reduce flooding, remove pollutants, and provide other amenities.

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best management practice (BMP)

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The quantity of oxygen consumed during the biochemical oxidation of organic matter over a specified period of time, at a specified temperature, and under specified conditions.

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biochemical oxygen demand (BOD)

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A zone of existing vegetation adjacent to wetlands, stream or other areas of significant natural resource that can be used to spread flows and trap sediment.

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buffer zone (or buffer strip)

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An artificial open channel or waterway constructed for one or more of the following purposes: (a) transporting water, (b) connecting two or more bodies of water, and (c) serving as a waterway for watercraft.

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canal

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That area determined by topographic features within which falling rain will contribute to runoff to a particular point under consideration.

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catchment

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The widening, deepening, and headward cutting of small channels and water-ways, due to erosion caused by moderate to large floods.

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channel erosion

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The surface of separation between two adjacent air masses of different characteristics, usually temperature and humidity, and normally associated with a belt of cloud and precipitation in which colder air replaces warmer air.

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cold front

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The process of reducing the volume of a material by inducing the closer packing of its particles by rolling, tamping or other mechanical means.

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compaction

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An aquifer which is surrounded by formations of less permeable or impermeable material.

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confined aquifer

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A junction or flowing together of streams; the place where streams meet.

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confluence

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In physics, mass motions within a fluid, resulting in transport and mixing of the properties of that fluid, caused by the force of gravity and by differences in density due to nonuniform temperature.

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convection.

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That portion of the runoff which escapes from a reservoir through the underlying earth or rock strata, below any possible intercepting cutoff constructed at the dam.

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deep seepage

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The total runoff from a drain-age basin divided by its area.

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depth of runoff

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A reservoir in which water is stored for a relatively brief period of time, part of it being retained until the stream can safely carry the ordinary flow plus the released water.

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detention reservoir.

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The temperature to which air with a given concentration of water vapor must be cooled to cause condensation of the vapor.

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dew point

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The transfer of mass from one fluid phase to another across an interface, as for example liquid to solid, gas to liquid.

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diffusion

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the volume of water transported by a stream in a certain amount of time.

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discharge

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Occurring during a 24-hr period; diurnal variation.

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diurnal

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The amount of oxygen dissolved in water or other liquids, usually expressed as mg/l or percent saturation.

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DO (dissolved oxygen).

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A circular movement occurring in flowing water, caused by currents set up in the water by obstructions or changes and irregularities in the banks or bottom of the channel.

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eddy

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A stream that flows only in direct response to precipitation. Such a stream receives no water from springs and no long continued supply from melting snow or other surface source. Its channel is above the water table at all times.

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ephemeral stream

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The wearing away of the land surface by running water, wind, ice or other geological agents, including such processes as gravitational creep.

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erosion

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An erosion process in which numerous small channels only several centimetres deep are formed.

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rill erosion

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The gradual uniform removal of the earth's surface by splash and runoff, without the formation of rills or gullies.

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sheet erosion

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The spattering of small soil particles caused by the impact of raindrops on wet soils.

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splash erosion

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The process by which water becomes a vapor.

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evaporation

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The quantity of water held in a soil by capillary action after gravitational water is removed.

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field capacity

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Land which adjoins the channel of a natural stream and which is subject to overflow flooding.

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floodplain

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The movement of a stream of water and/or other mobile substance from place to place.

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flow

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An artificial open channel of wood, masonry or metal constructed on a grade, and sometimes elevated, with a clearly specified shape and dimensions which may be used for measurement of flow.

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flume

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An installation at a measuring site where water level and/or discharge records are regularly obtained.

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gauging station

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Subsurface water occupying the saturation zone from which wells and springs are fed.

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groundwater

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The upper surface of a body of unconfined groundwater.

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groundwater table

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The height of the free surface of fluid above any point in a hydraulic system; a measure of the pressure or force exerted by the fluid.

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head

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The right cross-sectional area of a stream of water divided by the length of that part of its periphery in contact with its containing conduit; the ratio of area to wetted perimeter.

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hydraulic radius

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Not allowing, or allowing only with great difficulty, the movement of water.

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impervious

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The flow or movement of water through the interstices or pores of a soil or other porous medium.

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infiltration

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The maximum rate at which the soil, when in a given condition, can absorb falling rain or melting snow.

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infiltration capacity

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the process by which precipitation falls on vegetative surfaces (the canopy), where it is subject to evaporation

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interception

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That movement of water of a given density in a reservoir or lake between layers of water of different density.

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interflow

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the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas)

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latent heat

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A formula used to predict the velocity of water flow in an open channel or pipeline:

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Manning formula (hydraulics)

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The roughness coefficient in the Manning formula for determination of the discharge coefficient.

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Manning roughness coefficient

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a concept based on the fundamental physical principle that matter can neither be created nor destroyed. Therefore, the mass of inputs to a process balances the mass of outputs.

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mass balance

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The runoff of sediment and other undesirable materials along with stormwater from diffuse sources

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non-point source runoff

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flow The flow of water over the ground or paved surface before it enters some defined channel or inlet, often assumed to be shallow and uniformly distributed across the width.

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overland flow

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An instrument for measuring pressure head in a conduit, tank, or soil.

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piezometer

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A single source of pollutants, such as a sewage treatment plant waste water outfall. Any discernable, confined, or discrete conveyance from which pollutants are ormay be discharged, including, but not limited to, any pipe, ditch, channel, tunnel, conduit, well, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft.

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point source

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(1) The quality of being porous or containing interstices. (2) The ratio of the aggregate volume of interstices in a rock or soil to its total volume. It is usually stated as a percentage.

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porosity

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an instrument used to measure shortwave (solar) radiation

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pyranometer

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curve A curve showing the relation between gage height and discharge of a stream or conduit at a given gaging station. It is a graphical representation of a rating or discharge table.

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rating curve

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The amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature.

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relative humidity

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The bank to the right of an observer facing downstream.

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right bank

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A very small stream through which water flows during and immediately after rain.

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rill

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Solid material, both mineral and organic, formed as a result of erosion, that is in suspension, is being transported, or has been moved from its site of origin by air, water, gravity, or ice, and has come to rest on the earth's surface either above or below sea level.

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sediment

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heat energy that can be directly sensed via measurement of the temperature

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sensible heat

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A graduated scale, vertical unless otherwise specified, on a plank, metal plate, pier, wall, etc., used to indicate the height of a fluid surface above a specified point or datum plane.

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staff gage

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The direct conversion of solids to the gaseous state and back to the solid state without apparent liquefication.

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sublimation

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The very fine soil particles that remain in suspension in water for a considerable period of time without contact with the solid-fluid boundary at or near the bottom.

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suspended sediment

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a calculation of the maximum amount of a pollutant that a waterbody can receive and still safely meet water quality standards.

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TMDL (Total Maximum Daily Load)

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The process by which water vapor is lost to the atmosphere from living plants.

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transpiration

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A condition in water or wastewater caused by the presence of suspended matter, resulting in the scattering and absorption of light.

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turbidity

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That portion of the lithosphere in which the functional interstices of permeable rock or earth are not (except temporarily) filled with water under hydrostatic pressure; that is, the water in the interstices is held by capillarity.

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unsaturated zone

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Surface runoff from an urban drainage area that reaches a stream or other body of water or a sewer.

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urban runoff

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the partial pressure of water vapor in the air.

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vapor pressure

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The balance in a hydrologic system between precipitation or other inputs, and the outflow of water by runoff, evapotranspiration, groundwater recharge, and streamflow.

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water balance

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The depth of water that would result if an accumulation of snow, at a point or over an area, is reduced to water by melting.

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water equivalent of snow

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The volume of water a free-draining soil can contain.

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water holding capacity (of soil)

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The chemical, physical, and biological characteristics of water with respect to its suitability for a particular purpose.

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water quality

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Water in various forms - such as groundwater, surface water, rain, snow, ice, or clouds - that is potentially useful for some purpose.

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water resources

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The surface of groundwater, or the surface below which the pores of rock or soil are saturated; the upper surface of the zone of saturation, except where that surface is formed by an impermeable body.

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water table

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The surface of a local zone of saturation held above the main body of groundwater by an unsaturated zone.

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perched water table

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A drainage basin's total yield of liquid water during some period of time.

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water yield

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a small overflow-type dam commonly used to raise the level of a river or stream.

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weir