Knowledge Base

MUNICIPAL AND INDUSTRIAL WATER USE — Water supplied for municipal and industrial uses provided through a municipal distribution system.

MACROPHYTE — A member of the macroscopic plant life, especially of a body of water.

MAIN — A relatively large pipe in a distribution system for drinking water or in a collection system for municipal wastewater. Of or relating to utility distribution mains for transferring water. Often used in the plural, as in water mains.

MAIN CANAL SYSTEM — A canal that delivers water from a primary source of supply to several points of diversion or canal-side turnouts to smaller distribution systems.

MAINSTEM — The major reach of a river or stream formed by the smaller tributaries which flow into it.

MAJOR FLOODING — Flood conditions resulting in extensive inundation and property damage. Typically characterized by the evacuation of people and livestock and the closure of both primary and secondary roads.

MAKEUP WATER — Water added to the flow of water used to cool condensers in electric power plants. This new water replaces condenser water lost during passage of the cooling water through cooling towers or discharged in blowdowns.

MANAGEMENT INDICATOR SPECIES (MIS) — (Environmental) A species selected because its welfare is presumed to be an indicator of the welfare of other species in the habitat. A species whose condition can be used to assess the impacts of management actions on a particular area. Managing for these species usually requires significant allocations of land or resources.

MANAGERIAL CONTROLS — (Irrigation) Methods of nonpoint source pollution control based on decisions about managing agricultural wastes or application times or rates for agrochemicals.

MANMADE LAKE — Any manmade body of water, including lakes, ponds, lagoons, and reservoirs (excluding tank-type reservoirs which are fully enclosed and contained), that are filled or refilled with water or reclaimed wastewater from any source and used for recreational, scenic, or landscape purposes, except swimming pools.

MANOMETER — An instrument for measuring pressure which usually consists of a U-shaped tube containing a liquid, the surface of which in one end of the tube moves proportionally with changes in pressure on the liquid in the other end. The term is also applied to a tube-type differential pressure gage.

MARE CLAUSUM — A navigable body of water, such as a sea, that is under the jurisdiction of one national and closed to all others.

MARE LIBERUM — A navigable body of water, such as a sea, that is open to navigation by vessels of all nations.

MARE NOSTRUM — A navigable body of water, such as a sea, that is under the jurisdiction of one nation or that is shared by two or more nations.

MARICULTURE — The cultivation of marine organisms for use as a food resource.

MARINA — A water-based facility used for storage, service, launching, operation, or maintenance of watercraft.

MARINE — (1) Of or pertaining to the sea; having to do with the ocean or the things peculiar to the ocean. (2) A system within the Wetlands and Deepwater Habitat Classification System.

MARINE LIFE — Plants and animals of the sea, from the high-tide mark along the shore to the depths of the ocean. These organisms fall into three major groups: (1) Benthos — plants such as kelp and animals such as brittle stars that live on or depend on the bottom; (2) Nekton — swimming animals such as fishes and whales that move independently of water currents; and (3) Plankton — various small to microscopic organisms that are carried along by the currents.

MARITIME LAW — Branch of law relating to commerce and navigation on the high seas and on other navigable waters. Specifically, the term refers to the body of customs, legislation, international treaties, and court decisions pertaining to ownership and operation of vessels, transportation of passengers and cargo on them, and rights and obligations of their crews while in transit.

MATHEMATICAL MODEL — A representation of physical laws or processes expressed in terms of mathematical symbols and expressions (i.e., equations). The model is used as a basis for computer programs for examining the effect of changing certain variables in the analysis of the effect of flow changes in a water delivery system, for example.

MATTER — Anything which is solid, liquid, or gas and has mass.

MAXIMUM DEPTH (RESERVOIR) — The greatest depth of the body of water measured in feet and 10ths of feet.

MAXIMUM PROBABLE FLOOD — The largest flood for which there is any reasonable expectancy.

MAXIMUM SUSTAINABLE YIELD — The greatest amount of a renewable natural resource (e.g., forests or wildlife) that can be removed without diminishing the continuing production and supply of the resource.

MAXIMUM WATER SURFACE (RESERVOIR) — The maximum water-surface elevation is the highest water surface elevation for which the dam is designed. It is also the top of the surcharge capacity.

MEADOW — An area of moist low-lying grassland usually along a watercourse supporting a more dense stand of grasses and perhaps dwarf shrubs as compared to adjacent more arid uplands.

MEADOW, DRY — An area where during the spring, early summer, and in some open winters there is a greenup of succulent vegetation. These areas are relatively few in number and highly important for sustaining animal populations within whose habitat these meadows exist. During the summer and fall there is normally dry vegetation.

MEADOW, WET — A perennial wet area where the water table is maintained at or close to the ground surface to maintain shallow rooted water-dependent vegetative complexes.

MEAN ANNUAL FLOOD — The average of all the annual flood stages or discharges of record. It may be estimated by regionalization, correlation, or any other process that can furnish a better estimate of the long-term average than can the observed data. Some investigators arbitrarily define the mean annual flood as the stage or discharge having an exceedence interval of 2.33 years.

MEAN ANNUAL PRECIPITATION — The average of all annual precipitation values known, or an estimated equivalent value derived by such methods as regional indexes or Isohyetal maps.

MEAN ANNUAL RUNOFF — The average value of all annual runoff amounts usually estimated from the period of record or during a specified base period from a specified area.

MEAN ANNUAL TEMPERATURE — The average of the daily maximum and minimum temperatures.

MEAN DEPTH — The average depth of water in a stream channel or conduit. It is equal to the cross-sectional area divided by the surface width.

MEAN HIGH WATER (MHW) — The average height of the high water over 19 years.

MEAN LOW WATER (MLW) — The average height of the low water over 19 years.

MEAN LOWER LOW WATER — The average height of the lower of two unequal daily low tides over 19 years. Tides of the northeastern Pacific Ocean are characterized as mixed, with two unequal highs and two unequal lows daily. The plane of reference for navigation channels is the long term average of the daily lower lows, termed mean lower low water.

MEAN SEA LEVEL (MSL) — The level of the surface of the sea between mean high and mean low tide; used as a reference point for measuring elevations.

MEAN TIDE LEVEL — A plane midway between mean high water and mean low water.

MEANDER — The turn of a stream, either live or cut off. The winding of a stream channel in the shape of a series of loop-like bends.

MEANDER AMPLITUDE — The distance between points of maximum curvature of successive meanders of opposite phase in a direction normal to the general course of the Meander Belt, measured between centerlines of channels.

MEANDER BELT — The zone along a valley floor that encloses a meandering river.

MEANDER BREADTH — The distance between the lines used to define the Meander Belt.

MEANDER LENGTH — The distance in the general course of the meanders between corresponding points of successive meanders of the same phase.

MEANDER LINE — A line delineated by government survey for the purpose of defining the bends or windings of the banks of a stream or the shore of a body of water, and as a means for ascertaining the quantity of land embraced by the survey.

MEAN MONTHLY TEMPERATURE — The average of the mean monthly maximum and minimum temperatures.

MEASUREMENT UNCERTAINTY — The estimated amount by which the measured quantity may depart from the true value.

MECHANICAL TURBULENCE — The erratic movement of air or water influenced by local obstructions.

MEDIAN — (Statistics) In a set of observations, the middle-most value with an equal number of observations lying above and below the median value.

MEDIAN STREAM FLOW (MEDIAN HYDRO) — The rate of discharge of a stream for which there are equal numbers of greater and lesser flow occurrences during a specified period.

MEDIAN TOLERANCE LIMIT — The concentration of a test substance at which just 50 percent of the test animals are able to survive for a specified period of exposure.

MEDIUM-SIZE WATER SYSTEM — A water system that serves 3,300 to 50,000 customers.

MEGAWATT (MW) — A unit of electricity equivalent to 1 million watts or 1,000 kilowatts (KW).

MELTWATER — Water that comes from the melting ice of a glacier or a snow bank.

MEMBRANE — A plastic material used in the electrodialysis and reverse osmosis processes. Electric current is the driving force that moves salt ions through solution in electrodialysis, and hydraulic pressure the driving force in reverse osmosis.

MEMBRANE FILTER — Filter made of plastic or modified cellulose and having a known pore diameter. Such filters are used in the bacteriological examination of water and the separation of suspended matter before laboratory analyses. In additional to their analytical use, these filters area also used for public health purposes as well as for the sterilization of liquids. The membranes are available in a variety of sizes, with a diameter of 47-50 millimeters being the most common. Membrane filter water purification technologies are rapidly emerging as a viable and cost effective water treatment option for municipalities confronted with complex regulatory issues and increasingly stringent water treatment regulations. Membranes can be used as the primary means to remove materials from water, but they can also be used in conjunction with other physical, chemical, or biological processes to either separate the phases of water treatment or isolate specific organisms.

MEMBRANE FILTER METHOD — A procedure used to recover and count bacteria in samples of liquid substances, such as water. The liquid is drawn through a Membrane Filter using a slight vacuum, with the bacteria in the liquid being retained on the filter. The filter disk is then transferred to a medium suitable for the growth and incubation of the bacteria.

MESOTROPHIC (WATER) — Pertaining to a lake or other body of water characterized by moderate nutrient concentrations such as nitrogen and phosphorous and resulting significant productivity. Such waters are often shallow, with algal blooms and periods of oxygen deficiency. Slightly or moderately eutrophic water can be healthful and support a complex web of plant and animal life. However, such waters are generally undesirable for drinking water and other needs. Degrees of Eutrophication typically range from Oligotrophic water (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic water (minimum transparency, maximum chlorophyll-a, maximum phosphorus).

METEOROLOGY — The science that deals with the phenomenon of the atmosphere, especially weather and weather conditions.

METER — A unit of length which constitutes the basis of the Metric System, was intended to be, and is very nearly, one ten-millionth part of the distance measured on a meridian of the earth from the equator to the pole, being equal to 39.37 U.S. inches or about 3 feet 3-3/8 inches.

METRIC SYSTEM — A decimal system of measures and weights with the meter and the gram as bases. The units of the metric system at the outset were all derived from the unit of length, the Meter, which was intended to be, and is very nearly, one ten-millionth part of the distance measured on a meridian of the earth from the equator to the pole, being equal to 39.37 U.S. inches or about 3 feet 3-3/8 inches. Upon the meter were originally based the other primary units of measure: the square meter (area), the cubic meter (volume), the Liter (liquid volume), and the Gram (mass and weight). It was found, however, that masses could be compared with a higher degree of accuracy than that with which volumes could be determined, and it was therefore preferable to have a material standard of mass specifically defined rather than one derived from the unit of length through the unit of volume. A definite mass, the International Prototype Kilogram was, therefore, adopted as the standard of mass, and the unit of volume, the liter, was then redefined in terms of the standard of mass; the liter being defined as the volume of a kilogram of pure water at the temperature of its maximum density (4C or 39.2F), and equal to 1.000027 cubic decimeters.


[1] Length



United States



6.2137 miles



0.62137 miles



328 feet 1 inch



393.7 inches



39.37 inches



3.937 inches



0.3937 inches



0.03937 inches

[2] Area



United States



2.471 acres



119.6 square yards



1,550 square inches

[3] Volume



Cubic Measure

United States




1 cubic meter

1.308 cubic yard

1.308 cubic yard



0.1 cubic meter

2.838 bu./26.418 gal

2.75 bu./22.00 gal



10 cubic dm

1.135 pk./2.6418 gal

8.80 qt./2.200 gal



1 cubic dm

0.9081 qt./1.0567 liq qt

0.880 quarts



0.1 cubic dm

6.1025 cu. in./0.845 gill

0.704 gill.



10 cubic cm

0.6102 cu. in./0.338 fl. oz.

0.352 fl. oz.



1 cubic cm

0.061 cu. in./0.27 fl. dram

0.28 fl. dram.

Volume Table Notes:

dm = decimeter = 1/10 meter
cm = centimeter = 1/100 meter
bu = bushel = 4 pecks = 32 quarts
pk = peck = 1/4 bushel = 8 quarts
qt = quart = 2 pints = 1/4 gallons
liq qt = liquid quart = 1.1635 (dry) quarts
gill = 1/4 pint
fl dram = fluid dram = 1/16 ounce = 27.34375 grains = 1.772 grams

[4] Weight





Metric Ton


1 Cubic Meter

2204.6 lb



1 hectoliter

220.46 lb.



1 decaliter

22.046 lb.



1 liter

2.2046 lb.



1 deciliter

3.5274 oz.



10 cubic centimeters

0.3527 oz



1 cubic centimeter

15.432 grains



0.1 cubic centimeter

1.5432 grains



10 cubic millimeters

0.1543 grains



1 cubic millimeter

0.0154 grains

MIDSTREAM — The middle part of a stream.

MIGRATION — The movement of oil, gas, contaminants, water, or other liquids through porous and permeable rock.

MILLDAM — A dam constructed across a stream to raise the water level so that the overflow will have sufficient power to turn a mill wheel.

MILLSTREAM — The rapid stream of water flowing in a Millrace.

MILL WHEEL — A wheel, typically driven by water, that powers a mill.

MINE DRAINAGE — Water pumped or flowing from a mine.

MINERAL — Any naturally occurring inorganic material with an orderly internal arrangement of atoms and specific physical and chemical properties.

MINERALIZATION — (1) The general process by which elements present in organic compounds are eventually converted into inorganic forms, ultimately to become available for a new cycle of plant growth. (2) The process whereby concentrations of minerals, such as salts, increase in water, often as a natural process resulting from water dissolving minerals found in rocks and soils through which it flows.

MINERAL SOIL — Soil composed of predominantly mineral rather than organic materials.

MINERAL WATER — Naturally occurring or prepared water that contains dissolved mineral salts, elements, or gases, often used therapeutically.

MINIMAL FLOOD HAZARD AREAS — Areas between the 100-year and the 500-year flood boundaries are termed Moderate Flood Hazard Areas. The remaining areas are above the 500-year flood level and are termed Minimal Flood Hazard Areas.

MINIMUM FLOW APPROPRIATION — An appropriation designed to preserve a specified minimum flow in a stream. When the flow in the stream drops to that which is specified in the appropriation, junior appropriations will be required to stop diverting water in order to maintain the minimum flow.

MINIMUM MOISTURE CONTENT — The amount of water in soil during the driest time of the year.

MINIMUM POOL — A term used to describe the lowest level of reservoir capacity safe for maintaining fish and aquatic life or for some other designated beneficial purpose. This term differs from Dead Storage Capacity in that the reservoir level may still be reduced below minimum pool, whereas the dead storage capacity represents a level below the lowest outlet level.

MINIMUM STREAMFLOW — The specific amount of water reserved to support aquatic life, to minimize pollution, or for recreation. It is subject to the priority system and does not affect water rights established prior to its institution.

MINIMUM TILLAGE FARMING — A farming technique that reduces the degree of soil disruption. Crop residues are not plowed under after harvest, and special planters dig narrow furrows in the crop residue when new seeds are sown. Advantages of the technique include reductions in energy consumption by farm equipment, less soil erosion, and lower soil moisture losses during the fallow season. Disadvantages include the possibility of encouraging insect pests by leaving the crop residue in the field and the use of herbicides to control weeds in the place of mechanical cultivation. Sometimes incorrectly termed No-Till Farming.

MINING (of an Aquifer) — Withdrawal over a period of time of ground water that exceeds the rate of recharge of the aquifer.

MINING WATER USE — Water use for the extraction of minerals occurring naturally including solids, such as coal and ores; liquids, such as crude petroleum; and gases, such as natural gas. Also includes uses associated with quarrying, well operations (Dewatering), milling (crushing, screening, washing, flotation, and so forth), and other preparations customarily done at the mine site or as part of a mining activity, such as dust control, maintenance, and wetland restoration. Generally, most of the water used at a mining operation is self-supplied.

MINOR FLOODING — Flooding resulting in minimal or no property damage but some public inconvenience.

MITIGATION — (1) (Environmental, General) Actions designed to lessen or reduce adverse impacts; frequently used in the context of environmental assessment. (2) (NEPA) Action taken to avoid, reduce the severity of, or eliminate an adverse impact. Mitigation can include one or more of the following:
[1] avoiding impacts;
[2] minimizing impacts by limiting the degree or magnitude of an action;
[3] rectifying impacts by restoring, rehabilitating, or repairing the affected environment;
[4] reducing or eliminating impacts over time; and
[5] compensating for the impact by replacing or providing substitute resources or environments to offset the loss.

MIXED LIQUOR — (Water Quality) In wastewater treatment, the liquid in the aeration tank of an activated sludge system; a mixture of activated sludge and water containing organic matter undergoing activated sludge treatment in an aeration tank.

MODERATE FLOOD HAZARD AREAS — Areas between the 100-year and the 500-year flood boundaries are termed Moderate Flood Hazard Areas. The remaining areas are above the 500-year flood level and are termed Minimal Flood Hazard Areas.

MODERATE FLOODING — Flood conditions characterized by the inundation of secondary roads, transfer of property to higher elevations, and some evacuations of people and livestock. Also see Major Flooding and Minor Flooding.

MOISTURE — (1) Diffuse wetness that can be felt as vapor in the atmosphere or condensed liquid on the surface of objects; dampness. (2) The state or quality of being damp.

MOISTURE EQUIVALENT — The ratio of: (1) the weight of water which the soil, after saturation, will retain against a centrifugal force 1,000 times the force of gravity, to (2) the weight of the soil when dry. The ratio is stated as a percentage.

MOISTURE STRESS — A condition of physiological stress in a plant caused by a lack of water.

MOISTURE TENSION — The equivalent negative pressure in the soil water. It is equal to the equivalent pressure that must be applied to the soil water to bring it to hydraulic equilibrium, through a porous permeable wall or membrane, with a pool of water of the same composition.

MONITORING — Sampling and analysis of air, water, soil, wildlife, and other conditions, to determine the concentrations of contaminants.

MONITORING WELL — (1) A well used to obtain water quality samples or measure groundwater levels. (2) (Water Quality) A well drilled in close proximity to a waste storage or disposal facility, or hazardous waste management facility or Superfund Site to check the integrity of the facility or to keep track of leakage of materials into the adjacent groundwater.

MOUTH OF STREAM — The point of discharge of a stream into another stream, a lake, or the sea.

MUD — (1) A slimy sticky mixture of solid material with a liquid and especially water; especially soft wet earth. (2) Also, wet soft earth composed predominantly of clay and silt — fine mineral sediments less than 0.074 mm (0.0029 inch) in diameter.

MUD BALLS — (Water Quality) Accretions of siliceous incrustations on the exterior of sand grains in a rapid sand filter; typically removed by backwashing. Such deposits interfere with effective filtration.

MUDFLOW — Flow of a well-mixed mass of rock, earth, and water that behaves like a fluid and flows down slopes with a consistency similar to that of newly mixed concrete.

MUDSLIDE — A condition where there is a river, flow or inundation of liquid mud down a hillside usually as a result of a dual condition of loss of brush cover, and the subsequent accumulation of water on the ground preceded by a period of unusually heavy or sustained rain. A mudslide may occur as a distinct phenomenon while a landslide is in progress.

MULCH — A natural or artificial protective layer of suitable materials, usually of organic matter such as leaves, straw, or peat, placed around plants that aid in soil stabilization, soil moisture conservation, prevention of freezing, and control of weeds, thus providing micro-climatic conditions suitable for germination and growth of selected vegetation.

MULCHING — The use of plant residues or other suitable materials on the soil surface, primarily to reduce evaporation of water and erosion of soil.

MULTI-CROPPING — The practice of producing two or more crops consecutively on the same parcel of land during a 12-month period. Also referred to as Double Cropping.

MULTIPLE-PURPOSE RESERVOIR — A reservoir planned and constructed to provide water for more than one purpose, e.g., irrigation, recreation, and flood control.

MULTIPLE USE — Harmonious and coordinated management of the various surface and subsurface resources, without impairment of the land, that will best meet the present and future needs of the people. Does not necessarily connotate the combination of uses that will yield the highest economic return or greatest unit of output.

MUNICIPAL AND INDUSTRIAL WATER USE — Water supplied for municipal and industrial uses provided through a municipal distribution system for rural domestic use, stock water, steam electric powerplants, and water used in industry and commerce.

MUNICIPAL DISCHARGE — The discharge of effluent from waste water treatment plants which receive waste water from households, commercial establishment, and industries. Combined sewer/separate storm overflows are included in this category.

MUNICIPAL SEWAGE — Sewage (mostly liquid) originating from a community which may be composed of domestic sewage, industrial wastes, or both.

MUNICIPAL WASTEWATER FACILITY — Refers to those facilities that receive or dispose of wastewater derived principally from residential dwellings, business or commercial buildings, institutions, and the like. May also include some wastewater derived from industrial facilities.

MUNICIPAL WATER — Municipal water may come from either ground water or surface water sources. Once water has entered a municipal water system, from whatever source, it will be considered municipal water.

MUNICIPAL WATERSHED — The watershed from which the runoff is used for drinking purposes in a city.

MUNICIPAL WATER SYSTEM — A water system which has at least five service connections or which regularly serves 25 individuals for 60 days.