Water — page 19 of 31

Water terms

1801. Lowland Flooding Inundation of low areas near the river, often rural, but may also occur in urban areas.
1802. Lysimeter An isolated block of soil, usually undisturbed and in situ, for measuring the quantity, quality, or rate of water movement through or from the soil.
1803. Macroclimate The climate representative of relatively large area.
1804. Macrohabitat An extensive habitat presenting considerable variation of the environment, containing a variety of ecological niches and supporting a large number and…
1805. Macrophytes A plant large enough to be seen by the naked eye.
1806. Magma Molten or partially molten rock at temperatures ranging from 1,260 F to 2,880 F (700 C to 1600 C).
1807. Magnitude A rating of a given earthquake, independent of the place of observation. It is calculated from measurements on seismographs and it is expressed in…
1808. Magnuson-Stevens Fishery Conservation and Management Act The Magnuson-Stevens Fishery Conservation and Management Act (MSA) is the primary law governing marine fisheries management in United States federal…
1809. Main The principal pipe artery to which branches may be connected.
1810. Main channel The deepest or central part of the bed of a stream, containing the main current.
1811. Main channel pool Reach of a stream or river with a low bed elevation, relative to rapids or riffles.
1812. Main Stem The reach of a river/stream formed by the tributaries that flow into it.
1813. Mainstream (mainstem) The main course of a stream where the current is the strongest.
1814. maintenance The patent fees due at 4, 8 and 12 years needed to keep a U. S. utility or plant patent in force for its full life.
1815. Maintenance management system Any organized system used to ensure that all operations and maintenance activities (e.g.
1816. Major facility A term used by Reclamation to describe those facilities for which an examination is conducted every third year, alternately conducted by the Denver and…
1817. Major Flooding A general term including extensive inundation and property damage. (Usually characterized by the evacuation of people and livestock and the closure of…
1818. Management/Managing Agency or Authority The federal, state, commonwealth, territorial, local, or tribal entity or entities with legal authority to designate, promulgate regulations for, and/or…
1819. Manifold (Header) A large pipe to which a series of smaller pipes are connected.
1820. Manning's roughness coefficient (n) A coefficient used to describe the relative roughness of a channel and overbank areas; used in hydraulic computations.
1821. Manometer An instrument for measuring pressure.
1822. Mantle The main bulk of the Earth, between the crust and core, ranging from depths of about 40 to 3,480 kilometers.
1823. Manuals. See publications.
1824. MAP 1. verb: to determine the relative positions of loci (genes or DNA sequences) on a chromosome.
1825. MAP (Mean Areal Precipitation) The average rainfall over a given area, generally expressed as an average depth over the area.
1826. Marble Metamorphic rock formed by the "baking" and recrystallization of limestone.
1827. Marginal land Land which, in its natural state, is not well suited for a particular purpose, such as raising crops.
1828. Marine Environment (U.S.) ocean or coastal waters (note: coastal waters may include intertidal areas, bays, or estuaries); an area of the Great Lakes or their connecting…
1829. Marine Managed Area Any area of the marine environment that has been reserved by federal, state, territorial, tribal, or local laws or regulations to provide lasting…
1830. Marine Managed Areas (MMA) Inventory (MMA) An earlier (2001-2007) database of U.S. aquatic, coastal, or marine sites that have been set aside for the protection of some or all of the natural and…
1831. Marine Planning Areas Distinct marine locations subject to site-specific, ongoing management or regulatory planning within fixed boundaries.
1832. Marine Protected Area Any area of the marine environment that has been reserved by federal, state, territorial, tribal, or local laws or regulations to provide lasting…
1833. Marine Protected Areas (MPA) Inventory (MPA) A comprehensive inventory of U.S. marine protected areas established or managed by federal, state, or territorial agencies or programs.
1834. Marine Reserve A type of MPA where extractive uses are prohibited (also referred to as "no-take" reserve)
1835. Marine Resource Areas Broad or multiple geographic areas defined by an underlying, mapped marine resource that is afforded some degree of protection through state laws…
1836. Marine Sanctuary As defined by the U.S. government are areas of the marine environment with special national significance due to their conservation, recreational…
1837. Marine Spatial Planning Marine Spatial Planning (MSP) is a comprehensive, ecosystem-based process through which compatible human uses are objectively and transparently allocated…
1838. Marine Waters As defined by U.S. Executive Order 13158 on MPAs: Waters under tidal influence, extending to the Mean High Water mark on land, and into river mouths to a…
1839. Market-based rates Rates for power or electric service that are established in an unregulated, competitive market.
1840. Marketer An agent for generation projects who markets power on behalf of the generator. The marketer may also arrange transmission, firming or other ancillary…
1841. Masonry Material such as brick, rock, or stone.
1842. Masonry dam Any dam constructed mainly of stone, brick or concrete blocks jointed with mortar.
1843. Mass care center A facility for providing emergency lodging and care for people made temporarily homeless by an emergency or disaster.
1844. Mass Concrete Any large volume of concrete cast-in-place, generally as a monolithic structure.
1845. Mass Curve A graph of the cumulative values of a hydrologic quantity (such as precipitation or runoff), generally as ordinate, plotted against time or date.
1846. Massive head buttress dam A buttress dam in which the buttress is greatly enlarged on the upstream side to span the gap between buttresses. See solid head buttress dam.
1847. Mastic A soft sealing material.
1848. Maximum Contaminant Level (MCL) (MCL) The highest level of a contaminant that is allowed in drinking water. MCLs ensure that drinking water does not pose either a short-term or long-term…
1849. Maximum Contaminant Level Goal (MCLG) The level of a contaminant in drinking water below which there is no known or expected risk to health.
1850. Maximum controllable water surface The highest reservoir water surface elevation at which gravity flows from the reservoir can be completely shut off.
1851. Maximum credible earthquake (MCE) The largest hypothetical earthquake that may be reasonably expected to occur along a given fault or other seismic source could produce under the current…
1852. Maximum demand The greatest of all demands of the load that has occurred within a specified period of time.
1853. Maximum design earthquake (MDE) The earthquake selected for design or evaluation of the structure. This earthquake would generate the most critical ground motions for evaluation of the…
1854. Maximum flood control level The highest elevation of the flood control storage.
1855. Maximum Spillway Discharge Spillway discharge (cfs) when reservoir is at maximum designed water surface elevation.
1856. Maximum unit weight The dry unit weight defined by the peak of a compaction curve. See unit weight.
1857. Maximum water surface (maximum pool) The highest acceptable water surface elevation with all factors affecting the safety of the structure considered.
1858. Maximum wave The highest wave in a wave group.
1859. 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.
1860. Mean number The average number.
1861. Mean sea level (MSL) (MSL) The arithmetic mean of hourly water elevations observed over a specific 19-year tidal epoch.
1862. Meander Big bend and loops in a river channel as the river snakes through a flat land area.
1863. Meander Belt The area between lines drawn tangential to the extreme limits of fully developed meanders.
1864. median A statistics term. The middle value in a set of measurements.
1865. Medium-height dam A dam between 100 and 300 feet high. See low dam and high dam.
1866. Medium-size water system A water system that serves greater than 3,300 and less than or equal to 50,000 persons.
1867. Medium-thick arch dam An arch dam with a base thickness to structural height ratio between 0.2 and 0.3 (previously defined as between 0.3 and 0.5).
1868. mega A prefix meaning "million".
1869. Megawatt (MW) (MW) A measure of instantaneous electric power consumption or production. Equal to one thousand KW.
1870. Megawatt-hour (MWh) One million watt- hours of electrical energy.
1871. Membrane (diaphragm) A membrane or sheet or thin zone or facing, made of a flexible impervious material such as asphaltic concrete, plastic concrete, steel, wood, copper…
1872. Memorandum of Understanding (MOU) A formal document that states the intentions and/or responsibilities of the signatory parties.
1873. Meniscus The curved top of a column of liquid in a small tube caused by surface tension.
1874. Mesh In wire screen, the number of openings per lineal inch.
1875. Mesotrophic A lake classification describing middle-aged bodies of water between oligotrophic (young) and eutrophic (old) classifications.
1876. Metalimnion Middle layer of a thermally stratified lake or reservoir with a rapid temperature decrease with depth. See stratification and thermocline.
1877. Metamorphic Rock compressed or changed by pressure, heat, or water. A rock formed from a preexisting rock that is altered ("baked") by high temperatures and…
1878. Meteoric Water Water derived from precipitation.
1879. Mica Group of minerals that form thin, platy flakes, typically with shiny surfaces, especially common in metamorphic rocks.
1880. Micro Small. A prefix meaning "one millionth".
1881. Microclimate The local climate of specific place or habitat, as influenced by landscape features.
1882. Microgram per liter Equivalent to 1 part per billion.
1883. Microhabitat A small, specialized, and effectively isolated location. See macrohabitat.
1884. Micron One thousandth of a millimeter.
1885. Microsystem irrigation Method of precisely applying irrigation water to the immediate root zone of the target plant at very low rates.
1886. Migmatite Rock composed of a complex mixture of metamorphic rock and igneous granitic rock.
1887. Migratory Moving from one area to another on a seasonal basis.
1888. MIL A unit of length equal to 0.001 of an inch. Used in measuring the diameter of wires, and the thickness of fabric and plastic sheeting.
1889. Milestone A measurable action, state, or goal which marks a point of achievement on the way to solving the problem.
1890. Military crest A ridge that interrupts the view between a valley and a hilltop.
1891. Mill A common monetary measure equal to one-thousandth of a dollar or a tenth of a cent.
1892. Milli A prefix meaning "one thousandth".
1893. Milligram per liter (mg/l) Equivalent to 1 part per million.
1894. Million acre-feet (maf) The volume of water that would cover 1 million acres to a depth of 1 foot.
1895. Millisecond delay (short period delay) A type of delay cap with a definite but extremely short interval between initiation, or passing of current, and explosion.
1896. Mine tailings dam An industrial waste dam in which the waste materials come from mining operations or mineral processing.
1897. Miners' Inch A rate of discharge through an orifice one inch square under a specific head.
1898. Minimum flow Negotiated lowest flow in a regulated stream that will sustain an aquatic population of agreed-upon levels. Flow may vary seasonally.
1899. Minimum operating level The lowest level to which the reservoir is drawn down under normal operating conditions.
1900. Mining Usually removal of soil or rock having value because of its chemical composition.