Dabble To bob forward and under in shallow water so as to feed off the bottom.
Daily Flood Peak The maximum mean daily discharge occurring in a stream during a given flood event.
Daily Record A summary of streamflow, sediment, or water-quality values computed from data collected with sufficient frequency to obtain reliable estimates of daily mean values.
Daily Record Station A site for which daily records of streamflow, sediment, or water-quality values are computed.
Daily Temperature Range The difference between the highest and lowest temperatures recorded on a particular day.
Dalton A unit of molecular weight; a unit of mass convenient for the expression of the mass of atoms, being one-sixteenth the mass of an oxygen atom.  It equals approximately 1.65 X 10-24 grams.  Named after the English chemist and physicist John Dalton (1766-1844).  Used frequently for sizing particles trapped by semipermeable membrane filters.
Dam A structure of earth, rock, or concrete designed to form a basin and hold water back to make a pond, lake, or reservoir.  A barrier built, usually across a watercourse, for impounding or diverting the flow of water.  General types of dams include:
1)  Arch Dam - Curved masonry or concrete dam, convex in shape upstream, that depends on arch action for its stability; the load or water pressure is transferred by the arch to the Abutments.
2)  Buttress Dam - A dam consisting of a watertight upstream face supported at intervals on the downstream side by a series of buttresses.
3)  Cofferdam - A temporary watertight enclosure that is pumped dry to expose the bottom of a body of water so that construction, as of piers, a dam, and bridge footings, may be undertaken.  A "diversion cofferdam" prevents all downstream flow by diverting the flow of a river into a pipe, channel, or tunnel.
4)  Crib Dam - A barrier or form of Gravity Dam constructed of timber forming bays, boxes, cribs, crossed timbers, gabions or cells that are filled with earth, stone or heavy material.
5)  Embankment Dam - A dam structure constructed of fill material, usually earth or rock, placed with sloping sides and usually with a length greater than its height.  Types of embankment dams include:  Earthfill or Earth Dam - A dam in which more than 50
6)  Gravity Dam - A dam constructed of concrete and/or masonry that relies on its weight for stability.
7)  Inflatable Dam - A dam constructed of heavy-duty rubber or similar material and inflated with air or water and used for small-scale impoundment of flood flows or as flashboards for regulating the overflow of larger dams..
8)  Masonry Dam - A dam constructed mainly of stone, brick, or concrete blocks that may or may not be joined with mortar.  A dam having only a masonry facing should not be referred to as a masonry dam.
9)  Weir - A dam in a river to stop and raise the water, for the purpose of conducting it to a mill, forming a fishpond, or the like.  When uncontrolled, the weir is termed a fixed-crest weir.  Other types of weirs include broad-crested, sharp-crested, drowned, and submerged.
Damage-Frequency Curve A graph showing the flood damages and their probabilities of occurrence.  The total area under the curve represents the annual damage.
Damages Prevented The difference between the amount of damages without a particular water project and the damages with the project in place.
Damp Slightly wet; somewhat moist or wet.
Dap (1) To dip lightly or quickly into water, as a bird does.  (2) To skip or bounce, especially over the surface of water.
Darcy's Law An empirically derived equation for the flow of fluids through porous media.  It is based on the assumption that flow is laminar and inertia can be neglected, and states that velocity of flow is directly proportional to Hydraulic Gradient.  For groundwater, this is equivalent to the velocity being equal to the product of the hydraulic gradient and the effective subsoil conductivity or permeability.  See Specific Discharge (Specific Flux).
Data In its strictest sense, data may be defined only as the raw numbers (or descriptions, in the case of qualitative data), either in Time-Series format (data covering observations over specific periods of time), Cross-Sectional format (data consisting of a number of observations taken at a specific point in time or about a specific event or phenomenon), or a combination of these two.  Also see Information.
Data Bank A well-defined collection of data, usually of the same general type, which can be accessed by a computer and may readily be used for further analysis, presentation, and forecasting.  Also referred to as a Data Base.
Data, Cross-Sectional -(Statistics) Data which describe the activities or behavior of individual persons, firms, or other units at a given point in time.
Data Management The act, process, or means by which data is managed.  This may include the compilation, storage, safe-guarding, listing, organization, extraction, retrieval, manipulation, and dissemination of data.  In its strictest sense, data may be defined only as the raw numbers for numeric or quantitative data (or descriptions, in the case of qualitative data), either in time-series format (data covering observations over specific periods of time), cross-sectional format (data consisting of a number of observations taken at a specific point in time or about a specific event or phenomenon without regard to its behavior over time), or a combination of these two.  Information, on the other hand, deals more specifically with the manipulation, re-organization, analysis, graphing, charting, and presentation of data for specific management and decision-making purposes.  Also see Information Management.
Data, Primary Typically, data acquired by direct interaction, such as direct observation through measurements, tabulation, or surveys.  Contrast with Secondary Data.
Data, Secondary Typically, data acquired from published sources as opposed to data acquired from direct observation or measurement such as a survey.  Contrast with Primary Data.
Data, Time-series (Statistics) Data which describe the movement of a variable over time, e.g., monthly, quarterly, annually.
Datum Any numerical or geometric quantity or set of such quantities that may serve as a reference or base for other, comparable quantities.  For example, Mean Sea Level (MSL) is the datum used on most topographic maps.  However, most river gages use an arbitrary elevation above the National Geodetic Vertical Datum (NGVD) of 1929 for use as a zero datum (e.g., datum equals 3412.6 feet above NGVD of 1929).  Datums are always chosen so there will never be negative stages.
Daylight In the restoration field, a verb that denotes the excavation and restoration of a stream channel from an underground culvert, covering, or pipe.
DDT (Dichlorodiphenyltrichloroethane) A colorless odorless water-insoluble crystalline insecticide C14H9Cl5 that tends to accumulate in ecosystems and has toxic effects on many vertebrates.  DDT was used extensively prior to 1972 at which time the U.S. Environmental Protection Agency (EPA) banned its production and distribution.  Although banned from usage for a number of years, the inert nature of such toxic chemicals and their low biodegradability (15-year half-life) allow them to exist in soils, river sediment, and plants and animals for many years.
Dead End The end of a water main which is not connected to other parts of the distribution system.
Deadman A log, block of concrete, rebar, or other object buried in a stream bank that is used to tie in a revetment with cable or chain.
Dead Storage (1) The volume of water in a reservoir stored below the lowest outlet or operating level.  (2) Storage in a reservoir that cannot be released by the dam.
Dead Time The time required for the response to a change of input to a system to reach the location of a sensor (i.e., the time for a control initiated surge wave to travel from an upstream control check gate to a downstream sensor in a canal.)
Dead Zone (Gulf of Mexico) (Ecology) A term referring to an extensive area, recorded to be as large as 7,000 square miles (July 1995), that develops every summer at the bottom of the Gulf of Mexico.  The area consists of a lifeless area devoid of oxygen that results from an ecological chain reaction precipitated by fertilizers, sewage, and runoff that flows from the Mississippi River.  While many sources contribute to this phenomenon, the primary nutrient cause consists of fertilizer runoff from agriculture within the Mississippi River Basin.
Debacle (1) The breaking up of ice in a river.  (2) A violent flood.
Debouch To emerge; issue, as a river into which a large stream debouches.
Debouchure An opening or mouth, as of a river or stream.
Debris Accumulated material; any material, including floating or submerged trash, suspended sediment, or bed load, moved by a flowing stream.
Debris Basins Storage for sediment and floating material provided by a dam with spillway above channel grade, by excavation below grade, or both.  Water retention is not an intended function of the structure.
Debris Dam A barrier built across a stream channel to retain rock, sand, gravel, silt, or other material.
Debris Flow (1) A moving mass of rock fragments, soil, and mud with more than one-half of the material being larger than sand size.  (2) A mass movement involving rapid flowage of debris of various kinds under various conditions; specifically, a high-density Mudflow containing abundant coarse-grained materials and resulting almost invariably from an unusually heavy rain.  (3) The rapid mass movement of a dense, viscous mixture of rock fragments, fine earth, water and entrapped air that almost always follows a heavy rain.  A mudflow is a debris flow that has predominately sand size or smaller particles.
Debris Guard A screen or grate at the intake of a channel, drainage, or pump structure for the purpose of stopping debris.
Decant To draw off the upper layer of liquid after the heaviest material (a solid or other liquid) has settled.
Decay The disintegration of organic materials into simpler forms, or into their original elements, by action of bacteria, fungi, or other microorganisms.
Dechlorinate To remove Chlorine from water.
Dechlorination The partial or complete reduction of residual chlorine in a liquid by any chemical or physical process.  Commonly used dechlorinating agents include activated carbon and sulfur dioxide.
Deciduous (Plant) (Botanical) (1) Any plant that sheds all of its leaves at one time each year (typically in autumn).  (2) Plants characterized by a specific growth and dormancy cycle, with certain parts falling at the end of the growing period, as leaves, fruits, etc., or after anthesis, as the petals of many flowers.  (2) Plants having leaves of this type.  As contrasted with Evergreen which remains verdant throughout the year.
Deciduous Stand A plant community where Deciduous trees or shrubs represent more than 50 percent of the total areal coverage of trees or shrubs.
Deciles (Drought Index) The deciles drought index system is based on a relative frequency distribution of long-term precipitation divided into tenths of the overall range of distribution.  Each tenth division or precipitation category is termed a "decile" and ranges from the lowest (drought) ten percentile of precipitation levels to the highest (wet) ten percentile.  By definition, the fifth decile is the median (middle-most) and is the precipitation amount not exceeded by 50 percent of the occurrences over the period of record.  One disadvantage of the deciles drought index system is that a long climatological record is required for accurate deciles classifications.  As a drought index, the deciles are grouped into five classifications as follows:
deciles 1-2 (lowest 20%) - much below normal
deciles 3-4 (next lowest 20%) - below normal
deciles 5-6 (middle 20%) - near normal
deciles 7-8 (next highest 20%) - above normal
deciles 9-10 (highest 20%) - much above normal
Also see Drought Indexes (Indices).
Declared Underground Water Basin An area of a state designated in some states by their respective State Engineers to be underlain by a ground water source having reasonably ascertainable boundaries.  By such a designation, the State Engineer assumes jurisdiction over the appropriation and use of ground water from the source.  May not be applicable in states which already claim regulatory rights over both surface and ground waters.
Decomposer Any of various organisms (as many bacteria and fungi) that feed on and break down organic substances (such as dead plants and animals).
Decomposition The breakdown of matter by bacteria and fungi, changing the chemical makeup and physical appearance of materials.
Decorative Water Feature Any manmade stream, fountain, waterfall, or other such water feature that contains water that flows or is sprayed into the air, constructed for decorative, scenic, or landscape purposes.
Decree The judgement of a court, an official order, or settlement.
Decree 731 (Interim Walker River Decree) (Nevada) In response to the suit filed in 1902 (Miller et Lux v. Rickey), subsequently renamed to the Pacific Livestock Company v. Antelope Valley Land and Cattle Company, water rights adjudication in the Federal District Court for Nevada resulted in the issuance
Decree C-125 (Final Walker River Decree) (Nevada) In adjudication of the 1924 filing of United States v. Walker River Irrigation District, et al., Decree C-125 for waters of the Walker River was issued on April 14, 1936 by the Federal District Court for Nevada.  In addition to recognizing the water right
Decreed Rights (Water) Water rights determined by court decree.
Dedicated Natural Flow River flows dedicated to environmental use.  Also see Environmental Flows.
Dedications (Water) A controversial water rights policy that involves a trade-off in which a user can begin pumping groundwater in exchange for a guarantee to buy and retire a like amount of surface water in the future.  Critics of the policy argue that dedications are often difficult to enforce and can lead to overuse of groundwater when a user fails to fulfill on the guarantee.
Deep Carbonate Aquifer (Nevada) An aquifer within the Great Basin which is comprised of a thick sequence of carbonate rock, generally lying below basin fill deposits.
Deep-Draft Harbor A harbor designed to accommodate commercial cargo vessels having drafts greater than 15 feet (4.6 meters).
Deep-Lava Theory (Geophysics and Climatology) A theory first espoused by a geophysicist from the University of Hawaii whose research found a strong Correlation between periodic patterns of undersea volcanoes (and related seismic activity) within what is known as the East
Deep Percolation (Loss) (1) Water that percolates below the lower limit of the Root Zone of plants into a ground water aquifer and cannot be used by plants.  (2) Percolation of (irrigation) water through the ground and beyond the lower limit of the root zone of plants into groundwater.
Deep Seepage (Losses) That portion of applied irrigation water that, in excess of the leaching requirement, passes through the rooting zone and is subsequently unavailable for crop use.
Deep-Water Of, relating to, or carried on in waters of a relatively great depth, for example, a deep-water port or a deep-water drilling for oil; Of, relating to, or characterized by water of considerable depth, especially water able to accommodate oceangoing vessels.
Deepwater Habitats (Ecology) In conjunction with Wetlands, Deepwater Habitats constitute the spectrum of an ecological classification system to better understand and describe the characteristics and values of all types of land and to wisely and effectively manage such ecosy
1)  Marine
2)  Estuarine
3)  Riverine
4)  Lacustrine
5)  Palustrine
The first four of these classifications include both wetland and deepwater habitats, but the Palustrine Wetlands System includes only wetland habitats.  Also see Wetlands and Wetlands, Palustrine.  (See Appendix D-2 for an explanation of the Wetland and Deepwater Habitat Classification System.)
Deep Well A well whose pumping head is too great to permit use of a suction pump.
Deep-Well Disposal Transfer of liquid wastewater to underground strata; usually limited to biologically or chemically stable wastes.
Deep-Well Injection Deposition of raw or treated, filtered hazardous waste by pumping it into deep wells, where it is contained in the pores of permeable subsurface rock.
Deflocculate To cause the particles of the disperse phase of a colloidal system to become suspended in the dispersion medium.
Deflocculating Agent A material added to a suspension to prevent settling.
Defluoridation (Water Quality) A process by which the level of fluoride in a water is reduced to prevent mottling of teeth or fluorosis in consumers.  Either activated alumina or bone charcoal is used in the process.
Defog To remove condensed water vapor from a surface.
Defrost (1) To remove ice or frost from.  (2) To cause to thaw.
Degasification A water treatment process that removes dissolved gases from the water.
Degradation (River Beds or Stream Channels) The general lowering of the streambed by erosive processes, such as scouring by flowing water.  The removal of channel bed materials and downcutting of natural stream channels.  Such erosion may initiate degradation of tributary channels, causing damage similar to that due to gully erosion and valley trenching.  Opposite of Aggradation.
Degrade The lowering of a stream-channel bed with time due to the erosion and transport of bed materials or the blockage of sediment sources.
Degree Day The difference, expressed in degrees, between the mean temperature for a given day and a reference temperature (usually 0?C).
Degree of Protection The amount of protection that a flood control measure is designed for, i.e., 100-year, as determined by engineering feasibility, economic criteria, and social, environmental, and other considerations.  Also see Level of Protection.
Dehumidify To remove atmospheric moisture from.
Dehydratase (Biochemistry) An Enzyme that catalyzes the removal of oxygen and hydrogen from organic compounds in the form of water.
Dehydrate (1) To remove bound water or hydrogen and oxygen from (a chemical compound) in the proportion in which they form water.  (2) To remove water from (as foods).  (3) To remove water from; make Anhydrous.  (4) To Lose water or moisture; become dry.
Dehydration (1) The process of removing water from a substance or compound.  (2) Excessive loss of water from the body or from an organ or a body part, as from illness or fluid deprivation.
Dehydrator (1) A substance, such as sulfuric acid, that removes water.  (2) A container or an engineered system designed to remove water from substances such as absorbents or food.
Deice To make or keep free of ice; melt ice from.
Deicer (1) A device used on an aircraft to keep the wings and propellers free from ice or to remove ice after it has formed.  (2) A compound, such as ethylene glycol, used to prevent the formation of ice, as on windshields.
Deionization The removal of all charged atoms or molecules from some material such as water.  For example, the removal of salt from water involves the removal of sodium ions (Na+) and chloride ions (Cl-).  The process commonly employs one resin that attracts all positive ions and another resin to capture all negative ions.  Also see Capacitive Deionization.
Deionize To remove ions from water by Ion Exchange.  See Deionization.
Deionized Water Water that has been passed through resins that remove all ions.  Also see Deionization.
Delay Time Duration of time for contamination or water to move from point of concern to the well; analogous to time-of-travel.
Delegated State A state (or other governmental entity such as a tribal government) that has received authority from the U.S. Environmental Protection Agency (EPA) to administer an environmental regulatory program in lieu of a federal counterpart.  As used in connection with National Pollutant Discharge Elimination System (NPDES), Underground Injection Control (UIC), and Public Water System (PWS) programs, the term does not connote any transfer of federal authority to a state.  Also see Primacy.
Delineation The process of deciding where something, for example, the boundaries of a Wetland, begins and ends.
Deliquesce (1) To melt away; to disappear as if by melting.  (2) (Chemistry) To dissolve and become liquid by absorbing moisture from the air.
Deliquescence The process whereby substances absorb water from the air, and eventually form solutions.
Delivery (Irrigation) (1) The release of water from turnouts to water users.  (2) The amount of irrigation water delivered to a water-user's headgate during the irrigation season.
Delivery Box An irrigation structure for diverting water from a canal to a farm unit, often including measuring devices.
Delivery Concept The mode of making deliveries with respect to time; types are rotation, scheduled, or demand deliver concepts.
Delivery Flexibility The flexibility that water users have in requesting delivery changes and the ability of the canal system to accommodate the request.
Delivery/Release The amount of water delivered to the point of use and the amount released after use; the difference between these amounts is usually the same as the Consumptive Use.
Delivery System A system which conveys water from a single source, such as a storage reservoir, to a number of individual points of use.  The delivery system is a common classification.  It is associated with irrigation, municipal and industrial use, and fish and wildlife canal systems.
Delta (1) An alluvial deposit made of rock particles (sediment and debris) dropped by a stream as it enters a body of water.  (2) A plain underlain by an assemblage of sediments that accumulate where a stream flows into a body of standing water where its velocity and transporting power are suddenly reduced.  (3) The low, nearly flat, alluvial tract of land deposited at or near the mouth of a river, commonly forming a triangular or fan-shaped plain of considerable area enclosed and crossed by many distributaries of the main river.  Originally so named because many deltas are roughly triangular in plan, like the Greek letter delta (?), with the apex pointing upstream.
Deluge (1) A great flood.  (2) A heavy downpour.
Demand (Water) (1) Maximum water use under a specified condition.  (2) The amount of water that a water-right owner calls for or requests in any one irrigation season.
Demand Delivery A method of irrigation water delivery whereby the project delivers water to the headgate upon farm irrigator demand; usually is associated with high head (cfs) delivery rates.  Unrestricted use of the available water supply with limitations only on maximum flow rate and total allotment.
Demand Management Alternatives Water management programs that reduce the demand for water, such as water conservation, drought rationing, rate incentive programs, public awareness and education, drought landscaping, etc.
Demersal (1) Dwelling at or near the bottom of a body of water, such as demersal fish.  (2) Sinking to or deposited near the bottom of a body of water, such as demersal fish eggs.
Demineralization, also Demineralize The act or treatment process that removes dissolved minerals or mineral salts from a liquid, such as water.
Demineralized Water Water which has been passed through a mixed-bed ion exchanger to remove soluble ionic impurities.  Nonelectrolytes and Colloids are not removed from water so treated.  Also referred to as Deionized Water.
De Minimis Derived from the Latin meaning that the law does not care for or take notice of very small or trifling matters.  De minimis water uses are those deemed by law to be too insignificant to notice.
Demographics Relating to the statistical study of human populations to include such characteristics and factors as population counts, births, deaths, migration, sex, age, and related statistics.
Demography The statistical science dealing with the distribution, density, vital statistics, and other related characteristics of population.  Demographics is the adjective describing the various characteristics of a population.
Dendritic (1) A drainage pattern in which tributaries branch irregularly in all directions from and at almost any angle to a larger stream.  (2) A tree-like pattern, typical of most drainage networks.  From an aerial view, it resembles the branching pattern of trees.
Dendrochronology (1) Dating an object by means of tree rings.  (2) The technique of dating events, determining climatic conditions, growth patterns, etc. through the use of tree rings.  Also see Dendrohydrological Reconstruction.
Dendrohydrological Reconstruction Tree-ring reconstructions of streamflow can be highly useful in augmenting existing instrumental streamflow data.  Trees are natural recorders of climatological changes and have proven to be useful for extending the records of climate and streamflow back hundreds of years.  Tree growth is relatively sensitive to a variety of climatic and non-climatic factors which are integrated into the growth patterns associated with annual tree ring widths.  In this manner, tree rings can be effective proxies for streamflow, because trees in selected locations typically respond to a set of climate-related factors, including precipitation and evapotranspiration, that also influence streamflow changes.  In particular, trees growing in the semi-arid western United States depend on winter precipitation to recharge soil moisture, and thus are useful for reconstructing annual streamflow records.
Denitrification The removal of nitrate ions (NO3-) from soil or water; involves the Anaerobic biological reduction of nitrate to nitrogen gas.  The process reduces desirable fertility of an agricultural field or the extent of undesirable aquatic weed production in aquatic environments.  Also see Denitrifying Bacteria.
Denitrifying Bacteria Bacteria in soil or water that are capable of anaerobic respiration, using the nitrate ion as a substitute for molecular oxygen during their metabolism.  The nitrate is reduced to nitrogen gas (N2), which is lost to the atmosphere during the process.
Denizen (Ecology) An animal or a plant naturalized in a region.
Density (1) Matter measured as mass per unit volume expressed in pounds per gallon (lb/gal), pounds per cubic foot (lb/ft3), and kilograms per cubic meter (kg/m3).  The mass of quantity of a substance per unit volume.  (2) (Biology) The number per unit area of individuals of any given species at any given time.  A term used synonymously with Population Density.
Density Current (1) A flow of water maintained by gravity through a large body of water, such as a reservoir or lake, which retains its identity because of a difference in density.  (2) Submerged gravity-driven flows which occur when inflows to a water body are denser than the ambient water.  The inflow subsequently plunges and continues as a distinct flow which can be envisioned as a submerged stream.  Density currents, also called Underflows, are known to form intermittently on coastal continental shelves, in reservoirs and at effluent discharge sites.
Density Stratification The arrangement of water masses into separate, distinct horizontal layers as a result of differences in density.  Such differences may be caused by differences in temperature or dissolved and suspended solids.  Also see Thermal Stratification.
Deoxygenate To remove dissolved oxygen from a liquid, such as water.
Department of Conservation And Natural Resources (Nevada) The mission of the Department is to conserve, protect, manage, and enhance the Nevada's natural resources in order to provide the highest quality of life for Nevada's citizens and visitors.  The Department consists of nine divisions and/or agencies which include:
1)  Division of Conservation Districts - Regulates the activities of the state's locally elected conservation districts which work for the conservation and proper development of the state's renewable natural resources by providing services to individual landowners and coordination with other public and private agencies.
2)  Division of Environmental Protection (DEP) - Responsible for the administration and enforcement of all environmental statutes and regulations; issues permits, monitors for air and water pollution and inspects solid and hazardous waste management.  The Division consists of the Bureau of Air Quality, the Bureau of Water Pollution Control, Bureau of Mining Regulation and Reclamation, Bureau of Water Quality Planning, Bureau of Corrective Actions, Bureau of Waste Management, and the Bureau of Federal Facilities.  The State Environmental Commission is also part of the Division and is responsible for adopting necessary environmental rules, regulations and plans authorized by statute.  (See Appendix E-4 for a more complete description of DEP's functional responsibilities.)
3)  Division of Forestry - Manages and coordinates all forestry, nursery, endangered plant species and watershed resource activities on certain public and private lands; responsible for protecting structural and natural resources through fire protection, prevention and suppression.  The Division also conducts the Forestry Conservation Camps Program which coordinates and supervises the outside work performed by inmates residing in Department of Prison conservation camps.
4)  Division of State Lands - Acquires, holds, and disposes of all state lands and interests in lands; provides technical land-use planning assistance, training, and information to local units of government or other agencies; develops policies and plans for the use of lands under federal management and represents the state in its dealings with the federal land management agencies.
5)  Division of State Parks - Plans, develops, and maintains a system of parks and recreational areas for the use and enjoyment of residents and visitors.  The Division also preserves areas of scenic, historic, and scientific significance in Nevada.
6)  Division of Water Planning - Provides technical, financial and economic assistance to government agencies and individual citizens concerning regional and local water supplies; develops and implements a statewide water resource management plan and policy initiatives on a watershed basis; conducts hydrologic, climatologic, and socioeconomic data collection, research, modeling, forecasting and data analysis; develops and implements water resource public information and education programs; provides technical and financial assistance and outreach programs to assist local governments, watershed planning groups, and other agencies with respect to water resource matters; and develops and implements a statewide water conservation program.
7)  Division of Water Resources - Responsible for protecting the health and safety of Nevada citizens through the appropriation of public waters.  Other responsibilities include the adjudication of claims of vested water rights; distribution of water in accordance with court decrees; review of water availability for new major construction and housing projects; review of the construction and operation of dams; appropriation of geothermal resources; licensing of well drillers and water right surveyors; review of flood control projects; maintenance of water resource data and records; and providing technical assistance to government boards, offices, and agencies.
8)  Division of Wildlife - Preserves, protects, manages and restores wildlife and its habitat within the state for aesthetic, scientific, recreational and economic benefits; tasked with promoting safety for persons and property in the operation of equipment and boating vessels
9)  Natural Heritage Program - Serves as a centralized repository containing detailed information on sensitive (threatened and endangered) species of animals, plants, and communities; provides information on biology, habitats, locations, population and conservation status, and management needs.
(United States) Department of the Interior (USDI) Originally established by Congress in 1849 as the executive department of the United States government, the USDI's function has changed from that of performing housekeeping duties for the federal government to its present role as custodian of the nation's
Department of Water Resources (DWR) (California) The California state agency within The Resources Agency that is responsible for long-term water planning, operation of the State Water Project, and state water conservation programs.  The basic goal of the DWR is to ensure that California's needs for wate
Depauperate (Biology) An area poor in species quantities and/or diversity; an aquatic sample showing few life forms.  Impoverished habitat.
Dependable Supply (1) That water which can be expected to be available at a time and place with the quality demanded; sometimes the amount of water available is at a stated percentage of time.  (2) The average annual quantity of water that can be delivered during a drought period.
Dependable Yield The maximum annual supply of a given water development that is expected to be available on demand, with the understanding that lower yields will occur in accordance with a predetermined schedule or probability.  More frequently referred to as Firm Yield.
Depletion (1) The water consumed within a service area or no longer available as a source of supply; that part of a withdrawal that has been evaporated, transpired, incorporated into crops or products, consumed by man or livestock, or otherwise removed.  (2) Net ra
Depletion (Ground Water) The withdrawal of water from a ground water source at a rate greater than its rate of recharge, usually over an extended period of several years.
Depletion (Streamflow) The amount of water that flows into a valley, or onto a particular land area, minus the water that flows out of the valley or off from the particular land area.
Depletion (Water) That portion of the water supply that is consumptively used.
Depletion Curve (Hydraulics) A graphical representation of water depletion from storage-stream channels, surface soil, and groundwater.  A depletion curve can be drawn for base flow, direct runoff, or total flow.
Deposit Something dropped or left behind by moving water, as sand or mud.
Depositing Substrates Bottom areas where solids are being actively deposited; often occurring in the vicinity of effluent discharges.
Deposition The accumulation of material dropped because of a slackening movement of the transporting medium, e.g., water or wind.  Also, the transition of a substance from the vapor phase directly to the solid phase, without passing through an intermediate liquid phase, also referred to as Sublimation.
Depression Storage (1) Water contained in natural depressions in the land surface, such as puddles.  (2) Water that is temporarily detained on the surface of the earth in puddles and cavities that have little or no surface outlet.
Depth, often Depths A deep art of place, as the ocean depths.
Depth-Area-Duration Analysis Determination of the maximum amounts of precipitation within various durations over areas of various sizes; used to predict flood events.
Depth Finder An instrument used to measure the depth of water, especially by radar or ultrasound.
Depth of Runoff The total runoff from a drainage basin divided by its area.  For convenience in comparing runoff with precipitation, depth of runoff is usually expressed in inches during a given period of time over the drainage area expressed in inches per square mile.
Depth Sounder An ultrasonic instrument used to measure the depth of water under a ship.
Depuration A process during which an organism, such as an oyster or clam, eliminates dangerous chemicals or microorganisms when placed in uncontaminated water.
Derelict (Legal) Land left dry by a permanent recession of the water line.
Dereliction (Legal) (1) A gaining of land by the permanent recession of the water line.  (2) The land so gained.  Also see Reliction and Doctrine of Reliction.
Desalination, or Desalinization (1) To remove salts and other chemicals, as from sea water or soil, for example.  Usually used with respect to the salt contained in water.  (2) Specific treatment processes to demineralize sea water or brackish (saline) water for reuse.  Also referred to as Desalting.
Desalinize See Desalination or Desalinization.
Desalting A term used to refer to any process by which the dissolved solids content of saline water or seawater is reduced.  Also known as Desalination, Desalinization, or Saline Water Conversion.
De-Seasonalization (Statistics) A process which removes the seasonal effects from time series data.  One way to determine if a de-seasonalization transformation of the data is necessary is to examine the autocorrelations.  If, for monthly data, the twelfth autocorrelation is abnormally high, or for quarterly data, the fourth autocorrelation abnormally high, then the data is seasonal in nature and requires de-seasonalization before attempting to fit a model to its behavior.  More frequently referred to as Seasonal Adjustment (S.A.).  Also see Seasonal Adjustment, Seasonal Adjustment Factors, Seasonal Factors, and Seasonality.
Desert A barren or desolate area, especially one characterized by dry, often sandy conditions of little rainfall, typically less than 10 inches of rain per year, extreme temperatures, and sparse vegetation.  Also see Biome.
Desert Pavement Surfaces of tightly packed gravel that armor, as well as rest on, a thin layer of silt, presumably formed by weathering of the gravel.  They have not experienced fluvial sedimentation for a long time, as shown by the thick varnish coating the pebbles, the pronounced weathering beneath the silt layer, and the striking smoothness of the surface, caused by obliteration of the original relief by downwashing into depressions.
Desert Stream Valley The valley of a perennial stream that is fed from mountain sources and is erosionally-cut through several desertic Semi-Bolsons.
Desert Varnish A dark coating (from 2 to 500 microns thick) that forms on rocks at and near the Earth's surface as a result of mineral precipitation and Eolian influx.  The chemical composition of rock varnish typically is dominated by clay minerals and iron and/or manganese oxides and hydroxides, forming red and black varnishes, respectively.  With time the thickness or the coating increases if abrasion and burial of the rock surface do not occur.  As a result, Clastic sediments on alluvial fan surfaces that have been abandoned for long periods of time have much darker and thicker coatings of varnish than do younger deposits.
Desertification The transformation of arable or habitable land to desert, as by a change in climate or destructive land use.  The term is generally applied to the production of artificial deserts where people have intensified the problems caused by droughts through overgrazing marginal land, repeated burning of natural vegetation, intensive farming of arid land, aggressive removal of trees, and prolonged irrigation of arid land for agricultural use.
Desert Research Institute (DRI) (Nevada) The Desert Research Institute was created in 1959 by an act of the Nevada Legislature as a unit of the University of Nevada.  When the University of Nevada System was formed in 1968, DRI became an autonomous, nonprofit division of this system.  Since that
1)  Atmospheric Sciences Center (ASC) - The ASC is a nationally recognized leader in the field of atmospheric sciences.  The ASC's mission is to improve the fundamental understanding of the earth's atmosphere, particularly as it relates to the weather and to the climate of arid regions.  The ASC is the home of the strongest atmospheric modification research program in the United States.
2)  Biological Sciences Center (BSC) - The BSC focuses on plant and soil biology from an ecological perspective.  The BSC's mission is to improve the fundamental understanding of the earth's biosphere, thereby providing the knowledge needed to effectively manage biological resources important to the future use and habitation of the earth.
3)  Energy and Environmental Engineering Center (EEEC) - The EEEC largely conducts air resources research.  The EEEC's mission is to conduct high-quality research to understand current and future human impacts on the environment, especially air quality, an the technology that can be applied to mitigate these impacts.
4)  Quaternary Sciences Center (QSC) - The QSC is one of approximately 15 Quaternary research programs worldwide.  The QSC's mission is to improve the fundamental understanding of past climates and associated environmental responses and human adaptations to climate change during the Quaternary Period (covering the last 1.8 million years).
5)  Water Resources Center (WRC) - The WRC is the largest water research group focused on arid lands in the United States.  The WRC's mission to improve the fundamental understanding and knowledge of hydrologic systems, with special emphasis on arid lands, for more effective management of hydrologic resources.
(See Appendix E-3 for a more complete listing of the DRI's major laboratories operated and the principal skills and activities supported.)
Desert National Wildlife Refuge (NWR) (Nevada) One of the nine National Wildlife Refuges (NWR) located in the State of Nevada, the Desert NWR was established in 1936 and covers 1,588,459 acres (2,482 square miles) of the diverse Mohave Desert in southern Nevada and is the largest National Wildlife Ref
Desiccant A substance, such as calcium oxide or silica gel, that has a high affinity for water and is used as a drying agent.
Desiccate (1) To dry out thoroughly.  (2) To preserve (foods) by removing moisture.
Desiccation (1) Loss of water from pore spaces of sediments through compaction or through evaporation caused by exposure to air.  (2) (Geology) Used to refer to a long period of time between Pluvial (wet) episodes.
Desiccation Cracks Surface fractures that can result from the drying of soil or porous sedimentary rock.
Design Capacity (1) Volume of water that a channel, pipe, or other drainage line is designated to convey.  (2) The average daily flow that a water or wastewater treatment plant or other facility is designed to accommodate.
Design Flood (1) Commonly used to mean the magnitude of flood used for design and operation of flood control structures or other protective measures.  It is sometimes used to denote the magnitude of flood used in floodplain regulations.  (2) The flood magnitude selected for use as a criterion in designing flood control works.  The largest flood that a given project is designed to pass safely.  In dam design and construction, the reservoir inflow-outflow hydrograph used to estimate the spillway discharge capacity requirements and corresponding maximum surcharge elevation in the reservoir.
Design Flow The average flow of wastewater that a treatment facility is built to process efficiently, commonly expressed in millions of gallons per day (MGD).
Design Runoff Rate In irrigation, the maximum runoff rate expected over a given period of time.
Designated Floodway The channel of a stream and the portion of the adjoining floodplain designated by a regulatory agency to be kept free of further development to provide for unobstructed passage of flood flows.
Designated Groundwater Basin A basin where permitted ground water rights approach or exceed the estimated average annual recharge and the water resources are being depleted or require additional administration.  Under such conditions, a state's water officials will so designate a groundwater basin and, in the interest of public welfare, declare Preferred Uses (e.g., municipal and industrial, domestic, agriculture, etc.).  Also referred to as Administered Groundwater Basin.
Designated Groundwater Basin (Nevada) In the interest of public welfare, the Nevada State Engineer, Division of Water Resources, Department of Conservation and Natural Resources, is authorized by statute (Nevada Revised Statute 534.120) and directed to designate a ground water basin and declare Preferred Uses within such designated basin.  The State Engineer has additional authority in the administration of the water resources within a designated ground water basin. (A listing of Nevada's Hydrographic Regions, and designated Areas and Sub-Areas is presented in Appendix A-1 (hydrographic regions, areas and sub-areas), Appendix A-2 (listed sequentially by area number) Appendix A-3 (listed alphabetically by area name), and Appendix A-4 (listed alphabetically by principal Nevada county(ies) in which located).)
Designated Uses Those water uses identified in state water quality standards that must be achieved and maintained as required under the Clean Water Act (CWA).  Such uses may include cold water fisheries, public water supply, irrigation, recreation, minimum stream flows, etc.
Designated Watersheds Watershed areas that have been set aside as sources of municipal water or other similar purposes would be included in this category.  Other uses are either modified or excluded.
Designer Bugs A popular term for Microbes developed through Biotechnology that can degrade specific toxic chemicals at their source in toxic waste dumps, in ground water, or on the land surface.  May also be useful in cleaning (decomposing) oil spills.
Desilting Area An area of grass, shrubs, or other vegetation used for inducing the deposition of silt and other debris from flowing water.  Typically located above a stock tank, pond, field, or other area needing protection from sediment accumulation.
Desorption The removal of a substance adsorbed to the surface of an adsorbent.  Also see Sorption, which is the reverse process.
Destratification Vertical mixing within a lake or reservoir to totally or partially eliminate separate layers of temperature, plant, or animal life.
Detachment The removal of transportable fragments of soil material from a soil mass by an eroding agent, usually falling raindrops, running water, or wind.  Through this process, soil particles or aggregates are made ready for transport, the first stage in soil erosion.
Detectable Leak Rate The smallest leak (from a storage tank), expressed in terms of gallons or liters per hour, that a test can reliably discern with a certain probability of detection or false alarm.
Detection Criterion A predetermined rule to ascertain whether a tank is leaking or not.  Most volumetric tests use a threshold value as the detection criterion.  Also see Volumetric Tank Tests.
Detection Monitoring Program Groundwater monitoring at the boundary of a treatment, storage, or disposal facility (the point of compliance) to detect any contamination caused by leaks from the hazardous waste at the facility.  The materials for which the samples must be analyzed (the indicator parameters/constituents) are specified in the facility permit.
Detention Dam A dam constructed for the purpose of temporary storage of streamflow or surface runoff and for releasing the stored water at controlled rates.
Detention Basin A relatively small storage lagoon for slowing stormwater runoff, generally filled with water for only a short period of time after a heavy rainfall.  Also see Retention Basin.
Detention Facility A surface water runoff storage facility that is normally dry but is designed to hold (detain) surface water temporarily during and immediately after a runoff event.  Examples of detentional facilities are: natural swales provided with crosswise earthen berms to serve as control structures, constructed or natural surface depressions, subsurface tanks or reservoirs, rooftop storage, and infiltration or filtration basins.  Also see Retention Facility.
Detention Storage (1) The volume of water, other than Depression Storage, existing on the land surface as flowing water which has not yet reached the channel.  (2) Water temporarily detained in the non-capillary pores of the soil, free to move by gravity, which it generally does within about 24 hours of the event that filled the pores.
Detention Structure (Dam) A structure constructed for the temporary storage of floodflows where the opening for release is of a fixed capacity and not manually operated.
Detention Time (1) The theoretical calculated time required for a small amount of water to pass through a tank at a given rate of flow.  (2) The actual time that a small amount of water is in a settling basin, flocculating basin, or rapid-mix chamber.  (3) In storage reservoirs, the length of time water will be held before being used.
Detergent Synthetic washing agent that helps to remove dirt and oil.  Some contain compounds which kill useful bacteria and encourage algae growth when they are in wastewater that reaches receiving waters.
Deterministic Process (Statistics) An analytical and forecasting technique which assumes that the future can be predicted exactly from its past.  Consequently, it is assumed that the data series to be forecasted contains all the information necessary to predict its future beha
Detrital (Geology) Clastic; rock and minerals occurring in sedimentary rocks that were derived from pre-existing igneous, sedimentary, or metamorphic rocks.
Detritus (1) The heavier mineral debris moved by natural water courses, usually in the form of Bed Load.  (2) The sand, grit, and other coarse material removed by differential sedimentation in a relatively short period of detention.  (3) Bits of vegetation, animal remains, and other organic material that form the base of food chains in wetlands and many other kinds of habitats.
Deuterium Oxide An isotopic form of water with composition D2O, isolated for use as a moderator in certain nuclear reactors.  Also referred to as Heavy Water.  Also see Heavy Water Moderated Reactor and Light Water Reactor (LWR).
Developed Water Water that is controlled and managed (damned, pumped, diverted, stored in reservoirs or channeled in aqueducts) from rivers or otherwise developed for a variety of uses.
Deviation, Standard (Statistics) A measure of the average variation of a series of observations or items of a population about their mean.  In a normally distributed set of observations the interval of the mean plus or minus one standard deviation includes about two-thirds of the observations.
Dew The droplets of water condensed from air, usually at night, onto cool surfaces.
Dew Point (1) The temperature at which a gas or vapor condenses to form a liquid; the point at which dew begins to form.  (2) The temperature to which the air must be cooled in order to reach 100 percent relative humidity, or saturation.
Dewater, and Dewatering (1) To remove water from a waste produce or streambed, for example.  (2) The extraction of a portion of the water present in sludge or slurry, producing a dewatered product which is easier to handle.  (3) (Mining) The removal of ground water in conjunctio
Diadromous Relating to a fish  that migrates between salt and fresh waters.
Diameter at Breast Height (DBH) A measure of tree diameter determined at the standard height of 4.5 feet (1.4 meters) from the ground.
Diastrophic (Geology) Pertaining to processes by which the earth's crust is deformed, producing continents, oceans, basins, mountains, and other Geophysical features.  Also see Orogenic and Tectonic.
Diatom Any of the microscopic unicellular or colonial algae constituting the class Bacillarieae.  They have a silicified cell wall, which persists as a skeleton after death and forms kieselguhr (loose or porous diatomite).  Diatoms occur abundantly in fresh and salt waters, in soil, and as fossils.  They form a large part of the Plankton.
Diatoma A small genus of fresh-water diatoms typifying the family Diatomaceae.  They sometimes cause aromatic or disagreeable odors in water.
Diatomaceous Earth A yellow, white or light-gray material composed of the siliceous shells of Diatoms (fossilized diatoms) and used in water filtration to filter out solid waste in wastewater treatment plants; also used as an active ingredient in some powdered pesticides.  Also referred to as Diatomite.
Diatomite See Diatomaceous Earth.
Diel Of or pertaining to a 24-hour period of time; a regular daily cycle.
Diffluence A lateral branching or flowing apart of a glacier in its Ablation area.  This separation may result from the glacier's spilling over a preglacial divide or through a gap made by basal sapping of a Cirque wall, or from down-valley blocking at the junction of a tributary glacier.  Can be used to describe similar processes in water flow.
Diffused Air (Water Quality) A type of aeration that forces oxygen into sewage by pumping air through perforated pipes inside a holding tank.
Diffusion The movement of a substance from an area of high concentration to an area of low concentration.  Turbulent diffusion results from atmospheric motions diffusing water, vapor, heat, and other gaseous components by exchanging parcels called eddies between regions in space in apparent random fashion.
Diffusion Coefficient (1) The rate at which solutes are transported at the microscopic level due to variations in the solute concentrations within the fluid phases.  (2) The rate of dispersion of a chemical caused by the kinetic activity of the ionic or molecular constituents.  Also referred to as the Coefficient of Molecular Diffusion.  See Molecular Diffusion.
Diffusivity, Soil Water The hydraulic conductivity divided by the differential water capacity, or the flux of water per unit gradient of moisture content in the absence of other force fields.
Digester (Water Quality) In a Wastewater Treatment Plant, a closed tank that decreases the volume of solids and stabilizes raw sludge by bacterial action.
Digester Gas The gas produced as a result of the microbial decomposition of particulate organic matter under Anaerobic conditions.  Methane and hydrogen are major components.
Digestion (General) The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants.  (Water Quality) In wastewater treatment, the biological decomposition of organic matter in sludge.
Dike (1) (Engineering) An embankment to confine or control water, especially one built along the banks of a river to prevent overflow of lowlands; a levee.  (2) A low wall that can act as a barrier to prevent a spill from spreading.  (3) (groin, spur, jetty, deflector, boom) A structure designed to: (a) reduced water velocity as stream flow passes through the dike so that sediment deposition occurs instead of erosion (permeable dike), or (b) deflect erosive currents away from the stream bank (impermeable dike).  (4) (Geology) A tabular body of igneous (formed by volcanic action) rock that cuts across the structure of adjacent rocks or cuts massive rocks.
Diligence A persistent effort in the completion of a specific task, such as the construction of a water diversion project and putting water to beneficial use.
Diluent A substance used to dilute a solution or suspension.
Dilute To make thinner or less concentrated by adding a liquid such as water.
Dilution The reduction of the concentration of a substance in air or water.
Dilution Factor The extent to which the concentration of some solution or suspension has been lowered through the addition of a Diluent.
Dilution Ratio (Water Quality) The ratio of the volume of water in a stream to the volume of incoming waste.  The capacity of a stream to assimilate waste is reflected in the dilution ratio.
Diluvial, also Diluvian Of, relating to, or produced by a flood.
Dimictic Lake (or Reservoir) A stratified lake or reservoir that experiences two periods of full mixing or (Fall and Spring) Overturns annually.  The water in lakes layer in response to differences in the temperatures of surface and deep waters.  The surface water will be warmer because of radiant heating by the sun, and the bottom water will be cooler and therefore denser.  The waters in these two layers (termed the Epilimnion on the surface and Hypolimnion on the bottom) are separated by a boundary referred to as the Thermocline.  This layering is disrupted in response to variation in air temperature associated with changes in the seasons of the year.  As the epilimnion cools, it sinks, mixing th