acre-foot (af) a quantity or volume of water covering one acre to a depth of one foot; equal to 43,560 cubic feet or 325,851 gallons.

active storage capacity the total usable reservoir capacity available for seasonal or cyclic water storage. It is gross reservoir capacity minus inactive storage capacity.

afterbay a reservoir that regulates fluctuating discharges from a hydroelectric power plant or a pumping plant.

agricultural drainage (1) the process of directing excess water away from root zones by natural or artificial means, such as by using a system of pipes and drains placed below ground surface level; also called subsurface drainage; (2) the water drained away from irrigated farmland.

alluvium a stratified bed of sand, gravel, silt, and clay deposited by flowing water.

anadromous pertaining to fish that spend a part of their life cycle in the sea and return to freshwater streams to spawn.

angler-day the time spent fishing by one person for any part of a day.

applied water demand the quantity of water delivered to the intake of a city's water system or factory, the farm headgate, or a marsh or other wetland, either directly or by incidental drainage flows (this is primarily water for wildlife areas). For instream use, it is the portion of the stream flow dedicated to instream use or reserved under the federal or State Wild and Scenic Rivers acts.

aquatic algae microscopic plants that grow in sunlit water containing phosphates, nitrates, and other nutrients. Algae, like all aquatic plants, add oxygen to the water and are important in the fish food chain.

aquifer a geologic formation that stores and transmits water and yields significant quantities of water to wells and springs.

arid a term describing a climate or region in which precipitation is so deficient in quantity or occurs so infrequently that intensive agricultural production is not possible without irrigation.

artificial recharge addition of surface water to a ground water reservoir by human activity, such as putting surface water into spreading basins. See also ground water recharge, recharge basin.

average annual runoff for a specified area is the average value of annual runoff amounts calculated for a selected period of record that represents average hydrologic conditions.

average year water demand demand for water under average hydrologic conditions for a defined level of development.

average year supply the average annual supply of a water development system over a long period. For this report, the State Water Project and Central Valley Project average year supply is the average annual delivery capability of the projects over a 70-year study period (1922-91). For a local project without long-term data available, it is the annual average deliveries of the project during the 1984-1986 period. For dedicated natural flow, it is the long-term average natural flow for wild and scenic rivers or it is environmental flows as required for an average year under specific agreements, water rights, court decisions, and congressional directives.

benthic invertebrates aquatic animals without backbones that dwell on or in the bottom sediments of fresh or salt water. Examples: clams, crayfish, and a wide variety of worms.

best management practice (BMP) an urban water conservation measure that the California Urban Water Conservation Coalition agrees to implement among member agencies.

biota all living organisms of a region, as in a stream or other body of water.

brackish water water containing dissolved minerals in amounts that exceed normally acceptable standards for municipal, domestic, and irrigation uses. Considerably less saline than sea water.

bromide a salt which naturally occurs in small quantities in sea water; a compound of bromine.

chaparral a major vegetation type in California characterized by dense evergreen shrubs with thick, hardened leaves.

closed basin a basin whose topography prevents surface outflow of water. It is considered to be hydrologically closed if neither surface nor underground outflow of water can occur.

confined aquifer a water-bearing subsurface stratum that is bounded above and below by formations of impermeable, or relatively impermeable, soil or rock.

conjunctive use the operation of a ground water basin in combination with a surface water storage and conveyance system. Water is stored in the ground water basin for later use by intentionally recharging the basin during years of above-average water supply.

Decision 1485 operating criteria standards for operating water project facilities under Water Right Decision 1485 regarding the Sacramento-San Joaquin Delta and Suisun Marsh, adopted by the State Water Resources Control Board, August 1978.

dedicated natural flow river flows dedicated to environmental use.

deep percolation the percolation of water through the ground and beyond the lower limit of the root zone of plants into a ground water aquifer.

demand management alternatives water management programs-such as water conservation, drought rationing, or rate incentive programs-that reduce demand for water.

dependable supply the annual average quantity of water that can be delivered during a drought period.

depletion the water consumed within a service area and no longer available as a source of supply. For agriculture and wetlands, it is ETAW (and ET of flooded wetlands) plus irrecoverable losses. For urban water use, it is ETAW (water applied to landscaping or home gardens), sewage effluent that flows to a salt sink, and incidental ET losses. For instream use, it is the amount of dedicated flow that proceeds to a salt sink and is not available for reuse.

desalination a process that converts sea water or brackish water to fresh water or an otherwise more usable condition through removal of dissolved solids; also called desalting.

detailed analysis unit (DAU) the smallest study area used by Department of Water Resources for analyses of water demand and supply. Generally defined by hydrologic features or boundaries of organized water service agencies. In the major agricultural areas, a DAU typically includes 100,000 to 300,000 acres.

discount rate the interest rate used in evaluating water (and other) projects to calculate the present value of future benefits and future costs or to convert benefits and costs to a common time basis.

dissolved organic compounds carbon substances dissolved in water.

dissolved oxygen (DO) the oxygen dissolved in water, usually expressed in milligrams per liter, parts per million, or percent of saturation.

distribution uniformity (DU) the ratio of the average low-quarter depth of irrigation to the average depth of irrigation, for the entire farm field, expressed as a percent.

double cropping the practice of producing two or more crops consecutively on the same parcel of land during a 12-month period. Also called multi-cropping.

drainage basin the area of land from which water drains into a river; for example, the Sacramento River Basin, in which all land area drains into the Sacramento River. Also called, "catchment area," "watershed," or "river basin."

drought condition hydrologic conditions during a defined drought period during which rainfall and runoff are much less than average.

drought year supply the average annual supply of a water development system during a defined drought period. For this report, the drought period is the average of water years 1990 and 1991. For dedicated natural flow, it is the average of water years 1990 and 1991 for wild and scenic rivers, or it is environmental flows as required under specific agreements, water rights, court decisions, and congressional directives.

ecology the study of the interrelationships of living organisms to one another and to their surroundings.

economic demand the consumer's willingness and ability to purchase some quantity of a commodity based on the price of that commodity.

ecosystem recognizable, relatively homogeneous units, including the organisms they contain, their environment, and all the interactions among them.

efficient water management practice (EWMP) an agricultural water conservation measure that water suppliers can implement. EWMPs are organized into three categories: Irrigation Management Services; Physical and Structural Improvements; and Institutional Adjustments.

effluent waste water or other liquid, partially or completely treated or in its natural state, flowing from a treatment plant.

entrapment zone the portion of the Sacramento-San Joaquin Bay/Delta estuary where seaward-flowing fresh water overlays more dense, saline ocean water resulting in a two-layer mixing zone characterized by flocculation, aggregation, and accumulation of suspended materials from upstream.

environment the sum of all external influences and conditions affecting the life and development of an organism or ecological community; the total social and cultural conditions.

environmental water the water for wetlands, for the instream flow in a major river, or for a designated wild and scenic river (based on unimpaired flow).

estuary the lower course of a river entering the sea influenced by tidal action where the tide meets the river current.

evapotranspiration (ET) the quantity of water transpired (given off), retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively, it is usually expressed in terms of depth of water per unit area during a specified period of time.

evapotranspiration of applied water (ETAW) the portion of the total evapotranspiration which is provided by irrigation.

firm 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. See also dependable supply, project yield.

forebay a reservoir or pond situated at the intake of a pumping plant or power plant to stabilize water levels; also a storage basin for regulating water for percolation into ground water basins.

fry a recently hatched fish.

gray water waste water from a household or small commercial establishment. Graywater does not include water from a toilet, kitchen sink, dishwasher, washing machine, or water used for washing diapers, etc.

gross reservoir capacity the total storage capacity available in a reservoir for all purposes, from the streambed to the normal maximum operating level. Includes dead (or inactive) storage, but excludes surcharge (water temporarily stored above the elevation of the top of the spillway).

ground water water that occurs beneath the land surface and completely fills all pore spaces of the alluvium, soil, or rock formation in which it is situated.

ground water basin a ground water reservoir, defined by an overlying land surface and the underlying aquifers that contain water stored in the reservoir. In some cases, the boundaries of successively deeper aquifers may differ and make it difficult to define the limits of the basin.

ground water overdraft the condition of a ground water basin in which the amount of water withdrawn by pumping exceeds the amount of water that recharges the basin over a period of years during which water supply conditions approximate average.

ground water prime supply the long-term average annual percolation into the major ground water basins from precipitation falling on the land and from flows in rivers and streams.

ground water recharge increases in ground water storage by natural conditions or by human activity. See also artificial recharge.

ground water storage capacity the space or voids contained in a given volume of soil and rock deposits.

ground water table the upper surface of the zone of saturation, except where the surface is formed by an impermeable body.

hardpan a layer of nearly impermeable soil beneath a more permeable soil, formed by natural chemical cementing of the soil particles.

head ditch the water supply ditch at the head end of an irrigated field.

hydraulic barrier a barrier developed in the estuary by release of fresh water from upstream reservoirs to prevent intrusion of sea water into the body of fresh water.

hydrologic balance an accounting of all water inflow to, water outflow from, and changes in water storage within a hydrologic unit over a specified period of time.

hydrologic basin the complete drainage area upstream from a given point on a stream.

hydrologic region a study area, consisting of one or more planning subareas.

instream use use of water that does not require diversion from its natural watercourse. For example, the use of water for navigation, recreation, fish and wildlife, aesthetics, and scenic enjoyment.

irrecoverable losses the water lost to a salt sink or lost by evaporation or evapotranspiration from a conveyance facility, drainage canal, or in fringe areas.

irrigated acreage land area that is irrigated, which is equivalent to total irrigated crop acreage minus the amount of acreage that was double cropped.

irrigation efficiency the efficiency of water application and use. Computed by dividing evapotranspiration of applied water by applied water and converting the result to a percentage. Efficiency can be computed at three levels: farm, district, or basin.

irrigation return flow applied water that is not transpired, evaporated, or deep-percolated into a ground water basin but that returns to a surface water supply.

land retirement (as used in this report) taking land out of agricultural production by leaving it fallow or letting it return to a natural state.

land subsidence the lowering of the natural land surface in response to earth movements; lowering of fluid pressure (or lowering of ground water level); removal of underlying supporting materials by mining or solution of solids, either artificially or from natural causes; compaction caused by wetting (hydrocompaction); oxidation of organic matter in soils; or added load on the land surface.

laser land leveling use of instruments featuring laser beams to guide earth-moving equipment for leveling land for surface-type irrigation.

leaching the flushing of salts from the soil by the downward percolation of applied water.

leaching requirement the theoretical amount of irrigation water that must pass (leach) through the soil beyond the root zone to keep soil salinity within acceptable levels for sustained crop growth.

level of development in a planning study, the practice of holding constant the population, irrigated acreage, industry, and wildlife so that hydrologic variability can be studied to determine adequacy of supplies.

maximum contaminant level (MCL) the highest concentration of a constituent in drinking water permitted under federal and State Safe Drinking Water Act regulations.

megawatt one million watts; a measure of power plant output.

milligrams per liter (mg/L) the weight in milligrams of any substance dissolved in one liter of liquid; nearly the same as parts per million.

mineralization the process whereby concentrations of minerals, such as salts, increase in water, often a natural process resulting from water dissolving minerals found in rocks and soils through which it flows.

moisture stress a condition of physiological stress in a plant caused by lack of water.

multipurpose project a project designed to serve more than one purpose. For example, one that provides water for irrigation, recreation, fish and wildlife, and, at the same time, controls floods or generates electric power.

National Pollutant Discharge Elimination System (NPDES) a provision of Section 402 of the federal Clean Water Act of 1972 that established a permitting system for discharges of waste materials to water courses.

natural flow the flow past a specified point on a natural stream that is unaffected by stream diversion, storage, import, export, return flow, or change in use caused by modifications in land use.

net water demand (net water use) the amount of water needed in a water service area to meet all requirements. It is the sum of evapotranspiration of applied water (ETAW) in an area, the irrecoverable losses from the distribution system, and the outflow leaving the service area; does not include reuse of water within a service area (such as reuse of deep-percolated applied water or use of tail water).

nonpoint source waste water discharge other than from point sources. See also point source.

nonreimbursable costs project costs allocated to general statewide or national beneficial purposes and funded from general revenues.

normalized demand the process of adjusting actual water use in a given year to account for unusual events such as dry weather conditions, government interventions for agriculture, rationing programs, or other irregularities.

overdraft See ground water overdraft.

pathogens any viruses, bacteria, or fungi that cause disease.

peak load (power) the maximum electrical energy used in a stated period of time. Usually computed over an interval of one hour that occurs during the year, month, week, or day. The term is used interchangeably with peak demand.

perched ground water ground water supported by a zone of material of low permeability located above an underlying main body of ground water with which it is not hydrostatically connected.

per capita water use the water produced by or introduced into the system of a water supplier divided by the total residential population; normally expressed in gallons per capita per day (gpcd).

percolation the downward movement of water through the soil or alluvium to a ground water table.

perennial yield the maximum quantity of water that can be annually withdrawn from a ground water basin over a long period of time (during which water supply conditions approximate average conditions) without developing an overdraft condition. Sometimes referred to as sustained yield.

permeability the capability of soil or other geologic formations to transmit water.

phytoplankton minute plants, usually algae, that live suspended in bodies of water and that drift about because they cannot move by themselves or because they are too small or too weak to swim effectively against a current.

planning subarea (PSA) an intermediately-sized study area consisting of one or more detailed analysis unit(s).

point source a specific site from which waste or polluted water is discharged into a water body, the source of which can be identified.

pollution (of water) the alteration of the physical, chemical, or biological properties of water by the introduction of any substance into water that adversely affects any beneficial use of water.

project yield the water supply attributed to all features of a project, including integrated operation of units that could be operated individually.

pump lift the distance between the ground water table and the overlying land surface.

pumped storage project a hydroelectric powerplant and reservoir system using an arrangement whereby water released for generating energy during peak load periods is stored and pumped back into the upper reservoir, usually during periods of reduced power demand.

pumping-generating plant a plant at which the turbine-driven generators can also be used as motor-driven pumps.

recharge basin a surface facility, often a large pond, used to increase the percolation of surface water into a ground water basin.

recreation-day participation in a recreational activity, such as skiing, biking, hiking, fishing, boating, or camping, by one person for any part of a day.

recycled water urban waste water that becomes suitable, as a result of treatment, for a specific direct beneficial use. See also water recycling.

return flow the portion of withdrawn water not consumed by evapotranspiration or system losses which returns to its source or to another body of water.

reuse the additional use of previously used water.

reverse osmosis method of removing salts from water by forcing water through a membrane.

riparian located on the banks of a stream or other body of water.

riparian vegetation vegetation growing on the banks of a stream or other body of water.

runoff the surface flow of water from an area; the total volume of surface flow from an area during a specified time.

salinity generally, the concentration of mineral salts dissolved in water. Salinity may be measured by weight (total dissolved solids), electrical conductivity, or osmotic pressure. Where sea water is known to be the major source of salt, salinity is often used to refer to the concentration of chlorides in the water. See also total dissolved solids.

salinity intrusion the movement of salt water into a body of fresh water. It can occur in either surface water or ground water bodies.

salt sink a body of water too salty for most freshwater uses.

salt-water barrier a physical facility or method of operation designed to prevent the intrusion of salt water into a body of fresh water.

seasonal application efficiency (SAE) the sum of evapotranspiration of applied water and leaching requirement divided by the total applied water, expressed as a percentage: SAE = (ETAW+LR)/AW

secondary treatment in sewage, the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent from primary treatment systems. Secondary treatment is usually carried out through the use of trickling filters or by the activated sludge process.

sediment soil or mineral material transported by water and deposited in streams or other bodies of water.

seepage the gradual movement of a fluid into, through, or from a porous medium.

self-produced water a water supply (usually from wells) developed and used by an individual or entity. Also called "self-supplied water."

service area the geographical land area served by a distribution system of a water agency.

sewage the liquid waste from domestic, commercial, and industrial establishments.

soluble minerals naturally occurring substances capable of being dissolved.

spawning the depositing and fertilizing of eggs (or roe) by fish and other aquatic life.

spreading basin See recharge basin.

spreading grounds See recharge basin.

streamflow the rate of water flow past a specified point in a channel.

striped bass index in the San Francisco Bay/Sacramento-San Joaquin Delta system, a number representing the abundance of striped bass.

subsurface drainage See agricultural drainage.

supply augmentation alternatives water management programs-such as conjunctive use, water banking, or water project facility expansion-that increase supply.

surface supply water supply from streams, lakes, and reservoirs.

surface water treatment rule federal regulation promulgated on June 29, 1989 (54 FR 124) requiring filtration and rigorous disinfection of surface water supplies and ground water supplies directly under the influence of surface water.

surplus water developed water supplies in excess of contract entitlement or apportioned water.

tail water applied irrigation water that runs off the end of a field. Tail water is not necessarily lost; it can be collected and reused on the same or adjacent fields.

tertiary treatment in sewage, the additional treatment of effluent beyond that of secondary treatment to obtain a very high quality of effluent for reuse.

total dissolved solids a quantitative measure of the residual minerals dissolved in water that remain after evaporation of a solution. Usually expressed in milligrams per liter. Abbreviation: TDS. See also salinity.

transpiration an essential physiological process in which plant tissues give off water vapor to the atmosphere.

trihalomethane (THM) chlorinated halogen compounds such as chloroform, carbon tetrachloride and bromoform, formed by reactions between carbonaceous matter and chlorine or bromine.

visitor-day See recreation-day.

waste water the used water, liquid waste, or drainage from a community, industry, or institution.

water conservation reduction in applied water due to more efficient water use such as implementation of Urban Best Management Practices or Agricultural Efficient Water Management Practices. The extent to which these actions actually create a savings in water supply depends on how they affect net water use and depletion.

water demand schedule a time distribution of the demand for prescribed quantities of water for specified purposes. It is usually a monthly tabulation of the total quantity of water that a particular water user intends to use during a specified year.

water quality used to describe the chemical, physical, and biological characteristics of water, usually in regard to its suitability for a particular purpose or use.

water reclamation as used in this report, includes water recycling, seawater desalting, ground water reclamation, and desalting agricultural brackish water.

water recycling the treatment of urban waste water to a level rendering it suitable for a specific, direct, beneficial use.

water right a legally protected right to take possession of water occurring in a natural waterway and to divert that water for beneficial use.

water service reliability the degree to which a water service system can successfully manage water shortages.

watershed See drainage basin.

water table See ground water table.

water year a continuous 12-month period for which hydrologic records are compiled and summarized. In California, it begins on October 1 and ends September 30 of the following year.

Abbreviations and Acronyms

ACFC&WCD Alameda County Flood Control and Water Conservation District

af acre-feet

AW applied water

BDOC Bay-Delta Oversight Council

BMP Best Management Practice

CCWD Calaveras County Water District

CEC California Energy Commission

CMO Crop Market Outlook

CVP Central Valley Project

CCWD Contra Costa Water District

CVPIA Central Valley Project Improvement Act

CVWD Coachella Valley Water District

CVWUC Central Valley Water Use Committee

D-1485 State Water Resources Control Board Water Right Decision 1485

DAU detailed analysis unit

DBPs disinfection byproducts

DBCP dibromochloropropane

DFG California Department of Fish and Game

DWA Desert Water Agency

DWR California Department of Water Resources

EBMUD East Bay Municipal Utility District

EDCWA El Dorado County Water Agency

EDF Environmental Defense Fund

EID El Dorado Irrigation District

EPA federal Environmental Protection Agency

ESA Endangered Species Act

ETAW evapotranspiration of applied water

EWMP Efficient Water Management Practice

FERC Federal Energy Regulatory Commission

GCID Glenn-Colusa Irrigation District

gpcd gallons per capita daily

HBMWD Humboldt Bay Municipal Water District

HLWA Honey Lake Wildlife Area

IID Imperial Irrigation District

IFIM Instream Flow Incremental Methodology

LADWP Los Angeles Department of Water and Power

LR leaching requirement

maf million acre-feet

MCL maximum contaminant level

MID Merced Irrigation District or Modesto Irrigation District

MCWRA Monterey County Water Resources Agency

MMWD Marin Municipal Water District

MOU memorandum of understanding

MRWPCA Monterey Regional Water Pollution Control Agency

MWDSC Metropolitan Water District of Southern California

NMFS National Marine Fisheries Service

NMWD North Marin Water District

NPDES National Pollutant Discharge Elimination System

OCID Orange Cove Irrigation District

PCE perchlorethylene

PCWA Placer County Water Agency

PG&E Pacific Gas and Electric Company

P.L. Public Law

PSA planning subarea

PVWMA Pajaro Valley Water Management Agency

RCD resource conservation district

SAE seasonal application efficiency

SBVMWD San Bernardino Valley Municipal Water District

SCE Southern California Edison Company

SCVWD Santa Clara Valley Water District

SCWA Solano County Water Agency or Sonoma County Water Agency

SDCWA San Diego County Water Authority

SDWA South Delta Water Agency

SFWD San Francisco Water District

SJWA San Jacinto Wildlife Area

SJVDP San Joaquin Valley Drainage Program

SJRMP San Joaquin River Management Program

SMUD Sacramento Municipal Utility District

SNWA Southern Nevada Water Authority

SSWD South Sutter Water District

SWP State Water Project

SWRCB State Water Resources Control Board

SWTR federal Surface Water Treatment Rule

TCE trichlorethylene

TDS total dissolved solids

THM trihalomethane

TID-MID Turlock Irrigation District and Modesto Irrigation District

TROA Truckee River Operating Agreement

UCD University of California at Davis

USBR U.S. Bureau of Reclamation, Department of the Interior

USCE U.S. Corps of Engineers, Department of the Army

USFWS U.S. Fish and Wildlife Service

WSD water storage district

WSMP water storage management plan

YCFCWCD Yolo County Flood Control and Water Conservation District

YCWA Yuba County Water Agency