Hydrology Glossary

on 25 November 2024. Posted in Hydrology Engineering

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Aeration - Any active or passive process by which intimate contact between air and liquid are assured, generally by spraying liquid in the air, bubbling air through water, or mechanical agitation of the liquid to promote surface absorption of air.
Aeration Zone - The zone immediately below the land surface where the pores contain both water and air, but are not totally saturated with water. Plant roots can capture the moisture passing through this zone, but it cannot provide water for wells.
Applied Water - The volume of water that was applied and used by urban and agricultural sectors and was dedicated to the environment.
Applied Water Reduction - A decrease in the amount of water needed to meet the demand for beneficial use. Applied water reduction can be a supply for both new water and reused water.
Aquaduct - A pipe or conduit made to bring water from a source.
Aquifer - An underground geological formation of sand, soil, gravel and rock able to store and yield water.
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.
Artesian Well - A well tapping a confined aquifer. Water in the well rises above the top of the aquifer under artesian pressure, but does not necessarily reach the land surface. A flowing artesian well is a well in which the water level is above the land surface.
Atmosphere - The layer of gases that surrounds a planet or celestial body and is held in place by its gravity. On Earth, the atmosphere is the layer of gases that surrounds our planet and is composed primarily of nitrogen (78%), oxygen (21%), and trace amounts of other gases such as argon, carbon dioxide, and neon.
Atmospheric River - A weather pattern that forms a narrow corridor of concentrated moisture in the atmosphere that drops significant rain and snow as it passes over land.
Attenuation - The reduction in the peak of a hydrograph as it moves downstream, resulting in a broader, flat hydrograph.
Average Annual Runoff - For a specified area, it is the average value of annual runoff amounts calculated for a whole hydrologic cycle of record that represents average hydrologic conditions.
Average Year Water Demand - Demand for water under average hydrologic conditions for a defined level of development.

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Backwater - Water backed up or retarded in its course as compared with its normal or natural condition of flow. In stream gaging, a rise in stage produced by a temporary obstruction such as ice or weeds, or by the flooding of the stream below. The difference between the observed stage and that indicated by the stage discharge relation, is reported as backwater.
Bank Storage - The water absorbed into the banks of a stream channel, when the stages rise above the water table in the bank formations, then returns to the channel as effluent seepage when the stages fall below the water table.
Baseflow - Streamflow coming from groundwater seepage into a stream or river. Groundwater flows underground until the water table intersects the land surface and the flowing water becomes surface water in the form of springs, streams/rivers, lakes and wetlands. Baseflow is the continual contribution of groundwater to rivers and is an important source of flow between rainstorms.
Bed Material - The sediment mixture that a streambed is composed of.
Bedrock - Solid rock that forms the earth’s crust, it is intermittently exposed at the earth’s surface but is more commonly covered by soil.
Benthos - All plants and animals living on or closely associated with the bottom of a body of water.
Bog - Freshwater wetlands that are poorly drained and characterized by a buildup of peat.
Brackish Water - Water with a salinity that exceeds normally acceptable standards for municipal, domestic, and irrigation uses but has less salinity than seawater.
Braided Channel - A stream characterized by flow within several channels, which successively meet and divide. Braiding often occurs when sediment loading is too large to be carried by a single channel.
Buffer Strip - A barrier of permanent vegetation, either forest or other vegetation, between waterways and land uses such as agriculture or urban development, designed to interrupt and filter out pollution before it reaches the surface water resource.

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Canal - A constructed open channel for transporting water.
Capillary Water - Water located just above the water table, in the aeration zone, that moves upward from the water table by capillary action. This water can move slowly and in any direction. While most plants rely upon moisture from precipitation that is present in the unsaturated zone, their roots may also tap into capillary water or into the underlying saturated zone.
Cascade - A short, steep drop in streambed elevation often marked by boulders and agitated white water.
Channel - An area that contains continuously or periodically flowing water that is confined by banks and a streambed.
Channel Storage - The volume of water at a given time in the channel or over the flood plain of the streams in a drainage basin or river reach. Channel storage can be large during the progress of a flood event.
Check Dam - A structure placed bank-to-bank downhill from a headcut on a hillslope to help revegetate a gully.
Climate Change - Changes in long term average temperature, precipitation, wind, or other variables in a specific region.
Closed Basin - A basin in which no stream naturally exits the basin into another river or ocean.
Cloud Seeding - Typically occurs in the wintertime where special substances (silver iodide) are injected into the clouds that enable snowflakes and raindrops to form more easily.
Coastal Flooding - Inundation at locations normally above the level of high tide and often caused by storm surges occurring with high tides. Impacts include property damage and beach erosion.
Condensation - As water vapor rises, it cools and condenses into tiny droplets, forming clouds. These droplets combine to create larger water particles, which can result in rain or other forms of precipitation.
Confined Aquifer - An aquifer that exists where the groundwater is bounded between layers of impermeable substances like clay or dense rock. When tapped by a well, water in confined aquifers is forced up, sometimes above the soil surface. This is how a flowing artesian well is formed.
Confining Layer - Geologic material with little or no permeability or hydraulic conductivity such as clay or dense rock. Water does not pass through this layer or the rate of movement is extremely slow.
Conservation Tillage - A tillage practice that leaves plant residues on the soil surface for erosion control and moisture conservation.
Consolidated Rock - Tightly bound geologic formation composed of sandstone, limestone, granite, or other rock.
Containment - A chemical or substance that we would rather not be present in our environment, food, air, etc., but is present because of either natural occurrences and processes, or human induced processes.
Cover Crop - A close growing crop that provides soil protection, seeding protection, and soil improvement between periods of normal crop production or between trees in orchards and vines in vineyards. When plowed under and incorporated into the soil, cover crops may be referred to as green manure crops.
Crop Rotation - A system of farming in which a succession of different crops is planted on the same land area, as opposed to growing the same crop time after time.
Culvert - A buried pipe that allows flows to pass under a road.
Cut Bank - The outside bank of a bend, often eroding opposite a point bar.

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Debris Flow Flooding - Flows made up of water, liquefied mud, and debris that can form and accelerate quickly, reach high velocities, and travel great distances. They are commonly caused by heavy localized rainfall on hillsides denuded of vegetation.
Deep Percolation - The percolation of water through the ground and beyond the lower limit of the root zone of plants into a groundwater aquifer.
Depletion - The loss of water from groundwater aquifers or surface water reservoirs at a rate greater than that of recharge, when water is used faster than it is replaced.
Detention Basin - Storage site, such as a small unregulated reservoir, which delays the conveyance of water downstream.
Diffusion - Dissipation of the energy associated with a flood wave; results in the attenuation of the flood wave.
Direct Runoff - The runoff entering stream channels promptly after rainfall, exclusive of base flow. Direct runoff equals the volume of rainfall excess (total precipitation minus losses).
Discharge - An outflow of water from a stream, pipe, groundwater aquifer, or watershed; the opposite of recharge.
Ditch - A long narrow trench or furrow dug in the ground, as for irrigation, drainage, or a boundary line.
Diversion - The transfer of water from a stream, lake, aquifer, or other conduit to another watercourse or to the land, as in the case of an irrigation system.
Domestic Well - A water well used to supply water for the domestic needs of an individual residence or local small water system of four or fewer service connections or homes.
Downspout and Gutter Drainage System - An essential component of a building's water management system designed to control rainwater runoff from the roof. A well designed downspout and gutter drainage system is key to maintaining the longevity of a building and preventing costly repairs.
Drainage Area - The drainage area of a stream at a specified location is that area, measured in a horizontal plane, which is enclosed by a drainage divide.
Drainage Systems - The natural or man-made structures and processes that manage the flow of water across landscapes. These systems collect, convey, and dispose of surface water (from rainfall, snowmelt, or springs) and groundwater, preventing flooding, erosion, and damage to infrastructure.
Dredging - Removing material (usually sediments) from wetlands or waterways, usually to make them deeper and wider.
Drip Irrigation - A method of micro irrigation wherein water is applied to the soil surface as drops or small streams through emitters.
Drought - An extended period of dry weather with little or no precipitation; often affects crop production and availability of water supplies.
Dry Wash - A streambed that carries water only during and immediately following rainstorms.

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Ecology - The study of interrelationships of living organisms to one another and to their surroundings.
Eddy Current - A circular current of water, usually resulting from an obstruction, that develops when the main flow becomes separated from the bank.
Effective Porosity - The interconnected portion of the total voids or open spaces in alluvium and rocks that is capable of transmitting fluids.
Embankment - An artificial deposit of material that is raised above the natural surface of the land and used to contain, divert, or store water, support roads and railways, or for other similar purposes.
Environmental Restoration - Restoring natural water systems that have been impacted by human activities.
Erosion - The wearing down or washing away of the soil and land surface by the action of water, wind, or ice.
Evaporation - Water from oceans, lakes, rivers, and other water bodies heats up and converts into water vapor. This vapor rises into the atmosphere.
Evapotranspiration - The process by which water is transferred from the land to the atmosphere through two primary mechanisms, evaporation and transpiration.
Excess Rainfall - The volume of rainfall available for direct runoff. It is equal to the total rainfall minus interception, depression storage, and absorption.

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Filtering - The soil’s ability to dilute substances by retaining chemicals or dissolved substances on the soil particle surface, transforming chemicals through microbial biological processing, slowing movement, and capturing solid particles.
Flash Flood - A sudden flood of great volume, usually caused by a heavy rain. Also, a flood that crests in a short length of time and is often characterized by high velocity flows.
Flood - An overflow or inundation that comes from a river or other body of water, and causes or threatens damage. Any relatively high streamflow overtopping the natural or artificial banks in any reach of a stream. A relatively high flow as measured by either gage height or discharge quantity.
Flood Control - Managing rivers, lakes, and reservoirs to prevent flooding and mitigate damage to communities and infrastructure.
Flood Irrigation - A method of irrigation in which water is applied to the soil surface without flow controls, such as furrows, borders, or corrugations.
Flood stage - An above average elevation for the water level at high flows.
Floodplain - Lowland areas adjoining lakes, wetlands, and rivers that are susceptible to inundation of water during a flood. For regulatory purposes, the floodplain is the area covered by the 100 year flood or the area that has a 1 percent chance of flooding every year. It is usually divided into districts called the floodway and flood fringe. Areas where the floodway and flood fringe have not been determined are called approximate study areas or general floodplain.
Ford - A shallow place in a body of water, such as a river, where one can cross by walking or riding on an animal or in a vehicle.

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Gaining Stream - A stream in which groundwater discharges contribute significantly to the streamflow volume. The same stream could be both a gaining stream and a losing stream, which recharges the groundwater system, depending on the conditions.
Gray Water - Domestic wastewater composed of wash water from household sinks, tubs, and washers.
Greenbelt - Strip of natural vegetation growing parallel to a stream that provides wildlife habitat and an erosion and flood buffer zone. This strip of vegetation also retards rainfall runoff down the bank slope and provides a root system that binds soil particles together.
Groundwater - The water that exists beneath the Earth's surface, filling the spaces and cracks within soil, sand, and rock. It is stored in underground layers called aquifers, which consist of porous rock or sediment that allows water to move through it.
Groundwater Basin - The underground area from which groundwater drains. The basins could be separated by geologic or hydrologic boundaries.
Groundwater Overdraft - The condition of a groundwater 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.
Groundwater Prime Supply - Long term average annual percolation into major groundwater basins from percolation into major groundwater basins from precipitation falling on the land and from flows in rivers and streams.
Groundwater Quality - A measure of the chemical, physical, bacteriological, and radiological characteristics of groundwater. Groundwater may be contaminated by either naturally occurring or anthropogenic (human-caused) sources of contamination. Groundwater that becomes contaminated by anthropogenic sources is difficult to cleanup and may take on the order of decades for the water cycle to displace the contaminated groundwater with clean water.
Groundwater Recharge - The natural or managed infiltration or injection of water into a groundwater aquifer.
Groundwater Storage Capacity - The volume of void space that can be occupied by water in a given volume of a formation, aquifer, or groundwater basin.
Groundwater Subbasin - A subdivision of a groundwater basin created by dividing the basin by using geologic and hydrologic conditions or institutional boundaries.
Groundwater Subsurface Inflow - The amount of water that flows into a region underground.
Groundwater Subsurface Outflow - The amount of water that flows underground and out of a region, basin, or study area.
Groundwater Table - The upper surface of the zone of saturation in an unconfined aquifer.

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Hardpan - A layer of nearly impermeable soil beneath a more permeable soil, formed by natural chemical cementing of the soil particles.
Hard Water - Water high in multivalent cations, such as calcium and magnesium. This type of water does not lather easily when used with soap and forms a scale in containers when allowed to evaporate.
Headwater - Referring to the source of a stream or river.
Hungry Water - Clear water minus its expected suspended sediment load, usually released from an impoundment that has excess energy, which erodes sediment from the downstream channel.
Hydraulic Gradient - The change in height (pressure) to length between any two points. Or you could say the change in hydraulic head per unit distance along a flow path in a fluid system. It represents the driving force behind fluid flow and provides information about the direction and magnitude of flow within the system.
Hydraulic Radius - A parameter used in fluid dynamics to characterize the efficiency of flow in an open channel or pipe. It is a measure of the area cross-sectional of flow relative to the wetted perimeter of the channel or pipe. The hydraulic radius represents the average distance from the center of the flow to the channel boundary.
Hydroelectric Power - A form of renewable energy that uses the movement of water to generate electricity. It harnesses the energy of flowing or falling water, such as rivers, streams, or waterfalls to turn turbines that are connected to generators.
Hydrologic Cycle - The never ending movement of water through the atmosphere, ground and back again through its various states (vapor, liquid, solid); also known as the water cycle.
Hydrologic Region - A geographical division of the state based on the local hydrologic basins.

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Infiltration - Some of the water from precipitation seeps into the ground, replenishing groundwater supplies and aquifers. This infiltrated water can also be absorbed by plant roots.
Infiltration Basin - A shallow basin designed to infiltrate stormwater into the ground.
Infiltration Capacity - Rate at which water can enter soil with excess water on the surface.
Infiltration Rate - The quantity of water that enters the soil surface in a specified time interval. Often expressed in volume of water per unit of soil surface area per unit of time.
Injection Wells - Injection wells are used primarily to recharge confined aquifers. The design of an injection well for artificial recharge is similar to that of a water supply well. The principal difference is that water flows from the injection well into the surrounding aquifer under either a gravity head or a head maintained by an injection pump.
Ion Exchange - Processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid ion exchangers, such as sodium carbonate used for water softening.
Invasive Species - Non-indigenous plants or animals that adversely affect the habitats they invade economically, environmentally, and/or ecologically.
Irrigation - Designing irrigation systems for agriculture to efficiently use water resources.

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Kinetic Energy - The energy an object possesses by virtue of its motion. It is a scalar quantity and is dependent on the mass and speed of the object. If it moves, it has kinetic energy.
Karst - A geologic formation of irregular limestone deposits that dissolve forming sink holes, underground streams, and caverns.

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Landfill - A low area of land that is filled in with layers of garbage and soil.
Leaching - The flushing of minerals or pollutants from soil or other material by the percolation of applied water.
Leachate - Liquids that have percolated through a soil and that carry substances in solution or suspension.
Leaching - The process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals, or contaminants, are washed into a lower layer of soil or are dissolved and carried away by water.
Leaching Efficiency - The ratio of the average salt concentration in drainage water to an average salt concentration in the soil water of the root zone when near field capacity.
Levee - An embankment constructed to prevent a river from overflowing.

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Mean Daily Temperature -
Monitoring Well - A non-pumping well, generally of small diameter, that is used to measure the elevation of a water table or water quality. A piezometer, which is open only at the top and bottom of its casing, is one type of monitoring well.
Municipal Water System - A network of pipes, pumps, and storage and treatment facilities designed to deliver potable water to homes, schools, businesses, and other users in a city or town and to remove and treat waste materials.

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Natural Recharge - Replenishment of an aquifer generally from snowmelt and runoff, through seepage from the surface. Recharge of an aquifer that occurs without human interference.
Net Water Savings - In the context of agricultural water use efficiency, this represents the reduction in the amount of water used that becomes available for other purposes while maintaining or improving crop yield.
Net Water Use - The amount of water needed in a water service area to meet all requirements. It includes the consumptive use of applied water, irrecoverable water from the distribution system, and the outflow leaving the service area. It does not include reuse of water within a service area, including recoverable deep percolation.
Net Water Use - The amount of water needed in a water service area to meet all requirements. It includes the consumptive use of applied water, irrecoverable water from the distribution system, and the outflow leaving the service area. It does not include reuse of water within a service area, including recoverable deep percolation.
Non-potable - Water that is unsafe to drink because it contains contaminants and/or is untreated.

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Offstream Recharge - Offstream recharge uses suitable recharge sites outside a streambed. In some operations, water must be pumped some distance from its source to an offstream recharge area.
Optimal Fluoridation - When a water treatment facility and distribution system are able to provide a consistent level of fluoride at the appropriate prophylactic level.
Overwithdrawal - Withdrawal (removal) of groundwater over a period of time that exceeds the recharge rate of the supply aquifer.

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Peak Discharge from Drainage Basin Runoff - The maximum flow rate of water passing through a specific point in a drainage system (like a river or stream) after a rainfall or snowmelt event. It represents the highest volume of water per unit of time occurring at the outlet of a drainage basin or watershed during or after a storm.
Penman Equation - Used for estimating evapotranspiration, which is the combined process of evaporation from soil and plant surfaces and transpiration from plants.
Penman-Monteith Equation - A formula for estimating evapotranspiration, which is the process of water moving from the soil through plants and into the atmosphere. It combines both the energy and mass transfer approaches, providing a comprehensive way to calculate how much water is lost from soil, plants, and water bodies through evaporation and transpiration.
Precipitation - The discharge of water from the atmosphere, in either liquid or solid form.
Perched Groundwater - Groundwater supported by a zone of material of low permeability located above an underlying main body of groundwater.
Percolating Water - Water in underground basins and groundwater that has escaped from streams and is not subject to a permitting process.
Pollution - An alteration in the character or quality of the environment, or any of its components, that renders it less suited for certain uses. The alteration of the physical, chemical, or biological properties of water by the introduction of any substance that renders the water harmful to use.
Pore Space - Openings between geologic material found underground. Also referred to as void space or interstices.
Porosity - The measure of empty spaces or voids within a material. It is a property that describes the amount of empty space, or pores, present in a substance relative to its total volume. These pores can be interconnected or isolated, and they can vary in size, shape, and distribution.
Potable Water - Water of a quality suitable for drinking.
Power Output of a Dam - Depends on several factors, including the height of the water, the flow rate of the water, and the efficiency of the turbines and generators. The actual power can vary significantly based on the specific dam's design and water availability.
Precipitation - When clouds accumulate enough moisture, water falls back to the Earth's surface as rain, snow, sleet, or hail, depending on the temperature and atmospheric conditions.
Permeable Layer - A layer of porous material (rock, soil, unconsolidated sediment); in an aquifer, the layer through which water freely passes as it moves through the ground.
Psychrometer Constant - Used in the study of evapotranspiration and thermodynamics, particularly in meteorology and agriculture. It relates the rate of evaporation from a wet surface to atmospheric conditions such as air temperature and humidity.
Psychrometric Constant - A factor in atmospheric science and meteorology, particularly in the study of evaporation and transpiration processes. It relates the rate of change of water vapor pressure with temperature and is used in equations to estimate evapotranspiration (the process where water is transferred from land to the atmosphere by evaporation and plant transpiration).

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Raw Water - An untreated water supply.
Recharge Rate - The quantity of water per unit of time that replenishes or refills an aquifer.
Recharge Zone - An area where permeable soil or rock allows water to seep into the ground to replenish an aquifer.
Reclaimed Wastewater - Treated wastewater that can be used for beneficial purposes, such as irrigating certain plants.
Recycled Water - Volume of water that, as a result of treatment of waste, is suitable for a direct beneficial use or a controlled use, which would not otherwise occur. It includes wastewater treated, stored, distributed, and reused or recirculated for beneficial use.
Remediation - Containment, treatment or removal of contaminated groundwater. May also include containment, treatment or removal of contaminated soil above the water table.
Residual Risk - Residual risk is the likelihood of damage or other adverse consequence remaining after flood management actions are taken.
Retention Basin - Similar to a detention basin but water in storage is permanently obstructed from flowing downstream.
Reuse Groundwater - The amount of recoverable deep percolation from untreated raw applied and conveyance water.
Reuse Surface Water - The amount of untreated raw applied water recaptured for use through surface drainage facilities.
Riprap - A layer of large stones or broken pieces of concrete that are placed along shorelines, riverbanks, bridge foundations, steep slopes, or other areas susceptible to erosion.
Riprap Rock Size -
Root Zone - The portion of the soil profile through which plant roots readily penetrate to obtain water and plant nutrients, expressed in inches or feet of depth.
Runoff - Water that flows over the land to surface streams, rivers, and lakes.

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Salt Water - Water that contains a relatively high percentage (over 0.5 parts per thousand) of salt minerals.
Salt Water Intrusion - The movement of salt water into a body of fresh surface water or groundwater. It may be called seawater intrusion if it comes from the ocean.
Saturation Excess Overland Flow - Surface runoff occurring when the soil is saturated. Saturation excess overland flow is most common on near channel wetlands.
Saturated Zone - A subsurface zone in which all open spaces in soil or bedrock formation are filled with water, the area lying below the water table surface.
Safe Yield - The annual amount of water that can be taken from a source of supply over a period of years without depleting that source beyond its ability to be replenished naturally in wet years.
Saved Water - Saved water is water that is prevented from evaporating from soil or flowing to salt sinks, such as saline surface or groundwater or ocean.
Sea Level Rise - An increase in the height of the average or peak sea level at coastal or tidal locations, usually with regard to projected impacts resulting from climate change.
Sediment - Soil fragmental material that originates from weathering of rocks and is transported or deposited by air, water, or ice.
Seepage - The gradual movement of water into, through, or from a porous medium; also, infiltration of water into soil from canals, ditches, laterals, watercourses, reservoirs, storage facilities, or other water bodies, or from a field.
Septic System - A system used to treat household sewage and wastewater by allowing the solids to decompose and settle in a tank, then letting the liquid be absorbed by the soil in a drainage field. Septic systems are used when a sewer line is not available to carry wastes to a sewage treatment plan.
Slope Drainage System - Designed to manage water flow on sloped terrain, preventing erosion, landslides, and other types of soil instability. The system collects and directs surface water or groundwater away from slopes, ensuring that water does not accumulate or infiltrate the soil excessively, which could weaken the slope's structural integrity.
Slope of the Saturated Vapor Pressure Curve - The vapor pressure of a substance changes with temperature when the substance is in equilibrium between its liquid and vapor phases. The slope indicates how sensitive the vapor pressure is to changes in temperature.
Slow Rise Flooding - Slow rise flooding occurs as a gradual inundation as waterways or lakes overflow their banks and is most often caused by heavy precipitation, especially with heavy snowmelt. It includes riverine flooding in deep floodplains and ponding of water in low-lying urban areas, as well as gradual flooding in areas adjacent to local streams and creeks.
Soil Moisture - The water in soils; usually expressed as a percentage of the dry weight of the soil. It may also be expressed on a wet weight or a volume basis.
Source Water - The body of water from which water is taken for beneficial use.
Spring - A location where groundwater flows naturally to the land surface or a surface water body.
Stormwater - Runoff generated when precipitation from rain and snowmelt flows over land or impervious surfaces and does not percolate into the ground. As the water flows over the land or impervious surfaces such as streets, parking lots, and rooftops, it accumulates debris, chemicals, sediment, or other potential pollutants that could adversely affect water quality if the runoff is discharged into water bodies untreated.
Stormwater Runoff - Water that is originated during a precipitation event and may collect and concentrate diffused pollutants and carry them to watercourses, causing degradation. Runoff in the urban environment, both storm generated and dry weather flows, has been shown to be a significant source of pollutants to the surface waters of the nation.
Sublimation (less common) - Sublimation is the direct conversion of ice or snow into water vapor without passing through a liquid phase. This typically occurs in cold, dry regions like glaciers and snowpacks.
Subsurface Drainage System - A type of drainage system designed to remove excess water that accumulates below the surface of the ground, especially in areas with poorly draining soil. It helps prevent waterlogging, which can damage foundations, roads, agricultural fields, and other infrastructure.
Subsurface Drip Irrigation - Application of water below the soil surface through emitters, with discharge rates generally in the same range as drip irrigation. This method of water application is different from and not to be confused with subirrigation, where the root zone is irrigated by water table control.
Subsurface Flow (Groundwater Flow) - Water that has infiltrated into the ground can move through soil and rocks as groundwater. Some of this water eventually flows back into rivers, lakes, or oceans, completing the cycle.
Surface Irrigation - Irrigation in which the soil surface is used as the conduit, as in furrow and border irrigation, and as opposed to sprinkler, drip, and subirrigation.
Surface Runoff - Water that does not infiltrate into the ground flows over the surface as runoff. This water moves toward rivers, lakes, and oceans, contributing to the return of water to larger bodies of water.
Surface Runoff and Precipitation - Precipitation brings water from the atmosphere to the ground, while surface runoff is the movement of that water across the land towards larger water bodies.
Surface Water - Water above the surface of the land, including lakes, rivers, streams, ponds, floodwater, and runoff.

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Tsunami Flooding - Tsunami flooding occurs as a result of high-speed ocean waves triggered by mass movement that displaces a large volume of water. Earthquakes and underwater landslides may cause a tsunami, and the impact on land depends on wave height and inundation area.
Time of Concentration - The time it takes for water to flow from the most distant point in the watershed to the outlet or point of interest. It represents the longest time it takes for water to travel through the watershed, following the path of flow.
Total Dissolved Solids - A measure of the residual minerals dissolved in water and that remain after evaporation of a solution.
Transpiration - Plants absorb water through their roots and release it as water vapor through tiny pores in their leaves. This process contributes to the overall moisture in the atmosphere.
Turbidity - A cloudy condition in water due to suspended silt or organic matter.

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Unconfined Aquifer - An aquifer in which the water table is at or near atmosphere pressure and is the upper boundary of the aquifer. Because the aquifer is not under pressure the water level in a well is the same as the water table outside the well.
Unsaturated Zone - The zone between the land surface and the water table which may include the capillary fringe. Water in this zone is generally under less than atmospheric pressure and some of the voids may contain air or other gases at atmospheric pressure. Beneath flooded areas or in perched water bodies the water pressure locally may be greater than atmospheric.
Urban Energy Production - The amount of water needed for hydroelectric or thermoelectric power generation.
Urban Land Use Management - Planning for the housing and economic development needs of a growing population, while providing for the efficient use of water and other resources.
Urban Large Landscape Use - The amount of water used to irrigate recreational and large landscape areas, such as golf courses, parks, play fields, highway medians, and cemeteries.
Urban Runoff Management - A broad series of activities to manage both urban stormwater and dry weather runoff that carry pollutants.
Urban Water Use - The use of potable and non-potable water for urban purposes, including residential, commercial, industrial, recreation, energy production, and large landscape.
Usable Storage Capacity - The quantity of groundwater of acceptable quality that can be economically withdrawn from storage.

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Viscosity - The measure of the internal friction/resistance to the flow of a liquid. Lower viscosity fluids flow easily in pipes where high viscosity fluids have a higher pressure drop. Viscosity of fluids is typically temperature dependent and is not affected as dramatically by pressure as gas viscosity.
Void - The empty spaces or gaps between soil particles. These voids can be filled with air or water, depending on the moisture content of the soil. The concept of voids is crucial for understanding the behavior and properties of soils.

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Wastewater - Water that contains unwanted materials from homes, businesses, and industries; a mixture of water and dissolved or suspended substances.
Wastewater Treatment - Mechanical or chemical processes used to modify the quality of wastewater in order to make it more compatible or acceptable to humans and the environment.
Water Balances - Analyses of the total developed and dedicated supplies, uses, and operational characteristics for a region. The analyses show what water was applied to uses so that use equals supply.
Water Depletion - The amount of net water use minus water that can be recovered later, such as deep percolation and return flow to the developed supply.
Water Quality - The chemical, physical, and biological characteristics of water with respect to its suitability for a particular use.
Water Quality Management - Ensuring that water bodies remain free of harmful pollutants through proper monitoring and treatment techniques.
Water Supply Systems - A networks of infrastructure designed to deliver clean, potable water to homes, businesses, and other consumers.
Water Table - The surface of a groundwater body at which the water pressure equals atmospheric pressure. Earth material below the groundwater table is saturated with water.
Water Treatment Plant - A facility that treats water to remove contaminants so that it can be safely used.
Watershed - The land area from which surface runoff drains into a stream, channel, lake, reservoir, or other body of water; also called a drainage basin.
Wetlands - Areas where water saturation is the dominant factor in determining the nature of soil development and the types of plant and animal communities. Other common names for wetlands are sloughs, ponds, and marshes.
Wind Speed vs Wind Load -

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Tags: Hydrology Glossary

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