FINALS HYDROLOGY

Evaporation

process in which a liquid changes to the gaseous state at the free surface, below the boiling point, through the transfer of heat energy

Vapor Pressure

The rate of evaporation is proportional to the difference between the saturation vapor pressure (SVP) at the water temperature (ew) and the actual vapor pressure in the air (ea )

Temperature

The rate of evaporation increases with an increase in the water temperature and vice versa

Wind

Helps remove the evaporated water vapor from the zone of evaporation, thereby creating greater scope for evaporation

Atmospheric Pressure

A decrease in atmospheric pressure, such as in high altitude areas, increases the evaporation rate, assuming other factors remain constant

Soluble Salts

As solutes are dissolved in water, the vapor pressure of the solution is less than that of pure water and reduces the rate of evaporation

Heat Storage in Water Bodies

Its effect is to change the seasonal evaporation rates, and the annual evaporation remains unaltered

Evaporimeters

Water-containing pans that are exposed to the atmosphere, and the loss of water by evaporation is measured in them at regular intervals

Pan Coefficient

Used to mimic results for large water bodies, as evaporation pans are not exactly models of large reservoirs

Water-Budget Method

The simplest method but the least reliable. If the unit of time is kept very large, estimates of evaporation will be more accurate

Energy-Budget Method

An application of the law of conservation of energy. The energy available for evaporation is determined by considering the incoming energy, outgoing energy, and energy stored in the water body over a known time interval

Mass-Transfer Method

Based on theories of turbulent mass transfer in the boundary layer to calculate the mass water vapor transfer from the surface to the surrounding atmosphere

Transpiration

The process by which water leaves the body of a living plant and reaches the atmosphere as water vapor

Evapotranspiration

The total amount of water loss in the form of water vapors into the atmosphere from the surface of the soil, canopy interception, water bodies as well as from the aerial parts of the plants

Potential Evapotranspiration

Resulting evapotranspiration if sufficient moisture is always available to completely meet the needs of vegetation fully covering the area

Actual Evapotranspiration

The real evapotranspiration occurring in a specific situation

Field Capacity

The maximum quantity of water that the soil can retain against the force of gravity

Permanent Wilting Points

The moisture content of a soil at which the moisture is no longer available in sufficient quantity to sustain the plants

Available Water

The difference between the two-moisture content, field capacity and permanent wilting point, it is the moisture available for plant growth

Lysimeters

Special watertight tank containing a block of soil and set in a field of growing plants

Streamflow

Representing the runoff phase of the hydrologic cycle, it is the most important basic data for hydrologic studies

Stream

A flow channel in which the surface runoff from a specified basin drains

Hydronometry

Science and practice of water measurement, where the measurement of discharge in streams is an important branch

Perennial Streams

Water flows throughout the year, where the primary water source can be from groundwater, surface water, or a combination of both

Intermittent Streams

Water flows for part of most of the year but may carry no water during the dry season

Ephemeral Streams

Water flows only for a short time, usually after a large storm or snowmelt when there is an increase in water runoff

Stage of a RIver

Water flows only for a short time, usually after a large storm or snowmelt when there is an increase in water runoff

Staff Gauge

Simplest of stage measurements made by noting the elevation of the water surface in contact with a fixed graduated staff

Wire Gauge

Used to measure the water-surface elevation from above the surface, such as from a bridge or similar structure

Float-Gauge Recorder

Used to measure the water-surface elevation from above the surface, such as from a bridge or similar structure

Bubble Gauge

Compressed air or gas is made to bleed out at a very small rate through an outlet placed at the bottom of the river

Volumetric Method and Gravimetric Method

Applicable if the channel or stream cross sectional area is small and the flow is slow and laminar. The simplest and quickest method of determining the flow which can cause inaccuracies on flow measurements of larger channels

Slope-Area Method

Mostly used by civil engineers in the design channels like canals and drainage systems

Control-Section Method

These structures provide a unique control section in the flow such that the discharge will become a function of the water surface elevation measured from the specific datum

Runoff

The draining or flowing off of precipitation from a catchment area through a surface channel. The portion of rainfall that flows through rivers, streams, and other bodies of water

Natural Flow

Also known as virgin flow, it is the true runoff or streamflow in its natural condition unaffected by works of man

Yield

The total quantity of surface water that can be expected in a given period from a stream at the outlet of its catchment

Hydrograph

A result from an isolated storm, it is typically a single-peaked skew distribution of discharge. Known variously as storm hydrograph, flood hydrograph, or simply hydrograph

Rising Limb

Also known as the concentration curve, it represents the increase in discharge due to the gradual building up of storage in the channel and over the catchment surface

Crest Segment

One of the most important parts of hydrograph as it contains the peak flow

Peak

Occurs when the runoff from various parts of the catchment simultaneously contribute amounts to achieve the maximum amount of flow at the basin outlet

Recession Limb

Extending from the point of inflection at the end of the crest segment to the commencement of the natural groundwater flow, it represents the withdrawal of water from the storage built up in the basin during the earlier phase of the hydrograph

Surface-Flow Hydrograph

Obtained from the total storm hydrograph by separating the quick-response flow from the slow response runoff

Effective Rainfall

Also known as excess rainfall (ER), is that part of the rainfall that becomes direct runoff at the outlet of the watershed. The total rainfall in a given duration from which abstractions are subtracted

Effective Rainfall Hydrograph

Also known as excess rainfall hyetograph, it is the resulting hyetograph with the initial loss and infiltration losses are subtracted from it

Groundwater

In the hydrologic cycle, it is the precipitation that infiltrates through the soil to the water table

Hydrogeology

Also called groundwater hydrology, it is the study of the distribution and movement of groundwater

Water Table

Top of the saturated zone and may be located only a foot below the ground’s surface or can sit hundreds of feet down

Saturated Zone

Also called saturation zone, is the area where water fills the aquifer

Aquifer

Saturated formation of earth material which not only stores water but yields it in sufficient quantity

Aquitard

Formation through which only seepage is possible, this the yield is insignifcant compared to aquifer

Aquiclude

Geological formation which is essentially impermeable to the flow of water

Aquifuge

Geological formation which is neither porous nor permeable as there is no interconnected rock without any fractures

Recharge

The processes of infiltration and migration or percolation by which groundwater is replaced

Groundwater Discharge

Occurs where groundwater flows into a stream, escapes at the surface in a spring, or otherwise exits the aquifer

Capillary Fringe

Region above the water table where water rises due to capillary forces in the porous medium

Unconfined Aquifer

Water is in contact with atmospheric pressure, where a drill and well can hit the water table

Confined Aquifer

Recharge upgradient forces water to flow down and get trapped under an aquiclude

Artesian Well

Location where water flows to the surface under artesian pressure

Permeability

Measures the transmission property of the media and the interconnection of the pores

Henry Darcy

A French engineer who lived in the mid-16th century and formulated the Darcy’s Law

Darcy’s Law

States that if permeability remains uniform, the velocity of groundwater will increase as the slope of the water table increases

Hydraulic Head

The vertical difference between the recharge and discharge points

Hydraulic Gradient

The water table slope

Cone of Depression

A circular lowering of the water table immediately around the well in an unconfined aquifer

Well

A hole drilled into the ground to access water contained in an aquifer