introduction for hydrology

7/29/2019 Introduction for hydrology

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Introduction

A. Das Gupta

Emeritus Professor

AIT, Bangkok


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Content

Hydrology,

Global Water Distribution,

Hydrologic Cycle, and

Water Balance Equation.


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Hydrology

HYDROLOGY is the science of water that is

concerned with the origin, circulation, distributionand properties of waterof the earth.

(Hydro Water; Loge - Knowledge)

It is the study of occurrence, character, and movement of

water within and between the physical and biologicalcomponents of the environment

The practical application of hydrology is calledApplied Hydrology


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Basic Definition FOREST HYDROLOGY, RANGE HYDROLOGY,

WILDLAND HYDROLOGY is the branch of

hydrology which deals with the effects of land

management and vegetation on the quantity,

quality and timing of water yields, including

floods, erosion and sedimentation

Hydrology


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ImportantPointstoNote Adequate basic data are essential to any science, and hydrology is

no exception

Hydrologic phenomena are complex, interpretation and analysisbased on observed data is a must to understand and establish thesystematic pattern

Most countries have one or more agencies with responsibility fordata collection. It is important to know how these data are collected,the limitations on their accuracy, and the proper methods ofinterpretation and adjustment.

Typical hydrologic problems involve estimates of extremes rarelyobserved in a small data sample, hydrologic characteristics at

locations where no data have been collected or estimates of theeffects of human actions on the hydrologic characteristics of anarea.

Each hydrologic problem is unique in that it deals with a distinct setof physical conditions within a specific river basin.


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melting =latent

heat offusion

Solid water

Evaporation =latent heat of

vaporization

Water

vapor

Liquid Water

Energy

extracted

Energy

added

melting

freezing

StatesofWater


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Water can exist

in three states -

solid (ice), liquid

(water), and gas

(water vapor)

Water exists in

the air in the form

of water vapor,

clouds, fog, andprecipitation

Figure 4.1, p. 121

StatesofWater


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Water can exist

in three states -

solid (ice), liquid(water), and gas

(water vapor)

Water exists inthe air in the form

of water vapor,

clouds, fog, and

precipitation

StatesofWater


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This figure shows what happens to ONE gram (one ml) of water. The orange arrow on the

top represents adding heat, from left to right, and the blue arrows represent releasing heatfrom right to left on the bottom

StatesofWater


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Howmuchwaterdowehave?Total volume of water on the planet:

1386 Million cubic kilometer

Water is the signature feature of our 'blue planet' -70% of the Earth's surface is covered in water.


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The Earths Water

Distribution 97% of the water on earth isin the oceans

Only 3% of the water on

earth is freshwater

About 69% of the freshwater

on earth is permanently frozen

in glaciers and at the polar icecaps

About 30% of freshwater is

groundwater leaving only 0.3%of total water as surface water

Only about 0.03% of total

water on earth is in the rivers

and lakes


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majority of water occurs as ocean

saltwater (97%)

remaining water (2.8%) is accounted for by

glaciers and ice sheets, and groundwater

only 0.001% occurs in the atmosphere


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Hydrologic Cycle & Processes


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Water on earth exists :

in a space called Hydrosphere(15 km up into the atmosphere)

in the crust of the earth (1 kmdown into the Lithosphere)

Water circulates in the hydrosphere through themaze of paths constituting the Hydrologic Cycle

Hydrosphere15 km

1 km

Earth

Lithosphere

HydrologicCycle


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What is Hydrosphere ?

Various stores of water in the hydrosphere

The hydrosphere is the liquid water component of the

Earth. It includes the oceans, seas, lakes, ponds, riversand streams. The hydrosphere covers about 70% of the

surface of the Earth and is the home for many plants and

animals.


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It is the rigid outermostshell of a rocky planet.The lithospherecontains the crust andupper mantle.

What is Lithosphere ?

Oceanic lithosphere is typically about 50-100 km thick(but is no thicker than crust beneath the mid-oceanridges), while continental lithosphere is about 150 kmthick.

The Earth has two types of lithosphere: oceanic and

continental. The lithosphere is broken up into tectonic

plates.


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Water never leaves the Earth. It is constantlybeing cycled through the atmosphere, ocean,and land. This process, known as the water

cycle, is driven by energy from the sun. Thewater cycle is crucial to the existence of life

on our planet.


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HydrologicalCycle

Water in Circulation


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HydrologicalCycle


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During part of the water cycle, the sun heats

up liquid water and changes it to a gas by theprocess ofevaporation. Water that

evaporates from Earths oceans, lakes, rivers,

and moist soil rises up into the atmosphere.


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Evaporation

Evaporation: the conversion of water from a liquid into a

gas. Approximately 80% of all evaporation is from the

oceans, with the remaining 20% coming from inland waterand vegetation


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Evaporation happens in several ways Open water evaporation

Transpiration from leaves Evaporation from soil and land surface

Factors affecting evaporation Heat energy to supply latent heat of vaporization: air

temperature, net radiation

Capacity to transport vapor away from evaporative surface: wind,humidity

Water available to supply evaporative moisture: soil watercontent

Potential evaporation: water supply is not limiting

Evaporation


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The process of evaporation from plants is

called transpiration. (In other words, its likeplants sweating.)


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Transpiration Transpiration: transpiration is the evaporation of

water into the atmosphere from the leaves and

stems of plants.


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The process of water loss from plants through

stomata.

passive process that depends on:

~humidity of the atmosphere

~the moisture content of the soil

only 1 % of the water transpired used for growth

transports nutrients from the soil into the roots

and carries them to the various cells of the plant

keeps tissues from becoming overheated

(Stomata are small openings found on the underside ofleaves that are connected to vascular plant tissues.)

Transpiration


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TranspirationAccounts for ~ 10% of the moisture in theatmosphere

Depends on:

Temperature

Humidity

Insolation

Precipitation Soil type and saturation

Wind

Land slope


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As water (in the form of gas) rises higher in the

atmosphere, it starts to cool and become a liquidagain. This process is called condensation.

When a large amount of water vapor condenses, it

results in the formation of clouds.


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CondensationCondensation: the conversion of water from a gas into a liquid.Condensation is the change of water from its gaseous form (water vapor)

into liquid water. Condensation generally occurs in the atmosphere when

warm air rises, cools and looses its capacity to hold water vapor. As a

result, excess water vapor condenses to form cloud droplets.


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Whenthe

water

in

the

clouds

gets

too

heavy,

thewaterfallsbacktotheearth. Thisiscalledprecipitation.


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Precipitation

Precipitation: transfer of water from the atmosphere back

to earth. There are several forms of precipitation, the

most common of which is rain. Other forms ofprecipitation include; hail, snow, sleet, and freezing rain.


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When rain falls on the land, some of the water as it

moves infiltrates into the ground and the remainingflows along the surface may be into surface

depression, if any and most of the flow run directly

into streams or rivers. Water that collects in rivers,

streams, and oceans is called runoff.


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Runoff

Runoff: runoff is the movement of land water to the oceans,

mainly through the avenue of rivers, lakes, and streams.

Surface runoff consists of precipitation that neither evaporates,

transpires nor penetrates the surface to become groundwater.

Excess runoff can lead to flooding


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Part of the rainfall that infiltrates through the

ground surface percolates down into the storageof groundwater. Groundwater systems are

extensive underground and groundwater flows

from the areas of recharge to areas of dischargethat are surface bodies like streams, rivers or

oceans.


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Groundwater

Ground Water: groundwater is the water available

underground that has infiltrated through the earth's

surface and is found in subsurface soil layers.


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Hydrologic Water Cycle

In Circulation : 577,000 km3


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Quantitativeindicesofdifferentcomponentsoftheglobalhydrologicalcycle (annualvalues)

Land Ocean Total

Precipitation (km3) 119,000 458,000 577,000

Evaporation (km3) 74,200 502,800 577,000

Gain (km3) + 44,800 - 44, 800


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Distributionofnetgain(44,800km3)onlandTotal runoff of Earths rivers:42,600 km3/year

Direct groundwater runoff:

2,200 km3/year

(Principal sources of freshwater to

support livelihood and mans economicactivities)


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WaterBalanceEquationsNeed to define a spatial domain

to apply the water balance concept


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Watershed

WATERSHED, or

CATCHMENT, is a

topographic area that

is drained by a

stream, that is, the

total land area above

some point on astream or river that

drains past that point.

The watershed is

often used as aplanning or

management unit.

Natural environment

unit.


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Delineationof

a

Watershed


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RiverBasin

RIVER BASIN is a larger

land area unit that, althoughcomprised of numerous sub

watersheds and tributaries

still drains the entire basin

past a single point. Land

use, management and

planning is often diverse and

complex. River basins, likethe Chao Phraya and the

Mae Kong may drain an

ocean or inland sea.


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ManagementAspect

WATERSHED/RIVER BASIN MANAGEMENT is

the process ofguiding and organizing landand other resource use on a watershed/river

basin to provide desired goods and services

without affecting adversely soil and water

resources and the environment.

Management involves multi-dimensional

considerations including physical, technical,

institutional, socio-economic, and environmental

aspects


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HydrologicWater

Budget

A water budget is the scientific method for

measuring the amount of water entering,stored within, and leaving a watershed,

and it is also called a hydrologic budget or

a water balance

Hydrologic Budget on a Global Scale


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Hydrologic cycle

Atmospheric Subsystem

Surface Subsystem

Groundwater Subsystem

HydrologicBudgetonaGlobalScale



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Hydrologic cycle with global annual average water balance.

Average Water Balance in 1978Figures are in 103 km3




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Average Water Balance in 2005



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HydrologicWater

Budget

The hydrologic budget consists of inflows, outflows, and

storage as shown in the following equation:Inflow = Outflow +/- Changes in Storage

Inflows add water to the different parts of the hydrologicsystem, while outflows remove water. Storage is the retention

of water by parts of the system. Because water movement iscyclical, an inflow for one part of the system is an outflow foranother.

Precipitation = Evapotranspiration + Total Runoff,whereTotal Runoff = Direct Runoff + Base flow (groundwatercomponent of stream flow)

Evaporation (E)T i ti (T)


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One of the uses of the consideration of water balance is in the estimation ofsurface storage.

Storing and transferring a sufficient quantity of water has been one of the

major problems. What volume of water is stored in a surface reservoir/soil (expanding

the concept over a larger area) and how does the volume change overtime? What causes the water supply to be depleted or increased?

How are the storage and releases managed?

Subsurface Flow (B)

Rainfall Excess (R)

p ( )Transpiration (T)

Infiltration (F)

Precipitation (P)

Storage (S)

Schematic of hydrologic balance

components for a pond


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Subsurface Flow (B)

Rainfall Excess (R)

Evaporation (E)Transpiration (T)

Infiltration (F)

Precipitation (P)

Storage (S)

Based on the conservation of mass:

Input output = change in storageP + R + B - F - E - T = S

volumes are measured in units m3, L, ac-ft, f3, gal,

or in & cm over the watershed area

Water balance components in root zone


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Evapo-transpiration

Transpiration

Evaporation

Rain

Runoff

Drainage

Root ZoneWater Storage

Irrigation

Below Root

Zone

Waterbalancecomponentsinrootzone


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S


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Precipitation (P)

BoundaryInput(B

I)

Subsurface Flow = interflow + baseflow

Infiltration (F)

Rainfall Excess (R)

Transpiration (T)

Evaporation (E)

Area Boundary

Solar Energy

Depression

Storage

Storage (S)

BoundaryOu

tput(BO)

Evaporation (E)

Area Boundary

Sun

Subsurface Flow (B)

Simplified representation of a very dynamic process in a watershed

Subsurface Water Storage

Soil Moisture Storage

Equation for the mass balance can be written in this case in the same


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form as below,

Input output = change in storagebut can we use this equation (as given in the previous slide)

P + R + B - F - E - T = S

You need to reconsider all the terms in line with your schematization anddelineation of spatial boundary of reference domain

P + BI - R - F - E T - BO = S (with boundary in 3rd dimension, that isin vertical direction is the ground surface)

However, by considering the watershed with surface and subsurfaceincluding,

P + BI - R - B - E T - BO = S

note, BI and BO include both surface and subsurface input and output ,B includes both interflow, groundwater flow and baseflow

S includes changes in surface, soil moisture and GW storage

Note volumes are measured in units m3, L, ac-ft, f3, gal, or in & cmover the watershed area


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Whatto

do

about

units?

Rainfall is expressed in mm, in

Stream flow is expressed in cubicfeet/cubic meter per second/minute

Evapotranspiration is expressed in mm, in

Soil water storage?

How can we make a mass balance with

different units? Conversion


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WaterDepth

We have to use the same units; thus we

have to remove the area from ourcalculation

We need to convert volume into unit

depth; thus whats water depth:

Water depth (d) = Volume of water (V) /

Surface of the field (A)


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Conversion

1 acre-foot = 1317.25 m3


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Problem 1 Suppose there is a reservoir, filled with

water, with a length of 5 m, a width of 10m and a depth of 2 m. All the water from

the reservoir is spread over a field of 1

hectare. Calculate the water depth (whichis the thickness of the water layer) on the

field.


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Problem 2 A water layer 1 mm thick is spread over a field of

1 ha. Calculate the volume of the water (in m

3

),


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Answer 2 Given

Surface of the field = 10 000 m2Water depth = 1 mm =1/1 000 = 0.001 m

Formula: Volume (m) = surface of the

field (m) x water depth (m)

Answer

V = 10 000 m2

x 0.001 mV = 10 m3 or 10 000 liters


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Problem 3Over a two-month period of time, a catchment isexpected to receive 254 mm of rain with an

expected evapotranspiration estimated at 95mm and that lost to groundwater storage of 20mm. There is no other significant storage in the

watershed. What is the expected rainfall excessto a reservoir storage area if the catchment areais 65 km2? Express your answer in cubic meterand liter. Also determine how many people can

be serviced by this water if the per person perday water use rate is 160 liters.


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Problem 4Estimate the amount of depression

storage (inches and cubic feet) in a 6 acreparking lot using the following rainfall and

discharge data. The discharge data were

measured at the only inlet in the parkinglot. Rainfall = 0.88 in, Rainfall excess = 5

cfs average for one hour. Also list

assumptions for the other variables of thehydrologic cycle.


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WhatpercentoftheEarthstotal


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p

volumeofwaterisstoredintheatmosphere?

0.001%

Water vapor

Clouds(water vapor

condensed onparticulate)


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What two processes change liquidwater into vapor that can ascend into

the atmosphere?

Evaporation

Transpiration90%

10%What percent of the water inthe atmosphere comes from

evaporation?

Evaporation


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Evaporation

The process by which liquid water is transformed

into a gaseous state

Evaporation into a gas ceases when the gas

reaches saturation

The molecules that escape the condensed stage have

above-average energies.

Those left behind have below-average energies

Manifested by a decrease in the temperature of the

condensed phase.

Evaporation


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Evaporation

Energy breaks bonds that hold molecules

together Netevaporation occurs when the rate of

evaporation exceeds the rate of condensation

Removes heat from the environment:

Net Cooling

Primary mechanism for surface-to-atmosphere

water transport

Evaporationv.Precipitation


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About equal on a global scale

Evaporation more prevalent over the oceans than

precipitation

Over land, precipitation exceeds evaporation

Most water evaporated from the oceans falls backinto the ocean as precipitation

10% of water evaporated from the ocean is

transported over land and falls as precipitation Once evaporated, a water molecule spends ~ 10

days airborne


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Physicalcharacteristicsaffecting


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surfacerunoff- Land use

- Vegetation

- Soil type- Drainage area

- Basin shape

- Elevation- Topography, especially the

slope of the land

- Drainage network patterns

- Ponds, lakes, reservoirs, sinks,etc. in the basin, which preventor delay runoff from continuingdownstream

Humanfactorsaffectingsurface


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runoff

Urbanization -- more impervious surfaces

reduce infiltration and accelerate water

motion

Removal of vegetation and soil -- surfacegrading, artificial drainage networks

increases volume of runoff and shortens

runoff time to streams from rainfall andsnowmelt


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Mostrunoff Drains to a creek

To a stream

To a river

To an ocean Rarely runoff drains to a closed lake

May be diverted for human uses

GroundwaterbeginsasINFILTRATION


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Precipitation fallsand infiltrates into

the subsurface soil

and rock

Can remain in shallow soil layer

Might seep into a stream bank

May infiltrate deeper, recharging an aquifer

May travel long distances

May stay in storage as ground water


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Infiltrationreplenishedaquifers


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Slow process -- ground water moves slowly through the unsaturated

zone Recharge Rate determined by precipitation & depth

An aquifer in New Mexico, if emptied, would take centuries to

refill whereas a shallow aquifer in south Georgia may be

replenished almost immediately

SubsurfaceWater


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As precipitation infiltrates subsurface soil, it forms zones: Unsaturated -- interstitial spaces cannot be pumped

Saturated -- Water completely fills the voids betweenrocks and soil particles


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Hydrologic Residence Time in different storages


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Typical residence times of water foundin various storages

Reservoir

Average

Residence Time

Glaciers 20 to 100 years

Seasonal Snow

Cover2 to 6 months

Soil Moisture 1 to 2 months

Groundwater:

Shallow100 to 200 years

Groundwater:Deep 10,000 years

Lakes 50 to 100 years

Rivers 2 to 6 months

Water is continually cycled between

its various storages. The typical

residence times of water in the major

storages varied greatly.

On average water is renewed in

rivers once every 16 days. Water in

the atmosphere is completelyreplaced once every 8 days.

Slower rates of replacement occur in

large lakes, glaciers, ocean bodies

and groundwater. Replacement in

these reservoirs can take from

hundreds to thousands of years.

Hydrologic Time Scale


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The different storages and processes can occur at

vastly different time scales.

Surface processes (e.g. evaporation, precipitation and

surface runoff) occur much more rapidly than

subsurface processes (e.g. groundwater flow, infiltration,

recharge and discharge).

Hoursdaysmonthsyearsdecadescenturies--

millennia

Surface and near-surface processes can be considered

much more active processes.

Waterbalancecomponentsofah d h ( d )


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watershedwith(systemdiagram)


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introduction for hydrology

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