hydrology Topic 1

7/27/2019 hydrology Topic 1

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Hydrology

TOPIC 1

BASIC OF HYDROLOGY

The Concept of Hydrology

Discusses the hydrologic cycle, it’s processes, water balance, precipitation

types, estimation of precipitation, and analysis of precipitation data. Also methods of

measurement of stream flow, stage discharge relation, unit hydrograph theory,

Transposition of Hydrograph, Synthesis of hydrograph from basin characteristics,

stream flow routing, flood frequency analysis and attenuation of flood flows.

mphasis is gi!en towards the calculation of rain fall data and urban drainage concept

in de!eloping new areas.

"hat #s Hydrology$

a. The study of water on, under, and over the arth’s surface, and from its

origins to all its destinations on the earth is called hydrology.

b. The scientific study of water, see%ing to e&plain the water balance equation

in terms of time and space, and assessing the impact of physical andchemical processes and their role in ecosystems.

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Hydrology

'ses of ngineering Hydrology

ngineering Hydrology Helps in the following ways(

⇒ Hydrology is used to find out ma&imum probable flood at proposed sites

e.g. Dams.

⇒ The !ariation of water production from catchments can be calculated and

described by hydrology.

⇒ ngineering hydrology enables us to find out the relationship between a

catchment’s surface water and groundwater resources

⇒ The e&pected flood flows o!er a spillway, at a highway Cul!ert, or in an

urban storm drainage system can be %nown by this !ery sub)ect.

⇒ #t helps us to %now the required reser!oir capacity to assure adequate water

for irrigation or municipal water supply in droughts condition.

⇒ #t tells us what hydrologic hardware *e.g. rain gauges, stream gauges etc+

and software *computer models+ are needed for realtime flood forecasting

⇒ 'sed in connection with design and operations of hydraulic structure

⇒ 'sed in prediction of flood o!er a spillway, at highway cul!ert or in urban

storm drainage

⇒ 'sed to assess the reser!oir capacity required to assure adequate water for

irrigation or municipal water supply during drought

⇒ Hydrology is an indispensable tool in planning and building hydraulic

structures.

⇒ Hydrology is used for city water supply design which is based on

catchments area, amount of rainfall, dry period, storage capacity, runoff

e!aporation and transpiration.

-ranches of Hydrology

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Hydrology

Hydrological Cycle

igure /.0( Hydrologic Cycle

1efer to clause 0.0./, 'rban Stormwater 2anagement 2anual for 2alaysia

*2AS2A+ !ol. /( #ntroduction to the 2anual, the hydrologic cycle is the continuous,

unsteady circulation of water from the atmosphere to and under the land surface and

bac% to the atmosphere by !arious processes. #t is dynamic in that the quantity and

quality of water at a particular location may !ary greatly with time. Temporal !ariations

may occur in the atmosphere, on land surface, in surface waters, and in the

groundwater of an area. "ithin the hydrologic cycle, water may appear in all three of

its states3 solid, liquid, and gas. igure /.0 shows the hydrologic cycle in schematic

form. The important processes are described below with emphasis on factors that

influence each process and its significance in the planning, design, and operation of

stormwater management systems *"alesh, /454+.

How the water cycle wor%s

/. Solar energy heats up the oceans water surface, la%e, ri!er etc.

0. The water e!aporates and rises into the air.

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Hydrology

6. The !apor condenses into clouds and turns into rain.

7. 1ain falls bac% to the surface. Some of rain infiltrates in soil.

8. Surface runoff ma%es its way into ri!ers and streams.

9. 1i!ers flow bac% into the ocean due to the force of gra!ity.

:. The cycle starts all o!er again.

The ;rocess in Hydrological Cycle

a. !aporation

b. Condensation

c. ;recipitation

d. Surface runoff,

e. interception

f. Transpiration

g. #nfiltration

h. Subsurface runoff

i. Sublimation

!aporation

!aporation is the process by which water is con!erted from its liquid form to

its !apor form and thus transferred from land and water masses to the atmosphere.

The rate of e!aporation depends upon(

• "ind speed( the higher the wind speed, the more e!aporation

•

Temperature( the higher the temperature, the more e!aporation• Humidity( the lower the humidity, the more e!aporation

Condensation

The change of water from its gaseous form *water !apor+ into liquid *water+.

Condensation generally occurs in the atmosphere when warm air raises, cools and

looses its capacity to hold water !apor. As a result, e&cess water !apor condenses toform cloud droplets.

;recipitation

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Hydrology

;recipitation can occur primarily as rain. Annual amounts of precipitation are

unpredictable and !ariable, ranging from appro&imately /8<< mm to 7<<< mm in

!arious locations in 2alaysia. #n essence, precipitation is the most important process

in the hydrologic cycle because it is the =dri!ing force= pro!iding water that must be

accommodated in the urban en!ironment.

Surface runoff

Sometimes referred to as o!erland flow, is the process whereby water mo!es

from the ground surface to a waterway or water body. 'rbanisation usually

dramatically increase surface runoff !olume and rates.

#nterception

#nterception is the amount of precipitation that wets and adheres to

abo!eground ob)ects *primarily !egetation+ until it is e!aporated bac% into the

atmosphere. The annual amount of interception in a particular area is affected by

factors such as the amount and type of precipitation, the e&tent and type of

!egetation, and winds. #nterception is not li%ely to be an important process in urban

stormwater management programs.

Transpiration

Transpiration is the process by which moisture is carried through plants from

roots to small pores on the underside of lea!es, where it changes to !apor and is

released to the atmosphere. Transpiration is essentially e!aporation of water from

plant lea!es. Transpiration also includes a process called guttation, which is the loss

of water in liquid form from the unin)ured leaf or stem of the plant, principally through

water stomata.

n!ironmental factors that affect the rate of transpiration

/. >ight;lants transpire more rapidly in the light than in the dar%. This is largelybecause light stimulates the opening of the stomata *mechanism+. >ight alsospeeds up transpiration by warming the leaf.

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Hydrology

0. Temperature;lants transpire more rapidly at higher temperatures because water e!aporatesmore rapidly as the temperature rises. At 6<?C, a leaf may transpire threetimes as fast as it does at 0<?C.

6. HumidityThe rate of diffusion of any substance increases as the difference inconcentration of the substances in the two regions increases."hen thesurrounding air is dry, diffusion of water out of the leaf goes on more rapidly.

7. "ind"hen there is no bree@e, the air surrounding a leaf becomes increasinglyhumid thus reducing the rate of transpiration. "hen a bree@e is present, thehumid air is carried away and replaced by drier air.

8. Soil water

A plant cannot continue to transpire rapidly if its water loss is not made up by

replacement from the soil. "hen absorption of water by the roots fails to %eep

up with the rate of transpiration, loss of turgor occurs, and the stomata close.

This immediately reduces the rate of transpiration *as well as of

photosynthesis+. #f the loss of turgor e&tends to the rest of the leaf and stem,

the plant wilts.

#nfiltration

#nfiltration is defined as the passage of water through the airsoil interface.

#nfiltration rates are affected by factors such as time since the rainfall e!ent started,soil porosity and permeability, antecedent soil moisture conditions, and presence of

!egetation. #nfiltration is a !ery important process in urban stormwater management

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http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.html




Hydrology

and, therefore, essentially all hydrologic methods e&plicitly account for infiltration.

'rbanisation usually decreases infiltration with a resulting increase in runoff !olume

and discharge.

Subsurface runoff.

#nterflow, sometimes referred to as subsurface stormflow, is the process

whereby water mo!es laterally beneath the land surface, but abo!e the groundwater

table. #nterflow occurs until water enters a waterway or water body, or is

e!apotranspired. #nterflow is affected by the same factors as those for surface runoff.

#nterflow is rarely e&plicitly analyses3 it is usually considered part of the surface runoff.

Surface runoff, interflow, and precipitation falling directly on water bodies are

sometimes lumped together and called direct runoff.

The ffect of Soils 'se Toward Hydrological Cycle.

• "hen de!elopment occurs, the resultant alterations to the land can lead to

dramatics changes to the hydrology or the way water is transported and stored,

• #mper!ious manmade surfaces *asphalt, concrete, rooftops+ and compacted earth

associated with de!elopment create a barrier to percolation of rainfall into the soil,

increasing surface runoff and decreasing ground water infiltration.

Effects of Urbanization on Stor!ater "#inistr$ of En%ironent& '(()*

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Hydrology

Fi+,re 1-. / Re0ationsi2s bet!een i2er%io,s co%er an3 s,rface r,noff

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If over 10% of a watershed isconvered by impervioussurfaces ,stream quality maybe moderately impacted

Watersheds with over 25%impervious surfaces haveseverely impacted streams



Hydrology

• This disruption of the natural water cycle leads to a number of changes, including(

a+ #ncreased !olume and !elocity of runoff

b+ #ncreased frequency and se!erity of flooding

c+ ;ea% *storm+ flows many times greater than in natural basinsd+ >oss of natural runoff storage capacity in !egetation, wetlands and soil

e+ 1educed groundwater recharge

f+ Decreased base flow *the ground water contribution to stream flow+. This

can result in stream becoming intermittent or dry and also affects water

temperature.

The Hydrology Continuity quation

In2,ts can include(

• ;recipitation rain3

• roundwater influ& from an ad)acent aquifer or a transboundary *transri!er

basin+ aquifer3

• Snow melt3 and

•

#nterbasin transfer *water transferred into the basin from an ad)acent ri!erbasin+.

E4tractions include(

• !aporation3

• Transpiration3

• &traction for consumpti!e use from streams and ri!ers water for industrial or

domestic use and irrigation3

• &traction for consumpti!e use from groundwater aquifers3 and

• #nterbasin transfer *water transferred out of the basin to ad)acent ri!er basin+.

A simple approach to a water balance equation could be considered as *"anielista et

al. /44:+(

P 5 R 5 B 6 F 6 E 6T 7 8S

Abbre!iations(

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Hydrology

; B ;recipitation

1 B 1unoff or e&cess rainfall

- B Subsurface flow

B #nfiltration

B !apotranspiration

T B Transpiration

S B Change in storage in the saturated @one soil or groundwater

#nflow utflow B Change in Storage

# B dsEdt

# B FS

P 9 DRO 9 E 9 T6G 7 :S

G

P 9 " R 5 ET 5 G* 7 :S

&ample3

/+ elantan=s ri!er catchment=s e&pected to accept rain as much as 68< mm fromthe beginning ctober 0<<6 to December 0<<6. !aporation and infiltrationrespecti!ely was estimated at 68 mm and 08 mm in that time period. Thecatchment’s area was 4< %m0. There is a reser!oir in these catchments.stimate runoff !olume in m6 if le!el of reser!oir unchanged.

Solution (

i!en3

; B 68< mm , B 68mm, # B 08mm , A B 4<%m0

Hydrology equation balance(

#nflow utflow B Change in Storage

dsEdt * # + B Change in Storage

; * I # I D1 + B <

68< * 68 I 08 I D1+ B <

D1 B 04< mm G <.04mm

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Hydrology

Jolume of direct runoff, D1 B <.04m & * 4<%m0 & */<<<m +0

*/%m+0

B ')-1 4 1() ..

&ercise(

/+ #n 9 month period, Sungai >ui catchment’s were estimated will get rain as muchas 68< mm. !aporation were estimated as much as /<< mm and infiltration tosubsurface were estimated at the 7< mm. stimated the !olume of runoff incubic meters *m6+ that will be storage in reser!oir if area for catchment was 58%m0.

0+ Hydrology record for a catchment=s as wide as 8<< %m0 show e&cess rainfallannual and a!erage the surface runoff annual respecti!ely was 4< cm and 66cm. ne reser!oir as wide /:<< %m0 had planned the construction in the outlet

part of catchment area. The annual e!aporation a!erage to that reser!oir wase&pected as much as /8< mm. Determine storage !alues that occur in thatreser!oir.

6+ #n a year, a wide rain catchment area is /<6 %m0 accept rain as much as /<<<mmE year. Annual discharge of the ri!er is /4 m6Es. stimatede!apotranspiration to the catchment area.

7+ #n period three months, etereh district are e&pected to recei!e rain as muchas 078 mm. e!apotranspiration were estimate as 5< mm and diffusion to subsurface as much as 0< mm. "ide of basin was 69 %m0. stimate (

&cess rain depth calculate direct runoff !olume – #f direct runoff may be stored in a reser!oir, determine population

of people which can accept water supply for now if percapitadaily utili@ability was 0<< liters.

8+ A storage pool has as much as water total sa!ing 0< & /<6 m6, in times thatbeen ta%en. "here discharge reading inflow and outflow is /< m6E s and /8 m6Es. After an hour later flow reading in and out change to /8 m6E s and /9 m6 E s.Calculate water reser!e change and water total sa!ing that new after / hours.

9+ A catchment area as wide as 0.8 %m0 accepts rainfall intensity /<< mmE hourfor 9 hours. 1un !olume of water that noted in this period is :0<,<<< m6. etrate of water loss from rain 9 hours.

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Hydrology

:+ ne reser!oir 7<< hectare e&panse, produce e!aporation as much as 8< cm in07 hours. &pansion due to hea!y rain into reser!oir was in !alue 98 m6E s.Determine hectaremeter deep water=s !olume that seeping reser!oir policy onthat day if unchanged water le!el.

5+ Catchment area in uala rai has area /:0< %m0. Annual a!erage rainfall datais 60<< mm. There are two ri!ers which flowed to that catchment area, namelySungai uala Kal and Sungai rai. Discharge from Sungai uala Kal is 06m6Eswhile data from Sungai rai not obtained. 1ecord that made to show loss resultcondensation process and bypass is /0L from a!erage annual rainfall.Calculate discharge !alue for Sungai rai.

1eferences

/. http(EEwww.aboutci!il.comEusesofengineeringhydrology.html

0. http(EEmsmam.comEmsmamEchapter0ECh0n!ironmental;rocesses.html 6. http(EEtechali!e.mtu.eduEmeecEmodule</E!aporationandTranspiration.htm

7. http(EEwww.poweredbymothernature.comEwhatishydropower

8. http(EEwww.%unenera%.comEenEri!erEhydrologyEprinciplesIofIhydrologyEwaterIbala

nce.asp&

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http://www.aboutcivil.com/uses-of-engineering-hydrology.html


http://msmam.com/msmam/chapter2/Ch2-EnvironmentalProcesses.html


http://techalive.mtu.edu/meec/module01/EvaporationandTranspiration.htm

http://www.poweredbymothernature.com/what-is-hydropower

http://www.kunenerak.com/en/river/hydrology/principles+of+hydrology/water+balance.aspx




http://techalive.mtu.edu/meec/module01/EvaporationandTranspiration.htm

http://www.poweredbymothernature.com/what-is-hydropower



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hydrology Topic 1