Arba Mich University Arba Mich Institute of Technology Applied Hydrology (HE-612) Assignment one Q #1. Explain the hydrologic cycle in nature and its various phases involved with the help of a neat sketch. Answer : The movement of water on the earth's surface and through the atmosphere is known as the hydrologic cycle. OR it is the water transfer cycle, which occurs continuously in nature; the three important phases of the hydrologic cycle are: ( a) Evaporation and evapotranspiration (b) precipitation and (c) runoff and is shown in Fig. 1. The globe has one-third land and Two thirds Ocean. Evaporation from the surfaces of ponds, lakes, reservoirs. Oceans, etc. and transpiration from surface vegetation i.e., from plant leaves of cropped land and forests, etc. take place. These vapors rise to the sky and are condensed at higher altitudes by condensation nuclei and form clouds, resulting in droplet growth. The clouds melt and sometimes burst resulting in precipitation of different forms like rain, snow, hail, sleet, mist, dew and frost. A part of this precipitation flows over the land called runoff and part infiltrates into the soil which builds up the ground water table. The surface runoff joins the streams and the water is stored in reservoirs. A portion of surface runoff and ground water flows back to ocean. Again evaporation starts from the surfaces of lakes, reservoirs and ocean, and the cycle repeats. Of these three phases of the hydrologic cycle, namely, evaporation, precipitation and. runoff, it is the
Arba Mich UniversityArba Mich Institute of TechnologyApplied
Hydrology (HE-61! Assign"ent oneQ #1. Explain the hydrologic cycle
in nature and its various phases involved with the help of a neat
sketch. Ans#er:The movement of water on the earth's surface and
through the atmosphere is known as the hydrologic cycle. ! i t is
thewater transfer cycle" which occurs continuously in nature# the
three important phases of the hydrologic cycle are: $a% Evaporation
andevapotranspiration$b%precipitationand$c%runoffandisshownin&ig.
1. Theglo'ehasone(thirdlandandTwothirdscean.Evaporation from the
surfaces of ponds" lakes" reservoirs. ceans" etc. and transpiration
from surface vegetation i.e., from plant leavesof cropped land and
forests"etc. take place. These vapors rise to the sky and are
condensed at higher altitudes 'y condensation nucleiand form
clouds" resulting in droplet growth. The clouds melt and sometimes
'urst resulting in precipitation of different forms likerain" snow"
hail" sleet" mist" dew and frost. ) part of this precipitation
flows over the land called runoff and part infiltrates into the
soilwhich 'uilds up the ground water ta'le. The surface runoff
*oins the streams and the water is stored in reservoirs. ) portion
of surfacerunoff and ground water flows 'ack to ocean. )gain
evaporation starts from the surfaces of lakes" reservoirs and
ocean" and the cyclerepeats. f these three phases of the hydrologic
cycle" namely" evaporation" precipitation and. runoff" it is the
+runoff phase," which isimportant to a civil engineer since he is
concerned with the storage of surface runoff in tanks and
reservoirs for the purposes ofirrigation" municipal water supply
hydroelectric power etc.&igure 1. -llustration of .ydrologic
cycleQ#/. 0iscuss the 'asic conditions necessary for the occurrence
of precipitation. Thereare four basic conditions required for the
occurrence of precipitation; Accumulation of moisture in the
atmosphere (evaporation) Cooling of air to the dew point
temperature (saturation) Condensation of water vapor in the
atmosphere Growth of small water droplets (clouds) to the required
sizeAns#er: 1recipitation is any product of the condensation of
atmospheric water vapor that is deposited on the Earth's surface.
-t occurswhen the atmosphere" a large gaseous solution" 'ecomes
saturated with water vapour and the water condenses" falling out of
solution$i.e." precipitates%. Two processes" possi'ly acting
together" can lead to air 'ecoming saturated: cooling the air or
adding water vapourto the air. 1recipitation forms via collision
with other rain drops or ice crystals within a cloud.2oisture
overriding associated with weather fronts is an overall ma*or
method of precipitation production. -f enough moisture andupward
motion is present" precipitation falls from convective clouds such
as cumulonim'us and can organi3e into narrow rain 'ands.4here
relatively warm water 'odies are present" for example due to water
evaporation from lakes" lake(effect snowfall 'ecomes
aconcerndownwindofthewarmlakeswithinthecoldcyclonicflowaroundthe'acksideofextratropical
cyclones. 5ake(effectsnowfall can 'e locally heavy. Thunder snow is
possi'le within a cyclone's comma head and within lake effect
precipitation 'ands. -nmountainous areas" heavy precipitation is
possi'le where upslope flow is maximi3ed within windward sides of
the terrain at elevation.n the leeward side of mountains" desert
climates can exist due to the dry air caused 'y compressional
heating. The movement of themonsoon trough" or inter(tropical
convergence 3one" 'rings rainy seasons to savannah climes.)s
summery# the following three conditions are re6uired in order to
produce precipitation:1. ) continuous supply of water vapour
through evaporation and transpiration processes and the air
movement to transport the watervapour to the location of
rainfall./. 7ucleating particles such as dust" salt" pollen and
various atmospheric ions for condensation must 'e present.8. )
cooling mechanism sufficient to cause condensation and growth of
water droplets or ice crystals from water vapour.Q#8. The
hydrologic cycle is a phenomenon occurring continuously in the
troposphere(ocean(lithosphere(cryposphere continuum. 9utwhy the
outputs of the hydrologic cycle $precipitation" stream flow" etc.%
vary over time and space:)nswer: there are num'er of reasons such
as glo'al climate change $due to deforestation" relies of ;/ from
industries and vehicles tothe atmosphere" population density
increment" etc.%" variation of topographic features and
geographical location of the area. Q#1 km/. &or the month of
2arch" this lake had an inflow of 1.? m8@s and an outflow of 1.8A
[email protected] storage change of B>1="===m8 was recorded. -f the total
depth of rainfall recorded at the local rain gauge during the same
period was//A mm. Estimate the evaporation loss from the lake and
state any assumption you use during your computation.)nswer: -n a
time period Ct" the water 'udget for the lake can 'e written
as:-nput Dolume E utput Dolume F ;hange in Gtorage $-Ct B 1.)% E
$QCt B E.)% F CG# 4here" - F average inflow rate" Q F average
outflow rate" 1 F precipitation" E F evaporation" ) Fsurface area
of the lake and CG F change in the lake storage volume.Assu"ption:
)ssume that a lake had 'oth inflow and outflow totally in one month
$i.e. month of 2arch having totally 81 days%..ence" Ct F 1 month of
2arch F 81 x /< x H= x H= F /.H>?< 2illion seconds in a
month of 2arch.CG F $%&1M"' (given value! -nflow volume F -Ct F
1.? x /.H>?< F (%)11M"'utflow volume F QCt F 1.8A x
/.H>?< F '%61*)(M"'-nput due to precipitation F 1.) F //A mm
x =.>1km/ F $%1*+&*M"'utput due to evaporation F E.) F E x
=.>1km/ F E , $%&1M"
! $=.>1 E % 2m8 F ( 8.H1A?< 2m8 E =.>1E2m/. Evaporation
loss from a lake F =.I//88?=/? 2m ! Evaporation F I//88?.=/?m
F+-'')-$)""Q#A. The following data are o'tained in stream gauging
operation. ) current meter with a cali'ration e6uationv = (0.32N +
0.032)m/s " where 7 is revolution per second was used to measure
the velocity at =.HJd. Ksing $a% 2id(section and $'% 2ean(
sectionmethods" calculate the discharge in the stream. 0istance
from theright 'ank $m%= / < H I 1/ 1A 1? /=0epth $m% = =.A 1.1
1.IA /./A 1.?A 1.A =.>A =7um'er ofrevolutions= ?= ?8 118 18I 1/1
11< >= ='servation time $s% = 1?= 1/= 1/= 1/= 1/= 1/= 1A=
=Ans#er: 0istance
fromtheright'ank$m%)veragewidth$m%0epth$m%!evolutions$7Fm%'servationtime$tFs%
7s F !@t$m@s%)rea"C)Delocity" CD 0ischarge" CQ=.HD F Di=./D and
=.?D F$Di(1 BDiB1%@/2id(sectionmethod 2ean(sectionmethod= = = = =
=.=======.=== =.=========.========/ /./A =.A ?= 1?= =.= 1A= =.
