Download EVAPORATIon, TRANSPIRATION and

Hydrology Engineering
Lecture 7
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IR HERMONO S. BUDINETRO, M. ENG
HYDROLOGI
General
HYDROLOGI
HYDROMETRI
CLIMATOLOGY
AWLR, Peil scal
RAINFALL
ARR, ORR
EROSIFITAS
POINT RAINFALL
WATER LEVEL
Observation
SEDIMEN TRANSPORT
AREAL RAINFALL
Current meter
RATING CURVE
Analisa frekuensi
DESIGN RAINFALL
RIVER DISCHARGE
Sintetis
Frequency Analysis
DESIGN
DISCHARGE
Maximum discharge (at maximum water level)
Minimum discharge (at dry season) and
Design discharge (design flood) and
Water availibility
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EVAPORATIon, TRANSPIRATION and
EVAPOTRANSPIRATION
Evaporation
 Evaporation is a process of change in the form of water,
from liquid or solid form, to forms of gas due to the
caloric intake (the heat).
 In hydrology, evaporation is an important factor
because of evaporation influence on streamflow (river
discharge), reservoir capacity planning, use of water for
plants (consumtive use), etc.
Evaporation is influenced by. :
4  Sun Radiation: Sunshine energy change fluid become gas
 Wind: wind transport saturated water vapour, that replace with dry air
 Humidity: if the Relative humidity is high, the air's ability to absorb low
vapor. Conversely, if Relative humidity is low (which means the air is
dry), then the ability of air to absorb water, is high.
 The air temperatur : the higher temperature, the air's ability to absorb
water vapor higher, because:
 the relative humidity will be lower
 there will be upward air flow, the air flow will transport the water
vapor above.
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Evapotranspiration
In the reality in the field is not possible differentiates between
evaporation by transpiration, it especially if the soil is covered by
vegetation. Therefore, evaporation and transpiration are
interrelated with unclear boundaries, then in practice usually
called evapotranspiration.
 Evapotranspiration is the evaporation that occurs on the
surface of the water, the land surface, and the leaves are on
the places.
 There are several ways to get an idea, a large evaporation
and evapotranspiration, both obtained from direct
measurements or by empirical formulas.
Estimation of Evaporation
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 Evaporastion pans
This pan was made to replicate the conditions of a free water surface
evaporation. There are several kinds of pan evaporation are:
a. Installed on the ground, namely: :
Class A Pan Evaporation (The Standar National Weather Service Class A Pan)
diameter 48 inchi and height 10 inchi.
48
inchi
10 inchi
Ground
Class A Pan
Evaporation =
Water is contained + precipitation (if any) - water left the next morning.
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PAN EVAPORASI
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b. Implanted in soil  Colrado Sunken Pan
48 inchi
10 inchi
tanah
tanah
tanah
c. Floated on the water
48 inchi
10 inchi
air
air
air
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Evaporation value, at the pan is always higher than in the surface
of the water that is more larger (wider) as lakes, reservoirs, etc.
because:
 ability to keep warm, on the lake / reservoir is larger than the
pan;
 water in a pan no waves, therefore air turbulence over the
pan is smaller than lakes / reservoirs;
 heat exchange occurs between pan with the atmosphere, soil
and water around it;
 Additional solar radiation on the sides of pan;
 because the pan of water surface area is very small,
compared to the wide lake / reservoir, so that the temperature
and humidity influence is not the same as the large surface
such as lakes / reservoirs.
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Therefore, to calculate the evaporation on the reservoirs,
the measurement results of the pan, shall be multiplied by
coefficient of pan
EL = K x Ep
Where:
EL = Eavaporation from lake/reservoir
Ep = Evaporation from pan
K = pan coeffisient
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Some empirical formula for calculating
evapotranspiration
 Penman
 Blaney-Criddle
 Thornthwaite
 Turck
 Hargreaves
 Or with field measurements : Lysymeter
Evapotranpiration
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field measurements
Lysymeter
Rainfall + Additional water (sprinkle)
Evapotranspiration =
Rainfall + additional water – water seeping out
The water seeping are collected and measured