1. Hydrology Engineering IR HERMONO S. BUDINETRO, M. ENG
Lecture 7 1 2 3 4 5 6
IR HERMONO S. BUDINETRO, M. ENG

2. HYDROLOGI General HYDROLOGI HYDROMETRI CLIMATOLOGY RAINFALL
AWLR, Peil scal
RAINFALL
ARR, ORR
EROSIFITAS
WATER LEVEL
POINT RAINFALL
Observation
Current meter
SEDIMEN TRANSPORT
Observation
RATING CURVE
AREAL RAINFALL
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

3. EVAPORATIon, TRANSPIRATION and EVAPOTRANSPIRATION
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.

4. Evaporation is influenced by. :
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.

5. 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.

6. Estimation of Evaporation
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.
Ground
10 inchi
48 inchi
Class A Pan
Evaporation =
Water is contained + precipitation (if any) - water left the next morning.

7. PAN EVAPORASI

8. b. Implanted in soil  Colrado Sunken Pan
c. Floated on the water

9. 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.

10. 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

11. Some empirical formula for calculating evapotranspiration
Penman
Blaney-Criddle
Thornthwaite
Turck
Hargreaves
Or with field measurements : Lysymeter

12. field measurements Lysymeter
Evapotranspiration =
Rainfall + additional water – water seeping out