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

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

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.

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.

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 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.

PAN EVAPORASI

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

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.

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  

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

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