#2 pengantar hidrologi evaporasi
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PENGANTAR HIDROLOGIPENGANTAR HIDROLOGI
Evaporasi
evaporation
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definitiondefinition
• Evaporation is the process by which a liquid is changed into a gas– The process of evaporation can occur
naturally only if there is an input of energy either directly from the sun or indirectly from the atmosphere itself, and is controlled by the rate at which the water vapor produced can diffuse away from the earth’s surface by means of molecular and turbulent diffusion processes
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Evaporation from free water surface
• Dalton (1802) wind speed & vapour pressure• Meteorological factors
– Solar energy (Linsley et.al. 1958)– Humidity– Diffusion processes
• Physical factors– Salinity– Water depth– Size of surface
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Miller, 1953
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From ASCE, 1949
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Depth factor Kempton park reservoir & Lake Superior
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Rate Evapotranspiration vs surface (thornwaite & mather, 1955)
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http://web.ipb.ac.id/~tpb/tpb/files/materi/bio100/Gambar/trans_tnm/evaporasi.jpg
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Faktor yang mempengaruhi Faktor yang mempengaruhi evaporasievaporasi
• TemperaturTemperatur yang diukur sebagai kombinasi energi potensial & kinetik dari atom penyusun suatu benda. Kapasitas panas mempengaruhi laju dan waktu terjadinya evaporasi
• Kelembaban dan tekanan uapKelembaban dan tekanan uap. Bila tekanan uap naik, maka evaporasi dari tubuh perairan menurun.
• RadiasiRadiasi adalah pancaran energi panas oleh gelombang em. Energi radian panas. Energi radian dapat dipantulkan, diserap, dan dipancarkan. Temperatur dan radiasi berkorelasi tinggi.
• Kecepatan anginKecepatan angin
seeRh
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Pengukuran evaporasi Pan A
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Evaporasi di daerah tropis
• 3 – 6 mm/hari 5
• Per tahun ? 1800-an mm/th
• Hujan 1500-3000 mm/th
• doline
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METODE PERHITUNGAN EVAPORASIMETODE PERHITUNGAN EVAPORASI
A. Metode Neraca/Imbangan
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Thornthwaite
• j = (tn/5) 1.514
• tn temperatur bulanan rata-2
• J = Sum(j)
• (lihat nomogram Sri-Harto hal 92)
• PE=1.6 (10t/J) a
• a = 675 10-9 J3 – 771 10-7 J2 + 178 10-4J +0.498
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Terima kasih
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quis
• Faktor apa saja yg berpengaruh dalam proses penguapan
• Mengapa perlu dilakukan perhitungan evapotranspirasi (selain evaporasi dan transpirasi)
• Sebutkan berapa cara pendekatan yg dapat digunaan untuk memperkirakan laju penguapan