Imbangan Air
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Transcript of Imbangan Air
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II. IMBANGAN AIR (WATER BALANCE)
Imbangan air merupakan perhitungan jumlah air yang masuk (inflow) dan yang
keluar (outflow) pada suatu daerah yang ditinjau selama perioda waktu tertentu.
Gambar 2.1 Sistem hidrologi sederhana
I = inflow per satuan waktu
O = outflow per satuan waktu
dS/dt = perubahan tampungan per satuan waktu
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Dasar : hukum konservasi massa
dS/dt = I – O
�S = I – O
Contoh :
�S = �I – �O
= P – (E +GWF + SR)
P = E + GWF + SR + �S
S = tampungan (storage)
�S = S2 – S1
= perubahan tampungan
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Imbangan ar di lautan:
�S = �I - �O
= (P + GWF + SR) – E
P = E – GWF – SR + �S
dengan
P = presipitasi (hujan)
E = evaporasi (penguapan)
SR = surface runoff (limpasan permukaan)
GWF = ground water flow (aliran air tanah)
�S = perubahan tampungan
Contoh hitungan imbangan air di waduk:
Bila diketahui : �t = 1 tahun QPLTA = 5 m3/s
A = 4000 ha Qirigasi = 7,5 m3/s
SI = 250.106 m3 WL = 20.106 m3
P = 1800 mm
E = 2051 mm
Ditanyakan :
a. Volume penguapan tahunan
b. Ground water flow
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Penyelesaian :
Dengan �t = 1 tahun, dapat dianggap �S � 0, sehingga A tetap
a. Volume E tahunan = E . A = 2,051 x 4000 x 104 m3
= 82,04 x 106 m3
b. �S = �I – �O , �S � 0
�I = �O � (P + SI + GWF) = (E + QIR + QPLTA + WL)
� GWF = E + QIR + QPLTA + WL – P – SI
QIR = 7,5 x 3600 x 24 x 365 = 236,52 x 106 m3
QPLTA = 5,0 x 3600 x 24 x 365 = 157,68 x 106 m3
P = 1,800 x 4000 x 104 = 72,0 x 106 m3
� GWF = [982,04 + 236,52 + 157,68 + 20) – (72 + 250)] x 106 m3
= 172,24 x 106 m3
= 172,24 MCM