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PERAMALAN PERISTIWA HIDROLOGI

PERAMALAN PERISTIWA HIDROLOGI. Adhi Muhtadi, ST., SE., MSi. Peristiwa Hidrologi. Hujan Banjir, Banjir tergantung oleh: pola, sifat & karakteristik daerah aliran Hujan max & banjir max mempunyai masa ulang (T) sangat lama : 1000 sd 10000 tahun

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PERAMALAN PERISTIWA HIDROLOGI

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  1. PERAMALAN PERISTIWA HIDROLOGI Adhi Muhtadi, ST., SE., MSi.

  2. Peristiwa Hidrologi • Hujan Banjir, Banjir tergantung oleh: • pola, • sifat & • karakteristik daerah aliran Hujan max & banjir max mempunyai masa ulang (T) sangat lama : 1000 sd 10000 tahun Oleh krn itu diperlukan : EXTRAPOLASI DATA

  3. Masa Ulang (T) • Adl: Interval waktu rata2 dr suatu perist akan dimulai/dilampaui 1x • Masa ulang = return period = periodicity = recurrence interval • Misal: Dlm pengamatan 100 thn terjadi rata2 4x perist hidrologi, mk masa ulang (T) adl : 25 thn • Ingat: BUKAN berarti setiap 25 thn sekali

  4. Kemungkinan Kejadian (p) • Kemungk suatu kejad besarnya disamai/dilampaui: p = 1/T • Perist tdk disamai/tdk dilampaui: p’ = 1-p • P(X > x)n = 1 – (1 – 1/1T)n • Misal: p(X > Q20)3= 1 – (1 – 1/20)3 = 0,143 = 14,3 % • Peluang 1% dr banjir 200 thnan akan tjd berapa thn yg akan datang? 0,01 = 1 – (1 – 1/200)n n = 2, jadi 2 th yad banjir 200 thnan akan tjd dg peluang 1 %.

  5. Utk peluang 8% dr banjir 200 thnan tdk akan tjd dlm brp thn yad ? p(X > Q200)n = 1 – 0,08 = 0,92 Jadi 0,92 = 1 – (1 – 1/200)n n = 503, berarti 500 thn yad banjir 200 thnan : * tdk akan tjd dgn peluang 8%, sebaliknya * banjir akan tjd dgn peluang 92%.

  6. n = log (1 – p (X > x)n log (1 – 1/T) • T = [ 1 – (1 – p (X > x)n) 1/n]-1

  7. Extrapolasi Data Pers. Weibull: T = (n + 1) / m, n = juml kejadian (data) m = no. ranking Versi lain: • Pers California: T = n / m • Pers Hazen : T = 2n / (2m – 1) • Pers Chegedayev: T = n + 0,4 /(m – 0,3)

  8. Metode Gumbel Asumsi: • Dist variabel2 hidrologi tak terbatas shg digun harga2 ekstrim max • Dist dr harga2 extrim yg dipilih dr n sample mendekati suatu bentuk batas kalau sample2nya meningkat • Harga T Gumbel = T Weibull = pers 10.8

  9. Pers Extrapolasi Gumbel: XT = 1/a YT + x – 1/a . Yn K = (YT – Yn )/ Sn σ/ Sn = 1/a

  10. Contoh Pers Dist Gumbel: • Banyak data : n = 15, m = 15 • p = n/m+1 = 1/15 +1= 0,0625 • y = - ln ln 1/p = -ln ln 1/0,0625 = -1,0198 • y2 = 1,0400 • Yn = tot y/n = 0,5128 • Sn = (tot y2 – Yn . tot y) / 15 = 1,0206

  11. TERIMA KASIH Adhi Muhtadi, ST., SE., MSi.

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