Tahap 1 Data :

Lengkung Debit

Bentuk penampang Material dasar sungai b (lebar dasar sungai) m (kemiringan dasar sungai) Kemiringan dasar sungai (I) Koefisien kekasaran (Manning) Q100 (debit banjir rencana 100 tahunan)

= = = =

Persegi Lempu ng 27 0 (Lihat Tabel 1 m

=

0,002

pada lampiran)

=

0.035

=

275

m3/det

0,5

Gambar 1 Sketsa Penampang Sungai

Perhitungan : Asumsi 1 : h A P R R2/3 I1/2 V Q = = = = = = = = 3,8 b*h b + 2h A P 2,06402 0,04472 1/n * R2/3 * I1/2 V*A m3/s m = = = m = = (1/0,035) * 2,06402 * 0,04472 2,63731 * 102,6 275 m3/s 2,637 31 270,5 = 88 = Asumsi m/s m3/ s 27 * 3,8 27 + 2 * 3,8 102,6 34,6 = 102,6 = 34,6 2,965 = 32 m2 m m

Q = 270,588 Asumsi 2 : h A P R R2/3 I1/2

Q100 =

salah, ganti kembali nilai h

= = = = = = = =

3,84067 b*h b + 2h A P 2,07547 0,04472 1/n * R2/3 * I1/2 V*A

m = = = m = = (1/0.035) * 2,07547 * 0,04472 2,65194 * 103,69809 = 2,65194 = 275,001 02 m/s m3/ s 27 * 3,84067 27 + 2 * 3,84067 103.69809 34,68134 103,698 09 34,6813 = 4 = = 2.99003 m2 m m

V Q

Q = 275,00102

m3/s Q100 = 275 m3/s Asumsi sudah benar

Tabel 2 Perhitungan Lengkung Debit h (m) 0 1 2 3 3.5 3.6 3.7 3.8 3.840 52 3.840 62 3.840 63 3.840 64 3.840 65 3.840 66 3.840 67 A ( m2 ) 0 27 54 81 94.5 97.2 99.9 102.6 103.694 04 103.696 74 103.697 01 103.697 28 103.697 55 103.697 82 103.698 09 P (m) 27 29 31 33 34 34.2 34.4 34.6 34.681 04 34.681 24 34.681 26 34.681 28 34.681 3 34.681 32 34.681 34 R (m) 0 0.931 03 1.741 94 2.454 55 2.779 41 2.842 11 2.904 07 2.965 32 2.989 93 2.990 00 2.990 00 2.990 01 2.990 01 2.990 02 2.990 03 R2/3 (m) 0 0.953 48 1.447 73 1.819 62 1.976 83 2.006 44 2.035 50 2.064 02 2.075 43 2.075 46 2.075 46 2.075 46 2.075 47 2.075 47 2.075 47 I1/2 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 0.044 72 V ( m/s ) 0 1.218 31 1.849 84 2.325 03 2.525 90 2.563 74 2.600 87 2.637 31 2.651 89 2.651 92 2.651 92 2.651 93 2.651 93 2.651 94 2.651 94 Q ( m3/s ) 0 32.8943 4 99.8915 5 188.327 04 238.697 22 249.195 38 259.826 72 270.587 97 274.984 70 274.995 58 274.996 67 274.997 76 274.998 84 274.999 93 275.001 02

Gambar 2 Grafik Lengkung Debit Kesimpulan : Q100 (Debit banjir 100 tahunan ) maka h100 (tinggi muka air banjir) = 275 m3/s, = 3.84067 m