Pengendalian banjir-sungai
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Transcript of Pengendalian banjir-sungai
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Pengendalian
Banjir Sungai
Bahan Kuliah Hidraulika
(Teknik Sungai)
Dr. Ir. Istiarto, M.Eng.
Jurusan Teknik Sipil dan Lingkungan FT UGM
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Pengendalian Banjir Sungai2
Referensi:
Jansen, P. Ph., van Bandegom, L., van den Berg, J., de Vries, M.,
Zanen, A., 1979, Principles of River Engineering, The Non-tidal
Alluvial River, Pitman, London
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Pengendalian Banjir Sungai3
Sungai
Saluran drainasi alam
tempat penampung dan penyalur alamiah
air dari mata air sampai muara
tempat air dansegala sesuatu yang bersamanyayang berasal daridaerah aliran sungaike muara
air – sedimen – polutan
DAS
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Pengendalian Banjir Sungai4
Air + Sedimen
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Pengendalian Banjir Sungai5
DAS
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Pengendalian Banjir Sungai6
DAS Serang di
Kedungombo
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Pengendalian Banjir Sungai7
Hidrograf
Hubungan antara
muka air dan waktu, h(t)
debit dan waktu, Q(t)
h
t
Q
t
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Pengendalian Banjir Sungai8
= WILAYAH SUNGAI (WS) = CEKUNGAN AIR TANAH
= D A S= SUNGAI
L A U T
DAS ADAS B
DAS CDAS D
DAS E
DAS F
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Pengendalian Banjir Sungai10
Terunjam-Makmur
A i r Beng
kulu
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Pengendalian Banjir Sungai12
Siklus Hidrologi
aliranair tanah
air permukaan
lapisankedap air
recharge
djoko luknanto
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Banjir
Bencana Banjir
Banjir
Aliran debit besar
Banjir (bencana banjir)
Aliran yang melebihi kapasitas tampang
sungai, terjadi limpasan keluar badan
sungai, terjadi genangan di kawasan yang
tidak seharusnya tergenang, dan terjadi
kerugian
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Banjir
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Bencana banjir
Bengkulu
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Planet Banjir, Dompet Dhuafa,
Harian Republika
Bencana banjir
Jakarta 2002
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Pengendalian Banjir Sungai17
Banjir air+sedimen
S. Boyong 1995
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Penyebab (Bencana)
Banjir (1)
Kapasitas tampang sungai berkurang
Pendangkalan dasar sungai– sedimentasi
Penciutan alur sungai atau bantaran– hambatan di alur (misal bangunan)
– hambatan di bantaran (permukiman)
Hambatan atau penutupan muara sungai– lidah pasir di muara
– pasang air laut
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Penyebab (Bencana)
Banjir (2)
Peningkatan debit sungai
hujan bertambah besar atau lama
– perubahan klimatologis yang mengakibatkan
peningkatan intensitas hujan
respon DAS terhadap hujan berubah
– peningkatan volume aliran permukaan
– hujan bertambah cepat sampai ke sungai
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Penyebab (Bencana)
Banjir (3)
Perubahan tata guna lahan di DAS
Dataran banjir berkurang
– kawasan retensi banjir berubah fungsi
Land subsidence
– penurunan muka tanah
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Penyebab (Bencana)
Banjir (4)
Bencana alam
Erupsi gunung vulkanik
– peningkatan debit sedimen
Tsunami
– gelombang dan pasang air laut
Tanah longsor
– suplai sedimen yang besar dalam waktu singkat
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Penyebab (Bencana)
Banjir (5)
Kegagalan fungsi bangunan pengendali
banjir sungai
Tanggul atau bendungan jebol
Pintu air tak berfungsi
Pompa air macet
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Pengendalian Banjir
Tujuan
Penurunan tingkat risiko ancaman terhadap
jiwa manusia dan harta benda akibat banjir
sampai ke tingkat toleransi
Meminimumkan dampak bencana banjir
(mitigasi bencana banjir)
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Tingkat Risiko Banjir
0,7 1,1
2,0
kedalaman banjir (m)
kecepata
n a
liran (
m/s
)
risiko
tinggi
risiko
sedang
risiko
rendah
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PROSES TERJADINYA MASALAH BANJIR
KONDISI ALAM (STATIS)
• Geografi
• Topografi
• Geometri alur
sungai:
kemiringan dasar
meandering
“bottle-neck”
sedimentasi
ambal alam
PERISTIWA ALAM
(DINAMIS)
* curah hujan tinggi
* pembendungan:
dari laut/pasang
dari sungai induk
* amblesan tanah
* pendangkalan
KEGIATAN MANUSIA (DINAMIS)
* PEMBUDI DAYAAN
DATARAN BANJIR
* tata ruang/peruntukan
dataran banjir yg tdk sesuai
* tata ruang/pengelolaan DAS
• permukiman di bantaran
sungai
* pembangunan drainase
* bangunan sungai/silang
* sampah padat
* prasarana pengendali
banjir yang terbatas
* amblesan permukaan tanah
* persepsi masyarakat yang
keliru thd banjir
* kenaikan muka air laut
akibat “global warming”, dsb.
MASALAHBANJIR
siswoko
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UPAYA MENGATASI MASALAH BANJIR SCR. MENYELURUH
UPAYA STRUKTUR (conventional)*)* MENCEGAH MELUAPNYA
BANJIR SAMPAI KETINGGIAN
TERTENTU, DENGAN TANGGUL
* MERENDAHKAN ELEVASI
MUKA AIR BANJIR DENGAN:
NORMALISASI, SUDETAN,
BANJIR KANAL, INTERKONEKSI
* MEMPERKECIL DEBIT BANJIR
DENGAN: WADUK, WADUK
RETENSI BANJIR, BANJIR KANAL
INTERKONEKSI,
* MENGURANGI GENANGAN
DENGAN: POLDER, POMPA
DAN SISTEM DRAINASE,
*) berdasarkan debit banjir rencana
(design flood)
UPAYA NONSTRUKTUR, a.l:* PRAKIRAAN BANJIR DAN
PERINGATAN DINI
* PENANGGULANGAN BANJIR
(FLOOD FIGHTING), EVAKUASI
* PEMINDAHAN/RELOKASI
* PENGELOLAAN DATARAN BANJIR
(FLOOD PLAIN / RISK MNAGEMENT),
* FLOOD PROOFING THD.BANGUNAN
* TATA RUANG, PENGHIJAUAN,
REBOISASI DAN DAL. EROSI DAS
* RETENTION & DETENTION PONDS
* PENETAPAN SEMPADAN SUNGAI
* INFORMASI PUBLIK & PENYULUHAN
* PENEGAKAN HUKUM,
* PENGENTASAN KEMISKINAN
* MANAJEMEN SAMPAH.
MENGURANGI BESARNYA KERUGIAN AKIBAT
BANJIR(“FLOOD DAMAGE MITIGATION”)
siswoko
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UPAYA MENGATASI MASALAH BANJIR SECARA MENYELURUH
STRUCTURAL FLOOD
MITIGATION MEASURES
a) LEVEES AND FLOODWALLS
b) CHANNEL MODIFICATIONS
c) BY-PASS FLOODWAYS
d) RETARDING BASINS AND FLOOD
STORAGE AREAS
e) FLOOD MITIGATION RESER-
VOIRS
f) DRAINAGE EVACUATION
SYSTEMS
NON-STRUCTURAL FLOOD
MITIGATION MEASURESa) LAND USE MANAGEMENT
b) PROPERTY ACQUISITION AND
FLOODWAY CLEARANCE
c) MODIFICATION OF CATCHMENT
CONDITIONS AND ON-SITE STORAGE
d) FLOOD FORECASTING AND
WARNING
e) PUBLIC INFORMATION AND
EDUCATION
f) FLOOD PROOFING OF BUILDINGS
g) EVACUATION FROM ENDANGERED
AREAS
h) FLOOD FIGHTING
i) FLOOD RELIEF
j) FLOOD INSURANCE
k) FLOOD ADAPTATION
FLOOD DAMAGE MITIGATIONSUMBER: MANUAL ESCAP
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Pengendalian Banjir Sungai29
Bangunan
Pengendali Banjir
Pengaturan dan normalisasi alur sungai
Tanggul
Tembok banjir (parapet wall, flood wall)
Saluran bypass
Kanal banjir
Waduk penampung banjir
Kolam retensi
Sistem drainase dan pompa
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Faktor Pengaruh Penetapan
Jenis Pengendali Banjir
Debit banjir sungai
Keadaan alur sungai dan DAS
Karakteristik hidraulis sungai
Tingkat kerugian akibat banjir
Standar debit banjir rencana
Akseptabilitas masyarakat
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Pengaturan Alur
Normalisasi
Tujuan Peningkatan kapasitas tampang sungai
Penurunan muka air banjir
Jenis bangunan Pelurusan kelokan (sudetan, cut-off)
Pelebaran atau pendalaman alur
Penurunan hambatan aliran (penurunan koefisien kekasaran)
Pengendalian alur (pengaturan arah aliran)
Perlindungan dasar atau tebing sungai
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Pengendalian Banjir Sungai32
Pemukiman
Jala
n P
ropin
si
Jem
bata
n
Pemukiman
Pemukiman
Solusi
• Sudetan
Masalah
• Permukiman
penduduk
terancam
• Pengarah arus
S. Katingan
Kalteng
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Pemukiman
Jala
n P
ropin
si
Jem
bata
n
Pemukiman
Pemukiman
Masalah
• Debit tahunan
cenderung
naik
• Resultan gaya
berpindah
saat banjir
• Jembatan
terancam
Debit
Normal
Debit Banjir
Solusi
• Pembangunan
krib
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revetment dengan
bronjong
krib permeabel dengan
tiang pancang
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Tanggul
Tembok Banjir
Tujuan
Mencegah aliran keluar dari alur dan
bantaran
Jenis bangunan
Tanggul timbunan tanah
Tembok pasangan batu
Tembok beton bertulang
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perbaikan alur +
tanggul
perbaikan alur +
tembok banjir
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Pengendalian Banjir Sungai38
Saluran Bypass
Kanal Banjir
Tujuan
Pengalihan (sebagian atau seluruh) aliran dari sungai ke tempat lain
Jenis bangunan
Percabangan alur sungai
Di hilir aliran kembali lagi ke sungai asal → saluran bypass
Saluran bermuara di tempat lain (tidak sama dengan sungai asal) → banjir kanal
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floodway
by-pass channel
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Waduk
Kolam Retensi
Tujuan
Menampung sebagian debit puncak banjir untuk
sementara waktu
Pengaturan debit yang mengalir ke hilir sesuai
dengan kapasitas tampangnya
Jenis bangunan
Bendungan
Tanggul
Pelimpah
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Kawasan Retensi
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perbaikan alur +
tanggul +
kawasan retensi banjir
saat banjir datang
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perbaikan alur +
tanggul +
kawasan retensi banjir
saat banjir surut
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Sistem Drainase
Pompa
Tujuan
Pembuangan air berlebih dari suatu
kawasan melalui jaringan saluran
Aliran secara gravitasi atau dipompa
Jenis bangunan
Saluran (terbuka, tertutup), pipa
Pompa
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