Teknik SungaiDwita S K MarsudiantoroDepartemen Teknik SipilFakultas Teknik Universitas IndonesiaKampus UI Depok 16424Telp.: (021) 727 0029 atau (021) 786 3458Fax.: (021) 727 0028 atau (021) 727 0025Email: dwita@eng.ui.ac.idHP: 0811 82 4878

TOPIK 6 Hidrolika SungaiKLASIFIKASI ALIRAN SUNGAI

Open Channel Flow ClassificationSteady FlowUniform flowNon-uniform (Varied flow)Gradually varied flowRapidly varied flowUnsteady FlowUnsteady uniform flow (rare)Unsteady flowGradually varied unsteady flowRapidly varied unsteady flow

Problems StagingStage 1: study of the problem for uniform steady flow conditions (equilibrium conditions and constant discharge)Stage 2: study of the problem for non-uniform conditions (backwater curves)Stage 3: study of the problem for non-uniform, and unsteady conditionsStage 4: study of three dimensional effects, for steady flow conditions

KLASIFIKASI ALIRAN DI SALURAN TERBUKA

TYPE ALIRAN DI SALURAN TERBUKA

Steady Flow and Unsteady`Flow :Waktu yang menjadi kriteriaUniform Flow and Varied Flow : Tempat/ruang yang menjadi kriteriaKEADAAN ALIRANEffect of Viscosity (R) : Reynold number (R) :R = VL/

Effect of gravitasi (Fr) :Froude Number (Fr) :Fr = V/(gh)

Steady Uniform Flow (Stage 1)A computation for uniform flow conditions may serve to:Study the feasibility of a projectObtain a general insight into a problemStudy a case where uniform flow really exists (in rivers hardly never the case, but occurs often in irrigation canals)

KEADAAN ALIRANEffect of Viscosity (R) : Reynold number (R) :R = VL/Laminar : R < 500Turbulent : R > 2000Transitional : 500 < R < 2000 Effect of gravitasi (Fr) :Froude Number (Fr) :Fr = V/(gh)Subcritical (Fr < 1)Critical (Fr = 1)Supercritical (Fr > 1)

Steady Non-Uniform Flow (Stage 2)The water level surface profile (backwater and drawdown curve) are important to know as:Local water levels are often a design criteriaThe backwater curve (or drawdown curve) should be known to compute erosion and sedimentationEtc.

Unsteady Non-Uniform Flow (Stage 3)In river the flow will generally be non-steady and the water level at a certain place will change with time :Short waves, due to wind navigation or opening of gateDesign of bank protection due to variation in rainfall which is influence on the variation in discharge and water level

1995-1998In Collaboration withJakarta Office of Environmental Protection(KPPL-DKI)

BackgroundThe idea of developing Jakarta northwards socalled Jakarta Waterfront City concerns the JOEP relating the flood amplification induced by sediment blockage at Angke river mouth Java Sea

Cengkareng Drain System

Three Dimensional Flow (Stage 4)For the understanding for phenomena of local scour it is necessary to use a three dimensional approach :Flow in River BendsThe motion of fluid particle following a curved motion can be described with the help of cylindrical coordinates

SUNGAI MEANDER

MEANDER SUNGAI CILIWUNG

MEANDER S. CILIWUNG DI DAERAH KALIBATA

ALIRAN DI DAERAH MEANDER

Effek Debit terhadap Pergerakan Meander (U.S. Army Corps of Engineers, 1945).

Effek Kemiringan terhadap Ukuran Lengkung (U.S. Army Corps of Engineers, 1945).

PENGGAL SUNGAI MATI (OXBOW LAKE) AKIBAT NORMALISASI SUNGAI

STABILISASI TEBING SUNGAI DENGAN RUMPUT VETIVER

PERSAMAAN-PERSAMAAN POKOK YANG DIPERGUNAKANAliran pada sungai alam adalah aliran 3 (tiga) dimensi Selalu berubah menurut arah sumbu x, y dan z.Persamaan-persamaan aliran dapat dituliskan menurut sistim koordinat rectangular orthogonal cartesian Sumbu z sebagai axis dengan notasi positip vertikal keatas terhadap bidang datar x-y. Aliran sungai secara dinamik dipengaruhi oleh tegangan yang bekerja pada partikel-partikel air

TEGANGAN2 YANG BEKERJA PAA PARTIKEL AIRArah sumbu x :

Arah sumbu y :

Arah sumbu z :

ZXYZYYYXYZXXXYXZZXZYZ

Penerapan Sistem Koordinat di Sungai Alam zKomponen kecepatan dalam arah x, y, z dinotasikan dengan U, V, W

PERSAMAAN GERAK ALIRANPersamaan Kontinuitas Aliran (Persamaan Kekekalan Massa) : Persamaan Dinamika Aliran (Persamaan Kekekalan Momentum) :

PERSAMAAN BERNOULLI

SfSwS0

Persamaan DasarPersamaan Gerak (Equation of Motion)

W = flow resistancePersamaan Kekekalan Masa (Continuity of Mass)(1)(2)

Steady Uniform Flow(3)

hzvyx

LatihanJika diketahui saluran berbentuk trapesium dengan lebar dasar saluran 5 m dengan data2 sebagai berikut : I = 10-4 ; D50=0,5*10-3 m ; D90=1*10-3m; k = 10 cmMaka tentukan rating curve dari saluran tersebut dengan tinggi muka air rendah adalah 0.5 m dan muka air tinggi 4 m.

Computation for Uniform Flow ConditionWith uniform or parallel flow :

so equation (3) reduces to :

is the bed slope, I,

Persamaan DasarPersamaan Gerak (Equation of Motion)

W = flow resistancePersamaan Kekekalan Masa (Continuity of Mass)(1)(2)

Catatan:Sf = Ie = kemiringan garis energiSw = Iw = kemiringan permukaan airS0 = Ib = kemiringan dasar alury = h

Computation for Non Uniform Steady Flow ConditionUntuk Froude Numbers kecil

(4)

Non Uniform Steady FlowUntuk Froude Number besar

(5)

NoticeIn the case of supercritical flow, the boundary condition is situated upstream of the section considered (computation of water level profile has to be carried out in downstream direction)In the case of subcritical flow the boundary condition is situated downstream of the section considered (computation has to be carried out in upstream direction)From the boundary to the section considered, the water level converges to the equilibrium depthAt the transition from supercritical to subcritical flow a hydraulic jump exists

Klasifikasi Profil Aliran

Horizontal SlopeYn > YcMild SlopeYn > YcCritical SlopeYn = YcSteep SlopeYn < YcAdverse Slope

Points of Inflection

Variasi Profil Aliran, karena:Penampang melintang yang bervariasiAdanya berbagai bangunan pengatur maupun pengendaliDll.

Flow Scheme Computation Backwater Curve(4)(5)(3)(2)(1)

RemarksIf the steps are not taken too large (4) can be left outFor the computation of equation (3) is used, but is assumed.With every step this can be checked by computing andIf is large compared to the other terms (in cases of rapid change in cross-section), the value of can be corrected.

Contoh PerhitunganQ = 1000 m3/s500 m250 m500 mhe = 2,92 mhe = 4,64 mhe = 2,92 mIb = 10-4C = 40 m1/2/sq = 2 m2/sq = 2 m2/sq = 4 m2/sAB

Contoh Perhitungan

Step NoDistance upward from B (km)Depth at the beginning of step(m)

(x 10-5)h-waterPer step(cm)h-bedPer step (cm)Depth (cm)Depth at the end of step(m)010,52,92040,020,0515,03,07021,03,07034,517,2512,23,19231,53,19230,715,4510,43,29642,03,29626,014,059,03,38652,53,38625,612,857,83,46463,03,46423,912,057,03,53473,53,53422,911,456,43,59884,03,59821,610,855,83,65695,03,65620,520,51010,33,759106,03,75919,019,0109,03,849117,03,84917,517,5107,53,924128,03,92416,616,6106,63,9901310,03,99015,731,42011,44,1041412,04,10414,529,0209,04,1941514,04,19413,527,0207,04,2641619,04,26412,964,55014,54,4091724,04,40911,658,0508,04,4891829,04,48911,155,5505,54,544

Latihan (tgl. 6 Mei 2013)Kapasitas Banjir Kanal Barat akan diperbesar menjadi 600 m3/detik.Jika data geometrinya adalah sebagai berikut:Lebar B = 200 mSlope I = 0,0002Bilangan Chezy C = 40 m1/2/detik

Berapakah kedalaman normal Banjir Kanal yang diperlukan untuk melalukan debit rencana tersebut?Pada tabel berikut ini disajikan perhitungan profil muka air akibat pengaruh pasang laut. Kedalaman air di muara adalah setinggi 4,0 m. Selesaikan perhitungan tersebut hingga pada jarak 25 km dari muara.Berapakah jarak pengaruh pasang tersebut terhitung dari muara ke arah hulu?

Langkah KeJarak dari Muara (m)Kedalaman h pada Awal Langkah (m)Perubahan Elevasi Air (m)Perubahan Elevasi Dasar (m)Perubahan Kedalaman h (m)Kedalaman h pada Akhir Langkah (m)00110004,000,000090,090,20-0,113,89220003,890,000100,100,20-0,103,78330003,780,000100,100,20-0,103,69440003,690,000110,110,20-0,093,60550003,606750071000081250091500010200001125000

Prop. SUMBAR

Daerah Rawan BanjirPropinsi Sumatera Barat

NoKabupatenKawasanKlasifikasiHunian (Ha)Kegiatan Usaha (Ha)Prasarana Transportasi (Km)Ket.PerkotaanPedesaanSawah &TambakPerkebunanJalan RayaJalan K.ABandara PelabuhanHaHaHaHaKmKm1.Kab. PasamanBt. PasamanRegional-10.00 50.00 ----Bt. SumpurRegional-40.00 295.00 -2.00 --2.Kab. AgamBt. Agam, Sianok/Regional-435.00 725.00 -3.00 --Durian3.Kab. SawahluntoBt. Ombilin/LasiRegional--1,145.00 ----Bt. Kuantan, TimpehRegional-770.00 1,940.00 1,350.00 2.06 --4.Kab. Pd. PariamanBt. Pariaman,Regional-124.00 130.00 670.00 ---Bt. MangorBt. AnaiRegional-1,100.00 1,800.00 ----Bt. TikuRegional-5.00 70.00 ----5.Kodya PadangBt. Arau, Kuranji danNasional1,990.00 -1,510.00 ----Bt. Air Dingin6.Kab./Kodya SolokBt. LembangRegional335.00 -720.00 ----Bt. BangkoRegional-1,500.00 4,500.00 ----7.Kab. Lima Puluh KotaBt. Sinamar/LampasiRegional-200.00 1,300.00 ----8.Kab. Pss. SelatanBt. Lunang/SindangRegional-150.00 1,200.00 3,650.00 1.00 --Bt. Tapan/IndarpuraRegional-100.00 3,620.00 1,200.00 ---Bt. SurantihRegional-30.00 35.00 ----Bt. Kapas/TuikRegional-30.00 30.00 ----Jumlah2,325.00 4,494.00 19,070.00 6,870.00 8.06 0.00 0.00

LATIHANBerdasarkan informasi yang ada pada gambar berikut, tentukan dimensi alur Bt.Arau di muara:Keadaan dengan banjir kanalKeadaan tanpa banjir kanal