Prediction of sand transport in the coastal zone

Sediment Transport in Open Channel

Settling VelocityConstant Velocity = Settling velocity (fall velocity

Threshold of Sediment Transport

Threshold of Sediment

Natural condition the critical Shields parameter : 0.03 - 0.06

Shields DiagramShields Diagram

Converted the Shields diagram by Madsen (1976)

BedformsRipples: weak flow intensity; fine material with d50 0.6 mmPeningkatan intensitas aliran, dunes berkembang dan kedalaman air di puncak dunes menjadi lebih kecil. Ini berarti bahwa kecepatan yg tinggi pada puncak, dune akan hilang dan high stage flat bed terbentuk.

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BEDFORMS IN THE LABORATORY AND FIELD: DUNESDunes on an exposed point bar in the meandering Fly River, Papua New Guinea

Dunes in a flume in Tsukuba University, Japan: flow turned off. Image courtesy H. Ikeda.AntidunesAntidune: Fr > 1; Tinggi gelombang pada permukaan air sama dengan ketinggian antidunes; wave surface tdk stabil dan pecah dlm arah upstream yang menggerakkan antidune upstream

Bed roughnessBed roughness, ks biasa disebut sebagai Equivalent Nikuradse grain roughness; diperkenalkan oleh Nikuradse dal percobaan aliran pipa, dimana butiran dilem pada dasar halus dinding pipaJika dasar datar terdiri dari butiran seragam, maka ks = diameter butiranHarga kekasaran dasar diperoleh dari pengukuran dan fitting kecepatan yang mencakup variasi daerah aliran dengan butiran sedimen yg berbeda

Effective Shear Stress

Effective Shear Stress

When viscosity and velocity system becomes turbulent.

Transport ModesHow does the sediment move after exceeding the threshold ?Wash load: very fine particles transported by the water and which are normally not represented in the bed. Neglected computing the total sediment .

Bedload: Almost continues contact with the bed carried forward by rolling, sliding and siltation or hopping.

Suspended load: maintained in suspension by turbulence in the flowing water for considerable periods of time without contact with bed

Transport RegimesBedload regime: if the Shields number exceed the critical value, sediment particle start to roll, slide and jump over each other, but the bed remain flat or covered with relict bedforms. The sediment is transported as a bedload in a layer of a few grain sizes thick.Ripple regime: If the Shields parameter increase further, bedforms are developed and transition bedload to ripple regime is occurred.Sheet-flow regime: for larger values of the Shields parameter (0.8 -1.0) ripple are washed out and the bed become plane. A thin moving layer of sand with high concentration occur (100-1000 kg/m3) and a thickness is about 10-100 grain sizes.

Transport RegimesBatas antara bed-load dan suspended-load masih dlm perdebatan:Einstein (1950): boundary adalah beberapa diameter butiran, 2 d50 di atas dasar, namun tidak realistis jika terjadi ripples

Bijker(1971) : bedload transport mengambil tempat didalam layer dengan ketebalan sama dengan kekasaran dasar (tinggi ripples)Bed-load Transport FormulaeBed-load transport qB sering dirumuskan dalam bentuk dimensionless:

Kalinske-Frijlink (1992)

Bed-load Transport FormulaeEinstein-Brown formula

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