ALLUVIAL BEDFORMS AND ROUGHTNESS
Transport Sedimentation Paper Lecturer: Dr. Very Dermawan, ST.,MT
Munfarid (135060400111035 )
Adam Wiguna (135060401111014 )
Reta Lilyananda Puspasari (135060401111016 ) Hana Arum Rossy Tamaya (135060401111018 ) Marianty Patabang (135060401111022 ) Danang Kiswanto (135060401111036 ) Rifqi Muhammad Iqbal (135060401111038 ) Annida Lisyahadah (135060401111048 ) Ria Puspasari (135060401111058 ) Moh. Ali Mabrur (135060401111059 ) Ivan Dwi Prabowo (135060401111066 ) Ganisa Elsina Salamena (135060401111068 ) Yuvika Rega Siswanti (135060407111027 )
Ministry of Education and Culture Brawijaya University
Faculty of Engineering Water Resources Engineering
I. GENERAL
The basic form sediments which occur in alluvial channel flow rate related to the flow regime. Flow regime, which is a form that affects the flow of the layer configuration. The following classification shows the relationship between flow velocity and sediment transport modes (sediment transport), the concentration of the transported sediment and forms the basis of the relationship between phase and water (surface water).
Flow regime can be related to the Froude number characterizes whether flow will be calm or fast. Froude number is an expression of the ratio between the inertia (the force needed to stop the moving particles) and gravity.
F <1 tranquil flow (lower flow regime)
F = 1 critical flow conditions (flow regime transition) F> 1 rapid flow (upper flow regime)
In general, the basic shape of the flow regime, sediment is classified into: A. Regime low flow
A. Regime Low Flow
(Froude number <0.4 to 1 with ramps transition)
1. Flat bed, is a sediment transport without deformation and the movement details are tossing and turning. And the magnitude of the shear of stress is exactly above from the critical.
3. Dunes, all sizes of sediment and the shear of stress increases to the front side. The front side is slope slightly, the back side is steeper. Erosion can occur on all sides of the upper reaches, and deposition occurs at the bottom of the downstream side.
4. Dunes, all sizes of sediment and the shear of stress increases to the front side. The front side is slope slightly, the back side is steeper. Erosion can occur on all sides of the upper reaches, and deposition occurs at the bottom of the downstream side.
B. Regime transition flow
(basic configuration of the dunes towards the plane bed or anti-dunes)
C. Regime high flow
1. Plane bed, Plane bed, has a flow rate gradually rising, sediment transport has a flat height. The movement of the Grain is rolling or sliding and changes at a particular place. A fine material occurs saltasi.
2. Antidunes, has sediment materials occurs in the upstream dunes, erosion on downstream. More or less symmetrical waveforms. Antidunes move downstream and occurs at Fr> 1
I. Bedform Forecast
Determining the criteria of bedform, approach used by the sediment continuity equation as follows:
s + = 0
description:
s = specific weight of bed material y = height of bedform at x along the river t = time
qs = sediment flow in a weight unity wide and time
The first limitation showed a decrease in the rate of sediment at the base, and the second limit sediment transport shows the change in the change of the distance x along the river. It turns out that both these limits gradually always
opposite in sign, when the base is formed positive and negative.
The image above shows the cross-sectional shape at time t and t + dt from the bedform that moves downstream. In the upper part of the lower forms of the
basic situation which is a function of time, so negative.
From this equation, seemingly that positive, so that qs increases
continuously until it reaches its peak.
Exner (1925), assumed that: qs = Ao. uo
Ao = constant
Uo = flow velocity near the base
By entering Ao and Uo into the sediment Equalition continuity before, then obtained :
s + Ao = 0
In 1963, Kennedy introduced the relation between the wavelength L of a change in the bedform of the Froude number
Results of Kennedy’s investigationed to the dominant wavelength of the form - the bedform is:
= distance which can lead to changes in local sediment flow deceleration and
ᵟ
change of pace near the base
Pictured above is the theoretical curve obtained kennedy with entering data into the equation the dominant wavelength (the relationship between Fr and kd).
Seen in Fr2, greater than (1 / kd) tanh kd, and the kd <2
Curve Fr2 = (1 / kd) tanh kd give upper limit for ripples and dunes Fr. Transition area between Fr = 1 and Fr = 0.844
Kennedy proposed a simple relationship between the wavelength L antidunes with average speed U as follows:
U2 = This equation is known as the equation for the wave speed in
the water.
From experiments K/ennedy (1963) obtained results that were passed antidunes surface waves break when the position is steep. Comparison between wave height to wavelength is between 0.13 and 0.16 and between the retrieved value is 0.14 for the water wave steepness at the time began to break.
DAFTAR PUSTAKA
Dwi Priyantoro, Ir., Teknik Pengangkutan Sedimen, Himpunan Mahasiswa Pengairan FT-UB, Malang, 1987
http://geologipiece.blogspot.com/2009/12/flow-regime.html diakses 23 September 2014
