Bed form tracking
This article is a summary of subsection 5.5.2 of the Manual Sediment Transport Measurements in Rivers, Estuaries and Coastal Seas ^{[1]}. This article describes how to compute bed load transport from measured bed form profiles.
Contents
Principles and calculation of bed form tracking
The basic principle of bed form tracking is the computation of the bed load transport from bed form profiles measured at successive time intervals under similar flow conditions (Figure 1). Assuming steady flow conditions and undisturbed bed form migration, the bed load transport rate can be computed from the bed form dimensions (Engel and Lau, 1980^{[2]}, 1981^{[3]}, De Boer, 1996^{[4]}).
The bed load transport (in kg/sm) can be determined as:
[math]S_b=\alpha\,_s\rho\,_s(1p)fa\Delta\,[/math]
in which:
 [math]\alpha\,_s[/math] = coefficient (0.5 to 0.6),
 p = porosity factor (= 0.4),
 [math]\rho\,_s[/math]= density of sediment particles (= 2650 kg/m3),
 [math]\Delta\,[/math]= average bed form height (m)
 f = shape factor = [math]2V/(\Delta\,L))[/math] with: V = volume of bed form per unit width, L= bed form length.
 a = average migration velocity (m/s),
To apply this equation, the migration velocity and the bed form height must be determined from the bed profiles. The bed load transport rate can also be computed directly from the (successive) profile data using all data instead of selecting the characteristic parameters such as the average migration velocity and the bedform height (see Havinga, 1982^{[5]}). To collect the bed profile data along a prefixed course, an accurate threedimensional measuring system must be available consisting of a twodimensional horizontal positioning system and a onedimensional vertical sounding system.
In (isolated) field conditions, where an accurate positioning system is too complicated, a much simpler method can be used. By means of an analogue echo sounder two or more successive bedprofile registrations can be made in a longitudinal section between two welldefined crosssections (bank marker). Using a simple hand method, the average migration velocity and bedform height can be determined quite easily, as shown in Figure 1A.
Engel and Wiebe (1979^{[6]}) report an overall inaccuracy of about 40 to 50% for flume conditions. Figure 1B shows measured and computed transport rates for flume conditions (Simons et al, 1965^{[7]}). For field conditions the inaccuracy may be as large as 100%.
De Boer (1996^{[4]}) has developed a dunetrack computer program to estimate the bed load transport from successive bed profile measurements. The kfactor was found to be 0.64 for the Dutch IJssel river. The length of each profile should at least be between 1 and 3 km. The local bed load transport may vary between 50% and 200% of the average value for one profile.
See also
Summaries of the manual
 Manual Sediment Transport Measurements in Rivers, Estuaries and Coastal Seas
 Chapter 1: Introduction, problems and approaches in sediment transport measurements
 Chapter 2: Definitions, processes and models in morphology
 Chapter 3: Principles, statistics and errors of measuring sediment transport
 Chapter 4: Computation of sediment transport and presentation of results
 Chapter 5: Measuring instruments for sediment transport
 Chapter 6: Measuring instruments for particle size and fall velocity
 Chapter 7: Measuring instruments for bed material sampling
 Chapter 8: Laboratory and in situ analysis of samples
 Chapter 9: In situ measurement of wet bulk density
 Chapter 10: Instruments for bed level detection
 Chapter 11: Argus video
 Chapter 12: Measuring instruments for fluid velocity, pressure and wave height
 Argus video monitoring system
 Bed load transportmeter Arnhem (BTMA)
 HelleySmith sampler (HS)
 Delft Nile bed load and suspended load sampler (DNS)
References
 ↑ Rijn, L. C. van (1986). Manual sediment transport measurements. Delft, The Netherlands: Delft Hydraulics Laboratory
 ↑ Engel, P. and Lau, Y.L., 1980. Computation of Bed Load Using Bathymetric Data. Journal of the Hydraulics Division, ASCE, HY 3.
 ↑ Engel, P. and Lau, Y.L., 1981. Bed Load Discharge Coefficient. Journal of the Hydraulics Division, ASCE, HY 11.
 ↑ ^{4.0} ^{4.1} De Boer, A.G., 1996. The applicability of the dunetrack method (in Dutch). Department of Physical Geography, University of Utrecht, Utrecht, The Netherlands.
 ↑ Havinga, H., 1982. Bed Load Determination by Dune Tracking. Dir. Water Management and Water Motion, District South East, Rijkswaterstaat, The Netherlands.
 ↑ Engel, P. and Wiebe, K., 1979. A Hydrographic Method for BedLoad Measurement. Proc. Fourth Nat. HydroTechn. Conf. River Basin Man., Vol. I, page 98113. Vancouver, Canada.
 ↑ Simons, D.B., Richardson, E.V. and Nordin, C.F., 1965. Bed Load Equation for Ripples and Dunes. U.S. Geol. Survey Prof. Paper 462 H, Washington, USA.
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