View source for Bed form tracking

This article is a summary of sub-section 5.5.2 of the [[Manual Sediment Transport Measurements in Rivers, Estuaries and Coastal Seas]] <ref>Rijn, L. C. van (1986). ''Manual sediment transport measurements''. Delft, The Netherlands: Delft Hydraulics Laboratory</ref>. This article describes how to compute [[bed load]] transport from measured bed form profiles. 

==Principles and calculation of bed form tracking==
[[Image:H552figure2.jpg|thumb|right|300px|Figure 1: Bed form tracking]]
The basic principle of [[bedforms|bed form]] tracking is the computation of the [[bed load]] transport from [[bedforms|bed form]] profiles measured at successive time intervals under similar flow conditions  (Figure 1). Assuming steady flow conditions and undisturbed [[bedforms|bed form]] migration, the [[bed load]] transport rate can be computed from the bed form dimensions (Engel and Lau, 1980<ref>Engel,   P.  and Lau, Y.L., 1980. Computation of Bed Load Using Bathymetric Data. Journal of  the Hydraulics Division, ASCE,  HY 3.</ref>, 1981<ref>Engel,   P.  and Lau, Y.L., 1981. Bed Load Discharge Coefficient. Journal of the Hydraulics Division,  ASCE,  HY 11.</ref>, De Boer, 1996<ref name="boer">De Boer, A.G., 1996. The applicability of the dune-track method (in Dutch). Department of Physical Geography, University of Utrecht, Utrecht, The Netherlands.</ref>).

The [[bed load]] transport (in kg/sm) can be determined as:

<math>S_b=\alpha\,_s\rho\,_s(1-p)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 bed-form height (see Havinga, 1982<ref>Havinga, H.,  1982. Bed Load Determination by Dune Tracking. Dir. Water Management and Water Motion, District South East, Rijkswaterstaat,  The Netherlands.</ref>). To collect the bed profile data along a prefixed course, an accurate three-dimensional measuring system must be available consisting of a two-dimensional horizontal positioning system and a one-dimensional 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 bed-profile registrations can be made in a longitudinal section between two well-defined cross-sections (bank marker). Using a simple hand method, the average migration  velocity and   bed-form  height   can  be  determined  quite easily, as shown in Figure 1A.
Engel and Wiebe (1979<ref>Engel,   P.   and Wiebe,   K., 1979. A Hydrographic Method for Bed-Load Measurement. Proc.   Fourth Nat.   Hydro-Techn.  Conf.  River Basin Man.,  Vol.  I,  page 98-113. Vancouver, Canada.</ref>) 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<ref>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.</ref>). For field conditions the inaccuracy may be as large as 100%.
De Boer (1996<ref name="boer"/>) has developed a dune-track computer program to estimate the bed load transport from successive bed profile measurements. The k-factor 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]]

===Articles on related topics===
* [[Argus video monitoring system]]
* [[Bed load transportmeter Arnhem (BTMA)]]
* [[Helley-Smith sampler (HS)]]
* [[Delft Nile bed load and suspended load sampler (DNS)]]



==References==
<references/>

{{author 
|AuthorID=13226 
|AuthorFullName= Rijn, Leo van
|AuthorName=Leovanrijn}}

{{author 
|AuthorID=12969 
|AuthorFullName= Roberti, Hans
|AuthorName=Robertihans}}

[[Category:Coastal and marine observation and monitoring]]
[[Category:Observation of physical parameters]]