WORLD METEOROLOGICAL ORGANIZATION 
HOMS COMPONENT 

Explanation of the criteria for classification and numbering of components 
I09.3.01 (JUL 00) 

Explanation of the dates on the component's description  
THE CORRECTION TO THE ANNUAL LOAD OF MEASURED SUSPENDED SEDIMENT 

1. Purpose and objectives A method for correcting the estimated annual sediment load of a river, which compensates for the flow in the region near the bed where instruments
cannot normally reach. 2. Description The flow velocity, sediment concentration and sediment size distribution are measured at five or more different depths on a number of verticals and from these measurements composite vertical distribution curves or equations are derived for velocity and for concentration of each sediment size fraction. The velocity, sediment concentration, and percentages of each size fraction are averaged transversely across the section at each depth, and these averages are plotted against relative depth on logarithmic paper to give the composite curves. Parameters of the equations are determined from the slope and intercepts of straight lines drawn through the points. The curves can then be extrapolated towards the bed, into the region where instruments cannot reach, to provide more accurate estimates of mean velocity, sediment concentration, and sediment size fraction. The distribution curves can also be used to correct the annual load of
sediment as usually measured. A correction factor is computed for each
separate size fraction, and these are then used to compute a correction to
the total load (all size fractions). 3. Input Measured data of velocity, concentration and distribution of particle
size (at least five points in vertical, as near to the bottom as possible), and the annual load as usually measured. 4. Output Correction factor, corrected annual load. 5. Operational requirements and restrictions For use in large rivers. At least five points of velocity,
concentration, and particle size distribution should be measured on
sufficient verticals to give a good coverage of the river section. 6. Form of presentation Paper in English describing the method. 7 Operational experience The method has been applied to large rivers in China, especially the
Yangtze River. 8. Originator and technical support Bu Ce, Bureau of Hydrology, Yangtze Water Resources Commission, Wuhan,
China. 9. Availability From the HOMS National Reference Centre for China. 10. Conditions on use Free of charge.


(First entered: 15 APR 88  Last updated: 24 MAY 91) 