Sediment Transport Concepts - Sediment Transport in Irrigation Canals: A New Approach - page 139

◦ Procedure 3 : the total sediment transport is determined by computing

the sediment transport capacity of each stream tube and added up for
the whole area (the cross-section integrated approach):

n

Q s =

q s(i) d y (5.115)

i = 1

The total sediment transport for the total cross section is found by:

Q s = αBq s with q s = f ( ν ) (5.116)

where:
α

= correction factor for calculating the total sediment transport

in a non-wide canal.

B = bottom width (m)

v = mean velocity (m/s)

sediment transport capacity for the whole cross section (m 3 /s)

Q s =

sediment transport capacity per unit width (m 3 /s

q s = · m)

In this method the sediment transport follows from the quantity
obtained from the predictors by assuming that the canal is wide and then
the transport is corrected for the non-wide conditions and the side slope.
In order to compare the three procedures in terms of their ability to
compute the total sediment transport in non-wide canals, these procedures
have been applied to a selected set of laboratory data. A correct method to
compute the sediment transport should take into account the effect of the
cross section on the velocity distribution and the non-linear relationship
between the velocity and the sediment transport. Paudel (2010) selected
specific data from the Brownlie (1981a) compilation with flume and field
data. The selection criteria are based on the flow conditions and sediment
characteristics that normally exist in irrigation canals and include:
• sediment size less than 0.5 mm;

• Froude number less than 0.5;

• B / y ratio less than 8;

• sediment concentration 100-1500 ppm;

• geometric standard deviation of the bed particle size σ g less than 1.5;

• type of bed form is dune or less;

• data that include all the information needed for the sediment transport

computation.

Figure 5.27 shows the sediment size and the range of concentrations
in the data.
A total of 149 data sets were selected out of the Brownlie compilation
(Table 5.8). All the data are for rectangular flumes with a maximum width
of 2.4 m. The width for the sediment transport calculation in the three
procedures given above will be equal to the bed width.