Sediment Transport Concepts - Sediment Transport in Irrigation Canals: A New Approach - page 98

(1981a) compiled an extensive set of data on sediment transport and bed
forms from the laboratory and field data available at that time. For the
development of the computer program SETRIC (see Chapter 6), a selec-
tion of data was made from the compilation that was published in 1981
and this data was used to compare the various theories on bed forms.
The selection of the data was based on the flow conditions and the
sediment characteristics that are normally encountered in irrigation canals
(Méndez, 1995 and Paudel, 2010). The selection criteria included:
• the compiled data had to comprise all the quantities necessary to

compute the four classification parameters as mentioned in Table 5.1;

• the sediment size d 50 had to be smaller than 0.5 mm;

• the Froude number had to be smaller than 0.5;

the shear stress on the bottom had to be smaller than 5 N/m 2 ;

•

• the B / h ratio had to be larger than 10 in order to minimize the influence

of the sides;

• the compiled data had to include a detailed description of the bed forms.

The theories were compared on a relative basis, which means that
the number of relatively accurately predicted ( well-predicted ) bed forms
according to each theory was related to the total number of observed
bed forms. The predictability of each of the four theories was mea-
sured in terms of accuracy (number of well-predicted values), which is
represented by:

measured value
f

≤ predicted value ≤ measured value ∗ f (5.10)

number of well-predicted values
total values

accuracy (%) = ∗ 100 (5.11)

The accuracy of each method to predict the bed forms has been used to
draw some conclusions:
• the theories presented by van Rijn (1984c) and Simons and Richardson

(1966) appear to be the best theories to predict the bed form in
irrigation canals. The accuracy shows that approximately 82% and
77% respectively of the observed bed forms are predicted relatively
accurately ( well predicted ) by the two theories;

• all the bed forms described for the lower flow regime (ripples, mega

ripples and dunes) can be expected in irrigation canals.

According to van Rijn (1993), bed forms can be classified by the
following parameters:
- particle parameter D ∗ , which reflects the influence of density and
diameter of the particle, gravity and viscosity:

( s 1 / 3

− 1) g

ν 2

D ∗ = d 50 (5.12)