Geoscience Reference
In-Depth Information
Black, Toutle, and Yampa Rivers compiled by Williams and Rosgen (1989). In each
set of the selected field data, flow and sediment parameters were measured at the same
time, and the bed-load rate and bed-material size composition were averaged from
multiple samples across the same cross-section. These data sets cover a wide range of
flow and sediment conditions, with flow discharges up to 2,800 m
3
s
−
1
and sediment
sizes from 0.062 to 128 mm.
3.4.3 Comparison of bed-load formulas
Because of the complexity of sediment transport processes, all existing sediment trans-
port formulas are empirical or semi-empirical. Large discrepancies may exist among
these formulas when they are applied in real-life engineering. Therefore, evaluation of
their performances in various situations is very important.
Comparison of bed-load formulas using single-fraction data
Chien (1980; also see Chien and Wan, 1983) compared the formulas of Einstein
(1942), Meyer-Peter and Mueller (1948), Bagnold (1966), and Yalin (1972) with
measured data, as shown in Fig. 3.18. For weak sediment transport (
2),
the Yalin formula underpredicts the bed-load transport rate, and other formulas
provide reasonably good predictions. The Meyer-Peter-Mueller formula seems to pre-
dict better than the Einstein formula in the weak transport stage, but the situation
is reversed in the middle transport stage. However, for strong sediment transport
(
∗
>
2), the predictions of these formulas are significantly different. Because in
this range bed load and suspended load are very difficult to discern, and the mea-
sured data may have large errors, it is hard to judge which formula is better (Chien,
1980).
∗
<
Figure 3.18
Comparison of bed-load formulas (Chien, 1980).
