Geoscience Reference
In-Depth Information
Fig. 1
The great intake of Ohio River, where the gathering and sediments entry causes efficiency
decline (Neary et al.
1999
)
Therefore, considering the sediment problem in the intake channels is of great
importance. Extensive methods are tested and applied during the recent years to
control the sediments; the most common is the periodic dredging. The chief
difficulty in these methods is that they take high costs and time. Other measures
could be taken to the effect of improving the flow pattern, such as exerting optimal
conditions for the intake, for example, changing the deviation angle and geometric
shape of the intake. Full knowledge of the diversion flow pattern is a necessary
condition to study the intake sediments. The diversion flows are essentially three
dimensional. Some of their features are represented in Fig.
2
(Neary et al.
1999
).
These include a separation zone in the inside wall of the branch channel (Zone A),
a contracted flow zone in the branch channel, a secondary circulation beside the
outside wall of the branch channel, and a stagnation point near the junction of
the downstream edge and the main channel (Zone C). The recirculation flow at the
center of the separation zone is completely slow. The width of separation in the
surface is greater than that in the bed. At the junction downstream in the opposite
wall, there may occur a separation due to flow expansion (Zone B). The vertical
velocity profile in open channels is nonuniform. According to the no-slip condi-
tions, the velocity at the bed is necessarily zero, close to the water surface is high,
and in between these two surfaces is logarithmic.
As the flow comes close to the intake, it is accelerated laterally due to the suction
pressure at the end of the intake. The acceleration divides the flow into two parts:
one entering the inside of the intake, and the other continuing downstream of the
channel. The former is shown in Fig.
2
by a surface called the Dividing Stream
