Integrated River Management - River Dynamics and Integrated River Management - page 733

rivers the velocity varies within a small range, while the stream flow may spread over the channel and
the floodplain. The limit velocity law is important for river management. In general, the average velocity
increases with an increase in discharge when the discharge is small. As the discharge exceeds the
bank-full discharge, any further increase in discharge does not result in an increase in velocity. The
average velocity approaches a limit, which is the so-called limit velocity. The limit velocity, in most
cases, is below 2.5 m/s.

(a) (b)
Fig. 11.14 (a) Restoration of landscapes of Cheongyechon in Seoul, South Korea; (b) Beautiful Jiuzhai Creek in
Sichuan Province in southwest China has become a tourist attraction because of its protected landscapes

Figure 11.15 shows the velocity-discharge relations for the Lalin River at the Caijiagou Station, the
Huifa River at the Wudaogou Station, the Songhua River at the Jilin Station, and the Nenjiang River at
the Ayanqian Station, in which Q is the daily average discharge and V is the average velocity over the
cross section. The Lalin and Huifa rivers are tributaries of the Songhua River. With an increase in discharge,
the average velocity approaches a limit velocity.

Fig. 11.15 Velocity-discharge relations for the Lalin, Huifa, Songhua and Nenjiang rivers showing a limit velocity