Integrated River Management - River Dynamics and Integrated River Management - page 727

Fig. 11.10 Statistical distributions of the critical velocities when SI increases to 1 ( U c 1 ), begins to reduce from 1
( U c 2 ), and reduces to zero ( U c 3 ) for 36 species of adult fishes (a); spawning (b); fry fishes (c); and, juvenile fishes (d)
Dam construction on rivers reduces the flow velocity and extends the duration of water on the land,
which is accordance with Principle Ē . On the other hand, dams have some negative impacts on the
ecology mainly due to cutting off the path of migratory vertebrate species to their spawning sites. These
negative effects may be offset by building fish ladders. However, channelization, hardening banks,
cutting off meanders, and removing obstacles from the channel and floodplain to reduce the roughness
are against Principle I. Such actions may damage the ecology, and cause the death or poor health of
aquatic biota (Kingsford, 2000).
Meandering is natural for the nature stream channels. Artificial cutoff of meanders shortens the river
course and is counter Principle Ē . After the cutoff the flow energy converges, which may result in
intensive local scour and bank erosion, instability of the channel, and damage to aquatic habitats.
Recently an artificial cutoff has been suggested at the Paizhou Meander on the Yangtze River. The
meander is located downstream of Tongting Lake and upstream of Wuhan. There is a big argument
between Tongting people and Wuhan people. The former support the cutoff for reduction of flood risk.
The latter worries about that a flood may come to Wuhan quickly and threaten the safety of the city. A
flood wave may propagate through a shortened channel more quickly after cutoff and cause flooding
problems to the downstream reaches. Moreover, a meandering channel is more ecologicallysound than a
straight channel. Therefore, the artificial cutoff of meanders is not a good strategy.
The term channelization encompasses all the procedures of river channel engineering which are used
to control floods, improve drainage, maintain navigation, or restrain bank erosion. These procedures
include enlargement, realignment, hardening, embanking, or protection of an existing channel, or the