Mountain Rivers and Incised Channels - River Dynamics and Integrated River Management - page 156

and the bridge is endangered by the incision (left picture). In the upstream section with ribbing structures
(the ribbing structure is shown in Fig. 3.37(b)) the channel bed remains stable, no channel incision
occurred, and the bridge is safe. The two sections are only 6 km apart and the flow discharge is the same.
The Balan River is a tributary of the Songhua River in northeastern China. The bed slope is about
0.5% 1% and ribbing structures have developed on the bed. The ribbing structures are composed of
cobbles, gravel, and some boulders, as shown in Fig. 3.38. The structures have successfully controlled
channel incision and the channel bed is stable.
(a) (b)
Fig. 3.37 (a) In a section of a tributary of the East River without ribbing structures the channel bed is eroded down
by about 2 m and the bridge is endangered by the incision; (b) In a section of the same stream with ribbing structures
the channel bed remains stable (See color figure at the end of this topic)
Fig. 3.38 Ribbing structures in the Balan River, which is a tributary of the Songhua River in northeastern China.
The ribbing structure is composed of cobbles, gravel, and some boulders
3.3.3.2 Star-Studded Boulders
In mountain streams with gradient of 0.5% 1% a bed structure of star-studded boulders develops, which
consists of a series of sections with high bed gradient with star-studded boulders and supercritical flows
between two sections with gentle slope and sub-critical flows. In the Balan River, there are several
reaches with star-studded boulders. Many boulders with diameters around 0.5 1.5 m are scattered on the
channel bed. These boulders distribute on the channel bed randomly, and they emerge from the whole