Mountain Rivers and Incised Channels - River Dynamics and Integrated River Management - page 175

(a)
(b)
Fig. 3.60 (a) A step-pool system, composed of huge stones of diameter up to 2 m effectively mitigates the incision,
which endangered the Beifeng Bridge near Taichong; (b) The Mangfall River—a tributary of the Inn River in
Germanyr—is protected with artificial step-pools
for the effectiveness of the strategy are the size composition of the sediment fed to the river, and the
location and time of dumping. It has been proved that the strategy stopped the incision of the channel not
only in the section of dumping but also in the reaches downstream. Similar approaches have been tested
in the Danube River below Vienna (Go1z, 1994).
On the Drome River, the sediment budget is in disequilibrium as a result of upland afforestation,
which has reduced bed load supply from the catchment, gravel extraction from the channel, and
protection of alluvial banks from erosion. River managers have decided, on an experimental basis, to
permit sediment from a large landslide to be transported downstream (rather than remove it as would be
the standard procedure now) to augment bed load supply to incised downstream reaches (Piegay et al.,
1997b). Bed load supply can also be increased by permitting the river to erode its banks upstream. It may
require decades before the increased supply to the upper reaches has an effect downstream, but
monitoring of the effects is likely to provide extremely useful information for evaluating such strategies
elsewhere in the future. With elimination of most upstream gravel supply on the Sacramento River
(because of dam construction and gravel mining), bank erosion was an extremely important source of