Mountain Rivers and Incised Channels - River Dynamics and Integrated River Management - page 162

(Continued)

Undermining hill slopes Trigger landslides, which deliver

large quantities of sediment to the
channel

Fier River, France (Bravard et al., 1997)

Undermining of bridges Loss or costly repair of bridges Colorado (Lane, 1955); Tujunga Wash,

California (Scott, 1973); Arizona (Bull and
Scott, 1974); Apenine rivers, Italy (Tagliavini,
1978); Stony Creek, California (Kondolf and
Swanson, 1993); Loire River, France (Gasowski,
1994); Cache Creek, California (Northwest
Hydraulics consultants, 1995); western Iowa
(Lohnes, 1997); Arroyo Passajero, California
(Leclerc et al., 1997); Wooler Water, UK (Sear
and Archer, 1998); Arno River, Italy (Billi et al.,
1997); Kaoping River, Taiwan (Kondolf, 1997)

Undermining of dikes and
embankments

Loss or costly repair Otaki River, New Zealand (Soil and Water,

1985); Arve River, France (Peiry, 1993; Blanc et
al., 1989); Drome River, France (Landon et al.,
in press)

Undermining of pipeline
crossings

Loss or costly repair San Luis Rey River, Califronia (PBGS., 1994)

Arroyo Passajero, California (Leclerc et al.,
1997)

Reduced filtering of water
into water supply intakes

Reduced water quality, potentially
increased treatment expense

Russian River, California (Marcus, 1992) Mad
River, California (Lehre et al., 1993)

Lowering of alluvial water
table

Loss of alluvial groundwater
storage.
Dewatering and loss of hyporheic
habitat in river banks. Dewatering
roots of riparian vegetation and/or
prevention of new plants
establishing, modification of tree
growth and transpiration (e.g.,
poplar); Drainage of formerly
saturated active channel,
permitting establishment of
riparian forests. Dewatering of
floodplain wetlands and former
channels, converting vegetation
and invertebrate communities.
Modification of water
physico-chemistry

southeast Australia (Eyles, 1977); Enza River,
Italy (Tagliavini, 1978); Missouri River (Reilly
and Johnson, 1982); Zimbabwe (Whitlow,
1985); Ain River, France (Roux, 1986; Pautou
and Girel, 1986; Marston et al., 1995); Rhone
River, France (Pautou, 1988); Southwestern U.S.
(DeBano and Schmidt, 1989); Rhone River,
France (Creuzé des Cha.telliers and
Reygrobellet, 1990); Drome River, France
(SOGREAH, 1991); Laboratory (Rood and
Mahoney 1995); Russian River, California
(Sonoma County, 1992); Lake County,
California (Lake County, 1992)

The incision of the channel bed enhances the river capacity to discharge flood flow. The enhanced
channel capacity typically leads to more rapid transmission of floodwaters downstream. While this
reduces flood risk on-site and upstream, it increases flood hazard downstream because flood peaks are no
longer attenuated by channel and floodplain storage. Beaudelin (1989) showed that the travel time of
similar flood waves on the Garonne River decreased from 19 to 10 hours between Toulouse and Castelsarrazin
(60 km) from 1950 to the late 1980s as a result of incision, increasing flood risks downstream.
Channel incision can result in the loss of gravel bars, and, consequently, the loss of habitat and
biodiversity. It was reported that on the Isar and Lech Rivers in Bavaria (Reich, 1991, 1994), incision of
the riverbed caused the loss of the plants Myricaria germanica, as well as the birds that prefer these
plants for habitat. The encroachment of willow thickets and pine forest has reduced the number and area
of pioneer habitats, isolating areas of open gravel bars (i.e., creating gaps in this once continuous habitat),
and increasing the upstream to downstream distance between habitats, which has modified colonization