Using bankfull discharge to quantify the effects of urbanization on river morphology: study of the Yzeron river basin (France) O. Navratil (1), M-B. Albert (2)

URBANIZATION IMPACT ON RIVER MORPHOLOGY

3 RIVER BASINS CHARACTERIZATION Forest Grass land Urbanization

For an homogeneous regional context, many studies have shown that bankfull discharge of non-disturbed alluvial rivers increases with river basin area following simple power laws. Some of them highlighted a significant gap to this regional law for streams impacted by human activities (e.g. dams, channelization). To test the use of bankfull discharge as an indicator of physical disturbance of stream reaches following urbanization development, we carried out a comparative analysis on the Yzeron river basin (France).

Urbanization area in 1990

Figure 1: Map of urbanized area in 1970 and 1999 (source: Radojevic, 2002)

Qbf= 5.3 S 0.92 •the urbanized area (Fig. 2).

The Yzeron river basin (150 km²) is a tributary of the Rhone river. The catchments is homogeneous in term of precipitations (800mm), geology (granite and limestone), but shows very heterogeneous land uses (forest, urbanization, grassland). The urbanization has rapidly increased since 1970 in the lower part of the basin (Fig. 1).

100

>5% and 15%

10

1

Figure 3: Bankfull discharge v. drainage area relationship

0.1 10 Drainage area (km²)

•high urbanized area: area Fu>15% (6 sites). The first group was considered to diagnose potential impact of urbanization. Rural and urbanized groups have the same range of drainage area (from 1.1 to 33.9 km²). River reaches selected were self-formed channels and showed a well-marked floodplain on at least one bank.

0 -0.2 Elevation (m)

•low urbanized area: area 5%