| Abstrakt: |
Gross channel changes for the Durance were determined using topographic maps from the 1890s and 1980s. Various width parameters were measured at 1 km intervals over 189 km from the Rhone junction at Avignonto La Saulce, some 31 km downstream of the dam at Serre Poncon. During this period channel size has been considerably reduced. This can be attributed to four factors, two natural and two human induced. Firstly, there was a reduction in effective runoff at the end of the Little Ice Age (late 19th century). Secondly, runoff was further reduced with lower precipitation after about 1940. Thirdly, channel widths have been reduced by bank protection and by flood mitigation works. Finally, large-scale river regulation by EDF (Electricite de France), completed in the early 1960s, includes large dams to store alpine runoff, concrete canals to convey released water through some 20 power stations, and barrages to intercept tributary runoff and divert flows into the canals. In the lower Mediterranean part of the river, some of the diverted waters are discharged into irrigation and urban water canals (about 114 m3 s-1) and the rest into the Etang de Berre. Only about 1% of the mean discharge now reaches the Rhone. Discussion of available research provides insight into the four impacts, including additional comparative post-regulatory evidence from the Syndicat Mixte, a group concerned with environmental problems in the lower river. Evidence for channel change in lower parts of tributaries and for bed incision was found to be less conclusive. Such impacts may have been reduced by the interruptions of long-profile continuity by barrages and dams, and by lower discharges. Such discontinuities have adversely affected the ecology, low environmental flows and treated sewage dispersion. With some exceptions, environmental sustainability has not been a major issue because the Durance is such animportant economic resource in terms of power, urban and irrigation wa [ABSTRACT FROM AUTHOR] |
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