Elsevier, Developments in Earth Surface Processes, p. 779-803
DOI: 10.1016/s0928-2025(07)11164-0
Full text: Unavailable
In the 19th and 20th centuries, most alluvial rivers in the northern hemisphere were severely disturbed with respect to their hydro-morphology, connectivity, and bedload and discharge regimes. In Austria the relative frequency of braided reaches declined from 28% to 1% over the last century. Thus, several recent restoration efforts have concentrated on formerly dynamic gravel-bed rivers affected by channelisation and river-bed degradation. This paper examines the successes and constraints of selected restoration examples of different spatial extent along the Drau River, Carinthia. Both the hydro-morphological conditions and the status of the fish fauna are assessed using a 5-tiered scheme according to the EU Water Framework Directive (WFD) based on the type-specific physical environment. The results show clear improvements of the habitat and fish ecological situation in rehabilitated sites of the Drau River. In particular, juvenile stages of the key fish species – the grayling (Thymallus thymallus L.) – benefit from increased areas of shallow habitats; the ecological status improved between 0.2 and 0.9 ecological classes according to the WFD, depending on the spatial extent of the measures. Despite increased efforts in habitat rehabilitation, restoration success is still limited by remaining ecological deficits, such as the disrupted longitudinal river continuum and hydro-peaking, which were not addressed in the project. The presented analyses yield a better perspective on major ecological requirements for future restoration efforts of alluvial riverine landscapes.