Improvement of bed load transport and flood protection in accordance with the extension of a hydropower plant.

---

Silke Kainz, Michael Hengl

Tuesday 30 june 2015

12:39 - 12:42h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics, Poster pitches

Parallel session: Poster pitches: 5B. Sediment - River

---

The impact of the reconstruction of an old weir at the river Saalach at the border of Austria and Germany was investigated. At present there is a serious flood protection problem upstream of the existing weir due to insufficient bed load transport capacity. To reach a higher water level for higher energy production it is planned to install two inflatable weirs. To improve bed load transport the weir crest of the new construction will be lowered 1.2 metres and two sluices 5.2 metres below the existing weir crest will be placed in the outer bend. A physical model representing 1.6 kilometres of the river was built. On a scale of 1:60 the river reach, the surrounding floodplain and the weir were constructed. The main target of the physical model was to confirm the improved transport of bed load over the reconstructed weir whilst keeping or improving the flood characteristics. To control the changes in flood characteristics and bed load transport due to the new construction the existing weir plant was also built and investigated. The model was tested with several floods up to a 1000 year flood (1550 m³/s) and large amounts of bed load from upstream to cover future developments in the catchment. The comparison of the present and the future conditions showed that in the upstream head of the weir the water-table of the 100-year flood fell. The higher gradient due to the lower weir crest ensures a better bed load transport, which in the physical model resulted in a higher bed load output and a lower riverbed upstream of the weir compared to the present conditions. Further investigations showed the performance and impacts of the new weir in case of failure of a sluice and the debris-blocking sensitivity. Recommendations for the operating of the weir plant were given and a flexible scour protection for the new construction, taking into account the bed load transport was developed. Overall it can be shown that enlargement of hydropower plants, bed load transport and flood protection are not opposed.