Assessing the influence of large wood on sediment connectivity and river morphology in small streams in the Vienna Woods (Austria)

Depending on their geometry, in-stream large wood (LW) pieces can significantly influence the morphology and hydraulic properties, the water and sediment connectivity of river channels as well as the riverine biodiversity. Such depositions often form hydraulic resistance, change the flow velocity and reduce the transport capacity. This, in turn, might affect the water and sediment connectivity of a channel, resulting in increased sediment deposition. Furthermore, LW can form new morphological structures, such as riffles or pools or alter already existing ones, for example river banks. The deposition of LW in streams is also associated with positive effects on biodiversity, as changes in the channel and flow patterns can significantly improve the heterogeneity of habitats.
In Europe, a lack of studies related to in-stream wood and its effects on channel morphology and sediment connectivity exists, as most research on this topic has been conducted in North America. In addition, the predominantly applied methodology is very time-consuming and complex, as the influence of LW is mostly based on the determination of drag force. The aim of this study is therefore, to apply a simple method to investigate the influence of LW on water and sediment connectivity in small streams in the Vienna Woods (Austria). Furthermore, geomorphological mapping is used to asses the effects of LW on channel morphology.
The study has been conducted in four mid-mountain streams of the Vienna Woods, located in the vicinity of the city of Vienna (Austria). LW deposits and potential sediment sources are mapped, classified and counted according to predefined criteria. Sediment deposits are measured and visible morphological changes, both associated with LW, are documented. The collected data is then used to (1) create a map, indicating LW accumulations in the research area; (2) determine the amount of retained material; and (3) apply the recently introduced indices ID_LW (LW disconnectivity index) and RP_LW (LW sediment retention potential index) (Pöppl et al., 2024) to gain an overview over the disconnectivity and sediment retention potential the LW deposits exhibit.
First results of this study will be presented at the EGU General Assembly 2024.

 

Reference: Pöppl, R.E., Perez, J., Fergg, H., Morche, D. (2024) Introducing indices to assess the effects of in-stream large wood on water and sediment connectivity in small streams. Geomorphology 444, 108936