Abstract
A novel experimental setup for the laboratory was designed in order to investigate large woody debris accumulations and their influence on hydraulic flow conditions and channel morphology at a river cross-section. Real wood and mobile gravel bedload material were used to simulate morphodynamic interactions in a headwater stream, based on a New Zealand prototype river. The survey methodology employs Structure from Motion techniques, using an advanced multi-camera-array. In this study we present the experimental setup and initial results from our first experiments. With this research project we aim to investigate the dynamics of jam initiation and the characteristic evolution of the jam, for a given discharge, sediment load, and distribution of woody material. Furthermore, this study will elaborate more practical and efficient methodologies for observing wood jams, both in the laboratory and in the field. The project expands current knowledge about interaction processes between flow, sediment and woody debris, which are presently poorly understood and still represent a gap in research.
Highlights
Numerous studies have been carried out to investigate the influence and effects of large organic material in stream systems
The presence of the Large Woody Debris (LWD) accumulation at the critical cross-section (CCS) had a significant influence on the water level and bedload transport processes, during a simulated annual flood event
Upstream of the LWD accumulation, hardly any bedload transport occurred, significant changes could be clearly discerned at the downstream reach of the bridge
Summary
Numerous studies have been carried out to investigate the influence and effects of large organic material in stream systems. Large Woody Debris (LWD) is a characteristic feature in forested water courses all over the world, influencing both flow patterns and channel morphology to varying extents. Relative to channel width, and capacity for jamming, LWD can be a significant moderator of river morphodynamics, shaping the resultant channel pattern. This is considered to be an important process for nurturing a diversity of river flow environments for habitat [1, 2] and enhancing dynamic processes, such as meander migration and floodplain reworking. The critical cross-section (CCS), where the blocking probability of wood is highest, might already start to become blocked at lower water levels, resulting in a fully developed LWD accumulation at peak discharge, when most water and sediment is transported
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