An Overview of wood in rivers
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Abstract
Wood can be used to rehabilitate degraded water bodies (lakes and rivers). However wood has historically been removed from river systems to improve flood protection, inland navigation and drink water quality. These actions reduced and degraded the aquatic habitat of the effected river systems. Rijkswaterstaat is interested in reintroducing wood to rehabilitate the aquatic (and terrestrial) habitat of river systems.
In order to successfully reintroduce wood in river systems it is necessary to identify where the wood comes from? How is it transported? How does it accumulate? And what are the effects on stream ecology and geomorphology? This knowledge can be used to determine if already naturally occurring wood in river systems can be managed to achieve the goal of river rehabilitation. If no or too little wood is present in the river system, an engineered solution can be used. This engineered solution is known as Engineered Log Jam (ELJ). These structures use wood as construction material to rehabilitate rivers. The stability, design and implementation of ELJs in rivers is a complex process.
This report provides an overview on the identification, classification, importance and management of wood in river systems. Secondly the gives an overview of studies done on the stability of wood in rivers, the design (process) of ELJs and the geomorphological impact of ELJs on river systems.
From the studies reviewed in this report it is clear that wood plays an important role in river systems. Wood directly effect river ecology and geomorphology by forming log jams. Proper management of wood is therefore required if one wishes to retain a healthy river system. Where one wishes to (re)introduce wood in a river system using ELJ structures the design process is vital. The first step is to identify the characteristics and properties of the river section. The second step is designing the correct ELJs for the desired goals. The last step is constructing and monitoring the ELJs. Evaluation is important to obtain points of improvement.