How long will it take desnagged streams to recover a natural load of wood?  — ASN Events

How long will it take desnagged streams to recover a natural load of wood?  (10818)

Justin C Stout 1 , Ian Rutherfurd 1 , James R Grove 1 , James Webb 1
  1. University of Melbourne, Carlton, VIC, Australia

A growing worldwide literature is demonstrating the geomorphic and ecologic roles played by wood in streams. After a century of removing wood from streams in many parts of the world, many restoration projects now include extremely expensive reintroduction of wood. Over large stream networks, and centuries of time, wood is recruited to river channels by many processes. For planning of stream management works, the important question is how long it will take (decades to millennia) for streams to recover an adequate wood load, with and without interventions? I report on an initial study into rates of wood accession and depletion in Victoria, Australia. The study is based on possibly the world’s largest survey of in-channel wood mapped by high-resolution aerial photography in over 28,000 km of Victoria’s largest streams and rivers. This aerial data-set, combined with LiDAR data and field-truthed measures of reference sites, provides a cumulative estimate of the effects of the processes driving the mass balance of wood to these systems.

Assessing wood loads as a mass balance of inputs and outputs indicates dominant delivery and removal processes, and provides a framework to test hypotheses of future wood loadings and potential geomorphic impacts to the river. Assessing the mass balance of wood using a Monte Carlo simulation approach randomly draws from distributions of the rates of physical processes driving the addition and loss of wood within reaches across a river large network. The model provides best and worst case estimates of natural wood loads and potential recovery times of in-stream wood loads with and without intervening restoration activities.  I report on methods used to develop and apply the model to Australian rivers, specifically focusing on the recovery rates of desnagged rivers. 

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