Ecohydraulics of wood transport in streams: Empirical models from the north shore of Lake Superior

Wood provides diverse functions in streams, including habitat for invertebrates and fish, entrapment sites for CPOM, enhancement of transient storage, and facilitation of meandering and pool formation.  Wood transport is a critical process determining wood distribution and abundance in streams.  We examined wood transport in 12 streams in northern Minnesota (representing a gradient in size and geomorphology) by individually tagging 1,255 pieces of wood (> 5cm diameter for a portion > 1m).  Data were collected from each piece before and after a single overbank flow event in fall 2007 to examine mobilization (whether a stationary piece moves) and entrapment (where a piece, once mobilized, comes to rest) to generate models of wood transport.  Mobilization was primarily a function of submergence, size ratios (i.e., size of piece relative to size of the wetted stream channel), and whether the piece was braced or partially buried.  Entrapment was primarily a function of size ratios.  The model equations can be used to estimate the probability of mobilization or entrapment given ecohydraulic conditions and local geomorphology, along with attributes of the piece.  Mobilization and entrapment can thus be estimated around infrastructure, or at restoration sites where wood is desirable for its many ecological functions.