2.1 Flume configuration
Flume experiments took place at Colorado State University’s Engineering
Research Center using a 9-m long and 1.2-m wide flume with a rectangular
cross section and smooth sidewalls (Figure 1). Flow was delivered to the
flume via pipes and pumps from a reservoir of water. A cobble‐filled
baffle dissipated flow energy at the upstream end of the flume and a
reinforced 250-micron mesh screen at the downstream end of the flume
trapped any mobilized sediment. We sized sediment to maintain an
immobile bed and used a gravel subsurface sediment with a pebble
topcoat. A summary of all flume attributes is included as Supplemental
Information.
We used natural wood pieces of varying size to create logjams in the
flume (Figure 1). We ensured a similar wood load per jam by quantifying
the wood volume and number of large wood pieces per each jam. Each
constructed jam was pinned by one large immobile key piece of wood to
avoid jam mobility. To change the permeability of a single jam, we added
coarse particulate organic matter, mainly in the form of leaves, pine
needles, and bark. We also added a plastic impermeable material to the
jam to further reduce its permeability (Figure 1).