Effect of instream wood on vertical water flux in low-energy sand bed flume experiments

In streams, interaction of current with bed forms and solid objects can produce vertical water flux across the streambed. Instream wood is a major obstacle to flow and alters the bed topography of natural sand bed streams. In the present experimental study in large circulating flumes simulating sand bed streams with low constant slope, we compared systems with and without natural quantities of wood. The introduction of wood resulted in the production of irregular bed forms. As a result, flow resistance tripled, and vertical water flux across the streambed increased by a factor of 1.8 to 2.5. The mixing depth was spatially variable and seemed unrelated to the local bed form. After the addition of wood, surface water mixed deeper into the sediments, and the total sediment pore water volume involved in mixing increased by factors of 1.2 to 1.5. The practice of increasing instream wood should be a valuable tool for hyporheic rehabilitation of degraded sand bed streams.