Most drift floats at the water surface in a zone of surface convergence, generally where flow is deepest and fastest. As a result, floating drift is transported at about the average water velocity.
Submerged drift is carried to the banks and point bars by the slower, diverging flow near the bed.
Drift accumulates most frequently and in the greatest amounts where the path of floating drift encounters fixed objects that divide the flow. Accumulated drift remains intact for years unless removed, and sometimes is remobilized and transported downstream. Typical logs observed in this study lay approximately horizontal in the water, were exposed over their full length or nearly so, and did not rotate about a horizontal axis. Logs on the surface are not consistently aligned with the flow or across it, but rotate under the influence of large moving eddies. 118K GIF version of this photograph Figure 9.