Repeated cross section surveys indicate that the stream channel remained fairly stable until the peak flows in April, 2006. Since the peak flows in 2005 appear to have exceeded the mean annual peak flow, this relative stability is probably related to the strength of the root system.  While all of the trees on the floodplain were killed by the fire, it takes several years for the roots to decay to the point that they lose their strength. Some sort of critical threshold appears to have been exceeded between April 2005 and April 2006, since smaller peak flows in 2006 were able to dramatically erode the channel banks at a number of locations, including cross section 3, shown above. While the larger roots remain intact (see photo above), the smaller roots, which primarily control the bank strength, appear to have rotted away, resulting in the observed bank erosion.

The bulk of the bank erosion, near cross section 3 at least, appears to have occurred in a 3 day period around the 2nd peak in 2006. The diagram above shows the unit discharge estimated just downstream  of section 3 with an ADCP. The distribution of the flow reflects the channel shape and the bank location. Most of the bank erosion occurred between April 30 & May 2, 2005, but changes in the channel shape persisted at least until May 10, 2006. The velocity distributions collected with the ADCP  are shown below.

The figure above shows the measured velocity distributions near cross section 3 on April 30, May 2, May 4 and May 10, 2005. The approximate bed profile, reconstructed from the measured water depths, is shown using a dashed line. The ADCP unit is shown in the photo on the left.