Prior to construction, the channel was quite dynamic. Surveys of 13 cross sections before and after a flow of 55 m3 s-1 (peak stages reached mid-bank elevation) that occurred three months prior to construction indicated an average increase in cross-sectional area of 10% with bank retreat as great as 7.6 m. This event triggered 60 m of upstream migration of a 0.6-m high headcut and produced two chute cutoffs across point bars. However, the woody debris structures created conditions more conducive to stability.

Cross section 23 shortly after construction on 23 Aug 2000

About five months following construction, the project experienced a flow event with depths exceeding 2.5 m and near-bed velocities exceeding 1.5 m s^-1. Peak discharge (43 m³ s^-1) was equivalent to 57% of the two-year event computed using a regional regression formula. In response to this event, the thalweg became slightly lower, creating a narrower, deeper baseflow channel, while much sediment was deposited within the large woody debris structures along the toe of eroding banks. These patterns were associated with shifts in bed sediment size.

Cross section 23 on 24 Jan 2001.
Note fresh deposition at toe of left bank

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