LARGE WOODY DEBRIS DEFLECTORS

Sections of tree trunk were placed in 9 different parts of the river, all in or close to the lower middle reach (see map 2). The purpose of these is to promote the scouring of the river bed in relatively homogeneous areas, and create high physical diversity within the channel. Past practice of removing all naturally occurring woody debris has an adverse impact on juvenile and adult trout. LWD create simple flow deflectors and provide deeper pools used by adult fish, and smaller pools and shelter areas also. The tree section is orientated to reduce bank erosion and secured by staking and wiring. All sections point upstream.

All nine sections of tree trunk were secured by setting the “downstream” end into the bank to a depth of 0.6m to 0.9m feet. The exposed in-river lengths for six of the nine ranged between 1.5 and 2.5m, at an upstream angle of about 55 degrees to the bank. Six were set on the river bed and submerged by the flow. Three were set across riffles 4 and 5 and broke the surface of the water. One of the trunk sections (LWD 7, 3m) was set in a diagonal from bank to bank, all the rest fell short of this. Two other 3m sections were set in place upstream of this, LWD 8 at an acute angle to the bank, and LWD 9 at a diagonal and stopping just short of reaching bank to bank.

In addition to anchoring into the bank all sections of LWD were secured by at least two stakes in stream, and the stakes and trunk wired together with fencing wire held by heavy duty staples.

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