Forest Road Deactivation Practices
in the Pacific Northwest
21 - Wood Culvert Removal	Sequence of Activities, Peak Flow Estimates

General Considerations

The removal of all drainage structures must address water quality and slope stability concerns. Operators and supervisors should consult the pre-work checklist to avoid unnecessary delays, negative impacts and unexpected problems. Sediment control is difficult to achieve if the required tools are not at the work site.

If at all practical, it is preferable to work in dry conditions. This can be achieved by scheduling the work during the summer months, or by dewatering the stream. Remember that each stream crossing presents its own challenges. Deactivation specialists, supervisors and operators should discuss available options before work begins.

Suggested Sequence of Activities for Wood Culvert Removal

1. Know the water quality issues before deactivation starts.
2. Divert water flows, if at all practical, to work in the dry. However, in steep terrain, do not simply direct water down the ditch.
3. Install sediment control downstream from the culvert.
4. Remove the road fill from the vicinity of the culvert until the four corners of the culvert are visible.
5. Remove all surfacing from the culvert deck on the woods side.
6. Remove the fill from in behind the sill to within 0.3m (1ft) of the base. Leave some material on the upstream side (inlet) to maintain the water flow through the structure.
7. Slope the side of the channel to a stable angle.
8. Remove the wooden deck.
9. Move the excavator to the camp side; use puncheon if the creek is too wide to span with the machine tracks. Follow the principles of removing deep fills.
10. Remove puncheon and woods end sill from channel.
11. Excavate material from behind camp end sill and remove sill.
12. Complete cross-ditch and armour the channel as required.
13. Remove trapped sediment and sediment control devices once the water runs clear through the deactivated site.

Peak Flow Estimates

Be sure to know to what return flood you are managing water flows. Is it the Q-100 flood, i.e., the most amount of water you would expect once in a 100-year period? Ask your supervisor, as this affects the amount of armour required for newly established stream channels.

The cross-sectional area of a stream during a Q-100 flood is about 3 times bigger than the cross-sectional area of the stream during the annual peak flow. Therefore, estimate the annual high water mark, calculate the annual peak flow cross-section and multiply this area by three. Using the Q-100 peak flow area, you can estimate from that how high armour has to be placed to protect newly established stream channels.

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Introduction  1   Water Management  2   Waterbars & Ditchblocks  3   Safety and Road Surface  4   Revegetation  5   Sediment Control  6   Erosion Protection  7   Dewatering Streams  8   Cross-Ditches (Road Intact)  9   Cross-Ditches in Pullback  10   Partial Sidecast Pullback  11   Full Sidecast Pullback  12

13  Blanket Drains   14  Trench Drains   15  French Drains   16  Fords   17  Cross-Ditching Practices   18  Cross-Ditching in Pullback   19  Partial Pullback Practices   20  Full Pullback Practices   21  Wood Culvert Removal   22  Metal Culvert Removal   23  Stream Diversion Dams   24  Pre-Work Checklist

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