Tactic CR-4: Drainage Protection
Drainage protection is used to keep contaminants from moving off site. It may be needed during spring breakup and summer when contaminants are mobilized and water is flowing through culverts, or while using treatment tactics such as flooding (Tactic CR-7) or flushing (Tactic CR-8).
A culvert can be blocked using sheet metal, plywood barriers, inflatable culvert plugs, or adjustable weirs (Fig. 29). Plywood or sandbags can also be used as culvert blocks, but require more labor to install. Place blocking materials over the upstream end of the culvert. Plastic sheeting over the outside of the block will decrease the likelihood of water leaking through the block. Block water flow through a culvert only if the impounded water will not threaten the road or raise water levels sufficiently so that additional tundra becomes contaminated.
If blocking a culvert is likely to damage a road or flood uncontaminated areas, a boom may be deployed in a chevron or diversionary configuration, allowing water to flow while deflecting oil from the mouth of the culvert to collection sites along the road (Fig. 30). This technique is especially useful when there is sheet flow of water across the frozen tundra. Boom systems will not provide drainage protection from water-soluble contaminants.
Considerations and Limitations
- Culverts should be unblocked when spill response is complete, to avoid impounding water and possibly washing out the road.
- This tactic has been adapted from Tactics C-2 and C-3 in the Alaska Clean Seas Technical Manual ( ).
Equipment, Materials, and Personnel
- Boom (2 workers) – to deflect floating contaminants from culvert.
- Anchor system (2 workers) – to secure boom system.
- Visqueen (2 workers) – to prevent seepage through permeable culvert blocks.
- Inflatable culvert plug (2 workers) – to block culvert.
- Air compressor (1 worker) – to inflate culvert plug.
- Sheet metal or plywood barriers (2 workers) – to block culvert.
- Sandbags (2 workers) – to block culvert.
- Flatbed truck (1 worker) – to transport sandbags.
- Front-end loader (1 worker) – to unload sandbags.