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Blunder mapping Kallahne Creek #2799
Back To Discussion List Written: 2009.11.01 by: Paul Kubik

I noticed a major blunder in the National Topographic Series map Squamish 92 G/11. There's been some interest recently in improving the trail descriptions and waypoints around the new Porteau interchange on Highway 99. The access to Deeks Lake Trail, for instance, has been relocated to the east side of the highway. In trying to make sense of what various map sources such as the NTS and 103 Hikes (all editions) are showing as the location of Kallahne Creek in the vicinity of the highway and what is reality I discovered the map sources are universally incorrect.

What the map sources show is Kallahne Creek crossing the lower gravel pit and draining into the ocean at Porteau Cove, north of the interchange. However, if you take the Porteau Road exit from Vancouver, Kallahne Creek is on your right (south of the pit) and the gravel pit is straight ahead. The creek never crosses the gravel pit. Looking at Google maps satellite view, you can actually see the creek making a sharp turn to the south at the pit. It's difficult to see what happens below the highway but it appears that Kallahne and Bertram Creeks join briefly before flowing into Howe Sound.

In reflecting on the source of the error, it's possible that the original NTS map was created before the gravel pit was mined. There's the possibility that Kallahne Creek was diverted from its original path by the mine but the creek location was never subsequently revised on newer editions of the map.


Comments

#1373 - 2009.12.24 Frank W. Baumann - The creek moved (avulsed)
The Kallahne Creek fan extends from Porteau to the north to the south side of the present highway overpass. Over time, Kallahne Creek has "windshield wiper-ed" over the entire fan. As recently as the mid-1990's, part of it did actually overtop its present bank and flowed over the highway north of the present channel, and down the dirt road to Porteau camp.

What is interesting is that debris flows have occasionally come down Kallahne Creek almost to the highway- the large tongue of one such debris lobe is visible in the channel just east of the present overpass. The present Highway 99 culvert would not be large enough to pass a future event, which means that if a blockage ever occurred, Kallahne Creek would flow south down to the obvious low point (dip) in the highway, and then across the road and down into Howe Sound. Unfortunately, if this happened, the CN rail track might be taken out since there is only a relatively small culvert at this location to convey water. When the predecessors to CN Rail (B.C. Rail) assessed Kallahne Creek, they wisely decided to cross the creek with a bridge, rather than a culvert (bridges are able to pass debris more easily than a culvert).