I inspected this debris torrent on Oct.25/99. There was approximately 15 cm of snow on the ground in this clearcut. I found that a spring, which was actively flowing at this time, originated in the middle of this clearcut and flowed in a gully for approximately 100 metres before it had been diverted to the west by a large cedar log. This cedar log had been felled during the clearcutting and left behind as slash. The debris torrent originated approximately 30 metres below this diversion in a steep wet area of the clearcut. The stream gully above the diversion had been left choked with logging slash which had since been hand cleared. This clearcut was 6.1 hectares in size as derived from Slocan Forest Product's Forest Development Plan.

"On about June 19, a large debris flow descended a tributary of Slewiskin creek, crossing the forest road at 5.25 km and causing severe damage to it. The volume of debris was estimated at 5000 m3, and most of it would have entered Slewiskin creek. On the initial helicopter reconnaissance, the source of the debris flow was traced to a small landslide in a cutblock near the top of the tributary, about 1 km NW of Blue Grouse Pass.

The landslide originated at an elevation of 1540m, in the lower part of a cutblock of about 7 or 8 ha, logged in 1996. The block was cable logged from a road and landing at the top of the block. There was no evidence that water had flowed in the ditch or water bars, or on the road surface.

Most of the terrain in the cutblock, in my opinion would be rated as terrain stability class III, with some areas of class IV on steeper ground along the road and in very wet areas at the lower margin of the block.

About 30 or 40 m above the slide, a broken snag had fallen into the stream. It was obviously felled during logging, as pieces of it lay over stumps and logging debris. Sand and gravel had accumulated behind the snag, diverting the flow of water out of the channel and down a slope to the left. A short distance below, at a steep spot (slope locally 69%) it started the landslide. The area is quite wet, with abundant seepage and devils club.

The slide is very small, with an initial volume of about 20m3. It was obviously highly saturated on failure, as there are mud splashes on trees at the cut block edge 30 m below. The slide material flowed as a very fluid debris flow down a shallow swale, about 160m to the creek. Apparently, as it progressed the debris flow entrained more sediment from the creek banks, as well as organic material and trees which it uprooted, and became larger as it flowed down the entire 3 k m length of the creek.

It is quite unusual for a landslide this small to cause a debris flow this large. This channel must have had sufficient stored material along its length that it was "ready to go", and only a small disturbance was needed to trigger a large debris flow. Logging and roads adjacent to such channels increase the probability of debris flows by creating the opportunity for small landslides into the channel. A similar large debris flow is reported to have occurred in the next major tributary down Slewiskin creek in about 1982, and started a slide below a road and cutblock.

The landslide was apparently caused by the cutblock and/or road, but the exact mechanism is unclear. Two things were necessary to cause it: an increase in flow of the spring and small stream, which made the stream erode its channel and create a dam of sediment behind the fallen snag; and the fallen snag which obstructed the channel and caused the diversion of water. The increase in flow of water could have been due to two things. It is possible that some water intercepted by the road cut flowed subsurface down the road grade and was concentrated into the area above the spring. It is also possible that increased snowmelt rates in the clearcut were responsible. The cutblock is near the top of a ridge, and the local drainage area above the slide has been about 75% clearcut. No substandard practices of logging or road building or maintenance took place, which might have contributed to the landslide. This event appears to have been unavoidable bad luck."

When Mr. Jordan refers to a similar debris flow in the next major tributary down Slewiskin creek in about 1982, it is of note that a second debris flow occurred later in the eighties in this same tributary as a result of the 1979-80 road building and clearcutting above this tributary. I worked on the repair of the Slewiskin creek forest service road as a result of both of these debris torrents during my employment with the Ministry of Forests during the 1980's. Also in the 900 hectare area bounded by this tributary and the tributary of CP135-2 along the west and east and Slewiskin creek on the north two other debris torrents occurred in 1996 post clearcut logging and road building. One debris torrent started in the lower fill of the logging road that ran along the bottom of CP 111-119, which was clearcut in 1995, and the other debris torrent started beneath a culvert in a road accessing CP111-120 that had not been logged when the debris torrent occurred. These events total 5 debris torrents that occurred post clearcutting and road building in a 900 hectare area. Although 3 of these blocks, CP111-119, 120, CP135-2 were logged after the Forest Practices Code came into effect, the permits were approved before the FPC and therefore they are not considered FPC blocks.

The slide wiped out a major culvert and about 75 metres of the Forest Service Road. This picture is taken approx 100 metres above Slewiskin creek, an S3 stream identified by Slocan Forest Products in their Silvaculture Prescription as having Bull Trout, Kokanee, Rainbow Trout and Lake Chub. This was a narrow V gully, forested right to the creek edge. It has filled the gully in to a depth of approx 3 metres and a width of 35 metres.

This closeup of the cedar log in the cutblock that diverted the stream shows the sediment dam at the center of log and the diversion of water to the left along the log. The stream used to flow to the right.

I drove into Slewiskin on May 18, 2000 and hiked to the base of the slide. The slide hit the main creek in a bedrock shoot and the debris was carried approx 40 metres downstream to where some of it formed a dam diverting the main creek out of its channel and caused it to cut a new channel for 300 to 500 metres. It was still flowing in this new channel as of May 18, 2000.

Notice that Jordan made no reference in his landslide report about this diversion, yet he could not have missed it flying the area with a helicopter.

Jordan also is chairing the Perry Ridge Risk Assessment Panel.