# Chilcotin River landslide **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [August 2, 2024, 2:01am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130 "2024-08-02T02:01:31Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [August 2, 2024, 2:01am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/1 "2024-08-02T02:01:31Z")
On July 31, a large landslide near the town of Hanceville BC has dammed the Chilcotin River. A lake is forming upstream of the dam; downstream of it, the river is dry. This is obviously temporary: the lake will rise and flow over the dam, or leak through it and erode it, or (most likely) some combination. The danger is rapid erosion of the dam, which could release a major flood with potential to cause serious damage extending far downstream. Previous landslides have happened in this area, though apparently not in historic times. The Chilcotin is a tributary of the Fraser River, which flows past Hope, Abbotsford and Vancouver on its way to the ocean. ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [August 2, 2024, 2:10am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/2 "2024-08-02T02:10:15Z")
Some useful video in this [news report](https://www.youtube.com/watch?v=2uu845py58c&ab_channel=GlobalNews). ---
**Author:** ![EddyTeddyFreddy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eddyteddyfreddy/32/18796_2.png) [@EddyTeddyFreddy](https://boards.straightdope.com/u/EddyTeddyFreddy)\ **Post date:** [August 2, 2024, 2:30am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/3 "2024-08-02T02:30:19Z")
Yikes! How thickly settled is the potential flood plain below the landslide? ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [August 2, 2024, 2:50am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/4 "2024-08-02T02:50:11Z")
I’m not sure: the video article said that they are stopping service of the Lytton ferry which looks to be over 100 miles downstream, but they didn’t say if that was due to low water levels due to the lack of water from the tributary or due to flooding risk. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 2, 2024, 12:39pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/5 "2024-08-02T12:39:36Z")
If the landslide dam magically evaporated it would take 5 hours for water moving at 20mph to travel 100 miles downstream to Lytton. If the river course is flatter, or the dam failed more gradually, it would take even longer. Which would be plenty of time to notify the ferry to seek a dock and offload before the floodwaters got there. So I strongly suspect the actual reason is lack of water in the river course to float the boat. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 2, 2024, 5:21pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/6 "2024-08-02T17:21:52Z")
Or they’d prefer folks to get out of there gradually (as opposed to trying to evacuate everyone at once in the five hours warning before a flood), and they’re hoping that making things inconvenient by stopping ferry service will encourage that. ---
**Author:** ![ch51](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ch51/32/3111_2.png) [@ch51](https://boards.straightdope.com/u/ch51)\ **Post date:** [August 2, 2024, 8:00pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/7 "2024-08-02T20:00:57Z")
The Lytton ferry is a small cable ferry that crosses the Fraser River. The Fraser River is not running out of water. The river is not slow here. Lytton burned down two or three years ago. BC is very dry right now - a tinderbox like last year. I would hazard a guess that the concern is more earth making it’s way into any fast surging water - even more destructive than the water itself. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 3, 2024, 12:44am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/8 "2024-08-03T00:44:36Z")
No major developments. The lake caused by the landslide dam is now 11 km long. Expectation is that the water will eventually flow over the top of the dam, eroding it, rather than seeping through the dam, which could cause it to collapse more quickly. > **[Water behind B.C. landslide more likely to move over top than burst, minister...](https://www.cbc.ca/news/canada/british-columbia/chilcotin-river-landslide-aug-3-1.7283607)** > > On Thursday, officials warned a mass of water and debris could reach hundreds of kilometres downstream along the Chilcotin and Fraser Rivers. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 3, 2024, 12:57am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/9 "2024-08-03T00:57:13Z")
Just spitballing, here… Is it possible to install a big-ass siphon over the top of the dam, to keep the water from backing up more, without uncontrolled erosion? ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 3, 2024, 1:27am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/10 "2024-08-03T01:27:15Z")
I’m not an engineer, obviously, but three thoughts come to mind: 1. To be effective, any such siphon would have to be able to handle the upstream flow of the river. I think that would be a huge requirement, not something that could be whipped up in a few days. 2. The area is pretty isolated, I think, which probably means it doesn’t have the infrastructure (roads, residences, power supply) to allow for the siphon to be built on short notice. 3. The dam is likely pretty unstable. Could it bear the weight of such a large piece of equipment? More importantly, would it be safe for engineers and work crews to be on the dam, installing it? The speculation that the dam could collapse on short notice suggests it would be extremely hazardous. ---
**Author:** ![Dr.Drake](https://avatars.discourse-cdn.com/v4/letter/d/ad7895/32.png) [@Dr.Drake](https://boards.straightdope.com/u/Dr.Drake)\ **Post date:** [August 3, 2024, 1:59am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/11 "2024-08-03T01:59:23Z")
My house is about 2000 feet from the banks (Metro Vancouver). No danger, but we’ve certainly had warnings to stay away from the river. ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [August 3, 2024, 2:48am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/12 "2024-08-03T02:48:01Z")
> [@Northern\_Piper](#): > > To be effective, any such siphon would have to be able to handle the upstream flow of the river. I saw the flow rate reported as 200 cubic meters per second. A pipe to handle that would indeed be formidable. My back-of-the-envelope calculation says that in a pipe 2 meters in diameter the water would have to be flowing at a speed over 200 kph. ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [August 3, 2024, 5:48am UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/13 "2024-08-03T05:48:14Z")
To be fair, he did specify a big-ass siphon. Which would absolutely work, if there were any big-ass siphons available. Since there isn’t a big-ass siphon available, I suggest they use the old standard: Dynamite. Lots and lots of dynamite. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 3, 2024, 12:39pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/14 "2024-08-03T12:39:37Z")
And a whale. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 3, 2024, 1:13pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/15 "2024-08-03T13:13:37Z")
> [@Dag\_Otto](#): > > Since there isn’t a big-ass siphon available, I suggest they use the old standard: Dynamite. Lots and lots of dynamite. The landslide all being cleared away all of a sudden is exactly what we’re trying to avoid. That gets you a wall of water full of abrasive grit all suddenly coming downstream at high speed. What you want is some way to remove the blockage gradually, so there’s at worst a temporary slight rise in the water line downstream. The difficulty is that, as soon as you remove the blockage down to below the level of water behind it, water starts flowing over the top, which will itself remove more of the blockage, and very quickly grows out of control to the “all of a sudden” scenario. If a big-ass siphon isn’t available, then I suppose they could instead try a big-ass tarp over the crest, to slow erosion. That might be easier to procure and deliver. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 5, 2024, 1:25pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/16 "2024-08-05T13:25:52Z")
Bc’s emergency management ministry expects water to start overtopping the dam soon, likely today (Monday). > **[Over-top move of water at B.C. landslide site expected within hours, says...](https://vancouversun.com/news/over-top-water-bc-landslide-site-expected-within-hours-chilcotin-river)** > > Water is expected to start moving over the top of the massive landslide site currently blocking the Chilcotin River within hours ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 5, 2024, 1:34pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/17 "2024-08-05T13:34:04Z")
Sounds like they’re hoping it won’t be too serious, but there is of course the worst case scenario: > [@](#): > > The ministry statement says the most likely scenario to occur in the coming hours involves the trapped water moving through the slide area over 12 to 24 hours and resulting in flows downstream at the Fraser River resembling typical spring runoff, but higher peak water flows along the Chilcotin River. > > The ministry says a worst-case scenario could involve a rapid draining of the slide site, which could result in a 21-metre rise of the Chilcotin River near the Farwell Canyon Bridge, but typical spring freshet flows downstream along the Fraser River. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 5, 2024, 3:16pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/18 "2024-08-05T15:16:04Z")
Another article with details on the models of best and worst case scenarios. Best case: river tops the dam and then it takes about 24 hours to cut a channel deep enough to release the water from the temporary lake. Steady flow, similar to spring run-off, which is normally around 300 cubic metres per second. High point rise in the river: about 2 m. Worst case: water tops the dam and dam breaks, releasing all water in a few hours. Estimated rise in the river: 10 m; estimated water flow: 6,500 cubic metres per second. > “the dam is estimated to be 1,000 metres in length, 100 metres high and 30 metres in depth.” > “It also said the sudden lake from pooling water behind the dam is continuing to grow at a rate of 22 cm per hour.” > **[Water rise from Chilcotin River landslide may not be as high as feared: B.C....](https://globalnews.ca/news/10679886/chilcotin-river-landslide-update-aug-3-2024/)** > > The landslide dam on the Chilcotin River is estimated to be 1,000 metres in length, 100 metres high and 30 metres in depth. ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [August 5, 2024, 5:32pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/19 "2024-08-05T17:32:56Z")
Sources are saying that water has now overtopped the dam - as of about 9am local time. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 5, 2024, 6:58pm UTC](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130/20 "2024-08-05T18:58:48Z")
Article on the overflow starting. Some evacuation orders, covering a relatively small area: 3.5 km2 at one junction, and about 100 km2 total, along the river banks. > **[Water flowing over site of B.C. landslide that dammed Chilcotin River](https://bc.ctvnews.ca/water-flowing-over-site-of-b-c-landslide-that-dammed-chilcotin-river-1.6989482)** > > The Tsilhqot'in National Government says water has begun flowing overtop the landslide that dammed British Columbia's Chilcotin River. [Next page](https://boards.straightdope.com/t/chilcotin-river-landslide/1005130.md?page=2)