Chilcotin Slide

[IronNoggin]

CHILCOTIN SLIDE UPDATE, 3 P.M., SATURDAY, AUG. 3


The province just held an information briefing about the slide on the Chilcotin River, so since there's obviously interest in it, here's an update about where we are.


Lidar data has established that the slide is 1,000 metres long by 800 metres wide by 30 metres deep. Lidar is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver.


The 'lake' behind the slide site is rising at a rate of about 22 centimetres per hour. This is a slight decrease over the first couple of days, as the water now has more room to spread out behind the slide area.


There is no seepage at the toe of the slide, so overtopping of the slide is the most likely scenario based on what is known/being observed.


Worst Case Scenario: A one-hour breach scenario. In this scenario it would take 1.5 hours for water to reach Farwell Canyon, three hours to reach the confluence of the Chilcotin with the Fraser, 15 hours to reach Lillooet, 21 hours to reach Lytton, 24 hours to reach Boston Bar, and 29 hours to reach Hope (all times measured from the slide site).


In this scenario, peak flow between the slide site and Farwell Canyon would be 6,590 cubic metres per second (typical freshet flow is 300 cubic metres per second). Peak height above current would be 10 metres. At the confluence with the Fraser the peak flow would be 5,545 cubic metres per second and peak height above current would be four metres.


By the time the flow reached Lillooet it would be well below typical freshet flow but 1.8 metres above the current height. Same at Lytton, where it would 1.5 metres above current height; Boston Bar (1 metre above current height); and Hope, where the water would be 0.3 metres above current height.


Best Case Scenario: A 24-hour breach scenario. In this case, the water would take 9.5 hours to reach Farwell Canyon, and 11 hours to reach the confluence with the Fraser, where the peak height would be 2.1 metres above current.


It was stressed that this is an extremely dynamic situation, and that a lot of assumptions have had to be made to create the models. There is confidence, however, that there will be overtopping, and not a breach. Additional field data is being collected continuously, and all possibilities are being prepared for.


Debris may be part of the outflow, which could damage riverbanks and infrastructure. An evacuation order has been issued for properties along the Chilcotin River from Hanceville to the Fraser, and people are being warned to stay clear of the land and air space around the slide.


A question that has been asked is 'Will there be an effect on area highways?' The answer is 'No.' Highways 20, 99, and 1 are either far enough away from, or too high above, the Chilcotin and Fraser Rivers to be affected.


Attached picture (courtesy Marty Lauren/Facebook) shows water and debris backing up behind the slide site (l).


https://www.facebook.com/groups/2356...ibextid=RtaFA8

[IronNoggin]

As of 12:40 August 4th, the river remains completely blocked and a large lake continues to form behind the blockage.​

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As a result of the landslide, the River Forecast Centre has issued Flood Warning and Flood Watches for portions of the Chilcotin and Fraser Rivers. Multiple Evacuation Orders and an Evacuation Alert have been issued in these areas. For more information about the Chilcotin River Landslide event and associated issuances, go to https://www.emergencyinfobc.gov.bc.ca/event/31july24a/

Provincial personnel and external experts are assessing and monitoring the landslide 24/7 as part of a multi-agency coordinated response. Decisions are being guided by ongoing technical modelling and mapping, geotechnical assessments, remote sensing technology, Light Detection and Ranging (Lidar) data and environmental impact assessments.

The Province is continuing to co-ordinate with local authorities, First Nations and the federal government.

For daily updates on the current situation, go to the Resources page to find the latest Information Bulletins, presentations and more.

[Arctic Lake]

Hope everyone stays safe that like to spend time along the two rivers !
Arctic Lake

[high horse Hal]

Safety is paramount
but all the compassion effort and money will go into grief counseling

[CranePete]

Wait and do nothing is probably the worst decision.

Be prepared that they may have to close Highway 97.

Cheers

Why on earth would they close Highway 97N? The Chilcotin is nowhere near, and the Fraser downstream of the Chilcotin confluence is a very long way from Hwy 97N.
CranePete

[Quince2]

Better stop all hunting in bc... just to be safe.

[Walking Buffalo]

Video from today.
Projections that the water will overtop the dam tonight.

[Downtown]

Why on earth would they close Highway 97N? The Chilcotin is nowhere near, and the Fraser downstream of the Chilcotin confluence is a very long way from Hwy 97N.
CranePete

Well my Friend I drive the 97 several times per year (most recent last Week) from Hope to PG and further. Have you ever travel this stretch during Daytime ?
There are places where the Fraser almost touches Hyw 97 and the elevation from Water to Road is at times less then 5 Meters which is nothing should this Dam let go.

Cheers

[Downtown]

Video from today.
Projections that the water will overtop the dam tonight.

Thank you for your update. Unfortunately I understand only Enlish and German therefore I am wondering if you could include a translation for the Benefit of most British Columbians which are equally Language challenged then myself, thank you !
Cheers

[CranePete]

Respectfully, and not to belabour the point, but the Fraser River is invisible from the road at the start of Hwy 97N at Cache Creek to the confluence with the Chilcotin River. The Fraser River is visible again from Hwy 97N at Mcalister to Prince George. The Thompson River is visible along Highway 1 between Cache Creek and Lytton, where it joins the Fraser River.
Cheers