HISTORICAL NEWS SEARCH - Government of British Columbia

Winter 1992
Event type: Dam failure.
Precipitation: Not applicable.
Source: British Columbia Report, May 11, 1992.
During one of the winter storms, the dam in Deep Creek, one of Terrace’s two principal sources of water,
gave way. The small 30-year old structure washed out under the pressure of the water that had built up in a pond on the
Deep Creek water system, 4 mi. (6.4 km) north of Terrace. *1)
The water this system provides is mainly from the snowpack. Following an extremely mild and extremely
wet winter, the snowpack was very small. *2) When the dam let go, even this amount of water was lost. To augment its
water supply, Terrace was forced to drill a number of wells.
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*1) The Deep Creek system’s watershed is a relatively small area. Only about 4,000 ft. (1,200 m) above sea level, it is
not high enough for snow to remain on its slopes during summer.
*2) In November, December and January, Terrace had its highest recorded rainfall.
June 2-10, 1992
Event type: Debris slide.
Precipitation: Not available.
Source: The Times, June 16, 1992; Donna Creek Technical Investigative Team 1992; Evans (unpublished data).
On June 2 between 12 noon-2 p.m., a slide occurred in the Donna Creek area. Approximately 10-20 ha or 0.5
million m 3 of materials moved into Donna Creek and proceeded down the Manson River into the Manson Reach and
finally into Williston Lake The slide took out a bridge and caused a considerable amount of damage in the immediate
area but also in the creek, river and lake. (The Times, June 16, 1992).
Between June 2-10, catastrophic seepage erosion occurred in the Donna Creek watershed, 75 km northwest
of Mackenzie in the Omineca Mountains. It occurred within a forested sandy gravel fluvioglacial terrace and
culminated in a gradual process of seepage erosion in the gully initiated in 1990. Between 1990 and the 1992 event, a
total of 423,000 m 3 was removed from the gully. The dominant texture of the terrace is fine sand. Subsurface pipes
developed in eroding faces leading to collapse.
Debris flows transported the saturated materials away from the actively eroding face in 2 m-deep surges to
the Donna Creek valley. Erosion of the valley continued until June 10. Rapid melt of an above average snowpack was
a triggering factor for the 1992 event. In addition, forestry road construction upslope of the site had expanded the
natural catchment area by almost 10 times and concentrated runoff into the failure location (Donna Creek Technical
Investigative Team 1992). The flows destroyed about 3 km of Donna Creek. A forestry road bridge was washed out
and large volumes of sediment were deposited in the lower 4 km of the creek. According to Brian Blackman of Fish
and Wildlife and the Williston Compensation Program. “There is close to 40 km of (Manson) river that has been
affected by the slide.” One project was set for the release of 200,000 Kokanee into the river (The Times, June 16,
1992).
A multi disciplinary review team looked at the cause of the slide and made recommendations to the clean up
of the damage and restabilising the area and look at long-term solutions to avoid reoccurrence. It had not been
determined yet whether Fletcher Challenge’s nearby logging road had any effect on the slide.
Late September 1992
Event type: Flooding and debris slide
Precipitation: Kitimat 2 (143.3 mm/2 days), September 21-22, 1992; Kildala (146.6 mm/2 days), September 21-22,
1992; Kitimat 2 (62.7 mm/1 day), September 27, 1992; Nass Camp (60.4 mm/2 days), September 27-28, 1992; Stewart
A (107.8 mm/2 days), September 27-28, 1992; Terrace A (180.6 mm/2 days) September 27-28, 1992; Prince Rupert M.
Circ. (142.9 mm/2 days), September 27-28, 1992; Smithers (121.2 mm/30 days), September 1992.
Source: The Stewart Signal, October 2, 1992; The Interior News, October 7, 1992; Terrace Standard, October 7, 1992;
Alcan in British Columbia, Vol. 5, No. 5, November 1992; B.C. Forest Service Investigative Team P.R.F.R. Investigation
into the September 29, 1992 landslide Windfall Mainline near Meziadin Lake, Kalum F.D. November 1992; Evans
(unpublished data).
On September 28, Terrace recorded more a month’s rainfall in a single day. In the 24-hour period starting on the
evening of September 28, 124 mm of rain was recorded, breaking a record set in 1978. It was also the most rainfall for any
24-hour period since weather records were kept at the Terrace airport. Although it rained also hard in Kitimat, no record was
broken here.
According to weather specialist Harry Earle, unlike the 1978 flooding that was triggered by heavy rain and high
freezing levels resulting in snowmelt in the mountains, during this rain event most of the higher elevation snow had
melted two weeks earlier. (Terrace Standard, October 7, 1992).
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