Transcript Document

debris flow warning system
for public use
CRHNet October 2010
Debris Flow Initiation
1m
Britannia
Beach, BC
1921
56 fatalities
The Classic Fan
6
We know where debris
flows occur, but do we
know when they occur?
Are they possible to
forecast?
10 PM Pacific Standard Time (PST) on October 15, 2003.
10 PM Pacific Standard Time (PST) on October 16, 2003.
10 PM Pacific Standard Time (PST) on October 17, 2003.
10 PM Pacific Standard Time (PST) on October 18, 2003.
Vancouver
The discriminant classification
functions (2009 version)
4 week antecedent rainfall
(saturates soils)
2 day antecedent rainfall
(raises porewater pressures)
48 hour rainfall intensity
(during storm)
CSLS = - 11.85 + 0.031A4W + 0.116I48h + 0.081A2d
CSNL = - 4.58 + 0.017 A4W + 0.081 I48h + 0.025 A2d
IF CSL > CSNL debris flows are likely
IF CSL < CSNL debris flows are unlikely
Warning Level
Message
No watch
Due to current and forecasted weather conditions, it is very
unlikely that debris flows will occur in the North Shore
Mountains.
Watch 1
(conditions improving)
Due to current and forecasted weather conditions, it is
unlikely that debris flows will occur in the North Shore
Mountains, and it is unlikely that the Warning level will be
reached.
Due to current and forecasted weather conditions, it is
unlikely that debris flows will occur in the North Shore
Watch 2
Mountains, but it is possible that the Warning level will be
(conditions deteriorating) reached.
Warning
Due to current and forecasted weather conditions, it is
likely that debris flows will occur in the North Shore
Mountains.
Severe Warning
Due to current and forecasted weather conditions, it is very
likely that debris flows will occur in the North Shore
Mountains.
Winter ’08 - ’09
How is the system used?
• By the public via website and phone line
October – April
• must be combined with knowledge about
risks at specific sites and personal risk
tolerance
• By District staff – inspections, worker safety, fire
department
• By neighbouring municipalities and jurisdictions
• By our consultants – calibration based on actual
events
Implementation Considerations
•
Not 100% accurate and cannot predict the exact
location of debris flows nor their total number.
•
On average, 5 warnings per year and only one
to two debris flow-triggering storms will occur
(warning  debris flows)
At any given site, the probability of it having a
debris flow may be very low, but increases by
an order of magnitude for severe warnings
versus warnings
•
•
The only way to increase personal safety is to
evacuate
Debris flow warning system graph
www.geoweb.dnv.org
www.dnv.org/hazards
Summary
•
A debris flow warning system can be an
effective way to reduce risk
•
It is not fail-safe nor 100% accurate (system
redundancies can be built in)
•
The DNV system is based on sound science
and robust statistics
•
Public education is the key for successful
implementation and risk reduction