Estimating Tree Failure Risk Along Connecticut Utility Right-of-Ways Helen Poulos Wesleyan...
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Estimating Tree Failure Risk Along Connecticut Utility Right-of-Ways Helen Poulos Wesleyan University Ann Camp Yale School of Forestry and Environmental
Estimating Tree Failure Risk Along Connecticut Utility
Right-of-Ways Helen Poulos Wesleyan University Ann Camp Yale School
of Forestry and Environmental Studies
Slide 2
Research Problem Vegetation management= critical component of
right-of- way (ROW) maintenance for preventing electrical outages
Recent forest regeneration along ROW edges has increased the risk
of transmission line failure due to tree contact with lines
Slide 3
While many trees along ROWs disable power, tree susceptibility
to damage varies by Species Age Rooting habit Height to diameter
relationships Lean Crown characteristics Identifying the role of
these characteristics in determining a trees wind susceptibility is
an important step toward mitigating the risk of transmission line
failure from tree windthrow.
Slide 4
Environmental Influences on Hazard Tree Distributions
Topography Land use history Historical Storms Soils Substrate type
Understanding the environmental conditions associated with ROW
hazard trees could focus vegetation management efforts to locations
with a greater potential for tree failure. Source:
http://www.wesleyan.edu/ctgeology/CtLandscapes
Slide 5
hazard trees danger trees Northeast Utilities needs a decision
support system to differentiate hazard trees with a high
probability of failure from the large number of danger trees that
could make contact with power lines
Slide 6
Research Questions 1.What is the density and distribution of
hazard trees versus danger trees across 115 kV lines in
Connecticut? 2.Which key tree attributes differentiate hazard trees
(HTs) from danger trees (DTs)? 3.What environmental settings host
HTs? 4.Can the HT-environment relationships be used to develop a HT
distribution map for Connecticut to focus future management
activities?
Slide 7
Field Methods Systematically sampled 115 kV lines across
Connecticut (N = 200) Danger trees identified by triangulation
Recorded tree attributes SpeciesSubstrate GuildRooting habit
HeightHealth DBHCrown class Live crown ratio Height : diameter
Lean
Slide 8
Live Crown Ratio Crown Class Height to Diameter Ratio
Terminology
Slide 9
Environmental Variables GIS of 24 Raster Data Layers Land cover
Storm probability Distance to storm track elevation (slope, aspect,
etc.) Topographic position Flow accumulation Wind speed - 30 m, 50
m, 70 m, 100 m height Topographic exposure Wetness
Slide 10
Danger Tree Attributes (species, height, DBH, % live canopy,
height : ratios, substrate, rooting habit, health, canopy position,
guild) Danger Tree Attributes (species, height, DBH, % live canopy,
height : ratios, substrate, rooting habit, health, canopy position,
guild) HT Maps for Connecticut 2 Groups (Danger Tree / Hazard Tree)
GIS Environmental Data Random Forest Classification Environmental
Conditions for Hazard/ Hazard Trees Absent Cluster Analysis CART
Attributes of Hazard Trees
Slide 11
What is the density and distribution of hazard trees versus
danger trees across 115 kV lines in Connecticut?
Slide 12
Slide 13
Slide 14
Which key tree attributes differentiate danger trees from
hazard trees?
Slide 15
Hazard Trees = Tall, thin trees with live crown ratios greater
than 0.65 and height: diameter ratios greater than 82.6
Slide 16
Trees with high live crown ratios have a high probability of
falling because they had a larger area for wind resistance and/or
ice or snow loading during winter storms (i.e. bigger sails) Trees
with high height: diameter ratios have an increased swaying
frequency and decreased sway damping (i.e. ability of trees to
absorb energy) when exposed to mechanical stress Trees with a
higher sway amplitude and lower damping capability are especially
prone to breakage or uprooting.
Slide 17
What environmental settings host HTs? Can the HT-environment
relationships be used to develop a HT distribution map for
Connecticut to focus future management activities?
Slide 18
Slide 19
Environmental Influences on HT Distributions Historical storm
tracks had the greatest influence on HT distributions HTs were
absent from locations with high numbers of historical storms
Frequent storms probably removed hazard trees Young, short stature
stands most likely dominate these locations Trees may also be
better wind adapted on these sites Historical Storms Common
Slide 20
Land Use Land use was the second most important factor
influencing HT distributions Urban areas and waterways had few HTs
So while populated portions of the state are a source of public
concern, it may be more important to concentrate management efforts
on more heavily forested regions Urban Areas
Slide 21
Topography HTs were absent from upper slopes and ridgetops
Upper topographic positions are more exposed which could remove
trees in severe weather. Harsher growing conditions and shallower
soils on exposed ridgetops may have also hindered the development
of tall, deep rooted tree cover. Upper Slopes and Ridgetops
Slide 22
Hazard Tree Distribution Map Total Map Error 24.6%
Slide 23
Slide 24
Conclusions Hazard trees with a high probability of failure
were differentiated from danger trees by: Live Crown Ratios Tree
Height Height: Diameter Ratios
Slide 25
The key abiotic environmental influences on hazard tree
distributions in Connecticut were: Historical storm tracks Land use
Topography Topographic position (upper slopes and ridgetops)
Elevation
Slide 26
Management Applications The classification tree has direct
management applications for identifying hazard trees in the field.
It can be used with limited field equipment (i.e. a diameter tape
and a laser range finder) to determine whether a potential risk
tree poses a threat to power line transmission.
Slide 27
The hazard tree distribution map represents and additional
level of decision support. The hazard tree-environmental
relationships can be used to understand the environmental settings
influencing the presence or absence of hazard trees. The map itself
can be used to identify locations across Connecticut where hazard
trees present a threat to power transmission safety.
Slide 28
Questions? Poulos, H. M. and A. E. Camp. 2010. Decision Support
for Mitigating the Risk of Tree Induced Transmission Line Failure
in Utility Rights-of-Way. Environmental Management 45: 217-226.
Poulos, H. M., and A. E. Camp. 2011. Mapping Threats to Power Line
Corridors for Connecticut Rights-of-Way Management. Environmental
Management 47: 230-238. Helen Poulos [email protected]
