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Severe Thunderstorms, High Winds and Hail
The counties served by United Electric experienced a total of 254 separate thunderstorm and 419 hail events in the period from 2000 to 2010. It should be noted that the National Weather Service identified separate events in each county, but for the planning area the event involved one large storm. For instance, on June 13, 2000, NCDC data indicates there were thunderstorm events in Holt County, DeKalb County (two), Clinton County and Buchanan County within a period from 6:20 p.m. to 7:15 p.m. For planning purposes this was essentially one storm that affected four counties. A list of all thunderstorms, high wind and hail storms is included in the appendix.
High winds are one of the more damaging types of storms for United Electric. Based on cooperative experience, damage was estimated at less than 10 % of the system.
During a typical year, the cooperative expects as least one major wind event that causes damage. Lightning can cause outages, but usually does not result in damage to the system. In 2010, 4,990 consumers were affected by power outages from major events. Figuring half of these outages are the result of thunderstorms, the impact would be 2,495 customers, approximately 25 % of United’s customers.
Table 1.13
United Electric Cooperative Service Interruption Vulnerability Assessment Matrix
Hazard: ThunderstorM
|
Probability of Damage-Causing Hazard Occurrence
|
Less than 1% in any given year
|
1-10% chance in any given year
|
10- 99% chance in any given year
|
> Near 100% probability in any given year
|
Potential Extent of Impact
|
Less than 10% of customers report outages
|
|
|
|
|
10-25% of customers report outages
|
|
|
|
|
26-50% of customers report outages
|
|
|
|
|
More than 50% of customers report outages
|
|
|
|
|
Flood and Levee Failure
Flooding is a natural hazard that presents a recurring threat to United Electric’s infrastructure. Although primarily limited to locations near rivers, flooding presents a danger when power lines cross rivers. Workers are not able to access poles or lines that are damaged or need servicing. Workers are also in danger by working in the floodwater.
Major rivers in United Electric’s service area are the Nodaway, 102 and Platte rivers. The largest is the Missouri River, which borders Holt, Andrew and Buchanan counties. Federal and non-federal levees exist in these three counties. Figure 4 depicts the 100-year floodplain in relation to the cooperative’s boundaries.
Figure 4 – Floodplain map
Inundation data for levee failure is not currently available for these areas. Figure 5 shows the location of known state and federal levees within the cooperative’s boundaries.
Figure 5 – Levees
From 2000 to 2010, United Electric’s service area experienced 124 separate flood events. During the 2011 Missouri River flooding, assets in Holt and Andrew counties were affected, with power discontinued to a portion of the service territory that experienced long-term flooding for approximately three months.
Flooding is considered a significant, but not major hazard, affecting less than 10 % of United’s assets. Most of the damage associated with flooding is caused by being unable to access lines for repairs.
Table 1.14
United Electric Cooperative Infrastructure Vulnerability Assessment Matrix
Hazard: FLOOD
|
Probability of Hazard Occurrence
|
Less than 1% in any given year
|
1-10% chance in any given year
|
10- 99% chance in any given year
|
Near 100% probability in any given year
|
Potential Extent of Damage
|
Less than 10% of damage to system
|
|
|
|
|
10-25% damage of system
|
|
|
|
|
26-50% damage of system
|
|
|
|
|
More than 50% damage of system
|
|
|
|
|
When compared with the total number of customers served by the cooperative, it can be projected that less than 10 % of customers may report outages during any given flood event.
Table 1.15 demonstrates the probability of occurrence, with the potential impact on customers.
Table 1.15
United Electric Cooperative Service Interruption Vulnerability Assessment Matrix
Hazard: FLOOD
|
Probability of Damage Causing Hazard Occurrence
|
Less than 1% in any given year
|
1-10% chance in any given year
|
10- 99% chance in any given year
|
> Near 100% probability in any given year
|
Potential Extent of Impact
|
Less than 10% of customers report outages
|
|
|
|
|
10-25% of customers report outages
|
|
|
|
|
26-50% of customers report outages
|
|
|
|
|
More than 50% of customers report outages
|
|
|
|
|
Severe Winter Weather
From 2000 to 2010, the service area for United Electric experienced 170 severe winter weather events. These include significant snowfall events, ice storms and blizzards. The probability for severe winter weather in the cooperative’s region is 100 %. (170 events/10 years > 100 %).
Ice is the single natural hazard with the greatest potential to cause damage to United’s assets. Ice can accumulate on an electric line, greatly increasing the weight on the line. The line can then break and in some cases, cause the pole to fall as well. This can result in what the utility calls “cascading” when one pole falls, tugging on the line and causing successive poles to follow. Ice storms often occur in wide bands, putting a significant amount of United’s assets at risk. In addition, ice accumulating on tree limbs can cause the limb to snap and fall on lines.
The damage to the system for severe winter weather was determined to be 10 to 25 %.
Table 1.16
United Electric Cooperative Infrastructure Vulnerability Assessment Matrix
Hazard: SEVERE WINTER
|
Probability of Hazard Occurrence
|
Less than 1% in any given year
|
1-10% chance in any given year
|
10- 99% chance in any given year
|
Near 100% probability in any given year
|
Potential Extent of Damage
|
Less than 10% of damage to system
|
|
|
|
|
10-25% damage of system
|
|
|
|
|
26-50% damage of system
|
|
|
|
|
More than 50% damage of system
|
|
|
|
|
The impact of severe winter weather on customer outages is evident in the outage data from 2006 to 2010. In December 2007, northwest Missouri experienced a major ice storm that disrupted power throughout the entire region. In 2007, United reported about 2,300 outages affecting 16,300 customers. This number, for all outages during the year, is larger than the total number of 10,000 customers.
The average number of outages for 2006, 2008, 2009 and 2010 – which did not have major ice storms – was 321 outages affecting about 4,600 customers. While not every instance of severe winter weather causes outages of this magnitude, it can be projected that 25 to 50 % of customers could report outages during a severe winter weather event.
Table 1.17
United Electric Cooperative Service Interruption Vulnerability Assessment Matrix
Hazard: Severe Winter
|
Probability of Damage Causing Hazard Occurrence
|
Less than 1% in any given year
|
1-10% chance in any given year
|
10- 99% chance in any given year
|
> Near 100% probability in any given year
|
Potential Extent of Impact
|
Less than 10% of customers report outages
|
|
|
|
|
10-25% of customers report outages
|
|
|
|
|
26-50% of customers report outages
|
|
|
|
|
More than 50% of customers report outages
|
|
|
|
|
Wildfire
The region served by United Electric is largely rural. It does not contain any large forests, although there are areas of heavy trees. Rural areas are a combination of pasture and grasslands and row crops. In 2010, there were 184 forest fires that affected 1,330 acres in the eight-county region, according to the Missouri Department of Conservation.
In the 10-year period from 2000 to 2010, there were 2,255 fires that affected 35,377 acres, according to the Missouri Department of Conservation. This results in a near 100 % probability of wildfire in any given year. (2,255 events/10 years > 100 %)
Although wildfire is common in the United’s service territory, it has not had an impact on delivering electricity. There have been no known instances of damage to the system because of wildfire or of customer outages related to wildfire. Table 1.18 shows information from the Missouri State Hazard Mitigation Plan that lists wildfires for the UEC region from 2004 to 2008.
Table 1.18
|
Wildfire Summary By County
|
County
|
Wildfires 2004-2008
|
Average Annual # of Wildfires
|
Likelihood Rating
(1-5)
|
Acres Burned
(2004-2008)
|
Average Annual Acres Burned
|
Total Buildings Damaged
|
Andrew
|
117
|
23
|
1
|
872
|
174
|
2
|
Buchanan
|
177
|
35
|
2
|
1,102
|
220
|
3
|
Clinton
|
127
|
25
|
1
|
998
|
200
|
0
|
DeKalb
|
164
|
33
|
2
|
4,103
|
821
|
3
|
Gentry
|
118
|
24
|
1
|
3,575
|
715
|
1
|
Holt
|
66
|
13
|
1
|
543
|
109
|
0
|
Nodaway
|
181
|
36
|
2
|
2,375
|
475
|
7
|
Worth
|
43
|
9
|
1
|
998
|
200
|
1
|
United Area
|
993
|
198
|
1.38
|
14,566
|
2,914
|
17
|
Source: Missouri State Hazard Mitigation Plan
|
The service territory had 993 fires during this period, burning a total of 14,566 acres. The average fire (14,566 acres/993 fires) affected 14.67 acres. A fire of that size would affect only a small amount of United’s assets. Further study will be required to create a model for damage assessments related to wildfire.
Table 1.19
United Electric Cooperative Infrastructure Vulnerability Assessment Matrix
Hazard: WILDFIRE
|
Probability of Hazard Occurrence
|
Less than 1% in any given year
|
1-10% chance in any given year
|
10- 99% chance in any given year
|
Near 100% probability in any given year
|
Potential Extent of Damage
|
Less than 10% of damage to system
|
|
|
|
|
10-25% damage of system
|
|
|
|
|
26-50% damage of system
|
|
|
|
|
More than 50% damage of system
|
|
|
|
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