ASSIGNEMNT

Assignment



Assignment

Our modern communities are underpinned and increasingly dependent on multiple layers of interconnected infrastructure (for example: electricity, gas, oil, water, storm-water, sewage, telephone, Internet). Continued operation of these lifeline services during emergencies is essential to maintain economic activities and the health and safety of communities. Hence, utility-management organisations are generally bound by legislative or consumer/contractual requirements to maintain operations during emergency events, including volcanic eruptions.

Table 1: Key iconic infrastructure and electricity Grid Exit Point (GXP) sites in the Taranki region considered in this analysis

Site

Distance from volcano

Bearing from volcano

Plant replacement cost

Staff

Power

(km)

(o from N)

($ million)

Whareroa Dairy Factory

41.8

150

1045

950

Co-generation plant 69 MW, connected to National Grid

Kapuni (Fonterra Lactose)

22.4

155

207

120

Power from neighbouring Kapuni gas treatment plant

Kapuni (gas treatment plant)

22.4

155

80

25 MW co-generation plant

Oanui gas treatment plant

24.5

242

n/a

n/a

11 kV supply via Opunake GXP

Pohakura gas treatment plant

38.4

29

n/a

None. Operated remotely from New Plymouth

33 kV supply from Pwercos' Waitara West Substation

Opunake GXP

16

229

3.5-4

n/a

Moturora GXP

26.2

355

3.5-4

n/a

Carrington GXP

24

6

16.5-17

n/a

Huirangi GXP

31.8

31

7.2-8

n/a

Stratford GXP

22.6

101

45.8-46.5

n/a

Hawera GXP

37.1

144

10.5-11

n/a

Assuming that 1 year BP is equivalent to 1 calendar year, and that the last event was in 1854 (154 years ago) the probability of no eruption in the next t years is (Turner et al. 2008)

(1)

where f(t) is the probability density of the renewal process. If there is no eruption in the interim, then the annual eruption probability in year y will be

AEP(y)=1-Pr(t>y+1|t>y)

which is shown in Fig. 3. Annual eruption probability is presently close to its minimum of about 0.9%. The annual probability will climb steadily after 2020, approximately doubling over the next 200 years.

The hazard at a given site due to tephra fall can then be calculated as the probability (in y years) that a fall of thickness greater than T0 occurs, i.e., the exceedence probability

Table 2: Distribution of the number of eruptions in a 50 year period

Number of eruptions, i

Pr (i eruptions occur in 50 years)

0

0.631

1

0.294

2

0.067

3

0.007

> 3

0.001

The last element is to combine the models for eruption probability and tephra fall via Eq. ...