This page describes the local hazards we face in Porirua that could cause an emergency.
Emergency management organisations and researchers around the world have found that when people understand the hazards that they face, and realise they can do things that will help their families and friends in an emergency, then the response to the issue is much better and communities recover faster.
Hazards in Porirua
So what hazards do we face in Porirua?
Wind – The Wellington region is infamous for its strong winds, and Porirua is no exception. North-westerly and southerly winds can bring sustained wind speeds of 100km/hr and gusts of 150km/hr in exposed places. Strong winds can bring down trees and power lines, lift roofing, and push vehicles around on the road.
Heavy rain – The same weather patterns can bring heavy rain to Porirua. If too much rain falls in a short time, rivers, streams, creeks, and stormwater systems can’t cope, causing flooding.
Thunderstorm – In addition to strong winds and heavy rain, thunderstorms produce lightning. Lightning strikes can disrupt power and telecommunications, and start fires. Thunderstorms can also produce hail, which can damage property.
Drought & extreme heat – Too much rain is a problem, but so is too little. Droughts increase the risk of wild fire, and there is a threat to public health if there is a water shortage or a long period of excessive heat.
Flooding happens when rivers, streams, creeks, and pipes, or even just the ground, can’t hold all the water being received. This can be caused by heavy rain, blockages, high tides and storm surges. Floodwaters can cause a lot of damage as they frequently contain debris, such as branches, rocks, and sewage. People can be swept away and drown. Most floodwaters leave a considerable amount of contaminated silt behind when they recede, and clean-up afterwards can take months.
Landslides can be triggered by an earthquake, but are more commonly caused by rainfall in our area. Our main transport links are quite vulnerable to landslides, and it is not uncommon for roads to be blocked by small slips. With all the hills around Porirua, many houses are located in areas that are vulnerable to landslides.
Rural fire – Most rural fires in Porirua are the result of human action, sometimes accidental, and sometimes deliberate. Some are caused by lightning. Fires are most common between November and March when vegetation dries out.
The intensity of a rural fire depends on past and present weather conditions. Strong winds and high temperatures are the worst combination for rural fires. Rural fires can damage crops, farmland, forests, sensitive ecosystems, commercial buildings, houses, recreational facilities and essential infrastructure. Fires can cause death and injuries, though in most cases it is possible to evacuate people from the path of a fire. The costs of fighting fires are high. Smoke, evacuations and restricted access can cause social disruption, and the fires may have some permanent environmental effects.
Urban fire – Urban fires can be caused accidentally or deliberately. They may happen because of a natural event, such as an earthquake, or lightning. Large urban fires are most likely to occur in areas where highly flammable materials are stored, or where there are industrial processes involving heat. Urban fires can cause death and injury, as they often spread very quickly. The economic consequences are significant, as property and infrastructure can be damaged, and business activities can be disrupted. The problems can be worse if fires are in an industrial area, or involve hazardous substances.
There are many toxic substances stored in our city, and we are on the main trunk rail line and State Highway 1 runs through Porirua, so a lot of dangerous goods pass through our city each day. The most commonly spilled substances in the region are sulphuric acid, ammonium nitrate (fertiliser), caustic soda, hydrochloric acid, petrol/diesel/oils, CNG, natural gas, and chlorine. Some are explosive (like fuel and natural gas), some are corrosive (like acid), many can cause injury or health problems, and permanent environmental damage. Some substances, like milk, may not be harmful to people if spilled, but they can have significant environmental impacts.
Sometimes the lights go out due to a power cut, the phone stops working, and there’s no water. This can be due to scheduled maintenance, system failures, accident, or a natural event – like the wind knocking down a tree onto power lines. Sometimes having one utility fail causes overloads on others and several can fail at the same time – water pumps stop working when the power goes out. Some can be fixed quickly, but other can take months to be repaired. A burst water main in Wellington took out the gas supply to the central business district for months!
Transport accidents (trucks, trains, buses, planes, etc.) can be caused by human error, mechanical breakdown, system failure, or by a natural hazard event, such as an earthquake or bad weather. Accidents on the highway or the main railway line can cause significant disruption. Hazardous substance spills can happen during accidents like these.
Communicable diseases, food, and waterborne illnesses and damage to the physical environment (e.g. hazardous substance accidents or biosecurity incursions) are the main causes of public health emergencies.
Examples of public health hazards include:
- new and emerging diseases affecting humans, such as SARS and pandemic influenza strains
- water supply incidents leading to communicable disease outbreaks (e.g. cryptosporidium, salmonella, giardia, or E. coli contamination)
- mosquito-borne illnesses (e.g. Dengue fever, malaria)
- outbreaks of severe communicable disease (e.g. meningitis, measles, tuberculosis)
- a severe and prolonged heat wave or cold spell
- bioterrorism using biological agents (e.g. anthrax, smallpox)
The Wellington region rests on a geologically active zone near the junction of the Australian and Pacific tectonic plates. This means that earthquakes are a very real problem for us. They are the disaster which is most likely to cause widespread disruption and destruction. Wellington, Porirua and the Hutt Valley have the highest potential in the country for social and economic losses from earthquakes.
Earthquakes can cause liquefaction – where the shaking makes the ground behave like a liquid, especially if there is groundwater as well. Other effects can be surface fault ruptures (big cracks in the ground), landslides, and sometimes tsunami.
Tsunami are a series of ocean wave or surges that are usually caused by undersea earthquakes, landslides or volcanic activity. Porirua is vulnerable to tsunami that are generated either close to New Zealand (local tsunami), or across the Pacific Ocean (distant source tsunami). On the open coast, tsunami can carry sediment and debris at speeds of up to 70kph, and can run a kilometre inland in low lying areas, and cause seiching (sloshing) in harbours and flooding. Tsunamis can destroy coastal properties and infrastructure. In a local tsunami, an earthquake may be the only warning you get, so move to higher ground as quickly as possible. With distant source tsunami, we may have several hours warning, so mass evacuation of affected areas would be possible.
There aren’t any volcanoes in the Wellington region, so why could volcanic eruption be a hazard for us? The prevailing wind conditions in the region mean that ash from eruptions of the central North Island volcanos can blow our way, and could contaminate our water supply, cause power and telecommunication outages, and affect people’s health, especially those with respiratory problems.
Links to more emergency information
Porirua City Council links:
Local Weather Sites