Beach erosion and flooding
Coastal erosion and flooding occurs in the Bay of Plenty, and can cause significant
problems if people build too close to the coast. Beaches move constantly, and naturally
oscillate between periods of erosion and accretion (onshore collection of beach
sediment). Sometimes these fluctuations reach extremes. Extreme fluctuations are
only ever a problem when humans develop buildings or infrastructure too close to
the coast. Coastal hazards occur when dynamic coastal movements interact with static
human resources that we have placed along the coast.
There are a large range of biological hazards that if not controlled or avoided,
could cause significant loss of life or severely affect New Zealand's economy, agricultural
and fishery industries, health (human and animal), and infrastructure (e.g. water
supply and treatment networks). Due to our economic dependence on horticultural,
agricultural and forestry industries, and limited historical exposure to disease,
New Zealand is very susceptible to biological hazards.
Cliff failure can occur in a number of ways from slumping to large block failures.
Climate is changing. Future changes in temperature, precipitation, and other climate
variables will alter Bay of Plenty's soil moisture and mean sea level. Some locations
will be more susceptible to floods and droughts.
By virtue of its mid-ocean geographical position between the sub-tropical and mid-latitude
belts, and its land-mass structure, New Zealand is vulnerable to a range of climate
conditions with potential to create severe weather hazards. The major effects of
severe weather over the Bay of Plenty include:
- Rainfall (affecting all or any part of the region)
- High Winds (affecting all or any part of the region)
- Storm Surge and Storm Tides (affecting coastal areas)
Drought occurs due to a deficiency of rain over an extended period of time, usually
a season or more. Drought can be defined in various ways. An 'agricultural drought'
is a period when the soil is estimated to be 'moisture deficit'. A significant agricultural
drought can impact on Bay of Plenty’s agricultural and horticultural industries.
A 'hydrological drought' is when the effects of low rainfall affect hydrological
systems. A hydrological drought can result in a water supply shortage, although
storage capacity and demand are also important factors.
The Bay of Plenty is one of the most seismically active areas of New Zealand. Earthquake
activity is greatest in the central part of the region, within the area encompassed
by the Taupo Volcanic Zone and the North Island Shear Belt, the latter being a zone
of faulting which runs down the spine of the North Island from Whakatane southwards.
Seismic hazard in this area, which encompasses Whakatane District and part of Rotorua
District, may be significantly higher than previously estimated.
Although 20.1% of the Bay of Plenty is covered in production forests with indigenous
forests covering another 47.3%, the risk of a major fire event that would require
the declaration of a local state of emergency is considered to be low. However the
potential exists for a declaration to be needed where residential areas are located
adjacent to forest areas. The impact of a large exotic forest fire would be devastating
for local industry based economies dependant on tree harvest and log export. It
is likely that current and future planned management mechanisms would restrict any
outbreak and it would certainly be unlikely to develop into an event warranting
a local state of emergency.
Vulnerability to flooding varies throughout the region. The greatest threat exists
to Opotiki and settlements on the Rangitaiki Plains, some parts of which are below
sea level (in part a result of the 1987 Edgecumbe earthquake). Flash flooding can,
however, affect any area where drainage is restricted or unable to cope with unusually
heavy downfalls. Flooding may also bring with it problems and hazards of landslip
on any of the steeper soils of the region. An eruption or earthquake may also cause
changes in drainage . landslides blocking rivers or rapid overspill of lakes like
Tarawera from the present outlet. These events could cause floods in several river
catchments. Major events will affect both rural and urban areas simultaneously.
Urban stormwater flooding (for example, Utuhina Stream in Rotorua or Waimapu in
Tauranga) are district events and may be caused by localised thunderstorms in the
Within and around the recognised thermal areas there is an ever-present possibility
of hydrothermal eruption, caused by superheated underground water undergoing a drop
in pressure and flashing to steam. The consequent expansion of the steam is capable
of producing large craters and scattering debris over a wide area. Minor hydrothermal
eruptions are common within the thermal areas.
Hazards from outside BOP
Hazards that occur in regions outside of the Bay of Plenty can also affect people
and communities in the Bay of Plenty.
Landslides and Debris Flows
Erosion and slope failure is common throughout the Bay of Plenty. Land instability
is often made worse by human activities.
Tornados frequently occur in the Bay of Plenty but are much smaller than the very
large ones that occur in the midwest of the United States.
The Bay of Plenty Region encompasses a wide range of volcanic sites within its territorial
boundaries, each capable of producing a risk to the public and to infrastructure.
The region may also be affected by eruptions occurring in other volcanic centres
i.e. Taupo, Egmont (Taranaki), Tongariro National Park, Auckland, and Kermadecs.
Submarine volcanoes to the north-east of White Island present additional risk.
Pandemics are the spread (potentially rapidly) of a disease across a wide geographical
area. The widespread occurrence of a disease can overload medical infrastructure
and can cause community disruption through limitations on movement and contact.