Overseas hazard management examples useful in the New Zealand context
Lahar hazards in Pierce County, Washington, USA
The United States Geological Survey mapped the lahar hazard for Pierce County (within Washington State), and the County adopted the maps and decided to regulate based on lahar travel times (time between warning system activation and arrival of debris flow). The County also developed rules to ensure that development in volcanic hazard areas (as mapped) is low density. The philosophy is two fold: keep development out of higher risk areas to prevent damage, and limit the number of people in the area to facilitate evacuation.
The following table is from the Pierce County (Washington State) Development Regulations for volcanic hazard areas, which summarises their requirements. These are based on volcanic hazard area standards and travel times, details of which are outlined here.
Volcanic hazard area standards
Table 18E.60.040 Volcanic Hazard Area Standards |
||||
|---|---|---|---|---|
Facility/ Occupancy List |
Case I Lahar Inundation Zone |
Case II Lahar Inundation Zone |
Case III Lahar Inundation Zone |
Pyroclastic Flow |
Bonus Densities |
Not Allowed |
Not Allowed |
Not Allowed |
Not Allowed |
Essential Facilities |
Not Allowed |
Not Allowed |
Not Allowed |
Not Allowed |
Hazardous Facilities |
Not Allowed |
Not Allowed |
Not Allowed |
Not Allowed |
Special Occupancies |
In Travel Time Zone A - limited to 100 persons occupancy load In Travel Time Zone B - limited to 500 persons occupancy load In Travel Time Zone C - limited to 1000 persons occupancy load In Travel Time Zone D - limited to 5000 persons occupancy load |
In Travel Time Zone A - limited to 100 persons occupancy load In Travel Time Zone B - limited to 500 persons occupancy load In Travel Time Zone C - limited to 1000 persons occupancy load In Travel Time Zone D - limited to 5000 persons occupancy load |
Not Allowed |
Not Allowed |
Covered assemblies |
In Travel Time Zone A - limited to 100 persons occupancy load In Travel Time Zone B - limited to 500 persons occupancy load In Travel Time Zone C - limited to 1000 persons occupancy load In Travel Time Zone D - limited to 5000 persons occupancy load |
In Travel Time Zone A - limited to 100 persons occupancy load In Travel Time Zone B - limited to 500 persons occupancy load In Travel Time Zone C - limited to 1000 persons occupancy load In Travel Time Zone D - limited to 5000 persons occupancy load |
Not Allowed |
Not Allowed |
Other Occupancies |
No Limit |
No Limit |
No Limit |
No Limit |
Overview of site-specific tsunami options
No one solution will fully address tsunami risk in all situations. Professional advice and design input should be sought when considering the following measures to reduce the risk of damage caused by a tsunami.
Slowing techniques
These involve creating friction that reduces the destructive power of waves. Specially designed forests, ditches, slopes and berms can slow and strain debris from waves.
Steering techniques
These guide the force of tsunamis away from vulnerable structures and people by strategically spacing structures, using angled walls and ditches, and using paved surfaces that create a low-friction path for water to follow.
Blocking
Hardened structures such as walls, compacted terraces and berms, parking structures, and other rigid construction can block the force of waves. Blocking, however, may result in amplifying wave height in reflecting or in redirecting wave energy to other areas.
Building design
Where buildings are to be constructed in a tsunami hazard area, the design and construction of the buildings (including construction materials, building configuration and tsunami-specific design features), can reduce loss of life and property damage. Design and construction of new buildings should address forces associated with water pressure, buoyancy, currents and waves, debris impact, scour and fire. Substantially constructed buildings of concrete, masonry and heavy steel frames are likely to perform fairly well in a tsunami unless compromised by earthquake shaking. Wood-frame buildings, manufactured housing and light steel-frame structures at lower elevations close to the shoreline are likely to fare poorly in a tsunami.
