48 BUILD 121 December 2010/January 2011

SUN, SEA, SURF

REDUCING RISK ON URBAN COASTLINESThe length of coastline and exposed location in the South Pacific places New Zealand at risk from several coastal hazards, but good urban design can protect coastal communities and minimise the risk.By Wendy Saunders, Natural Hazards Planner, GNS Science, Lower Hutt

Effective management of natural hazards requires a holistic approach integrating land-use planning, emergency manage-ment (warnings and response), design

and construction. While urban design projects often consider heritage, transport, landscape and urban ecology, the consequences of natural hazards are often overlooked.

Good urban designThe New Zealand urban design protocol, published by the Ministry for the Environment in 2005, states that quality urban design ‘avoids or mitigates the effects of natural and man-made hazards’. Through the design principles of connectivity, creativity and custodianship, the effects of natural hazards can be mitigated through good design. These urban design principles are defined as: ❚ custodianship – reduces the environmental impacts (or in this case, consequences of The New Plymouth coastal walkway.

Figure 1: Downtown redevelopment plan for Hilo, Hawaii, with the seven key principles for incorporating tsunami risk into design (adapted from the National Tsunami Hazard Mitigation Program 2001).

1. Risk

2. Avoidance

3. Configuration of development

4. Design and construction

5. Land use change

Hilo Bay

waterfront promenade

realigned highway

lower loop road

parking service lane

mall

tsunami forests

existing shops relocated to upper level

tsunami

7. Evacuation

BUILD 121 December 2010/January 2011 49

natural hazards) of towns and cities through environmentally sustainable and responsive design solutions

❚ creativity – encourages creative and innovative approaches

❚ connectivity – enhances choice, supports social cohesion, makes places lively and safe, and facilitates contact among people.

Urban design can successfully incorporate natural hazards to reduce the risk to the community. The two examples below – the New Plymouth coastal walkway and the tsunami risk in Hilo, Hawaii – show how the protocol’s principle of custodianship can be achieved while retaining and improving connectivity with the landscape.

Coastal protection in New PlymouthThe coastal walkway in New Plymouth is a 7 km path that forms an expansive sea-edge promen-

ade stretching almost the entire length of New Plymouth city. Originally built in the early 1900s as part of the city’s reclamation, the seawall also provides valuable protection for the railway and road (now a state highway), which accesses the port. Prior to the walkway project, the coastal strip, which had a small unattractive gravel path and no amenities, was not well used.

Rebuilding of the original seawall began in 1999 and has resulted in a walkway that complements the greater coastal landscape. The promenade is designed without a hard edge, to accentuate the sense of being on the edge of the sea, and the walkway design is a compromise between raising the path above the waves and setting it back. Once the wave climate was assessed (large waves will likely close the walkway approximately six times every year), a 3 m setback was considered appropriate, resulting in 3 m of coastal engin-eering works between the sea and the walkway. The curved seawall and the path’s location provide protection from all but the largest waves, and the design uses robust and simple materials to stand up to the character of the west coast.

The walkway is an example of a highly engineered coastal protection structure that has minor environmental impacts and benefits the community by providing access, recreational opportunities and links between the central business district and the foreshore.

Coastal protection in Hilo, Hawaii In 1946 and 1960, the city of Hilo on the island of Hawaii suffered the direct impact of devastating tsunamis. To ensure the damage did not recur, the Hilo Downtown Redevelopment Plan was adopted in 1974 to redevelop the town centre based on tsunami inundation lines (see Figure 1). The redevelopment was subject to

Seven principles for planning and designing for tsunami hazards

urban design and building standards, such as: ❚ growing tsunami forests to dissipate wave energy

❚ relocating shops to upper levels ❚ requiring structures below the 20-foot elevation contour lines to be designed and constructed to withstand a major tsunami

❚ using parking structures as protective barriers for structures further inland.

A similar response could be applied to at-risk areas in New Zealand. The Hilo redevelopment provides a good-practice example of how custodian ship and creativity can result in reduced risks from a tsunami. Ideally, all natural hazards should be taken into account at the predevelop ment stage. However, Hilo highlights that, once develop ment has occurred, a planned, staged redevelop ment can still take place based on the risk.

Designing with hazards in mindLandslides, tsunamis, earthquakes and several other natural hazards can affect the design of a subdivision. While it is up to the Territorial Authority and developer to determine how to manage those hazards (if at all), some design principles can be incorporated voluntarily. The New Zealand urban design protocol encourages innovative urban design principles that include natural hazard mitigation measures. Developers can incorporate these into their design processes to reduce the risk of natural hazards.

The New Plymouth and Hilo examples show how designers can reduce the risk of natural hazards where development has already taken place. For new developments, at-risk areas should be avoided in the first instance, depend-ing on the social, economic and environ mental consequences of the hazard.

Do you have examples of urban design that incorporate natural hazard risk? If so, please forward them to w.saunders@gns.cri.nz.

1. Know your community’s tsunami risk.2. Avoid new developments in tsunami

inundation areas.3. Locate and configure new developments

that do occur in tsunami inundation areas to minimise future losses.

4. Design and construct new buildings to minimise tsunami damage.

5. Protect existing developments through redevelopment, retrofit, and land reuse.

6. Locate and design infrastructure and critical facilities to minimise tsunami damage.

7. Plan for evacuation.