Beyond the sea wall: a changing climate calls for dynamic solutions
By Jessica Halliday
15 March 2018
Photo courtesy of Foreground
Image: A footbridge over the Avon River in Christchurch, New Zealand that was dismantled after successive earthquakes in the region.
Although nearly 7,000 miles apart, the cities of Christchurch, New Zealand and San Francisco share climatic similarities. Associate Professor of Landscape Architecture & Environmental Planning and Urban Design Kristina Hill has examined the two sites through “bifocal lenses of geology and landscape” causing unexpected parallels to emerge.
In both Christchurch and San Francisco, residents face similar challenges: “how to adapt their coastal and estuarine environments to sea level rise, how to live with a high and rising ground water table, how to factor increasing salt and fresh water flooding into planning their urban environments and infrastructure while surviving, and preferably thriving, in highly active seismic zones.”
Hill visited Christchurch in July 2017 to discuss strategies for creative adaptation to sea level rise in seismic zones. Christchurch, unlike San Francisco, has already experienced “the big one” of this century. The series of earthquakes resulted in dramatic alterations to the landscape of Christchurch.
In response to these earthquakes, over 6,000 houses were cleared near the Ōtākaro Avon River between the central city and the sea. This region was coined the “red zone” due to the land’s high water table, likelihood of flooding and liquefaction,and significant lateral spread.
The red zone is now owned by the central government, and Hill sees this space as an opportunity and adaptation.
“Landscapes can be muscular, they can provide functions other than recreation and do work that supports human and other life to thrive.” Hill acknowledges, however, that we need to be willing to create this future by sensitively manipulating and working with the landscape’s own materials and processes.
Of the potential adaptation design options, Hill suggests fixed or dynamic walls and fixed or dynamic landforms. Fixed walls include concrete highway “lids,” sea walls, and floodwalls, such as the sea walls of New Orleans. Dynamic walls include tide gates, movable surge barriers, and temporary walls, such as the Thames Barrier protecting London.
Fixed landforms include dikes, canals, levees, mounds, and breakwaters. Fixed landforms are some of humankind’s oldest mechanisms for managing waters and have been designed and mastered by the Dutch over hundreds of years. Finally, dynamic landforms mimic nature’s own structures and include beaches, sand dunes and bars.
Hill finds dynamic landforms to be most promising, especially in terms of seismically active landscapes. Considering the landscape of these environments is changing so rapidly, Hill believes that dynamic landforms are necessary to adapt to the changes without becoming obsolete.
Hill argues that walls separate people from changing environments and disrupt ecosystems. She states that in Christchurch especially, “communities value the coastal plants and animals whose habitats would be eradicated by fixed seawalls.”
Furthermore, fixed solutions pose a significant risk of failure, especially in seismically active zones. And in places like San Francisco and Christchurch, they also pose a risk of tsunami.
Alternatively, dynamic landforms have a great deal of social, economic, and environmental benefits. They can be built using readily available, local materials such as sand and silt, which are in abundance in Christchurch.
In addition to reducing costs, dynamic landforms allow future generation to easily adjust the landforms by adding or removing material. Dynamic landforms also restore and enhance natural environments which produce improved habitats for plants and animals. Thus, these landforms will expand biodiversity and increase land value.
Hill believes the adaptive landforms to be particularly effective. One of the greatest repercussions of sea level rise is wave argue which results in erosion and damage. Research shows that a 60-meter strip of wetland can reduced storm surge up to 75 percent.
Hill also advocated the use of adaptive landforms to control freshwater flooding. Presently, stormwater in Christchurch is channeled into the Ōtākaro Avon River. Hill suggests adapting the red zone to clean and temporarily store the storm water.
This could be achieved through storage ponds which would “restore this area’s original wetlands to clean the stormwater before it enters the river. The ponds would slow its release, reducing flooding in neighbouring suburbs.”
Most importantly, Hill encourages the use of “thoughtful, research-based design that promotes three public goods: a courage to invest in public works, greater shared resourcefulness to be able to live with change, and expanded compassion that understands the needs of diverse communities and benefits non-human species.”