Flood-Resilient Cities:

Given the unpredictability of extreme weather, the idea of “peacefully co-existing with floods” has begun to gather steam around the world. And Taiwan is getting in step with this international trend in both its thinking and its action with regard to enhancing flood tolerance through environmental design.

When birds return and ecologies are restored, people again have the chance to experience the simple beauty of nature.

When birds return and ecologies are restored, people again have the chance to experience the simple beauty of nature.

From flood prevention to resilience

Taiwan, located beside the North Pacific Gyre at the convergence of the Kuroshio and Oyashio currents, each year has as much as 2,500 millimeters of rainfall, mainly from the “plum rains” of May and June and from summer typhoons. Taiwan has many high mountains, and the majority of its rivers run westward down the steep slopes to the plains below. Moreover, the timing and location of precipitation is highly variable, and some areas often experience extreme rainfall. During our interviews with Wang Yi-fung, deputy director general of the Water Resources Agency of the Ministry of Economic Affairs, and Liao Kuei-hsien, a professor in the Graduate Institute of Urban Planning at National Taipei University, both emphasized the challenges of managing Taiwan’s water resources.

Humans have traditionally settled close to rivers, and in Taiwan many people live in alluvial plains where they are exposed to the threat of flooding. Building dikes to hold back water and enable cities to develop is the classic “flood prevention” approach to river management. But in recent years there has been a trend toward increasingly intense rainfall in ever shorter periods of time. Although Taipei City has previously designed its flood prevention measures to cope with a 200-year flood (a water level that has a one-in-200 chance of occurring in any given year), it has not been able to avert serious flooding events. Water management agencies have gradually adopted new ways of thinking, turning away from focusing mainly on controlling waterways through engineering measures such as embankments and river straightening, and moving towards management of entire river watersheds, says Wang Yi-fung.

The past focus on designing flood prevention infra­structure based purely on scientific calculations is in fact unable to guarantee safety from floods. As the issue of climate change has become more prominent, people from all stakeholder groups are calling for a change in thinking. They want instead to approach the issue from the perspective of resilience in order to explore new possibilities for flood management.

Wang Yi-fung says that the amendments to the Water Act, adding a chapter on runoff sharing and outflow control, are a sign that flood management is no longer a matter just for government, but also a responsibility for all citizens.

In densely populated urban areas, environmental management of waterways can provide better opportunities for residents to access the riverside for various activities.

Creating a flood-resilient homeland

Liao Kuei-hsien explains: “The term ‘resilience’ refers to a system’s ability to cope with disruption by self-­adjustment and so to maintain its normal operation. That is, after a system is disturbed, it can rapidly recover and revert to its original functionality, status, or basic internal structure.”

The basic underlying concept of resilience is adaptation to change. Liao notes that rivers are always changing, and siltation of river beds, scouring of river banks, and flooding are all normal phenomena. She clarifies that while “flood disasters” always involve flooding, these terms are not entirely synonymous. Flooding is a natural event and the word is a neutral term; any waterside or low-lying area may experience flooding. Flood disaster, meanwhile, refers to the harm caused when flooding occurs in areas of human settlement. But even in such areas, flooding does not necessarily cause harm, as long as appropriate preparations are made.

Liao explains that “flood resilience” means that society should develop the capability to endure flooding without suffering disasters. This is to say that communities need to become “flood tolerant,” which describes a situation in which when flooding occurs there is no loss of life or damage to property, and society is able to operate normally rather than being paralyzed.

Designing urban areas to be “sponge cities” is one approach to enhancing flood tolerance. Liao was the earliest advocate of this notion in Taiwan. The sponge city concept turns away from the traditional idea of draining off water to other locations as quickly as possible, and instead emphasizes the use of natural mechanisms such as evapotranspiration, infiltration, and retention to reduce stormwater runoff. Through appropriate design, urban areas can be made able to absorb precipitation like a sponge and reduce the likelihood of flooding. “We can create cities that mimic the water cycle of forests and have hydrological patterns that are similar to those of nature.” Feasible methods of creating sponge cities include installing green roofs on buildings, transforming roadside verges into ecological grass ditches, and turning parts of parks into “rain gardens” (a.k.a. “bioretention facilities”) or “constructed wetlands.”

The concept of flood resilience has brought with it changes in perspectives and techniques, offering government agencies an alternative approach to flood management. In 2019, the Water Act was amended to incorporate the strategy of “runoff sharing and outflow control,” which is to say that stormwater runoff that was previously discharged exclusively via waterways will now be shared between waterways and land. “This means that every piece of land used by people should handle its proper share of stormwater and play a role in flood prevention,” explains Wang Yi-fung. Prime examples of this policy can be seen in Taipei’s Yongchunpi Wetland Park and Dagangqian Park.

Liao Kuei-hsien advocates for “flood resilience,” which means that society should develop the capability of coping with floods without suffering harm.

Finding new ways to peacefully coexist with rivers is part of a sustainable future.

Flood detention at Yongchunpi

Walking out of the Xiangshan Metro station, after a stroll of about 20 minutes we arrive at Yongchunpi Wetland Park, beside the Four Beasts Mountains (Leopard Mountain, Elephant Mountain, Tiger Mountain, and Lion Mountain).

Yongchunpi lies in a natural depression alongside the Four Beasts Mountains. In former times it was a pond used for irrigation, but after World War II it was concreted over and turned into a military base. After the base was relocated, Yongchunpi was repurposed as a wetland park with the dual functions of stormwater detention as a means to reduce flooding, and ecological restoration. The first constructed urban wetland environment in Taipei City, it won the top-ranking Outstanding Award for 2020 from the Taiwan Institute of Landscape Architects, as well as an Award of Excellence at the 2020 Africa, Asia–Pacific, and Middle East (AAPME) Awards of the International Federation of Landscape Architects.

Liu Po-hung, founding principal of the consultancy firm Classic Landscape Design and Environmental Planning, says that there were two main guiding principles in designing the wetland park: The first was a desire to extend the ecosystem of the Four Beasts Mountains into the wetland, while the second was to meet the need for a public park.

“Rivers in Taiwan are short and fast-flowing, so environmental engineering is needed at or near the foot of the mountains to catch rainwater. This is in keeping with the concept of the resilient city.” The creation of the wetland park offered an opportunity to do something along these lines. The contractors dug up the large areas of concrete that had prevented water from infiltrating into the soil, and used the waste material to create hills and depressions of various heights into which they routed the water of the Leopard Mountain Creek, creating areas of open water of varying depths. When it rains heavily, the park functions as a basin that stores and absorbs water. Some 86% of Yongchunpi’s surface area is covered by vegetation or ­water. The park can store nearly 4,900 cubic meters of ­water, enough to detain sudden torrential rains for 8.77 hours.

Liu Po-hung also recommends that we visit Da­gang­qian Park, inside the Neihu Technology Park. It was formerly the site of the Taipei Flower Market, but after the market relocated all that remained was a large expanse of concrete surrounded by office buildings. “The site had no natural water sources, so how could we use it to enhance resilience? We turned it into a park that can store water,” says Liu. As with Yongchungpi, they used the spoil from breaking up the concrete that covered the site as infill to create a rolling topography that forms an integrated stormwater detention and drainage system hidden under the park’s lawns. This has a capacity of 2,900 cubic meters, which is six times the water retention index for the site. “It already exceeds the statutory requirements for runoff sharing, so besides covering its own needs, it also serves as a flood detention basin for the surrounding area.”

Liu Po-hung, founder of the consultancy Classic Landscape Design and Environmental Planning, endeavors to incorporate resilience into his designs in order to make this concept part of citizens’ daily lives.

Yongchunpi, a former military base beside Taipei’s Four Beasts Mountains, has been transformed into a park with the dual functions of stormwater detention and ecological restoration. (courtesy of the Geotechnical Engineering Office, Taipei City Public Works Department)

Dagangqian Park, where the former expanse of concrete has been turned into a green urban space, has large flood detention basins below its surface, putting the concept of resilience into practice.

Restoring vitality to rivers

With the previous focus of river management on flood prevention, the large-scale flood control and drainage works that so drastically altered the river environment changed our rivers from “teeming with life” to “mori­bund.” Liao Kuei-hsien chairs a non-governmental organization, Taiwan Rivers Network, which seeks to reassess the inappropriate measures of the past and find new ways for humans to peacefully co-exist with rivers, to the benefit of both. The group strongly advocates for river conservation and restoration, hoping to revive the ecological functions and biodiversity of rivers. Recently they have also begun promoting “nature-based solutions,” calling for the use of methods that are compatible with nature and can restore it, as a means to address the need for disaster preparedness and mitigation in the context of the climate emergency.

Liu Po-hung also mentions a landscaping project at Wanhe No. 1 Park in Taipei’s Wenshan District. A tributary of the Jingmei River used to run through here, and the project restored the water flow and preserved the old trees on the riverbank, using a wide variety of plants to conserve the landscape so that children can get a sense of the location’s history and former appearance.

The government’s Forward-Looking Infrastructure Development Program also aims to revitalize rivers. Wang Yi-fung points for example to Taitung’s Dongda River, the Kangqiao River project at National Chung ­Hsing University, Changhua’s Lugang River, and the Teng­liao­keng Ravine in New Taipei City. Such multi-­objective river management projects, which are in tune with the local environment and take the needs of the local ecology into account, mark a very significant step.

Everyone can contribute

“The real shift in thinking is from ‘zero tolerance of flooding’ to ‘having no fear of flooding,’” says Liao Kuei-hsien. There must be a change not only in methods but also in thinking.

Wang Yi-fung points out that the amendments to the Water Act, adding a chapter on runoff sharing and outflow control, mean that flood management is no longer a matter for the government alone, but a mission for all citizens. Both the public and private sectors share responsibility for enhancing resilience.

As an expert in landscape design, Liu Po-hung says: “When professionals are remaking spaces, they should make flood resilience a core aspect of their designs and make the concept of resilience part of everyday life. That’s the only way to change public attitudes.”

In her book Urban Retrofit, published in 2009, Liao Kuei-hsien sowed the seeds of change by promoting the concept of “sustainable urbanism.” As well as monitoring the government’s river policies, the Taiwan Rivers Network recently launched a “river academy” which offers an introductory course on healthy river ecology, with the aim of encouraging more people to get involved in issues related to river management.

In building a sustainable future, we all have roles to play and responsibilities to fulfill, so don’t under­estimate your own power!

The reality of extreme weather is prompting people to reconsider the issue of how to harmoniously co-exist with flooding.