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SeoAhn Total Landscape
3.6 miles (5.84 km) long
~$380 million USD - Total project; ~$120 million USD - Landscape portion
References & Resources
Landscape Performance Benefits
- Provides flood protection for up to a 200-year flood event and can sustain a flow rate of 118mm/hr.
- Increased overall biodiversity by 639% between the pre-restoration work in 2003 and the end of 2008 with the number of plant species increasing from 62 to 308, fish species from 4 to 25, bird species from 6 to 36, aquatic invertebrate species from 5 to 53, insect species from 15 to 192, mammals from 2 to 4, and amphibians from 4 to 8.
- Reduces the urban heat island effect with temperatures along the stream 3.3° to 5.9°C cooler than on a parallel road 4-7 blocks away. This results from the removal of the paved expressway, the cooling effect of the stream, increased vegetation, reduction in auto trips, and a 2.2-7.8% increase in wind speeds moving through the corridor.
- Reduced small-particle air pollution by 35% from 74 to 48 micrograms per cubic meter. Before the restoration, residents of the area were more than twice as likely to suffer from respiratory disease as those in other parts of the city.
- Contributed to 15.1% increase in bus ridership and 3.3% in subway ridership in Seoul between 2003 and the end of 2008.
- Increased the price of land by 30-50% for properties within 50 meters of the restoration project. This is double the rate of property increases in other areas of Seoul.
- Increased number of businesses by 3.5% in Cheonggyecheon area during 2002-2003, which was double the rate of business growth in downtown Seoul; increased the number of working people in the Cheonggyecheon area by 0.8%, versus a decrease in downtown Seoul of 2.6%.
- Attracts an average of 64,000 visitors daily. Of those, 1,408 are foreign tourists who contribute up to 2.1 billion won ($1.9 million USD) in visitor spending to the Seoul economy.
The City of Seoul is in the process of an important paradigm shift, changing from an autocentric development-oriented urban landscape to one that values the quality of life of its people and the importance of functioning ecosystems. By demolishing an elevated freeway and uncovering a section of the historic Cheonggyecheon Stream, the Cheonggyecheon Restoration Project created both ecological and recreational opportunities along a 3.6-mile corridor in the center of Seoul. The project has proven catalytic, spurring economic growth and development in an area of Seoul that had languished over the last several decades.
- The restoration created a 3.6-mile continuous east-west green corridor for pedestrians, bicyclists, and wildlife.
- Connectivity within the greater transportation network was improved by adding 22 bridges (12 pedestrian, 10 for automobiles and pedestrians), connections with 5 nearby subway lines, and 18 bus lines serving the neighborhood.
- The restoration reestablished connections between waterways. The Cheonggyecheon eventually runs into Jungraechon stream, which leads out into the Han River. The wetlands at their meeting point are designated as an ecological conservation area.
- Because water is only naturally present in the Cheonggyecheon during the summer rainy season, 120,000 tons of water from the Han River and several subway pump stations is is pumped and treated to create a consistent flow with an average depth of 40 centimeters in Cheonggyecheon.
- Native willow swamps, shallows and marshes were constructed in 29 different locations along the restoration, creating habitat for fish, amphibians, insects, and birds.
- A fish spawning ground was created where the Cheonggyecheon and Jungnangcheon meet.
- Terraced vertical walls give visitors access as water levels change, create seasonal interest as levels submerge and re-emerge, and provide flood protection for the city.
- Natural stones bridge the two banks, creating walkways for adventurous pedestrians and to helping regulate water speeds and levels and various points along the stream.
- Construction materials were salvaged and re-used from the concrete deck structure and elevated highway demolition. All of the scrap iron and 95% of waste concrete and asphalt was reused.
The aging elevated freeway and concrete deck covering the Cheonggyecheon stream posed safety risks and needed to be repaired or removed. The government wanted to improve connectivity between the city’s north and south sides, which the freeway divided. Transportation experts were concerned that removing the elevated highway would increase traffic congestion and chaos in the northern end of the city since it carried 169,000 vehicles per day. The idea of removing the freeway also met initial opposition from many local business owners. The proposed stream restoration also presented challenges. Water is not naturally present in the Cheonggyecheon for most of the year except during the summer rainy season, making it difficult to create a consistent urban amenity.
The Seoul Metropolitan Government chose to dismantle the elevated freeway and concrete deck covering the stream. To improve north-south linkages, 22 bridges — 12 pedestrian bridges and 10 for automobiles and pedestrians — were proposed to connect the two sides of the Cheonggyecheon. To reduce traffic congestion, car use was discouraged in the city center, rapid bus lines were added, and improved loading and unloading systems were implemented. To address business owners’ concerns, the Seoul Metropolitan Government held over 4,200 meetings to build consensus. Economic support was given to businesses and special agreements were made with vendors who had to move due to project construction. To address the variable flow of the Cheonggyecheon, water from the Han River and several subway pump stations is treated and pumped to create a consistent flow with an average depth of 40 centimeters in the Cheonggyecheon.
Had the Cheonggyecheon Expressway remained, it would have required 100 billion won ($90 million USD) and 3 years of repairs to secure the safety of the aging structure. While these costs would be approximately 289 billion won ($260 million USD) less than the cost of the Cheonggyecheon Stream Restoration, the restoration has served as a catalyst for an estimated 22 trillion won ($1.98 billion USD) worth of capital investment in Cheonggyecheon-area redevelopment that would not have otherwise been invested.
- Design solutions must consider the needs of all users from the initial planning and design phase. With the Cheonggyecheon restoration, the needs of certain user groups, including those with visual impairments and mobility challenges, were overlooked. After complaints culminated in a protest march, elevators were installed at seven locations, and free wheelchairs were provided for users with mobility problems. Because these design interventions were added later, they were more costly and are not fully integrated accessibility solutions.
- A Seoul Development Institute study included the following suggestions for how the restoration could improve its ecological performance: replace granite with vegetated low-flow revetment to increase habitat area, install spur dyke to deepen water and decrease velocity to improve fish habitat in certain areas, conserve variation in river bottom to support invertebrates, create alternate detour channels for fish to encourage migration, and create vegetated filter strips to reduce contaminants entering the stream from motorway runoff.
Client: Seoul Metropolitan Government
Main Designers: Cheongsuk Engineering (Section 1) Saman Engineering (Section 2) Dongmyung Engineering (Section 3)
Landscape Architect: SeoAhn Total Landscape
Main Contractors: Daelim (Section 1) LG Construction (Section 2) Hyundai Construction (Section 3)
Independent Check Engineers: Suhyoung Engineering (Section 1) Cheil Engineering (Section 2) Cheongsuk Engineering (Section 3)
Role of the Landscape Architect:
After the civil engineers oversaw the first phase of the project, the landscape architects and designers directly oversaw the second and third stages of the construction in an attempt to create a more seamless environment. This is atypical for Korean construction projects, with the landscape architects managing three different landscape design groups, the civil engineering team, the bridge design team, and the lighting design team.
Case Study Prepared by:
Research Fellow: Alexander Robinson, Assistant Professor, University of Southern California
Research Assistant: H. Myvonwynn Hopton, MLA Candidate, University of Southern California
Special thanks to:
Landscape Performance Series