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Ecological construction methods have become crucial to the success of modern infrastructure projects, especially highways and roads. The East Caotun and Ailan interchanges on National Freeway No. 6 are model examples of how government policy can be translated into engineering solutions that balance both development and environmental goals.
To mitigate human impact on wetlands and wildlife located along the Nantou section of National Freeway No. 6, engineering firms collaborated with the Freeway Bureau to design wildlife corridors and ecoponds for the two interchanges. Both projects are resounding successes worthy of study by decision makers in government and the construction and engineering industry.
East Caotun Interchange
Belonging to tender C602, the three ecoponds for East Caotun Interchange form a network that covers a total of 9,326 m2. They were developed in Caotun Township close to agricultural land along the Wu River (also known as Dadu River and Black River), a region abundant with natural water resources and home to Squalidus iijimae, a species of freshwater cyprinid fish endemic to Taiwan.
The interchange ramp and elevated freeway section were designed to have fewer piers than most conventional highways. This solution leaves space for wildlife corridors and culverts, thereby reducing the number of obstacles for fish and other animals traveling under the interchange. Each pond was constructed at different elevations to facilitate natural flow, and gates were also installed to control water levels and maintain a more stable habitat that Squalidus iijimae need to thrive. A gravel service road provides convenient access for maintenance personnel.
Ailan Interchange
Two ecoponds were constructed for the Ailan Interchange, part of tender C608 and located in Puli Township close to the confluence of the Mei River and Nangang River. Originally farmland surrounded by wetlands and a pristine water supply, the area was a prime site to develop ecoponds and wildlife corridors that could strike a balance with National Freeway No. 6.
Water is supplied via irrigation canals to the two connected ecoponds, which are situated at different elevations and cover a total area of 10,903 m2. Stable water levels made it possible to construct artificial islands for a diversity of indigenous flora and fauna. The culvert linking each pond has pathways above water level to serve as an obstruction-free wildlife corridor. Fences along agricultural roads separate the pond areas from farmland. Although the pond areas lack service roads, maintenance personnel can still enter by three separate access gates.
Project details
1. Equipment
• Mini excavators and bulldozers for improved precision and reduced impact to surrounding areas during work
• Cranes and other equipment to store and obtain materials in accordance with the construction plan
2. Site preparation
• Recheck of measurements and survey drawings, especially the elevation of each ecopond and connecting conduits
• Clear staking and marking of work sites
• Minimal clearing of vegetation
• Excavation and grading
• Compaction of pond bottoms and earth embankments
3. Landscaping and pond construction
• Clay layer 60 cm thick with the construction supervision party taking one sample every 50 m2 for testing
• Filling of each pond with water followed by mixing of surface clay
• Upon settlement of suspended material and one week after a pond is full, permeability tests are performed to ensure that the clay layer prevents seepage — on a sunny day, water levels may not recede by more than 50 cm, and the test is repeated after refilling on a rainy day
• Placement of riprap and stone according to prior staking and marking while exercising caution so as not to break the clay layer
• Laying of sand and soil 30 cm thick after which the construction supervision party takes one sample every 100 m2 for testing
• Following settlement of sand and soil, placement of stone bottom layer with smooth, rounded stones measuring between 20 cm and 30 cm in diameter
• Subsequent addition of sand and soil to fill gaps between stones in the bottom layer
• Replanting and replacement of vegetation
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