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Figure 1: Habitat restoration in the Pingzhen System Interchange area (1/2)
The widening project of National Freeway No.1 from Wugu to Yangmei, connecting the Xizhi-Wugu Viaduct to the north and the Yangmei Toll Station to the south, covers approximately 40 kilometers in length. The widening project has been completed by building elevated viaducts alongside both sides of National Freeway No. 1. Besides, the first high-occupancy vehicle lanes in Taiwan are assigned on the inner lanes between Taishan transition and Chungli transition section. The new widening project commenced on October 28, 2009 and opened to traffic on April 20, 2013.
To avoid disruptions of the beautiful scenery and the ecological corridor, the route alignment bypassed the geologically sensitive areas, and the project sought to protect the ecological and landscape diversity by mitigating the impact to the eco-environment and adopting remedial and compensatory measures. The features and actions taken by this engineering project for ecosystem conservation are as follows:
1. Align Planning: Minimum Interruptions for Maximum Benefits
The project route was aligned along both sides of National Freeway No. 1 to minimize disruptions to the existing traffic flows by not intruding the guardrail along the freeway. Approximately 85% of the overall route length is constructed by elevated viaduct structures, with the exception of the Chungli transition section and the section from Linkou Interchange to where Taiwan High Speed Rail viaduct crosses over. The design was to separate the traffic flows of long journeys from short ones. Therefore, lane switching with the ground-level on National Freeway No. 1 is only allowed at the beginning, the end, the Taishan Transition, and the Chungli Transition. Four ramps were constructed at the Airport System Interchange, to service the traffic to and from the Taiwan Taoyuan International Airport via National Freeway No. 2. It was expected to effectively resolve the bottlenecks along National Freeway No. 1 by providing services for both medium and long-distance trips.
2. Structural Engineering: Disturbance Reduction
Some of the viaduct engineering works were built with a well foundation, to minimize the area directly affected. On the slope, construction work was conducted using working trestle in lieu of ground works access, to mitigate the impact on the local flora and fauna, as well as on soil porosity and water-holding capacity. The purpose was to ensure the recovery of the original landscape and ecosystem as soon as possible after construction completion.
3. Ecologically Friendly Construction Methods: Protecting the Ecosystem
With a rich variety of landscape and the alongside existing trees and vegetation, this road section is a lush green and beautiful corridor. Meanwhile, the project aimed for more than just maintaining regular traffic and safety on the Freeway during construction. It also sought to comb through the eco-networks along this corridor by reconnecting regional living space, landscape, and ecosystems, so that transportation functions and ecological restoration can both be achieved. The ecological conservation policies include the narrowing of disturbed areas, the mitigation of landscape impacts, the reuse of green resources, the planting/relocation of trees, the restoration of the landscape, and the habitat compensation. The purpose is to maintain the diversity of the ecosystem and the richness of the scenery along the freeway.
(1) Reduction of disturbances/impacts and restoration of habitats
a. A Green infrastructure was deployed on the Wugu section and the Airport System Interchange to connect with the Linkou Plateau forestry, the Dahan River eco-corridor and the Taoyuan's Reservoir and Canal Wetland ecosystem.
b. Restoring water birds habitats by connecting the eco-islands and multi-layer marsh pond in the Pingzhen System Interchange area. Using green materials along pond banks to create diverse eco-habitats. (Figure 1 and Figure 2).
Figure 2: Habitat restoration in the Pingzhen System Interchange area (2/2)
c. The ecological compensations along the Dakeng Creek- Biofiltration System design in different ways by reconstructing the banks with porous materials to create several types of microhabitats. Biofiltration System Design along the Taoyuan Highway No. 6 were constructed (Figure 3).
Figure 3: Biofiltration System Design along the Dakeng Creek
d. At the Half Moon Bent beside the Dakekeng Creek, the preserved roadside forests and new created marsh ponds develop a tapestry of aquatic habitats (e.g. slack waters, rapids, and battures), porous spaces and multi-storied forests surrounding the riverbank. The purpose is to reconstruct the eco-corridor along the Dakekeng Creek) and provide habitats for wildlife (Figure 4).
Figure 4: Marsh pond Habitats at Half Moon Bent beside the Dakekeng Creek
e. Without compromising the safety of roadbeds or ditches, this project constructed a natural drainage system (Figure 5), in conjunction with a raingarden. The design is to reduce the impact to downstream and improve the effectiveness of groundwater conservation.
f. The planning of the drainage channel took into consideration the necessity of animal escape ramps.
g. Artificial bat nests put in place beneath the overpass along the Dakeng Creek so that these night-time creatures have places to roost (Figure 6).
Figure 5: Eco-Friendly Drainage Covered with Pebbles
Figure 6: Beneath the Overpass on the Dakeng Creek
h. The lighting fixtures were adjusted so that the light does not disturb the surrounding ecosystems. For example, lamps with less insect luring effects were deployed to avoid bats being attracted to highways for food. Glare shields or hoods were adopted to mitigate light disturbance to forest habitats.
(2) Green ecosystem and environmentally friendly measures
This project divides the construction site into the disturbed areas and the non-disturbance areas, by which trees were transplanted or on-site preserved measures were decided along the route. Engineering techniques were used to minimize the size of disturbed areas and mitigate the impact on existing vegetation in the proximity.
a. Preservation of trees or vegetation in the non-disturbed areas:
As much as possible, this project sought to retain the first row of road trees on National Freeway No. 1. A temporary trestle for engineering works on the viaducts of cuts section to minimize disruptions to the environment and accelerate the ecosystem recovery.
b. Protection of the precious existing landmark trees – lemon scented gum trees in Kainan University
The towering lemon scented gum trees on the roadside of Kainan University are a valuable landmark for the area. However, the area for right of way is small. To maintain this green landmark, the university provided campus land for the widening construction so that these trees could be protected on-site.
c. Relocation of trees in the disturbed areas and reuse of topsoil:
Before the commencement of construction, topsoil was collated from the appropriate areas so that they could be used for planting. Existing trees and potential saplings were relocated to other interchanges or used by the local government for landscaping. Construction trestles were erected for limiting the machinery/tool access to reduce the impact on the surface vegetation (Figure 7 and Figure 8).
Figure 7: Tall Coral Trees Grown at the Tayuan Interchange
Figure 8: Trees Relocated to Suao Interchange on National Freeway No. 5
d. Potential saplings were preserved, heeled in, and replanted back to the habitat after the completion of construction, so that the original vegetation could recover quickly.
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