The Application of ACEModule™ for Creek Restoration at the Upstream of Shubu Concave Bridge, Baoshan Township, Hsinchu County, Taiwan

This presented case was part of the Yangang Creek drainage restoration project in Hsinchu, Taiwan. Yangang Creek basin belonged to the highland drainage situation and was a flood potential disaster area. Before the restoration, because of insufficient drainage section, many meanders and turns of the section have caused overgrown vegetation and severe siltation. Therefore, whenever torrential rains attacks, flooding disasters initiated by the overflow of waterways continue to occur. This project was conducted by improving the channel width to eliminate flooding disasters. The restoration combined the strategies of aesthetic landscape and eco-friendly environment construction to achieve harmony and equilibrium between the project and the natural environment. Based on the site conditions, the restoration consisted of two types of revetment: simple reinforced concrete and stacked ACEModule™. This case study focuses on the description of the latter construction.

The targeted creek was mainly located in an agricultural area. It mainly collected local farmland drainage and surface runoff when heavy rains occurred. Because the capacity of the flow section of the creek cannot accommodate the discharge of water in this area, the runoff was unable to drain efficiently and thus overflowed the riverbank and caused flooding in the surrounding area. The ravage seriously destroyed farmland, crops, and properties and significantly affected the lives of residents. In addition to the engineering difficulties, we also found ecological importance for the local environment. Many notable species, such as the Common kingfisher, Gray-throated martin, Fowlea piscator, and Hylarana guentheri, were observed along the creek, indicating that maintaining an eco-friendly environment was extremely necessary for living creatures at the site. Therefore, in addition to ensuring the creek's flood control and drainage function, particular attention should also be paid to reducing the biological and environmental impacts of the engineering facilities.

1. Design
The design strategy for the restoration was first to widen the drainage section to improve the flowing capacity and efficiency of the creek. Secondly, to construct dependable revetment system along the creek to prevent any possible hydraulic destruction or erosion of the riverbank. Based on the site conditions, the restoration consisted of two types of revetment: traditional reinforced concrete and ACEModule™ system. This case study focuses on a detailed description of the latter construction.
For sections along the creek with varied curvature, reinforced concrete structure revetment was practically not feasible because of complicated quality and higher cost of formwork. The designer introduced the ACEModule™, a patented stackable precast hollow concrete block revetment system developed by ACE Geosynthetics to solve the problem. Each concrete block, with an open face or with a face, has a standard dimension of 100cm long, 65cm wide, and 50cm high. The system was initiated by placing a 1.7-m thick reinforced concrete foundation as the base of the revetment. Then, four layers of ACEModule™ were stacked on the foundation to serve as the main structure of the revetment.
The rigid concrete structure of ACEModule^TM can withstand the direct attack of water flow, protect the riverbank and maintain stability. At the end of the curve section, the slope of the river bed was adjusted by the arc-shaped groundsill steps. Such a particular structure also can reduce the local scouring of the toe of the groundsill steps by the plunge-flow caused by the elevation differences.

The lower three layers of ACEModule™adopt structural units with porosity. Pebbles and boulders were backfilled to the hollow structure to provide porous habitat for aquatic organisms. Whereas the top layer of ACEModule™ adopted structural units without porosity, each module piece was backfilled with soil bags for planting to create a natural environment and green landscape. In addition, to maintain and respect the unique local ecological system, the designers used the existing reinforced concrete culverts in the revetment. They were not only for drainage but also skillfully designed as passages for animals up and down the river to support the maintenance of riparian biodiversity.

2. Construction
The foundation surface and the back of each ACEModule^TM layer were laid with a geotextile layer as a separator to prevent soil loss behind the revetment. The upper and lower layers of ACEModule^TM were stacked in a stretcher bond pattern. They were tightened up with anchor rebars to increase strength and stability. When each ACEModule^TM was lifted and assembled, it was arranged in sections in sequence. ACEModule^TM elements were designed with unique mortise and tenon structures for reliable connections, and particular odd blocks may be flexibly applied to those irregular curve or squiggle sections or the end of the structural edge. Such assembly makes it easy to achieve the accuracy required by the channel length and curvature design.

The ACEModule^TM system was used for river bank protection and flooding prevention in this case. Its precast concrete structure and hollow design facilitate the construction and present substantial benefits to safety assurance, simple construction, landscape beautification, and eco-friendly environment:

1. Safety Assurance: ACEModule^TM system comprises precast concrete structure units with sound quality. With its rigidity presenting high resistance to scouring and erosion, it can be applied for riverbank protection, thus reducing flooding disasters and ensuring people's and property's safety.

2. Simple Construction: ACEModule^TM construction is relatively simple compared with traditional riverbank structures. With unit modules and mortise and tenon assembly construction, materials, equipment, and manpower requirements for field works are uncomplicated. The installation also presents lower noise and vibration and lesser site disturbance.

3. Aesthetic Landscape: The assemblies of the module and tenon of the ACEModule^TM system can match different site conditions and the landscape needs of the riverbank, such as the curvature or squiggle shape of the meandering river. ACEModule^TM also provides landscape or seasonal planting spaces to enhance the overall visual beauty.

4. Ecological Restoration: The hollow design of the ACEModule^TM system is suitable for various natural or man-made materials to create an eco-friendly environment and space to enrich the ecological habitat of the river and diversify the species.