ENVIRONMENTAL CONNECTION / THIRD QUARTER 2025 / IECA.ORG 27 gullies to a depth of 131.2 feet (40 m), with approximately 78,4770 yard3 (600,000 m3) of material. To start this fill, a 0.43-mile (700-m) section of stream had to be diverted through 55-inch (1,400 mm) pipes. This work was completed under an online methodology that had to accommodate a one-in-100-year rainfall event (5.9 inches [151 mm] per 10 minutes). Once a small portion of the stream diversion was completed, the fill height was increased sufficiently to allow a small project is within a landscape of ecological and cultural significance. The area is characterised by mature podocarp forest and is home to many rare and threatened native species, including western brown kiwi (Apteryx mantelli). Toward the southern extent of the alignment is the regionally significant Mimi Wetland (Figure 1). Within this wetland are examples of the critically endangered swamp maire (Syzygium maire) and swamp forest ecosystems that include kahikatea (Dacrycarpus dacrydiodes) and pukatea (Laurelia novae-zelandiae). The project alignment has space and access constraints, steep slip-prone slopes typically greater than 20% and highly mobile silt-based substrates. The alignment intersects the Mangapepeke Stream and Mimi River catchments, which are flashy and softbottomed (mud and loose sediment) with high levels of natural erosion. The rough terrain, limited space and access to the site have driven some innovative solutions, such as the construction of a 0.7 mile (1.1 km) long cableway (Figure 2). This is the first of its kind to be used in New Zealand for the construction of a highway. The cableway provides access to the remote northern section of the project, which is otherwise only accessible by foot. With a load capacity of 44,092 pounds (20 tonnes), the cableway brings materials and machinery into the work area. Large machines must be transported in sections and built on-site. A custom eight-person gondola carries trained personnel on a 10-minute trip into the gully (Figure 3). When the gondola is not available, the alternative access route is scaffold staircases, with over 700 stairs and 656 feet (200 meters) of elevation gain (Figure 4). Access and space restraints have meant earthworks must begin before the installation of typical erosion and sediment controls (ESCs). In large parts of the site, these restraints have been a common problem. This situation has meant our team has developed innovative staging and designs to ensure construction could progress without adverse environmental effects. The largest fill site on the project is known as Fill 12 and requires the filling of three main sediment pond to be installed. This process repeated several times over the construction season with an additional two large sediment ponds constructed completely in fill to accommodate the dirty water catchment of the site. The period between having the ponds constructed meant all un-stabilised catchment had to be completed under a “cut-and-cover” methodology, meaning large areas of the site were covered with polythene and geotextile to eliminate sediment run-off. Since beginning INTERNATIONAL PEER REVIEW Figure 2. A cableway has been constructed to access the northern part of the project. >> Figure 3. The custom eight-person gondola used to transport staff into the northern zone.
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