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    Park road is greener than green

    Leighton Holdings

    IT IS only a 4.6 km long link road near the Noosa National Park, but every millimetre of Walter Hay Drive has been designed and built with environmental protection a high priority. The new two-lane road nearing completion, is considered one of the most thorough examples of environmental planning and execution yet produced in Australia. Project participants include Leighton Contractors , GHD and their client Noosa Shire Council.

    Leighton won the $19 million contract to build Walter Hay Drive – largely one-lane each way with two lanes at the road’s three interchanges – and one bridge linking Eenie Creek Road with the Sunshine Motorway at Noosaville in south-east Queensland.

    The road, of flexible pavement construction, has a crushed gravel base with a 45 mm asphalt surface with some 250 mm asphalt sections. The biggest cut for embankments is 3m to 4m. Of major concern for Noosa Council is that road construction must not impact the wildlife connectivity corridors to neighbouring Noosa National Park.

    In the very early planning stage, defining the road route had to take into account existing cleared areas, vegetation types and fauna corridors. The alignment was selected to correspond with eco changes to avoid dissecting vegetation patches and trees that provide feeding habitats for wildlife. Observing natural alignments and corridors then became a planning tool.

    Five different routes were offered to council and the community, before the final decider. Minimising the environmental impost on construction has been even more rigorous. The road has one of the narrowest construction corridors yet encountered with only a one-metre wide clearing boundary either side of the toe of the road alignment embankment, within the typically 15m wide road reserve.

    A further squeeze is that almost the full length of the alignment is a no entry or no go zone to keep the corridor green and preserve numerous eucalypts and wattle species. Not even secondary access via existing tracks is allowed. These two restrictions severely affect lay down areas and stockpile areas. The program of works has to plan for haulage to storage on the alignment and offsite storage. Very specific planning went into staging the works and materials handling.

    Even tighter controls apply to the Eenie Creek Floodplain which flows into the Weyba Lake running through the national park. Neither the creek bed nor banks could be disturbed. The 220m long bridge, two-lanes wide of concrete deck on bored piles, consists of nine spans of 20m deck units and a longer 35m T-Roff mid-section spanning the creek. The extra long bridge allows floodwaters to pass without any upstream impact from the bridge. It also allows for fauna to cross the alignment under nine spans that are generally dry. Additionally a fauna ledge on the northern abutment offers a wildlife escape route in a 100-year flood event.

    All riparian vegetation along the edge of Eenie Creek such as salt couch, lomandras and mangroves has been preserved to retain the integrity of the bank. To prevent any discharge into the natural environment, corrugated iron piling shrouds were placed within 0.5m of the edge of the creek as protection during the pre-auguring process for boring piles. Total retention and management of water in the wet piles was practised.

    Runoff from the bridge deck is collected in side drains to gross pollutant traps and is discharged overland to the creek. Working in boggy conditions, other erosion control measures include silt fences and rock checks in drainage lines along the road alignment to arrest sediment.

    Dedicated fauna crossings were carefully planned and built to accord with natural crossings and provide escape from floods. The largest – a 3m x 3m box culvert underpass – has a sophisticated below-floor drainage structure (no wet feet), an earth invert thoroughfare as well as an elevated timber log walkway for protection against predators.

    Almost 2 km of fauna fencing directs animals to the safe crossing points. Seeds were collected in the early days to propagate 35,000 indigenous plants and revegetate the site. Another 80 endangered species of wattle were transplanted off the road alignment. Work came to a stop when several species were spotted and relocated – two squirrel gliders, two blue tongue lizards, a python and several frogs.

    Only 17.5 ha of land has been cleared and 90,000m3 of soil excavated, much of it unsuitable for reuse. Walter Hay Drive will be the main route to Noosaville and possibly, one of the greenest corridors yet.

    Source: Construction Contractor

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