The New Perth to Bunbury Highway (NPBH) is a 70.0 km dual carriageway extension linking the Kwinana Freeway to the Old Coast Road at Lake Clifton. In the Shire of Waroona at the Tylers Pit Cutting section of the NPBH, the median and side swale drains required erosion protection from the excessive road stormwater runoff. Project civil consultants GHD calculated that the runoff velocity within the swale drains could reach 1.5 m/s so

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