Public Environment Report Tarkine Forest Drive ... - Transport

2.4.4 Rapid River Bridge replacementThe existing deteriorated timber bridge (currently closed) across the Rapid River (seeFigure 2.4) located on segment K (see Appendix A) will be replaced with a bridge whichis designed to Australian Standard AS5100. The proposed replacement bridge design isdepicted in Figure 2.5. It will have a 100 year design life span, SM1600 design loadingand pass a Q20 flood below the bridge soffit. Design allowances have been made toaccount for adequate passage of wildlife along the river banks under the bridge.Figure 2.4 - Existing bridge across the Rapid River2.4.5 Construction methodThe construction method proposed for the Rapid River bridge replacement is asfollows.Construction works will involve full road closure for approximately 4 weeks. Site shedswill be located to the side of the existing road at locations not requiring any vegetationclearance.The existing timber bridge (see Figure 2.4) will be demolished and the timber removedfrom site.An existing ford, located downstream of the existing bridge will be used for limitedconstruction traffic as required.A coffer dam will be required to be constructed in the middle of the river to allow forconstruction of the middle pier (see design depicted in Figure 2.5).This will be in place for approximately 3 weeks and will be constructed, used anddecommissioned during the lowest estimated river flow period to minimise impact onriver flow, bank erosion and scouring. At least half of the river will remain open toensure sustained river flow. The coffer dam will be constructed out of fullysalvageable materials (for example, precast concrete blocks or sand bags).If required, piles will be driven through the existing road embankment.Ref: HB09080H001 PER Tarkine Drive 33P Rev 00/DL/CL/jw 26