PART Response to Information Request · OPW11/0335

EP-SECP-01: Up-slope stormwater flow diversion
1. Objectives/Targets       To reduce the transport capacity of stormwater crossing the building site
2. Management Strategy      1) Divert up-slope stormwater around the building site;
                            2) Divert stormwater around areas of soil disturbance; and
                            3) Divert stormwater onto stable ground or areas where suspended sediment can
                            settle.
3. Tasks/Actions            Building site
                            1) Construct a perimeter bank along the upslope (eastern) edge of the development
                            to divert flow around the building site, and onto grassed or stabilised surfaces on the
                            edge of the building site;
                            2) Stabilise the perimeter bank with erosion mats (e.g. jute mesh mat anchored by
                            cold anionic bitumen emulsion); and
                            Erosion prone hot-spots
                            3) Place geo-logs/straw wattles within the building site, upslope of areas of high
                            disturbance or high erosion hazard. Direct flow onto grassed or stabilised ground.
                            Ensure secure pegging of geo-logs to prevent flow under the log. The edge of the
                            geo-log needs to overlap the stable or grassed surface.
4. Performance Indicators   1) Effective diversion of stormwater away from the building site, and in particular
                            away from areas of high erosion hazard;
                            2) No evidence of soil erosion on site, such as rills or sheet erosion.
5. Monitoring               1) Inspect the structural integrity of the perimeter bank and geo-logs;
                            2) Inspect the ground surface for erosion;
                            3) Inspect performance of the geo-log during a stormwater event (low turbidity of
                            diverted water, no erosion under the geo-log;
                            4) Effective direction of diverted water onto grassed or stable ground).
6. Frequency/Deadlines      1) Structural integrity & evidence of erosion: daily
                            2) Performance during stormwater event: During significant stormwater events.
7. Responsibilities         Building contractor.
8. Reporting and Review     Exception reporting to the site manager and senior management.
9. Contingency              When loss of control of the upslope flow diversion occurs:


                            1) Inspect existing structure for points of failure;
                            2) Report situation to site manager immediately, and request support;
                            3) If feasible redirect flow away from the point of failure onto stable ground;
                            5) Bridge points of failure with stable material (e.g. sandbags);
                            6) Collect water quality samples at inflow and outflow points (section 11)
10. Corrective actions      1) If necessary remove sediment mobilised on road surfaces with a spade and
                            broom. Do not use water.
                            2) Repair perimeter bank: reinstall berm, secure the jute mat.
                            3) Repair or replace geo-logs if damaged. Securely peg to the ground to ensure no
                            flow under log.
                            4) Add a second geo-log 1 to 4m upslope if necessary;
                            5) Improve the stability of ground surface that receives diverted water. Refer to EP-
                            SECP-05.