SRP-GOP-01 will capture runoff from an area of approximately 7.0ha during the earthworks associated with Gladstone Hill and Winner Hill. This pond has a designed minimum storage volume of 2,100m3 with an additional 210m3 forebay. The 7.0ha pond will incorporate two 1050mm concrete risers and a total of five T-bars divided between the two manholes. Both concrete manholes will need to be weighed down appropriately to ensure they do not float or tilt during periods when the pond is full of water. Each manhole will have a minimum 450mm diameter outlet pipe discharging to an existing overland flow path. Scour protection (e.g. rock riprap) will be placed below and around the outlets to minimise erosion. Contour drains will be installed prior to rain events by the Contractor to break up slope length and reduce erosion. Drop out pits (approximately 1m by 1m by 1m deep excavations) will be excavated at regular periods along the main dirty water diversions to promote deposition of heavy sediments prior to entering the SRP forebay. Additional erosion protection will be provided on dirty water diversions that exceed a grade of 2% where required. This may include lining steep sections with a geotextile, installing rock check dams, constructing pipe/flume drop structures. While TR2009/02 recommends that the maximum catchment area of a SRP is 5ha. In this case, to progress the earthworks efficiently and appropriately manage the earthworks during the initial excavation of both Gladstone Hill and Winner Hill, one SRP is the most efficient option, constructed between the two hills, rather than constructing two SRPs in this location. The benefits of this include: - One SRP is easier to manage for the construction team. - The open pit will be self-impounding earlier than if the works had to be staged. Once the GOP is inverted, then all runoff will be captured in the base of the pit and pumped to the Water Treatment Plant. A second SRP, SRP-GOP-02, will be constructed below the Sothern Stockpile. This SRP will capture runoff from an area of approximately 1.2ha. The initial design details for both SRPs has been provided in Appendix A. The SRPs will be sized in respect to their contributing catchment area and slope steepness. - Where slopes are less than 10% and less than 200m in length, the SRP will be constructed with a minimum volume of 2% of the contributing catchment. - Where slopes are greater than 10% and/or more than 200m in length, the SRP will be constructed with a minimum volume of 3% of the contributing catchment. An additional 10% of this volume is to be used as a forebay. The SRPs will be located to allow access for removing sediment from the pond. Any pumping of dirty water required throughout the duration of the Project will be to a SRP forebay or to the Water Treatment Plant for treatment prior to being discharged from the site. 3.4. Decanting Earth Bunds Decanting earth bunds (DEBs) are not proposed as part of this SSESCP. 3.5. Chemical Treatment The Chemical Treatment Management Plan (CTMP) provided as Appendix A of the Erosion and Sediment Control Assessment Report provides the methodology for determining the effectiveness and dose rates for chemical treatment to enhance the sediment retention efficiency of sediment retention ponds, decanting earth bunds and other water impoundment devices that will be used throughout the project.
RkJQdWJsaXNoZXIy MjE2NDg3