GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project E-2 Events – events can be set to occur at a given point in time or can be triggered where specified conditions are met. This allows conditions within the simulation to be changed, such as specifying a date from which a pond can safely overflow. Delays – delay elements account for the time that it takes information or material to pass from one point to another, for example, water to be treated then discharged. Results – results can be recorded to display final model conditions or the dynamic behaviour of a system over the simulation period. GoldSim enables model results to be viewed as deterministic for individual realisations or probabilistic where multiple model realisations have been run. Using these features detailed water balance models can be produced which simulate short term system responses and long term behaviour under a range of conditions. E-3 Waihi North Water Balance E-3-1 Model Categories The aim of the Waihi North Water Balance Model (WBM) is to capture all significant water movements across the site affected by mine operations. This is achieved through accounting for water sources, sinks and processes within the WBM that are summarised in the following categories: Rainfall on catchment areas Ohinemuri River flow Mine dewatering Seepage flow Sinks Evaporation Retained moisture Processes Pump rates Overflow rates Ore processing Water treatment rates The WBM is run as a probabilistic simulation for the duration of the Waihi North Project where the sources and model time step are defined at daily intervals. For each year modelled an annual rainfall time series is randomly selected from the database of daily rainfall records between 1916 and 2016. The model is run for 1000 realisations of the full project duration and statistical results are generated considering all realisations. Figure 1 shows a schematic of the WBM where each of the elements represents a container enclosing a model to represent the localised system. Linking each of the containers are arrows, which indicate the flow of water through the model. The colour coding of the arrows indicates the water type, where water requiring cyanide removal is red, minewater is grey, tailings slurry is brown and clean river water is blue. The following sub-sections contain a description of each of these containers and their functions. The WBM also includes functions to model water quality within the water management system. Contaminant concentrations are modelled from each source and a mass balance determines the discharge quality of water processed through the WTP.
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