Introduction
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The following assumptions are made when EDM is configured in Source:
- Water requirements are not additive - A basic assumption used in the EDM is that environmental water is not consumed and, as such, flow rule water requirements for more than one environmental asset can potentially use the same water in accounting for the success of their flow rules being met. For example the minimum flow requirement for fish passage is not necessarily a separate parcel of water from the minimum flow required to prevent an algal bloom;
- Flow rules can be co-dependent: A flow rule can be conditionally contingent on another flow rule also being met;
- Flow rules should only be attempted if their requirements are likely to be met: The EDM determines the daily demand, however before passing the demand for this day, the EDM checks to see if the total water required to complete the rule is available; and
- The highest priority environmental water demand is for environmental flow rules which have commenced but not yet completed. If an environmental flow rule has started to be met, then the continuation of meeting this flow rule requirement has precedence over commencing water ordering to meet a new flow rule.
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The basic approach to determining the water order is to consider the collection of flow rules and determine how much water is required for a given day to meet these rules. As water is not consumed by the EDM, the water order is simply the difference between the calculated water required and the forecast flow at the extraction point on the future delivery day.The EDM allows two forecasting periods, a short term and a medium term. This approach is to reflect real world water management decision making, whereby, depending on the size of the catchment, river operators can generally make a very accurate prediction of the likely flow for the next few days to weeks. After that time the prediction is less accurate. The EDM allows you to define the ‘look ahead’ period, which is the period that can be accurately forecasted. You can use the Expression Editor to define the method of forecasting. The recommended methods for determining the forecast period are to refer to an upstream node with a known travel time.