Agriculture Reference
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the event within the specified time horizon is relatively large. Conversely, as the time
since the last event increases, the implicit value of generating an event increases as the
maximum time required for a subsequent event increases, and the time remaining to avoid
the penalty decreases.
A more rigorous specification
A release strategy is a set of rules based on expected release requirements that
determine when to trigger a decision to release environmental water holdings in an
attempt to create a high flow event. There are four elements to the problem: defining the
expected water requirements needed to generate the event; the state transition function;
the loss function to be minimised; and the release strategy. Expected release requirements
are based on forecast river flow conditions. The state transition function defines the time
remaining until failure to generate a high flow event incurs a penalty. The loss function
includes both resources costs and the penalty for not meeting the environmental objective.
The release strategy includes the desired volume of water on call and the set of expected
release requirements that, if met, initiate the high flow event.
Expected flow requirements
It is more strategic to release water to induce a high flow event when the background
river flows are greater. This increases the chance that a successful high flow event will be
achieved, and reduces the amount of supplementary releases that are needed. At any point
in time, there is an (unknown) quantity of water that will be needed to induce a high flow
event. A daily time series model was fitted using historical river flows:
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