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For each dam, Source performs a water simulation based on the water balance between inflows, rainfall, evaporation, seepage, water usage and overflow components in each time step. Assumptions and detailed calculations for each element are described as follows.
Data requirements
For details of the input data requirements, parameter settings and descriptions, and output data, please see the Farm Dam Node chapter in the Source User Guide.
Water surface area
The water surface area in the farm dam (A) is used to convert a depth added (e.g., rainfall) or subtracted (e.g., evaporation or seepage) at each time step to a volume which can then be added to/subtracted from the current storage volume at that time step. The area is estimated as a function of storage volume and other parameters, with three possible options:
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a and b are user-inputted regression coefficients, as defined by McMurray (2004)1
Upstream flow
The total collected flow at an Onstream Farm Dam node consists of two parts:
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SpillVolt – The actual spill water volume from the farm dam at time step t
Vt - The final result of the storage volume at time step tFinal storage volume at time step t
Downstream Flow
Finally, flow directly downstream from the farm dam is calculated by Equation 28:
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Where:
DSFlowt – The actual water volume downstream of the farm dam at time step t
The Source simulation of onstream farm dams is based on a generalised water balance, and the final flow output downstream of the farm dam takes into account all components such as actual Interstation flow, actual diverted flows, actual inflow volume, actual bypassed flows, actual rainfall volume, actual evaporation volume, actual seepage, storage volume and downstream flow.
References
1 McMurray, D, 2004. Farm Dam Volume Estimations from Simple Geometric Relationships. Department of Water, Land and Biodiversity Conservation. South Australia. Report No. DWLBC 2004/48.