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Option 1: Assumes a constant surface area at each time step, as defined by the Max dam surface area input at the farm dam UI (Equation 1)
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Where:
At - The surface water area at time step t
C – a constant defined by the input parameter Max. Dam Surface Area
Option 2: Allows a variable surface area per time step calculated as a non-linear function of storage volume at that time step using default coefficients according to a regression relationship as defined by McMurray (2004) 1 (Equation 2):
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Where:
At - The surface water area at time step t
Vt-1 - The surface storage volume at the previous time step. If t is 1 (i.e., the first modelled time step), the initial water volume at the farm dam is used as defined by the Initial Storage Percentage
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Option 3: Allows a variable surface area per time step calculated as a non-linear function of storage volume at that time step using user-defined coefficients according to a regression relationship as defined by McMurray (2004) 1
Where:
At- The surface water area at time step t
a and b are user-inputted regression coefficients, as defined by McMurray (2004)
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ActISFlowt - contributing Interstation Flow
Total upstream flow is split in two directions: (i) flows diverted into the dam, and (ii) flows bypassed directly to the downstream of the farm dam. The Actual Diverted flow is defined by Equation 6 below, and the remainder of the total upstream flow will be accounted in the downstream flow (Equation 23).
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Where:
ActDivFlowt - The actual diverted flows into the farm dam at time step t
DivFract - The percentage or proportion of total upstream flow will be involved in the water balance calculation in the edited farm dam
However, the actual inflow into the farm dam is related to the dam bypass capacity. As defined in the original plugin, if the bypass flow capacity for the farm dam is larger than or equal to the estimated actual diverted flow ActDivFlowt, all flow will bypass and no flows will be diverted into the farm dam, and actual bypass flow and actual inflow are estimated as in Equation 7. Else, they are estimated by Equation 8:
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Where:
ByPassFlowCap - The farm dam’s bypass flow capacity, an inputted parameter
ActByPassFlowt - The actual bypass flow at time step t, controlled by the bypass flow capacity and actual diverted flows ActDivFlowt
ActInFlowt - The actual inflow to the farm dam at time step t, also controlled by the bypass flow capacity and actual diverted flows
Rainfall
The Rainfall volume to the farm dam is estimated by Equation 9:
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Where:
ACTRainVolt - The actual rainfall volume to the farm dam at time step t
Raint - The inputted rainfall timeseries parameter at time step t
At- The surface water area at time step t
The intermediate storage volume at the farm dam is then estimated by Equation 10:
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Where:
Vt – The intermediate storage volume at time step t
ActInFlowt - The actual inflow to the farm dam at time step t
ACTRainVolt - The actual rainfall volume to the farm dam at time step t
Losses
The seepage volume from the farm dam at time step t is estimated by Equation 11:
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.