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Figure 4 Farm Dam editor – Dam Information
a. Dam Information
The farm dam information is on the default interface of the farm dam editor (Figure 4). The parameters Dam Capacity, Max. Dam Surface Area and Initial Storage Percentage in Figure 4 are self-explanatory. Other parameters are described below.
- Diversion Fraction - decides diverted flows are not included in the water balance calculation. This parameter indicates how much of the “upstream” flow, which includes both the upstream flow and interstation inflow, will be involved included in the water balance calculation in for the edited farm damnode. The remaining water in the “upstream” flow will be diverted directly to the downstream flow.
- Dead Storage Volume (/Dead Storage Proportion) – is the volume of the farm dam stored below the level of the lowest outlet (the minimum supply level). The demand and release requirements cannot access this water, but the natural loss (e.g. evaporation, seepage) in this water still occurs. Dead Storage Volume can also be
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- input as
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- a percentage or proportion of Dam Capacity by ticking the Use Proportion checkbox. The parameter name will
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- change to Dead Storage Proportion when the Use Proportion checkbox is ticked. The user can click on the %/
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- proportion button to swap the type between percentage (%) and proportion.
Note that the values entered from different types (i.e., volume, percentage, and proportion) for the same farm dam
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will only be automatically converted
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once the configuration is saved by clicking on the OK button of the Editor interface.
The Dead Storage Volume can be entered
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as (a)
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a
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Value, (b)
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a Data Source
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- normally
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a time series
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, or (c)
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a Function.
The allowable range of Dead Storage Volume is between zero and max capacity.
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Percentage and proportion
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ranges are from 0 to 100 and 0 to 1 respectively. If the entered values are not within the permitted range,
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a run error will occur. The user then needs to fix this issue. The example screen of the error message (e.g. for entering -1) is shown in Figure 5. “166” in Figure 5 is the name of the associated farm dam node.
Figure 5
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Run error screen for unsuitable input of Dead Storage Volume
- Bypass Flow - defines the maximum capacity of the flow bypassed from the upstream flow directly to the downstream of the farm dam.
Now Bypass Flow can be entered by four types of data sources: (a) from a value, (b) from Data Source, normally it is a time series, (c) from the function and (d) a Monthly Pattern shown in Figure 6.
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- Release Volume - defines the voluntary water release requested from the farm dam. The volume(s) can be entered by three types: (a) from a value, (b) from Data Source, which normally is a time series and (c) from the function.
The Release Volume is also greater or equal to zero. If the entered value is negative, the running error will occur (Figure 7). The user then needs to fix this issue.
- Dam Surface Area Options - provides three options for the dam surface area during the water balance calculation:
- Constant dam surfaces area using ‘Max. Dam Surface Area’ parameter – The entered constant value of Dam Surface Area is used in water balance calculation such as converting rainfall and evaporation from the depth to volume in the farm dam storage.
- Allow dam surface area to vary according to dam volume - The area will be calculated on the basis of the storage volume, default equations and parameters. The storage volume is from the beginning of the time step. The calculated dam surface area at each time step will be used in water balance calculation. Custom Equation Parameters check box is unticked.
- Custom Equation Parameters – This function works only when the option Allow dam surface area to vary according to dam volume is selected and the Custom Equation Parameters check box is ticked. The dam surface area will be calculated based on the storage volume at the beginning of the time step, and the equation of Volume =A*Area^B. Where A and B are input parameters from the Interface. The calculated area at each time step will be used in water balance calculation.
b. Interstation Flow
Inflows into a farm dam in this farm dam model come from two alternative sources: (i) overflows from the upstream dam(s) and (ii) the local flow generated by the interstation area between the upstream dams and this dam.
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Figure 8 Farm dam editor – Interstation Flow
c. Seepage
Seepage from the farm dam into the underlying soil can be modelled by defining an exfiltration rate (e.g., mm/d). The water that seeps from the farm dam is lost from the catchment and does not re-enter the system downstream.
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Figure 9 Farm dam editor – Seepage
d. Demand
Clinking on the Demand in the left panel of Figure 4 will display the demand parameters in the right panel for configuration (Figure 10). The demand parameters include Demand Factor and Demand Timeseries Values/Data Source. The demand factor can be estimated from the ratio of the average annual demand of the farm dam volume.
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Figure 10 Farm dam editor – demand
e. Rainfall
Clicking on the Rainfall in the left panel of Figure 4 will display the rainfall parameters in the right panel (Figure 11). The parameter is the rainfall to the edited farm dam, and it can be configured by constant Values or timeseries data in Data Sources. Its unit is depth such as mm, and Source will convert it to volume by the dam area calculated as the description in section (1) The farm dam information.
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Figure 11 Farm dam editor – Rainfall
f. Evapotranspiration
Clicking on Evapotranspiration in the left panel of Figure 4 will display the evapotranspiration parameters in the right panel (Figure 12). The parameter is the evapotranspiration from the edited farm dam, and it can be configured by constant Values to timeseries in Data Source. Its unit is depth such as (mm/day) and Source will convert it to volume using the calculated dam area as the description in section (1) The farm dam information.
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