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The ‘Value Of Water’ indicates the importance given to a particular water user when involved in trade. In an economic term it would be equivalent to the price a water user would be willing to pay. As the Trade Manager is not designed to capture all economic conditions “value of water water” is used. ’ The value of water is sorted in descending order, where a ‘Value of Water’ of 2 will be ranked higher than a ‘Value of Water’ of 1. When there is no surplus water, water will be traded from the lower value to the higher value. The user can define the value of water through a fixed value, a data source or a function. Value of water is required to be greater than 0 and the default value is 1 as typically water should have a value, and it helps build the idea of value similar to economic terms rather than indicating priority.
If a water user is to be removed from the list of water users in the trade group, simply select the row that contains the water user and press delete. This will remove the water user from the list.
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As TM is a new functionality in core Source, there are new recorders associated with it and they are shown in the figure below (Figure 9). The main recorder ‘Trade Manager’ is visible under the ‘Miscellaneous’ option.
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The recorders and their descriptions are given below.
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Net Trade – Sum of water volume traded into/out of a trading group. A positive value indicates water traded in, and a negative value indicates water traded out.
Net Trade Water Year To Date – Cumulative net trade volume to date in a water year
Water Traded In –Water volume traded into a group
Water Traded Out – Water volume traded out from a group
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In the example model, as in Figure 10, there are nine water users each with a demand of 1 ML/d. 
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The Trade Manager (TM) in the model is configured as below. There are three trade groups participating in the trade and they are TG1, TG2, and TG3. Each trade group is assigned three water users; for example, TG1 is assigned Z1P1, Z1P2, and Z1P3, TG2 is assigned Z2P1, Z2P2, and Z2P3, and TG3 is assigned Z3P1, Z3P2, and Z3P3.
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As indicated in Figure 11, all the water users of TG1 and other trade groups are participating in the trade (Is Trading = 1). ‘Expression Value’ is selected as the expected use method. The ‘Expected Use Expression’ is defined by functions for all the water users in this case. The ‘Value Of Water’ is also defined using functions. The ‘Value Of Water’ does not have a unit, as it is used to indicate the importance or rank of that water user when involved in trading.
The Trade Rules are defined for each group in TM, as in Table 1.
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According to Table 1, the maximum trade in and out of each group cannot exceed 10 ML.
The Resource Assessment Explorer also needs to be configured to input the Accounts, Account Types and Account Hosts. In the given example, there is an Annual Account named ‘Accnt’, which has an account type – ‘Accnt1’ which in turn has nine accounts as in Figure 12. The entitlements and initial balances are also shown in the figure. The start of the water year is selected as 1st of July.
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In summary, the trade groups, water users assigned to each trade group, expected use methods and the expected use, available water (entitlements), and value of water are listed in the table below.
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Model simulation and results
Once the configuration is finished, the model is simulated for a period of two years, starting from 1/07/2023 to 30/06/2025.
Some of the results from the Results Manager are shown in the figures below.
The Group Trade Volume, which is the absolute value of water traded in or out between groups, is shown in the table format in Figure 13.
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The equilibrium value at which trade stops in the group trading process (Group
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Can Trade?
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Max Trade In (ML)
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Max Trade Out (ML)
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TG1
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1 (Yes)
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10
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10
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TG2
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1
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10
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10
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TG3
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1
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10
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Trade Value) is illustrated in Figure 14.
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The System Trade Volume, which is the absolute value of total water traded between and within groups is shown in Figure 15.
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The net trade of the three trade groups TG1, TG2, and TG3 is shown in Figure 16. The net trade of TG1 on the first day is -10, while the net trade of TG2 and TG3 are 5 and 5 respectively. This indicates that TG1 is trading out 10 ML water to groups TG2 and TG3 equally, as the maximum trade into and out of each trade group is 10 as per the TM configuration.
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The Net Trade of all the water users of all the trade groups is shown in table format in Figure 17 below.
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A summary of results for the first time step of the model run is provided in Table 3 to demonstrate the dynamics of trade in the TM functionality.
In the first time step, the group TG1 trades out 5 ML of water each to TG2 and TG3, thus making the Group Trade Volume 10 ML. This is because, as a group TG1 has surplus water, and TG2 and TG3 have water deficits. It only trades out 10 ML due to the max trade constraints. This 10 ML is equally shared by the water users Z1P1, Z1P2 and Z1P3 (3.33 ML each). Then Z1P1 and Z1P2 trade 94.14 ML and 8.19 ML water to ZP3 based on the surplus proportion to fulfill the water shortage of Z1P3. Thus the ‘Net Trade’ of Z1P1, Z1P2, and Z1P3 is the sum of trade between and within the group as shown in the last column of Table 3.
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For the water user Z3P3, which has a ‘Value of Water’ of 2, 94 ML of water is internally traded from Z3P1 as it has 100 ML available water, and its ‘Value of Water’ is 1. The remaining deficit of 5 ML (Z3P3 already has 1 ML available water) is supplied by the group TG1. Thus, the ‘Net Trade’ of Z3P1 is -94 ML and Z3P3 is 99 ML.
In the group TG2, Z2P3 has a deficit of 99 ML, and it receives 5 ML of water from TG1 as a part of group trade. As its value is 1, it does not get internal trade water from Z2P1 and Z2P2 (Z2P1 has the same value 1 and Z2P2 has a higher value of 2 and their available water is equal to expected water). Thus, the net trade of Z2P3 is 5 ML.
As explained in the recorder description, the ‘System Trade Volume’ in this case 203 (absolute value of sum of either all negative Net Trade values or positive Net Trade values) as given in Table 3. The Group Trade Volume is 10 ML. The Net Trade of TG1, TG2 and TG3 are -10, 5 and 5 respectively.
It is to be noted that in the above example, only the first time step (first day) is considered for detailed description, and for the other time steps the TM follows the same rules and conducts trade based on available water.