When more than one Water user is connected to the Priority node, a set of rules that defines how the available water is allocated in case of water shortage is required. Two different options are available:
1. Supply by priority: Each of the Water users is getting their demand fulfilled in order of priority, i.e. each water user is assigned a priority and the demands will be fulfilled according to the assigned priorities.
2. Supply by fraction of flow: Each Water user is assigned a fraction of the available water at the priority node. The sum of the assigned fractions must be equal to one.
If the Supply by priority rule is selected, a priority number has to be specified for each Water user. The number 1 specifies the highest priority, the number 2 the second highest priority and so forth. By default, Water users are given a priority according to the sequence the connections are digitised. The priority can be changed in the priority column.
If the Supply by fraction of flow is selected, a time series file needs to be specified for each water user. The time series must contain the fraction of the flow to be supplied to the Water user.
It is possible to use a combination of Supply by priority rule and Supply by fraction of flow by assigning the same priority to one or more groups of water supply priorities and then specifying the fraction of flow required from each water supply within the ‘shared priority’ group. The fractions for all water supplies within a ‘shared priority’ group must not exceed one at all times.
Example
In a Priority node, water is distributed to three Water user nodes. The available flow in the river is constant equal to 10 m3/s at the river node. The three water user nodes have the following water requirements: the City (W4) requires 5 m3/s, and the Village (W5) and the Industry (W6) each require 4 m3/s. The following rule was specified for the Priority node:
1st priority: City,
2nd priority: Village and Industry, sharing 50/50 (described by a time series).
The simulation yields the following supply to the water user nodes:
City: 5 m3/s, Village and industry: each 2.5 m3/s.
Note that the City is not restricted, whereas the Village and the Industry both experience an equal deficit.
