The monthly demand node is suitable for representing demands when these can be assumed to follow a fixed monthly pattern. A typical application might be to represent the demand pattern for a town water supply; another application might be to represent the demand pattern for irrigated paddy rice in a wet tropical environment. It can be used when modelling both unregulated and regulated river systems.
Scale
Implemented at the site scale.
Principal developer
eWater CRC
Scientific Provenance
Providing a pattern of monthly demands as input data is a basic, and well established, approach in river and water supply system, and storage behaviour modelling.
Version
Source version 2.17.
Dependencies
A Water User node is required by Source to access the monthly demand pattern node.
Theory
The monthly demand pattern is input as a set of 12 values of monthly volumes expected to be delivered at the demand node (see Parameters or settings). When a model time-step of less than one month is being used (eg daily) the value for a given month is distributed evenly across all time-steps in that month.
The Monthly Demand node provides a demand value to the Water User node at every model time-step. When modelling a regulated system, the Water User node supplies the Monthly Demand node with a value of maximum travel time (expressed in numbers of model time-steps). At a given model time-step, the demand value provided is the one for the appropriate number of time-steps in advance of the current time-step. When modelling an unregulated system, the demand value provided is the one that is applicable to the current model time-step. More information on how this value is further processed is available in the section of this Scientific Reference Guide.
Assumptions and Limitation
The key assumption is that the demands to be modelled can be adequately represented by a fixed monthly pattern. Amongst other things, while seasonal variations are represented, this assumes the demand in any given month does not change from year to year due to climate variability.
Input data
A fixed pattern of 12 monthly values is input. More information on this and other input data is given in Parameters or settings, below. Full details are provided in the Source User Guide.
Parameters or settings
Model parameters are summarised in Table 31.
Output data
Output comprises a time series of flows.
Model parameters
Parameter | Description | Units | Default | Range |
|---|---|---|---|---|
Travel time (only when modelling a regulated system) | Expected time for water to travel from nominated storage to the demand node | Days | 0 | Governed by maximum travel time in the system being modelled |
Monthly demand values (12 expected) | A file of demand values | ML/month | 0.0 | Positive number |
Information from an existing scenario | ||||
An expression defined by the modeller | ||||
Return Flow (see note below) | Percentage of volume of water supplied (which may differ from demand) | % | ||
A fixed volume | ML/month | |||
A volume defined using an expression | ML/month |
 Note that when the return flow is being calculated no mass balance check is carried out. While there should be no potential for a mass balance problem when the return flow is evaluated as a percentage of the water supplied, when either a fixed volume or a volume defined by an expression is used there is the potential to cause mass balance problems if an inappropriate value of the fixed volume or an inappropriate expression is used. |
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