Time series demand model - SRG

This node is provided to enable modellers to input a time series of demands. It is potentially useful when calibrating a Source model where a staged approach is used, for example where it is desired to calibrate storage behaviour using recorded historical outflows and inflows. It can be used when modelling both unregulated and regulated river systems.

Scale

Implemented at the site scale.

Principal developer

eWater

Scientific provenance

Providing a time series of demands as input data is a basic, and well established, approach in river system and storage modelling.

Version

Source version v4.3

Dependencies

A Water User node is required by Source to access the time series demand node.

Structure and processes

Time series of demands can be input:

via a data file;
from an existing scenario; or
via a function defined by the modeller.

The Time Series Demand node provides demand values to the Water User node at every model time-step. When modelling a regulated system and:

The time series of demands have been input via a data file, the Water User node supplies the Time Series Demand node with a value of maximum travel time, tmax (defined below). At a given model time-step, the demand value extracted from the input data file is the one for tmax time-steps in advance of the current time-step.
Demands come from an existing scenario. In this case the procedure operates in the same way as when the demands have been input via a data file. The information loaded from an existing scenario must have the same number of time-steps as used in modelling the current scenario.
Demands are calculated by evaluating the function defined by the modeller, no adjustment for travel time can be made as functions can only be evaluated based on current information (ie they cannot "look ahead"). In this case the demand value can only be the one that is applicable to the current model time-step (equivalent to t_max= 0).

Where t_max = the travel time from the upstream storage having greatest travel time between it and this Time Series Demand node, expressed in numbers of model time-steps.

In the first two cases, the extracted data value is used to update an array of demand values for the current time-step and t_max time-steps into the future, and this array is returned to the Water User node. In the third case, only a single value is returned to the Water User node.

When modelling an unregulated system, the demand value returned to the Water User node is the one that is applicable to the current model time-step, regardless of whether it comes from an input data file, from a scenario, or from evaluating a function.

More information on how this value is further processed is available in the Water User section of this Scientific Reference Guide.

Input data

When demands are entered in a time series data file or demands come from an existing scenario, there must be one value per model time-step with no missing values. Units must be specified. Information on other input data is given in Parameters or settings, below. Details are provided in the Source User Guide.

Parameters or settings

Model parameters are summarised in Table 1.

Table 1. 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
Demand data	A file of demand values	See list below	0.0	Positive number
	Information from an existing scenario
	A function defined by the modeller
Return Flow (see note below)	Percentage of volume of water supplied (which may differ from demand)	Percentage or proportion
	A fixed volume	Units can be selected
	A volume defined using a function	Units can be selected in the function editor

Note: 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 or proportion of the water supplied, when either a fixed volume or a volume defined by a function is used there is the potential to cause mass balance problems if an inappropriate value of the fixed volume or an inappropriate function is used.

Allowable units are:

Megalitres per day
Gigalitres per day
Megalitres per year
Cubic metres per second
Litres per second
Kilolitres per day
Kilolitres per year

Output data

The Time Series Demand node returns an array of demand values to the Water User node, or a single demand value for the current model time-step, as described above.