Reference & User Manual
|Last modified on: Thursday, 20-May-10 18:20 CEST|
WRM node class: Demand Nodes
A demand node (city, heavy industry including thermal power stations, light industry, commercial area, tourist resort, irrigation district, animal farms and feedlots) is primarily characterised by:
The following demand sub-types, grouped into sectors for a sectoral demand summary, all sharing sharing the same structure, are supported; the types are only used for bookkeeping purposes, they are all functionally equivalent:
Demand nodes are located behind a diversion node, so that there is no automatic correction for the conveyance loss in the extraction or diversion; being positioned behind a proper diversion node, the demand node is passive in terms of its water input. However, the diversion node can of course use the demand, corrected by the expected conveyance loss (using the demand multiplier) as its target extraction.
The demand node specifies a time series of water demand; this acts like the target flow of a control node, comparing the demand specified with the supply delivered from the upstream diversion. The SUPPLY (the flow of actually useable water arriving after conveyance) must consider the conveyance loss, i.e., this percentage is subtracted from the input provided by the upstream diversion. The loss (and symetrically at the return or outflow side of the demand node) is again split into two components: an evaporative component (lost from the system), and a seepage component, that can be added to a groundwater system.
The SUPPLY is then split into consumptive use, which is subtracted, and the return flow or output from the demand node. Consumptive use is either a constant percentage of the demand, or a time series of percentages, representing a time variable share (e.g., according to seasonal patterns).
For the return flow there is again a loss term that is equivalent to the conveyance loss on the input side. The return flow can be routed through a Treatment Node: the outflow can then be routed for re-use to other demand nodes such as irrigation, subject to water quality constraints.
Both loss terms can be associated with an aquifer as percolation or seepage to the groundwater. The input to the groundwater is again only a fraction of the loss, specified by another set of coefficients, splitting the loss between seepage or percolation and evaporation fractions.
The demand node is situated behind a diversion; that supplies the water (inflow); during coveyance, a fraction is lost, split between evaporative losses, and seepage. The latter can be linked to a groundwater body.
From the water reaching the demand node, the share corresponding to the expressed
demand is used, the rest bypassed to the return flow:
consumptive use fractions is "lost" from the system,
similar to the evaporative components of the conveyance losses.
The rest together with any flow in excess of the demand reaches
the return flow, that is again subject to conveiance losses,
then routed back through a confluence to the river
or any other downstream node that can re-use this return flow;
its quality can be modified by a treatment node.
Demand nodes produces the following output time series: