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:

• a water demand pattern, including a consumptive use fraction
• conveyance losses, for both inflow and return flow, both split into a true "loss" from the budget point of view, representing evaporative losses, and a seepage part that can be added to the groundwater system.

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:

1. DOMESTIC:
   • Demand, municipal;
   • Demand, touristic;
2. INDUSTRIAL:
   • Demand, heavy industry, including thermal power stations;
   • Demand, light industry;
3. AGRICULTURE:
   • Demand, irrigation;
   • Demand, agriculture.
4. SERVICES:
   • Demand, commercial;
   • Demand, services;
5. GENERIC:
   • Demand, generic, not otherwise specified;

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.

name	short, descriptive node name
object_link	optional link to the corresponding river basin object
node_type:	demand
sub_type	one of: generic, municipal, touristic, irrigation, agriculture, industrial, light industry, commercial, services.
consum_use	percentage of consumptive use (of municipal water demand); the remainder is available for return flow. This either a fixed percentage value, or points to a time series of percentage values.
convloss_in	Conveyance loss: percenateg of water lost during conveyance from the diversion to the actual water use.
convloss_out	Conveyance loss: percentage of water lost during conveyance from the diversion to the actual water use.
convloss_%_in	percentage of evaporative losses from the conveyance loss, input side; seepage: 100-conv_loss_coeff[in/out]
convloss_%_out	percentage of evaporative losses from the conveyance loss, output side; seepage: 100-conv_loss_coeff[in/out]
D_TS	water demand time series;
D_multiplier	water demand time series scaling factor;

1. net_supply (diversion minus conveyance loss, useful demand);
2. conveyance loss (water lost in supplying the demand)
3. conveyance loss evp./seepage (conveyance loss percentage)
4. consumptive use (percentage of supply taken our of the system);
5. return flow (supply minus consumptive use * loss factor)
6. return flow loss evp./seepage (return flow loss percentage)