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A Tank node in an urban Deveoper Scenario is used to store water collected from a roof surface. This stored water can be accessed to supply e.g. non-potable water demands.

Once linked, a rainwater tank can be a supply to all water end-use demands within a household.

The Tank node allows for the inflow of rainwater from a roof as well as the provision of trickle top-up from the mains supply, triggered to start and stop at a user-specified tank level.


There are restrictions on which node inputs and outputs you can connect together. See Urban Developer node connection rules.

The Tank node is available for Urban Scenarios only.


Table of Contents

Node Dependencies

  • Inflow: Inflow to a Tank node in an Urban Developer Scenario in Source is from a Roof node.
  • Top-up: Tank top-up is controlled by a parameter in the tank property editor (see below). The top-up function takes water from the mains supply.

Node Outputs

Node Properties

The tank parameters must be configured to represent the total number of dwellings in downstream Average or Behavioural Water Use nodes. For example, 4 houses with 10 m3 of tank volume each would need to be attached to a single tank node with 40 m3 total volume.

Properties of the Tank node are described in the table below and illustrated in Figure 1, with details of the Tank specifications in the Urban Developer Plugin SRG

Figure 1. Urban Developer storage tank definition.


VDetention       is the Detention Storage Volume (m³);

VRetention       is the Retention Storage Volume (m³);

VDead            is the Dead Storage Volume (m³);

hoff-taker         is the height of the supply off-take obvert from the base of the tank (m);

hretention         is the height of the retention storage volume (m);                  

hdetention        is the height of the detention storage volume (m);  

htank              is the height of the storage tank (m);

hTT On            is the height of the trickle top-up on trigger (m); and

hTT Off            is the height of the trickle top-up off trigger (m).

PropertyDescriptionUnitsDefault ValueRecommended Range



Cross-sectional areaDefines the cross-sectional area of the tank base.m22.5NA>= 0

Defines the total height of the tank. Includes detention and dead zone heightm2NA>= 0
Height of off-take invert

Defines the height of the offtake pipe on the tank; the offtake pipe supplies demands from the tank.

The invert level of the offtake is the height of the lowest point of the pipe above the tank base. Once the tank is filled above the offtake invert level, the water depth in the tank will never fall below this level.

Demand off-take occurs from the base of the tank just above the anaerobic or "dead" zone; a tank should therefore have a minimum "dead zone" depth of 0.1 m to allow for accumulation of sediment and other material. Water will never be drawn from the "dead zone".

m0.1[0, 2]>= 0
Initial water depthDefines the initial depth of water in the tank at the start of the model run.m0.1[0, 1000]>= 0

Overflow Configuration

Detention volume depth

Defines the detention (storage) volume depth of the tank. The detention volume depth is the depth from above the overflow outlet invert to below the tank spill/top of the tank

Detention volumes are used as buffers to decrease output flow rates in situations of high input flow. If the tank has no detention storage, set the detention volume depth equal to the overflow outlet diameter.

m0.1NA[0, 2]
Orifice diameterDefines the diameter of the overflow orifice, located at the base of the detention storage.mm100[10, 320][1, 1000]
Orifice discharge coefficientDischarge coefficient used in the evaluation of the orifice flow equation.NA0.86NANA

External top up

Enable external top-up

If enabled, allows for the tank to be topped-up with mains water so that the tank always maintains a user-specified water level. When you enable external top-up, Urban Developer handles the mains connection internally.NADisabledNANA
Top-up rateDefines the rate of mains water top-up in litres per second.L/s250NA>= 0
Top-up triggered onDefines the depth above the tank base at which the tank will start to top up.
This depth must be greater than the height of the off-take.
m0.2NA>= 0
Top-up triggered off

Defines the depth above the tank base at which the tank will stop automatically topping up.
This depth must be greater than the Top-up triggered-on depth.
m0.3NA> Top-up triggered on

First Flush System

Enable first flush systemIf enabled, changes the tank inflow behaviour so that a user-specified volume of water will bypass the tank before inflow to the tank occurs.NADisabledNANA
First Flush VolumeSpecifies the volume of water the first-flush device diverts.m30.015[0, 100]>= 0
First Flush Outlet flow rateSpecifies the outflow rate to the selected discharge outlet.m3/s0.01NA>= 0
Discharges Connection

Specifies the tank outlet that first-flush outflow is discharged through.

Detention outflow specifies that the first flush volume discharges via a connection to the detention outflow pipe.

Spill specifies that the first flush volume discharges via spilling from the tank.


User Interface

The Tank node is configured via the node Feature EditorNode properties are accessed through 4 levels:


1 Tank Dimensions 

2 External top-up

3 First Flush behaviour

4 Overflow configuration


This material has been adapted from:

eWater Cooperative Research Centre (2011) Urban Developer Product Specification: Storage Tank Routing v0.4. eWater Cooperative Research Centre, Canberra. 23 June 2011.