Hydraulic Units: Modelling Components

Flood Modeller model networks are build up from a series of individual 'building blocks' known as hydraulic units. Each unit represents a particular hydraulic attribute of the modelled network, e.g. a river section, a junction or a weir.

The icon associated to each unit is used in the following places within the Flood Modeller 1D Interface:

The following section lists the available units that can be utilised when constructing a model, together with a brief definition and links to more detailed descriptions.

Hydraulic Unit Icons


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Flow Time Boundary

Inserts a Flow Time Boundary Unit.

Flow Head Boundary

Inserts a Flow Head Boundary Unit.

Head Time Boundary

Inserts a Head Time Boundary Unit.

Normal / Critical Depth Boundary

NCDBDY unit generates a downstream flow-head relationship based on section data

US SCS Hydrograph

Inserts a US Soil Conservation Service Boundary Hydrograph Unit.

FSSR16 Boundary

Inserts a Flood Studies Supplementary Report 16 Boundary Hydrograph Unit.

FEH Boundary

Inserts a Flood Estimation Handbook Boundary Hydrograph Unit.

Rainfall / Evaporation Boundary

REBDY unit provides a rainfall and/or evaporation boundary inflow into a model network

FRQSIM Boundary

FRQSIM unit provides a bespoke, fully distributed rainfall-runoff method to generate an inflow hydrograph for a catchment or sub-catchment

ReFH Boundary

ReFHBDY unit is an alternative method (to FEH) to derive an inflow hydrograph for a catchment or sub-catchment.


Inserts an Abstraction Unit.

Q Rating

Inserts a Rating Curve Unit.

Irrigation Demand

Enables specification of abstraction rules to define an irrigation system


Gauge units can be applied to real-time forecasting applications where there is a need to improve existing models in real time by an updating process


Inserts a Culvert Bend Unit.

Culvert Outlet

Inserts a Culvert Outlet Unit.

Culvert Inlet

Inserts a Culvert Inlet Unit.

Tidal Boundary

Inserts a Tidal Harmonics Boundary Unit.

Notional Weir

Inserts a Notional Weir Unit.


Inserts a Open Channel Pump Unit.

Round Nosed Broad Crested Weir

Inserts a Round Nosed Broad Crested Weir Unit.

General Purpose Weir

Inserts a General Purpose Weir Unit.

Sharp Crested Weir

Inserts a Sharp Crested Weir Unit.

Gated Weir

Inserts a Gated Weir Unit.

Vertical Sluice

Inserts a Vertical Sluice Gate Unit.

Radial Sluice

Inserts a Radial Sluice Gate Unit.

Bridge (USBPR 1978)

Inserts a USBPR Bridge Unit.

Bridge (Arch)

Inserts an Arch Bridge Unit.


Inserts an Orifice Unit.

Inverted Syphon

Inserts an Inverted Syphon Unit (same as Orifice Unit).


Inserts an Outfall Unit (same as Orifice Unit).

Flood Relief Arch

Inserts a Flood Relief Arch Unit (same as Orifice Unit).

Bernoulli Loss

Inserts a Bernoulli Loss Unit.

General Head Loss

Inserts a General Head Loss Unit.


Represents a channel blockage using the proportion of the flow area obstructed.

Flow Head Control

Inserts a Flow Head Control Unit.

Crump Weir

Inserts a Crump Weir Unit.

Flat-V Weir

Inserts a Flat V weir. This is a long-based weir with a triangular longitudinal profile and a transverse symmetrical V-shaped crest having small side-slopes (common in UK).

Syphon Spillway

Inserts a Syphon Spillway Unit.

River Section

Inserts a River Unit.

CES Section

CES Section uses the Depth-Integrated Reynolds-Averaged Navier-Stokes Method to calculate conveyance for a River Section.


Inserts an Interpolate Unit.


Inserts a Replicate Unit.

Symmetrical Conduit

Inserts a Symmetrical Conduit Unit.

Full Arch Conduit

Inserts a Full Arch Conduit Unit.

Sprung Arch Conduit

Inserts a Sprung Arch Conduit Unit.

Rectangular Conduit

Inserts a Rectangular Conduit Unit..

Circular Conduit

Inserts a Circular Conduit Unit.

River Muskingum

Inserts a Muskingum Unit.

River Muskingum-XSEC

Inserts a Variable Parameter Muskingum Cunge Cross Section Unit.

River Muskingum-VPMC

Inserts a Variable Parameter Muskingum Cunge Routing Unit.

River Muskingum-RSEC

Inserts a Variable Parameter Muskingum Cunge Routing Section Unit.


Inserts a Junction Unit.

Energy Junction

Whereas the Open Junction unit equalises water levels at the junction, the Total Energy Junction equalises the total energy head at all nodes


Simulates discharge through a manhole from a surcharged culvert


Inserts a Comment Unit.

Wind Shear

Models the effects of wind shear on open-channel sections, which may be of particular significance in wide rivers and estuaries.

Spill Unit

Inserts a Spill Unit.

Flood Plain Section

Inserts a Floodplain Section Unit.


Inserts a Reservoir Unit.


Inserts a Pond Unit.

Lateral Inflow

Lateral Inflow unit distributes total inflow from a boundary between across multiple river reaches or reservoirs. Inputs can be divided according to reach length, surface area or user specified proportions.