Measurement:Canonical Units

• Part of: Measurement:Main_Page
• Related to: Measurement:Units

This page is the normative registry of canonical measurement quantities and units used by AOWIS.

The representation and conversion rules governing these quantities are defined in Measurement:Units.

UCUM is used for machine-readable physical unit identifiers.

Identifier and Field-Naming Rules

The canonical unit assigned to each measurement quantity in this registry is authoritative.

When a unit identifier is explicitly represented, it MUST use the canonical UCUM identifier defined here.

The AOWIS identifier suffix is an ASCII-safe naming convention used for fixed-schema field names, property names, database columns, and similar technical identifiers.

The suffix convention is:

• division is represented by _per_;
• multiplication is represented by _;
• unit symbols are normalized to lower case where required for identifier naming;
• quantity-specific semantic qualifiers MAY be included where a literal unit-only suffix would be ambiguous;
• dimensionless fields with canonical UCUM unit 1 normally omit a unit suffix.

For example:

m3/h        -> m3_per_h
m/s         -> m_per_s
kW.h/m3     -> kw_h_per_m3
mm2/(100.m) -> mm2_per_100m

The AOWIS identifier suffix is not itself a UCUM unit identifier.

For generic or dynamically typed measurement values, the resolved measurement quantity determines the canonical unit through this registry.

Length and Distance Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	UCUM Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
length	Linear spatial extent along an object or path	metre (m)	m	m	Pipe and link length
elevation	Vertical height relative to an engineering or hydraulic datum	metre (m)	m	m	Junction, tank, reservoir, and terrain elevation
altitude	Vertical position reported by a geographic positioning source	metre (m)	m	m	Geographic altitude; not necessarily suitable as hydraulic elevation
distance	Spatial separation between positions	metre (m)	m	m	Derived geometric distance
vertical_offset	Vertical difference between referenced elevations or heads	metre (m)	m	m	Elevation, tank-bottom, and reservoir-head offsets
link_diameter	Internal or nominal diameter of a pipe or valve	millimetre (mm)	mm	mm	EPANET pipe and valve diameter
tank_diameter	Internal diameter of a cylindrical storage tank	metre (m)	m	m	EPANET tank diameter
darcy_weisbach_roughness_height	Absolute pipe-wall roughness height used by the Darcy-Weisbach formulation	millimetre (mm)	mm	mm	EPANET Darcy-Weisbach pipe roughness

Geographic Coordinate Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	UCUM Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
latitude	Angular position north or south of the equator	degree (°)	deg	deg	WGS 84 latitude
longitude	Angular position east or west of the prime meridian	degree (°)	deg	deg	WGS 84 longitude
projected_easting	Eastward coordinate within a projected coordinate reference system	metre (m)	m	m	Projected-coordinate easting
projected_northing	Northward coordinate within a projected coordinate reference system	metre (m)	m	m	Projected-coordinate northing
local_x	X coordinate within an explicitly defined local engineering coordinate system	metre (m)	m	m	Local coordinates when the coordinate system is defined in metres
local_y	Y coordinate within an explicitly defined local engineering coordinate system	metre (m)	m	m	Local coordinates when the coordinate system is defined in metres

Area and Volume Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	UCUM Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
area	Two-dimensional spatial extent	square metre (m²)	m2	m2	Tank cross-sectional area and other geometric areas
volume	Three-dimensional spatial extent or storage capacity	cubic metre (m³)	m3	m3	Tank volume

Flow and Transport Quantities

Measurement Quantity Identifier	! Definition	! Canonical Unit	! UCUM Identifier	! AOWIS Identifier Suffix	! AOWIS Model / EPANET Mapping
volumetric_flow_rate	Volume transported per unit time	cubic metre per hour (m³/h)	m3/h	m3_per_h	Demand, link flow, leakage flow, emitter flow, and pump-curve flow
velocity	Rate of linear movement	metre per second (m/s)	m/s	m_per_s	Link flow velocity
molecular_diffusivity	Molecular diffusion coefficient of a chemical species	square metre per second (m²/s)	m2/s	m2_per_s	Physical molecular diffusivity used by the AOWIS multi-species model; backend-relative representations such as EPANET-MSX relative diffusivity are converted at the adapter boundary
longitudinal_dispersion_coefficient	Longitudinal dispersion coefficient describing axial spreading of a transported species	square metre per second (m²/s)	m2/s	m2_per_s	Multi-species longitudinal dispersion

Hydraulic Head, Pressure, and Stress Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	UCUM Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
hydraulic_head	Total mechanical energy per unit weight of fluid expressed as an equivalent fluid-column height	metre (m)	m	m	Junction, reservoir, and tank hydraulic head
pressure_head	Fluid pressure expressed as an equivalent fluid-column height	metre (m)	m	m	EPANET node pressure, pressure-driven demand thresholds, and pressure-control valve settings
water_level	Height of a water surface relative to a defined local reference level	metre (m)	m	m	Initial, minimum, maximum, and simulated tank levels
head_gain	Increase in hydraulic head across an energy-adding component	metre (m)	m	m	Pump curves and pump simulation results
head_loss	Reduction in hydraulic head across a hydraulic component	metre (m)	m	m	Pipes, valves, and other energy-dissipating components
head_loss_gradient	Hydraulic head loss per unit pipe length	metre per kilometre (m/km)	m/km	m_per_km	EPANET pipe head-loss reporting
pressure	Normal force per unit area within a fluid system	kilopascal (kPa)	kPa	kpa	Physical pressure measurements, sensors, SCADA data, and external exchange
stress	Internal force per unit area within a material	megapascal (MPa)	MPa	mpa	Structural and material analysis

Time Quantities

Measurement Quantity Identifier	! Definition	! Canonical Unit	! UCUM Identifier	! AOWIS Identifier Suffix	! AOWIS Model / EPANET Mapping
elapsed_time	Time elapsed from a defined simulation or process origin	second (s)	s	s	Simulation elapsed time and time-based control triggers
duration	Length of a time interval	second (s)	s	s	Simulation duration and time steps
time_of_day	Time elapsed since the start of the current day	second (s)	s	s	Simulation start time and clock-time controls

The canonical unit second does not imply integral-second resolution. Sub-second durations and time steps are represented as fractional seconds. For example, a time step of one millisecond is represented canonically as 0.001 s.

Hydraulic Coefficients and Other Dimensionless Quantities

The canonical UCUM unit identifier for all quantities in this section is 1. The AOWIS unit suffix is omitted.

Semantic terms such as ratio, factor, coefficient, multiplier, number, and exponent describe the quantity and are not unit suffixes.

Measurement Quantity Identifier	! Definition	! UCUM Identifier	! AOWIS Identifier Suffix	! AOWIS Model / EPANET Mapping
hazen_williams_roughness_coefficient	Hazen-Williams pipe roughness coefficient	1	none	EPANET Hazen-Williams roughness
chezy_manning_roughness_coefficient	Chezy-Manning pipe roughness coefficient	1	none	EPANET Chezy-Manning roughness
minor_loss_coefficient	Coefficient representing local hydraulic losses	1	none	Pipe and valve minor loss; TCV setting
darcy_weisbach_friction_factor	Darcy-Weisbach friction factor	1	none	Pipe simulation result
pump_speed_ratio	Pump rotational speed relative to nominal or reference speed	1	none	Pump setting, result, pattern, control, and rule values
pattern_multiplier	Factor applied by a hydraulic or energy pattern	1	none	EPANET pattern factor
demand_multiplier	Global factor applied to base demands	1	none	EPANET demand multiplier
pressure_exponent	Exponent used by the pressure-driven demand relation	1	none	EPANET pressure exponent
emitter_exponent	Exponent used by the emitter pressure-flow relation	1	none	EPANET emitter exponent
reaction_order	Order of a bulk, wall, or tank reaction equation	1	none	EPANET reaction order
specific_gravity	Fluid density relative to a defined reference density	1	none	EPANET specific gravity
relative_viscosity	Kinematic viscosity relative to the solver reference	1	none	EPANET relative viscosity
relative_diffusivity	Molecular diffusivity relative to a defined solver reference diffusivity	1	none	EPANET and EPANET-MSX relative diffusivity representations
peclet_number	Ratio characterizing advective transport relative to diffusive or dispersive transport	1	none	Multi-species dispersion; includes solver thresholds based on the Peclet number
mixing_fraction	Fraction of tank volume assigned to the applicable mixing zone	1	none	EPANET tank mixing fraction
hydraulic_accuracy	Relative hydraulic convergence criterion	1	none	EPANET hydraulic accuracy
hydraulic_damping_limit	Relative threshold controlling solver damping or status checks	1	none	EPANET damping limit
relative_error	Relative numerical error	1	none	Hydraulic and water-quality numerical error, tolerance, and simulation statistics
flow_balance_ratio	Ratio of total outflow to total inflow	1	none	EPANET flow-balance reporting
quality_mass_balance_ratio	Water-quality mass-conservation ratio	1	none	EPANET and multi-species quality mass-balance reporting

Percentage Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	UCUM Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
efficiency	Ratio of useful output to total input expressed as a percentage	percent (%)	%	percent	Pump efficiency and efficiency curves
relative_flow	Flow relative to a defined reference flow	percent (%)	%	percent	Valve characteristic curves
valve_position	Valve opening position relative to its operating range	percent (%)	%	percent	Position-control valves
source_trace_percentage	Proportion of water originating from a specified source node	percent (%)	%	percent	EPANET source-trace analysis
operating_time_percentage	Fraction of a reporting period during which equipment operates	percent (%)	%	percent	Pump energy reporting
demand_reduction_percentage	Reduction in delivered demand relative to requested demand	percent (%)	%	percent	Hydraulic statistics
leakage_loss_percentage	Leakage loss relative to total system inflow	percent (%)	%	percent	Leakage statistics

Reaction and Leakage Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	UCUM Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
first_order_bulk_reaction_coefficient	First-order reaction-rate coefficient within the bulk fluid	per day (d⁻¹)	/d	per_d	Global, pipe, and tank first-order bulk reactions
first_order_wall_reaction_coefficient	First-order reaction-rate coefficient at a pipe wall	metre per day (m/d)	m/d	m_per_d	Global and pipe first-order wall reactions
leak_area_per_100m_pipe_length	Effective leak area assigned per 100 metres of pipe length	square millimetre per 100 metres (mm²/100 m)	mm2/(100.m)	mm2_per_100m	EPANET 2.3 FAVAD leak area; EPANET uses 100 project length units and the adapter converts when required
leak_area_expansion_per_pressure_head	Increase in effective leak area per unit pressure head	square millimetre per metre of pressure head (mm²/m)	mm2/m	mm2_per_m_head	EPANET 2.3 FAVAD leak expansion

Water Quality Quantities

Measurement Quantity Identifier	! Definition	! Canonical Unit	! UCUM Identifier	! AOWIS Identifier Suffix	! AOWIS Model / EPANET Mapping
chemical_mass_concentration	Mass concentration of a chemical substance in water	milligram per litre (mg/L)	mg/L	mg_per_l	EPANET chemical quality; multi-species bulk species using a mass basis
chemical_amount_concentration	Amount-of-substance concentration of a chemical substance in water	millimole per litre (mmol/L)	mmol/L	mmol_per_l	Multi-species bulk species using an amount-of-substance basis
chemical_surface_mass_density	Mass of a chemical species associated with a surface per unit surface area	milligram per square metre (mg/m²)	mg/m2	mg_per_m2	Multi-species wall species using a mass basis
chemical_surface_amount_density	Amount of a chemical species associated with a surface per unit surface area	millimole per square metre (mmol/m²)	mmol/m2	mmol_per_m2	Multi-species wall species using an amount-of-substance basis
chemical_mass_flow_rate	Chemical mass introduced into or transported through the system per unit time	milligram per minute (mg/min)	mg/min	mg_per_min	EPANET mass-booster source strength; multi-species MASS source using a mass basis
chemical_amount_flow_rate	Amount of chemical substance introduced into or transported through the system per unit time	millimole per minute (mmol/min)	mmol/min	mmol_per_min	Multi-species MASS source using an amount-of-substance basis
water_age	Time elapsed since water entered the modelled distribution system	hour (h)	h	h	EPANET water-age analysis

Power, Energy, and Electrical Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	UCUM Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
power	Rate of energy transfer	kilowatt (kW)	kW	kw	Pump power and electrical power
energy	Work performed or energy transferred	kilowatt-hour (kWh)	kW.h	kw_h	Pump energy consumption
energy_intensity	Energy consumed per unit volume	kilowatt-hour per cubic metre (kWh/m³)	kW.h/m3	kw_h_per_m3	Pump energy-use reporting
electric_current	Rate of electric charge flow	ampere (A)	A	a	Electrical model
voltage	Electric potential difference	volt (V)	V	v	Electrical model
electrical_resistance	Opposition to electric current flow	ohm (Ω)	Ohm	ohm	Electrical model
capacitance	Ability to store electric charge	farad (F)	F	f	Electrical model

Context-Dependent Quantity Resolution

Some Model concepts resolve to different registered measurement quantities depending on their context. The representation requirements for such values are defined in Measurement:Units and, where applicable, the corresponding Measurement subsystem specification.

Model Concept	! Resolved Measurement Quantity
Valve setting	PRV, PSV, and PBV: pressure_head; FCV: volumetric_flow_rate; TCV: minor_loss_coefficient; PCV: valve_position; GPV: curve reference rather than a measurement value
Pump setting	pump_speed_ratio
Control trigger	water_level, pressure_head, elapsed_time, or time_of_day, depending on control type
Control or rule action setting	The measurement quantity supported by the target link type
Rule premise value	The measurement quantity selected by the rule variable
Initial or simulated standard water quality	chemical_mass_concentration, water_age, or source_trace_percentage, depending on quality-analysis mode
Standard quality-source strength	chemical_mass_concentration or chemical_mass_flow_rate, depending on source type
Multi-species bulk quality value	Mass-basis species: chemical_mass_concentration; amount-of-substance-basis species: chemical_amount_concentration
Multi-species wall quality value	Mass-basis species: chemical_surface_mass_density; amount-of-substance-basis species: chemical_surface_amount_density
Multi-species initial quality	The same quantity as the corresponding species value: bulk species resolve to chemical_mass_concentration or chemical_amount_concentration; wall species resolve to chemical_surface_mass_density or chemical_surface_amount_density
Multi-species absolute error tolerance	The same measurement quantity as the corresponding species value
Multi-species relative error tolerance	relative_error
Multi-species source strength	CONCEN, SETPOINT, and FLOWPACED sources resolve to chemical_mass_concentration or chemical_amount_concentration according to the species basis; MASS sources resolve to chemical_mass_flow_rate or chemical_amount_flow_rate. Wall species are not valid node-source species.
Reaction coefficient	The applicable reaction-coefficient quantity determined by reaction order
Molecular diffusion coefficient	molecular_diffusivity
Fixed longitudinal dispersion coefficient	longitudinal_dispersion_coefficient
Peclet-number dispersion threshold	peclet_number
Emitter coefficient	Equation-dependent coefficient in Q = C H^n; no single fixed canonical unit applies independently of n
Generic curve coordinate	The measurement quantity defined by the curve type
Report threshold	The measurement quantity of the corresponding report field
EPANET map or backdrop coordinate	The applicable geographic, projected, or local coordinate quantity after the coordinate representation is resolved