SAWGraph's hydrology (water) ontology - an adaptation and extension of concepts from HY_Features, HyFO, and GWML2
type: Ontology
creator: https://orcid.org/0000-0002-9070-3169
created: 2024-09-04
contributor: https://orcid.org/0000-0002-5331-5052
contributor: https://orcid.org/0000-0002-9070-3169
contributor: https://orcid.org/0000-0003-3271-6700
modified: 2025-08-01
publisher: sawgraph.github.io
issued: 2025-04-21
source: sawgraph-water-ontology.ttl
description: This ontology supports querying the SAWGraph Knowledge Graph. It adapts and extends concepts from HY_Features, HyFO, and GWML2
version info: 1.0

geo:defaultGeometry
type: ObjectProperty
sub property of: geo:hasGeometry
domain: geo:Feature
range: geo:Geometry
comment: The default Geometry to be used in spatial calculations. It is usually the most detailed Geometry.

geo:hasGeometry
type: ObjectProperty
domain: geo:Feature
range: geo:Geometry
comment: A spatial representation for a given Feature.

gwml2:gwAquiferSystem
type: ObjectProperty
domain: gwml2:GW_Aquifer
range: gwml2:GW_AquiferSystem
description: Relates an aquifer system part, which can be another system, aquifer or confining bed, with its aquifer system

gwml2:gwAquiferSystemPart
type: ObjectProperty
inverse of: gwml2:gwAquiferSystem
description: Relates an aquifer system with its parts, which can be other systems, aquifers or confining beds

gwml2:gwMonitoringHost
type: ObjectProperty
domain: gwml2:GW_MonitoringSite
range: hyfo:WaterFeature
description: Identifies the feature hosting the site [GW_MonitoringSite], e.g., a well, spring, lake or stream

gwml2:gwWellUnit
type: ObjectProperty
equivalent property: hyfo:tapsAquifer
domain: gwml2:GW_Well
range: gwml2:GW_AquiferUnit
description: Identifies the aquifers or confining beds intersecting the well

hyfo:tapsAquifer
type: ObjectProperty
description: Identifies the aquifer a well taps

hyf:downstreamWaterBody
type: ObjectProperty
sub property of: nhdplusv2:downstreamWaterBodyTC
inverse of: hyf:upstreamWaterBody
description: Identifies another waterbody immediately downstream, allowing network navigation without knowing an inflow or outflow of the catchment realized by the waterbody

hyf:realizedCatchment
type: ObjectProperty
domain: hyf:HY_CatchmentRealization
range: hyf:HY_Catchment
description: Identifies the one and only one catchment that is realized by a particular feature

hyf:upstreamWaterBody
type: ObjectProperty
inverse of: hyf:downstreamWaterBody
description: Identifies another waterbody immediately upstream, allowing network navigation without knowing an inflow or outflow of the catchment realized by the waterbody

nhdplusv2:containsFlowLine
type: ObjectProperty
domain: nhdplusv2:FlowLineCatchment
range: nhdplusv2:FlowLine
description: Connects a flowline catchment with its flowline(s)

nhdplusv2:downstreamWaterBodyTC
type: ObjectProperty
type: TransitiveProperty
domain: Class
range: Class
description: The transitive closure of the nhdplusv2:downstreamWaterBody object property

nhdplusv2:downstreamFlowPath
type: ObjectProperty
sub property of: nhdplusv2:downstreamFlowPathTC
sub property of: hyf:downstreamWaterBody
inverse of: nhdplusv2:upstreamFlowPath
description: Identifies another flowpath immediately downstream, allowing network navigation without knowing an inflow or outflow of the catchment realized by the flowpath

nhdplusv2:downstreamFlowPathTC
type: ObjectProperty
type: TransitiveProperty
sub property of: nhdplusv2:downstreamWaterBodyTC
domain: nhdplusv2:FlowPath
range: nhdplusv2:FlowPath
description: The transitive closure of the nhdplusv2:downstreamFlowPath object property

nhdplusv2:upstreamFlowPath
type: ObjectProperty
sub property of: hyf:upstreamWaterBody
inverse of: nhdplusv2:downstreamFlowPath
description: Identifies another flowpath immediately upstream, allowing network navigation without knowing an inflow or outflow of the catchment realized by the flowpath

nhdplusv2:partOfFlowPath
type: ObjectProperty
domain: nhdplusv2:FlowLine
range: nhdplusv2:FlowPath
description: Connects an elementary flowpath (e.g., NHDFlowline) to any non-elementary flowpath it is a part of

nhdplusv2:partOfMainStem
type: ObjectProperty
sub property of: nhdplusv2:partOfFlowPath
domain: nhdplusv2:FlowLine
range: nhdplusv2:MainStem
description: Connects an elementary flowpath (e.g., NHDFlowline) to its main stem

nhdplusv2:partOfWaterBody
type: ObjectProperty
domain: nhdplusv2:FlowLine
range: hyf:HY_WaterBody
description: Connects an elementary flowpath to a waterbody it lies within

nhdplusv2:associatedCatchmentArea
type: ObjectProperty
domain: nhdplusv2:FlowPath
range: hyf:HY_CatchmentArea
description: Identifies the one and only one catchment area that is associated with a particular flowpath

hyfo:isRepresentedByWFR
type: ObjectProperty
domain: hyfo:WaterFeature
range: hyfo:WaterFeatureRepresentation
description: Relates a water feature to a representation of that water feature

nhdplusv2:hasFlowPathLength
type: ObjectProperty
range: qudt:Quantity
description: Relates any flowpath to its length, represented as, for example, a qudt:Quantity object

wbd:primaryFlowPath
type: ObjectProperty
domain: wbd:DrainageBasin
range: nhdplusv2:MainStem
description: Relates a drainage basin (area) to the primary mainstem flowing through it

wbd:containingHUC
type: ObjectProperty
domain: nhdplusv2:FlowLineCatchment
range: wbd:DrainageBasin
description: Relates a flowline catchment to any WBD drainage basin it lies within

wbd:contributingDrainageBasin
type: ObjectProperty
inverse of: wbd:primaryFlowPath
domain: nhdplusv2:MainStem
range: wbd:DrainageBasin
description: Relates a mainstem to the drainage basin (area) it drains

qudt:quantityValue
type: ObjectProperty
range: qudt:QuantityValue

qudt:hasUnit
type: ObjectProperty

qudt:hasQuantityKind
type: ObjectProperty
range: qudt:QuantityKind

topological connection (spatial contact) (sawgraph)
type: ObjectProperty
sub property of: topological connection (spatial contact) (sawgraph)

topological connection (spatial contact) (sawgraph)
type: ObjectProperty

nhdplusv2:hasCOMID
type: DatatypeProperty
domain: Class
range: string
description: Relates an NHDPlusV2 feature to its COMID

nhdplusv2:divergence
type: DatatypeProperty
domain: nhdplusv2:FlowLine
range: string
description: Indicates if a nhdplusv2:FlowLine is the main-path or a minor-path of a divergence (no triple if no divergence)

nhdplusv2:hasFCODE
type: DatatypeProperty
domain: Class
range: string
description: Relates an NHDPlusV2 feature to its FCODE (see also nhdplusv2:hasFTYPE)

nhdplusv2:hasFTYPE
type: DatatypeProperty
domain: Class
range: string
description: Relates an NHDPlusV2 feature to its FTYPE (see also nhdplusv2:hasFCODE)

nhdplusv2:hasLevelPathId
type: DatatypeProperty
domain: nhdplusv2:FlowLine
range: string
description: The level path id of a flowline is the hydrologic sequence number of the most downstream flowline feature in the level path and is used to connect flowlines to their corresponding main stem

nhdplusv2:hasMainStemId
type: DatatypeProperty
domain: nhdplusv2:MainStem
range: string
description: Relates a nhdplusv2:MainStem feature to its unique identifier

nhdplusv2:hasReachCode
type: DatatypeProperty
domain: Class
range: string
description: Relates an NHDPlusV2 feature to its ReachCode

nhdplusv2:hasSlope
type: DatatypeProperty
domain: nhdplusv2:FlowLine
range: decimal
description: The numeric average slope of a flowline

geo:Feature
type: Class
subclass of: geo:SpatialObject
disjoint with: geo:Geometry
comment: A discrete spatial phenomenon in a universe of discourse.

geo:Geometry
type: Class
subclass of: geo:SpatialObject
comment: A coherent set of direct positions in space. The positions are held within a Spatial Reference System (SRS).

geo:SpatialObject
type: Class
comment: Anything spatial (being or having a shape, position or an extent).

gwml2:GW_Aquifer
type: Class
subclass of: gwml2:GW_AquiferUnit
description: A body of earth material that contains / potentially contains / potentially contained sufficient saturated permeable material to yield significant quantities of water to wells and springs (after Lohman, 1972)

gwml2:GW_AquiferSystem
type: Class
subclass of: gwml2:GW_AquiferUnit
description: A body of permeable and poorly permeable material that functions regionally as a water-yielding unit; it comprises two or more permeable beds separated at least locally by confining beds that impede groundwater movement but do not greatly affect the regional hydraulic continuity of the system; includes both saturated and unsaturated parts of permeable material (after ASCE, 1987)

gwml2:GW_AquiferUnit
type: Class
subclass of: gwml2:GW_HydrogeoUnit
subclass of: hyfo:AquiferWaterFeature
description: Denotes aquifer-related hydrogeological units: aquifer systems, aquifers, or confining beds

gwml2:GW_HydrogeoUnit
type: Class
description: Any soil or rock unit or zone that by virtue of its hydraulic properties has a distinct influence on the storage or movement of groundwater (after ANS, 1980)

gwml2:GW_MonitoringSite
type: Class
description: Site of observation related to groundwater

gwml2:GW_Well
type: Class
subclass of: hyfo:SubsurfaceWaterFeature
equivalent class: hyfo:WaterWell
description: A shaft or hole sunk, dug or drilled into the Earth to observe, extract or inject water (after IGH1397)

hyf:HY_Canal
type: Class
subclass of: hyf:HY_WaterBody
description: a body of surface water, participating in a hydrographic network, that is special due to its artificial origin (man-made)

hyf:HY_Catchment
type: Class
subclass of: hyf:HY_HydroFeature
description: captures the union of catchment and hydro nexus, and the multiple realizations of the holistic catchment concept

hyf:HY_CatchmentArea
type: Class
subclass of: hyf:HY_CatchmentRealization
description: Two-dimensional (areal) hydrology-specific realization of the holistic catchment

hyf:HY_CatchmentDivide
type: Class
subclass of: hyf:HY_CatchmentRealization
description: One-dimensional (linear) feature that is a hydrology-specific realization of the holistic catchment

hyf:HY_CatchmentRealization
type: Class
subclass of: hyfo:WaterFeatureRepresentation
description: based on the idea that there are multiple hydrology-specific perspectives of the holistic catchment concept that are used to describe a catchment as a unit of study shared across sub-domains and studies

hyf:HY_DendriticCatchment
type: Class
subclass of: hyf:HY_Catchment
description: a catchment which is determined by a single common downstream catchment

hyf:HY_Estuary
type: Class
subclass of: hyf:HY_WaterBody
description: a body of surface water, participating in a hydrographic network, made special due to branching and its interaction with the open sea

hyf:HY_FlowPath
type: Class
subclass of: hyf:HY_CatchmentRealization
description: realizes a catchment specifically as a path connecting the inflow and outflow of the catchment it realizes

hyf:HY_HydroFeature
type: Class
subclass of: geo:Feature
description: a basic feature to reflect the properties that all hydrologic features have

hyf:HY_Impoundment
type: Class
subclass of: hyf:HY_WaterBody
description: a body of surface water, participating in a hydrographic network, seen as being special due to being formed by collecting water, for example in the case of a dam

hyf:HY_Lagoon
type: Class
subclass of: hyf:HY_WaterBody
description: a body of surface water, participating in a hydrographic network, which is special due to its shallow depth and interaction with the open sea

hyf:HY_Lake
type: Class
subclass of: hyf:HY_WaterBody
description: a body of surface water, participating in a hydrographic network, made special due to its considerable size

hyf:HY_River
type: Class
subclass of: hyf:HY_WaterBody
description: a body of surface water, participating in a hydrographic network, which is special due to its property to permanently or temporarily flow

hyf:HY_WaterBody
type: Class
subclass of: hyf:HY_HydroFeature
subclass of: hyfo:SurfaceWaterFeature
description: A waterbody is part of the hydrographic network and is either standing in a depression or flowing in a channel, which are parts of the channel network

nhdplusv2:FlowLine
type: Class
subclass of: nhdplusv2:FlowPath
description: any atomic/elementary kind of HY_FlowPath within a given framework/context (for example, a single NHDFlowline instance)
description: area of associated catchment may be zero (per hydrologic fabric logic model)
description: can be part of at most one mainstem
subclass of: Restriction
  on property: nhdplusv2:partOfFlowPath
  max qualified cardinality: 1
  on class: nhdplusv2:MainStem

nhdplusv2:FlowLineCatchment
type: Class
subclass of: hyf:HY_DendriticCatchment
description: The catchment polygon for a nhdplusv2:FlowLine

nhdplusv2:FlowPath
type: Class
subclass of: hyf:HY_FlowPath
description: any non-atomic/non-elementary kind of HY_FlowPath comprised of a contiguous set of atomic/elementary flowpaths

nhdplusv2:MainStem
type: Class
subclass of: nhdplusv2:FlowPath
description: a named river or similar feature, represented from head to outlet (a composition of elemenatry flowpaths (flowlines) per hydrologic fabric logic model)

nhdplusv2:FlowPathLength
type: Class
subclass of: qudt:Quantity
description: The length of a flowpath

wbd:DrainageBasin
type: Class
subclass of: hyf:HY_DendriticCatchment
description: A HUC12 watershed (drainage area) from the WBD

hyfo:AquiferWaterFeature
type: Class
subclass of: hyfo:SubsurfaceWaterFeature
description: An aquifer water feature including water, container, and void

hyfo:HydroRockBody
type: Class
subclass of: hyfo:SubsurfaceWaterFeature
description: a hybrid physical object, such as aquifer, well, or lake, that consists partly of a rock body (a container), empty spaces therein (voids), and a water body inside the space

hyfo:SubsurfaceWaterFeature
type: Class
subclass of: hyfo:WaterFeature
description: A complete subsurface water feature including water, container, and void (for example, aquifer, well, et al.)

hyfo:SurfaceWaterFeature
type: Class
subclass of: hyfo:WaterFeature
description: A complete surface water feature including water, container, and void (for example: lake, river, marsh, et al.)

hyfo:WaterFeature
type: Class
subclass of: geo:Feature
description: A complete water feature including water, container, and void; includes surface and subsurface water features

hyfo:WaterFeatureRepresentation
type: Class
subclass of: geo:Geometry
description: A representation of a water feature (for example, a line or polygon)

hyfo:WaterWell
type: Class
subclass of: hyfo:SubsurfaceWaterFeature
equivalent class: gwml2:GW_Well
description: A water well, with focus on the hole/shaft itself (see gwml2:GW_Well)

qudt:Quantity
type: Class

qudt:QuantityKind
type: Class

qudt:QuantityValue
type: Class

qudt:Unit
type: Class