ESRIs ArcHydro 2

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ESRIs ArcHydro 2

• Objects
• And the
• GeoDatabase

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This is what we are trying to model
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This is where we ended last week
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Is a type of
1 to many relationship
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Set of Objects

• ArcHydro is a set of connected objects and
  features
• To understand the thing a few terms have to be
  defined
• Class (group of objects with similar behaviors
  and attributes)
• Object (Member of an object class
• Attributes of an object (what it is)
• Behavior (how it interacts with other objects)
• Interface (protocol for passing info in and out)

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ArcHydro Objects

• Three kinds
• Objects data tables that store only attribute
  data
• Features data tables that store spatial
  coordinates and attributes
• Network features Special pts and lines called
  junctions and edges in addition to their
  attributes and spatial coordinates
• Simple network features one feature
• Complex network features Several connected
  spatial features and only one attribute table

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ArcHydro Features

• ArcHydro features are different from any other
  kind of feature in ArcGIS
• In ArcGIS the ObjectID is a unique identifier of
  any object with a Feature Class assigned at
  object creation

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ArcHydro Features 2

• In ArcHydro all features are HydroFeatures and
  all carry the following attribures
• HydroID Integer that uniquely identifies the
  feature
• HydroCode Text that is a permanent public
  identifier of the feature

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Example

• A streamflow gage in stuck in ArcHydro
• It if given a HydroID 0123456
• The USGS gage has a site number of 0987656432
• And that is the HydroCode
• Now ArcHydro can link the junction (0123456) with
  the gage site 09876532 and thus be able to
  extract gage data as needed

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HydroID Structure

• Format
• Class number followed by a feature number
• HydroID 12000044
• Feature 44 in feature class 12
• HydroID is defined using a pair of tables
• LayerKeyTable
• HydroIDTable

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Ragionalization

• HydroID can be applied to regions by inserting
  another 2 digit number before the Class Number
• Thus you can have up to 100 regions
• And that makes it easy to break large areas up
  into smaller units for analysis

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Linking

• All Hydro features can be associated with other
  hydro features by storing the HydroID of the
  first feature as an attribute of the second.
• This allows the association of drainage areas
  with junctions on the network so you can get
  water from the drainage area to a stream

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The Concept

• that all Hydro features in the model are uniquely
  identified is a powerful idea for supporting
  behavioral modeling because it means that the
  database can be considered as an integrated whole
  rather than as a set of separate data layers!

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HydroID use

• Within ArcHydro all fields used to support
  HydroID-based relation ships are integer fields
• Easier to manage than text
• Queries are more efficient
• All ArcHydro attributes ending with ID are
  integer
• All ArcHydro attributes ending with CODE are text
  (string)

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ArcHydro Framework
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Feature Classes

• HydroEdge The blue lines describing streams
• HydroJunction
• Junctions at the ends of flow segments (edges)
• Topologically connected in ArcGIS geometric
  networks (Hydro Network)
• Waterbody ponds, lakes, etc.
• Watershed Drainage area
• Monitoring point gages, etc.

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