Hydrologic Objects for Modeling: One Viewpoint

1
Hydrologic Objects for Modeling One Viewpoint

• Thomas A. Evans
• US Army Corps of Engineers
• Hydrologic Engineering Center

2
What is HEC?
The Hydrologic Engineering Center (HEC) is an
office of the US Army Corps of Engineers
established to support the nation in its water
resources management responsibilities by
increasing the Corpss technical capability in
hydrologic engineering and water resources
planning and management. By means of programs
in research, training, planning analysis, and
technical assistance, HEC incorporates
state-of-the-art procedures and techniques into
manuals and comprehensive computer programs. The
products are developed for the Corps however,
they are available to the public.
3
Hydrologic and Hydraulic Models from HEC

• HEC-1 Flood Hydrograph modelnow superceded by
  HEC-HMS (Hydrologic Modeling System)
• HEC-2 River Hydraulics modelnow superceded by
  HEC-RAS (River Analysis System)

4
Watershed Analysis in HEC-HMS
5
HEC-HMS Basin Element Class

• Element ID Description (strings)
• Location (2D coordinate pair)
• Contributing Area (real number)
• Downstream Element (basin element)
• Upstream Elements (list of basin elements)
• Observed Hydrograph (time series)
• Output Hydrograph (time series)
• others...

6
Basin Element Subclasses

• Sub-basin
• Rainfall/Runoff method
• Loss Method
• Baseflow Method
• Routing reach
• Downstream Location
• Routing method

7
Basin Element Subclasses

• Reservoir
• Storage/Discharge method
• Diversion
• Second Downstream element
• Junction
• Source
• Sink

8
HEC-HMS Basin Model
9
What do basin elements do?

• Combine inputs to single Time Series
• Transform input Time Series into output Time
  Series (two output TS for diversion)
• Example a subbasin convolves input hyetograph
  with unit hydrograph to produce direct runoff
  hydrograph
• Geographic data represented as connections and
  coefficients in transformation equations

10
Rainfall/Runoff Transformation
11
Why is HEC Interested in GIS?

• Description of the physical environment is
  primary source of simulation parameters
• GIS and CADD systems are best methods for
  storage, distribution, and transformation of
  environmental data
• GIS is a powerful tool for communication
• GIS is a step toward more sophisticated modeling
  methods

12
Pre-Existing Complications

• Roots of HEC models (e.g. HEC-1, HEC-2) predate
  current GIS technology
• HEC needs to support non-GIS users
• HEC will not create dependencies on commercial
  and proprietary products (except MS Windows ?) in
  its core products

13
Pre-Processor/Post-Processor Approach

• Keep models and GIS separate
• Avoid dependencies on proprietary products
• Permit use of models without GIS
• Identify model parameters and data with GIS
  sources
• Define and publish data import and export methods
  for models
• Develop example GIS applications

14
Abstraction of Watershed Data

• Description
• Directly observable elevation, soil
  characteristics land cover, drainage elements
• Aggregation
• Basin, reach definitions characteristics still
  tied to observable phenomena
• Parameterization
• Mathematical description of limited behavior
  coefficients in equations tied to specific methods

15
HEC-HMS and GIS
GIS
Hydrologic Model
DEM, NHD, HUC, STATSGO, Land Use
Raw GIS Data
Rainfall Grids or Time Series
GeoHMS Basin Definition
Watershed River Topology
Watersheds Stream Network
or
Basin Components

HEC-HMS
Hydrologic Model Parameters
GeoHMS Model Parameterization
16
Possible Relationships between Arc Hydrology
Objects Basin Elements

• Basin Element represented as component of
  corresponding Hydrology Object
• Basin Elements and Hydrology Objects represent
  each other as interfaces
• Transformation between Hydrology Objects and
  Basin Elements handled by processes external to
  both