ArcGIS HEC-RAS Interface Data Model
Oscar Robayo, CRWR
Table of Contents
The automation of the floodplain analysis process has always been envisioned by the water resources community. Newly available technology is now offering an alternative to this end that relies on Geographic Information Systems (GIS) and in particular on concepts of Open GIS Architecture that enables seamless interaction with other external applications.
One one of the needed components for achieving the integration of all the floodplain mapping processes is the ability to readily generate a complete HEC-RAS model setup from a geospatial repository. The existing pre- and post- processors for HEC-RAS (GeoRAS) are designed to handle only the spatial entities of the model system allowing for support at generating the geometric aspects of the hydraulic model. To enable a complete HEC-RAS modeling setup it is necessary to extend the content of the dataset from just geometry to the full description of the needed model parameters (1 to 1 design). A complete HEC-RAS interface data model was developed to account for a complete description of the model and to readily store, modify, and generate new modeling scenarios off the IDM in a more comprehensive way that exposes the spatial character of all the modeling elements. The final goal then is to be able to store the complete HEC-RAS representation of the project at hand with all possible set up configurations and options.
In this light, the pre- and post-processing file structure of the HEC-RAS hydraulic simulation system is transformed into a GIS geodatabase format in which object and feature classes have been created to include all the needed components of the modeling system. Also, parameters associated to specific spatial features are located on object classes (tables) and connected to its corresponding features by means of permanent database relationships based on primary and foreign common fields of the related classes. Simply put, the complete information content in HEC-RAS’ input and output files is recreated in a geodatabase data model to promote model interface and take advantage of GIS spatial analysis and visualization capabilities. In this development, the model interface geodatabase for HEC-RAS will be called the HEC-RAS IDM.
ObjectivesTo provide a geographic database for HEC-RAS information content so that it can be migrated from or to the HEC-RAS hydraulic modeling system.
To take advantage of existing spatial functionalities in Arc Hydro data models and HEC-GeoRAS pre- and post- processor for floodplain analysis.
To facilitate model connectivity with external applications by:
Enhancing the data content of the models by georeferencing the main associated features with related input and output from the hydraulic model (i.e., water elevation and extent, bounding polygons, and flow velocity for each cross section, reach and for each flow event).
Storing time series datasets from the model using diverse format descriptors (ArcHydro Time Series format) to promote model connectivity, data analysis and display inside GIS.
A thorough understanding of the HEC-RAS file structure is necessary to create a logical and useable geodatabase structure (mapping the HEC-RAS model). To this end, the HEC has provided CRWR with documentation of the HEC-RAS file information content. Particular attention has been paid to the HEC's Data Storage System (DSS), for storing all the input runoff hydrograph time series datasets at corresponding flow change locations.
The design for the HEC-RAS Interface data model was created using a Unified Modeling Language (UML) design tool, Visio 2000. Through the UML diagrams the various object classes were created, feature classes, relationship classes, attributes, and coded value domains used in the HEC-RAS Interface data model. After the UML diagram (.vsd) is generated following the devised data model design for HEC-RAS, a repository was created which contains the data model design format that can be applied to any existing geodatabase, a process normally termed the schema application by which any geodatabase is formatted with the data model stored in the repository.
Main ComponentsHEC-RAS IDM: a geodatabase having a given model information content is called a “Model Interface Geodatabase” which is constructed according to the reading and writing formats of the modeling system we want to interface with. For the HEC-RAS hydraulic modeling system, five major feature datasets have been designed:
CrossFeature Component: a Feature Dataset containing the elements positioned across the river system being simulated. In particular, the Cross Sections, Surface Lines, Bridges, Culverts, and Inline Weirs. The main element being the Cross Section which is also an existing Arc Hydro feature built in compliance with its original structure. The Cross Section feature class in ArcHydro was extended to accommodate the roughness coefficient assignation on Cross Sections based on Land Used features intersecting the simulated floodplain.
LateralFeature Component: a Feature Dataset containing the elements positioned along the river system being simulated. In particular, the Stream Line , Bank Line, Flow Line, Levee Line, and Lateral Weirs. The main element being the Stream Line representing the hydraulic flow path for the main channel containing the reaches to be simulated. The Stream Line corresponds to the HydroEdge feature classs in the Arc Hydro data model and is built in compliance with its original structure.
AreaFeature Component: a Feature Dataset containing polygon elements representing on-the-river and off-the-river storage areas for definition of ineffective flow segments, network sources, and network sinks. In particular, the Ineffective Area and Storage Area elements. The Ineffective Area, defines potential ponding areas that in turn generate cross section segments with ineffective flow. The Storage Area, for all off-the-river water bodies in which water can be diverted into or from.
Control Component: a set of object classes (tables) containing the control files definition. The Project table definition with a registry of all the elements included in the model setup. The Plan Definition table having a particular combination of flow and geometry setup configuring a single modeling scenario. The Flow Definition table with descriptions of a given flow initial and boundary conditions. The Geometry List table with a list of all registered (in project) geometric definitions of the the river system under analysis.
Output Component: a set of object classes (tables) containing the output information. The Profile Name table with a list and description of all simulated hydraulic flow events/profiles. The BoundVertex table containing all the geometric vertices that define the boundary of the floodplain as delineated for a given flow profile. The ElevationExtentDefinition table having the water surface elevation and spatial extent definitions for each cross section and for a given flow profile. This output components are defined for each cross section and for each flow profile in the IDM by means of permanent relationships.
Pre-Process Component: a Feature Dataset containing all potential feature classes that support the implementation of the GeoRAS pre-processing tasks. In particular, the AreaBuffer feature class representing a polygon buffer of the study area, the LandUse feature class representing the land use partition of the study area and its association to manning roughness coefficients.
Post-Process Component: a Feature Dataset containing all potential feature classes that support the implementation of the GeoRAS post-processing tasks. In particular, the Floodplain feature class representing the entire bounding polygon of the flood inundation map.
Time Series Component: a set of object classes (tables) containing the input runoff hydrographs defining flow initial conditions at cross sections representing flow change locations. The time series tables enable the inclusion of regular time series and paired data that can potentially be used for model connectivity when the hydraulic modeling system needs to receive time series from another modeling system and to set up a new project file by means of a new flow file based on external applications and simulations.
The StreamLine, CrossSection, and LateralFeature datasets were "inherited" from the Arc Hydro data model as they underlie the geodatabase development of any river basin. I doing this, the HEC-RAS interface data model (HEC-RAS IDM) may take advantage of all the functionalities of an existing data model for water resources with valuable geospatial information, relationships, and parameterizations.
Final RemarksThe HEC-RAS interface geodatabase data model presented here is a work in progress and some refinements and extensions still need to be done. For instance, agreement on nomenclature, database normalization, value domains, coded value domains, etc. still needs to be done. This work is a cooperative effort with ESRI and USACE-HEC.
Oscar Robayo
Graduate Research Assistant
Center for Research in Water Resources
Department of Civil Engineering, University of Texas at Austin
(512) 471-0071
These materials may be used for study, research, and education, but please credit the authors and the Center for Research in Water Resources, The University of Texas at Austin. All commercial rights reserved. Copyright 2004 Center for Research in Water Resources.