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.
By this means, 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 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 database relationships that rely on primary and foreign common fields on the related classes. Simply put, the 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 RASHydro.
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 (in this case, 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 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. 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), which among other things, stores all input and output time series datasets.
The design for the RAS Interface model was created using a Unified Modeling Language (UML) design tool, Visio 2000. Through the UML diagrams we created the various object classes, feature classes, relationship classes, attributes, and coded value domains used in the RAS Interface model. After the UML diagram (.vsd) is generated following the 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, or applying the schema (i.e., your geodatabase is formatted with the data model set in the repository).
Main ComponentsRASHydro, a geodatabase with a given model information content is here 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 four major feature datasets have been designed.
The Geometry Import File Feature Dataset is the HEC-RAS input file that describes the topology of the stream network to be simulated. The file starts with a header content that gives the geographic projection of the data, the DTM name and location and the number of reaches and cross sections in the network. The stream network is subdivided into reaches by means of end and start nodes that are located in 3-D space. Thus, information specific for each reach and cross section object has to be captured in out geodatabase design.
The Geographic Data Export File corresponds to the HEC-RAS output file that describes for each simulated flow event the water surface elevation and extent, and the flow velocities for each cross section in the previously defined network.
In addition to the Import and Export files to pre-processing feature datasets were included. The ProfileLine and the CrossSection feature datasets. These two datasets are inherited from the Arc Hydro data model that underlies the geodatabase development of any river basin. I doing this, the HEC-RAS interface geodatabase (here called RASHydro) takes advantage of an existing and data model with valuable geospatial information and relationships.
The ProfileLine feature dataset is further subdivided to contain all the hydraulic flow paths needed to set up the HEC-GeoRAS system.
The Cross Section feature dataset in ArcHydro is also extended to accommodate for roughness coefficient assignation on Cross Sections based on Land Used features intersecting the simulated floodplain.
Finally, the system includes Time Series object classes to enable the inclusion of regular time series and paired data to be used for model connectivity when the systems need to receive time series from another modeling system to set up a new project file by means of a new flow file based on external simulations.
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, Feature classes to include bridges and culverts, levees, Ineffective flow areas, weirs, and blocked obstructions were not included in this first version of the geodatabase design. The final version of the RAS interface geodatabase should include all possible set up configurations and options to store the complete RAS representation of the project at hand.
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 2003 Center for Research in Water Resources.