Multi-purpose tool for river analysis26 April 2004
Adam Morstad explains how the RiverCAD software package from Boss International automates many of the processes in river and dam failure analysis that can be tedious and error-prone when done by hand
THE SWISS ARMY KNIFE must have seemed ingenious to its first users. Imagine the thrill of replacing what used to be a disorganised satchel of single-purpose tools with one multi-purpose contraption. The kind of convenience, reliability, and practicality that Karl Elsener designed into his new jackknife in 1891 was far ahead of its time, evidenced by the tool’s remaining popularity.
Fast-forward roughly one century. Though the world has mechanised and complex tools like the Swiss Army Knife have become commonplace, the need for that kind of convenience has not faded. In fact, for professional hydraulic engineers it has only grown.
By 1990, drafters, architects, and engineers alike were doing most of their technical drawing with computers. Programs like AutoCAD, DAMBRK, and HEC-2 were running on personal computers all over the country while many new modelling software components continued to arrive on the market. Technology was increasing productivity, but many different programs would often still be necessary to accomplish a single task. To cut through this confusion, Boss International sought to develop a Swiss Army Knife of its own for the river modelling industry in the form of RiverCAD, a modular, scalable software package for modelling and analysing river systems and water surface profiles.
Built with a CAD engine that supports HEC-RAS, HEC-2, UNET, and DAMBRK, RiverCAD has been developed to automate many of the mundane tasks that have made hydraulic engineering analysis so time consuming. RiverCAD can compute water surface profiles for modelling dams, bridges, culverts, spillways, levees, bridge scour, flood inundation, floodway delineation, floodplain reclamation, stream diversions, channel improvements, and split flows.
RiverCAD is integrated with its own 3D CAD system that is compatible with AutoCAD and MicroStation. The software’s graphical capabilities are extremely advanced, allowing multiple CAD drawings (.DWG files) to be opened simultaneously with each drawing having four separate viewports displayed. RiverCAD’s cross-section and profile plots can be output at any drawing scale, and a sophisticated 3D surface renderer allows users to quickly create professional 3D shaded plots of the river reach being studied.
Recently, RiverCAD was used to formulate emergency action plans, dam failure modelling studies, and inundation mapping for the Catskill and Delaware Watershed System in the US. The watershed contains six dams and respective reservoirs that provide 90% of the daily water for New York City. The engineering firm heading the project was paid US$3.4M to complete this study of the 4150km2 area containing over 650km of river reaches.
The first step in this huge undertaking involved the extraction of riverine cross sections (for dam failure modelling) and displaying the resultant water surface inundation areas through the use of BOSS RiverCAD. RiverCAD allows for the simultaneous use of the dam failure model (DAMBRK) and Digital Elevation Models (DEMs) to construct cross sections quickly and accurately. The results from the dam failure analyses were stored in AutoCAD format for electronic development of data, display of information, and printing of maps. Digital Raster Graphic (DRG) maps, scanned and geo-referenced images of standard quadrangle maps, served as a familiar base map for display. After the DAMBRK analysis was performed, the inundation areas were automatically overlaid onto the DRG base map through the use of RiverCAD’s Floodplain Mapping Module, one of the most useful snap-in tools available for the program. RiverCAD interpolated the edge of water between cross sections using DEM contour information.
A major element of the generation of inundation maps was the completion of a dam failure model. The DAMBRK model was used to predict dam failure wave formation and downstream progression due to a dam or dike failure. The DAMBRK model utilised input from riverine geometry in the form of cross sections to simulate the response of a flood wave travelling downstream. The outputs from the program provided hydraulic information at each river cross section. Information such as peak flows, maximum water surface elevations, arrival time of the leading edge, and maximum flood stage were used to identify key damage centers and other areas inundated by the flood wave.
RiverCAD consists of several program modules that integrate the functionality of AutoCAD and the added features of widely used programs such as DAMBRK and HEC-RAS to simplify the input and graphical display process. This makes digital generation of the riverine description and the subsequent generation of flood boundaries much simpler than with conventional means. The program allows users to cut cross sections digitally from Digital Elevation Model (DEM) maps and output the cross section geometry and the distance of the river cross section from the dam.
Digital Elevation Model (DEM) maps provide the topographic information that RiverCAD utilises to form representations of riverine cross sections. A DEM map is an array of elevation values at regularly spaced intervals. DEM maps are normally generated by sampling regular elevation values derived from topographic maps, aerial photographs and/or satellite images. The DEM map file is simply a text representation of ‘Z’ values (or elevation values) preceded by header information that specifies the spatial configuration (geo-reference) and separation of points. The accuracy of the elevation points varies depending on the source and manner in which the file was generated.
Within RiverCAD, the DEM Interface Module allows users to directly import a variety of DEM file formats. The DEM Interface Module automatically determines the map scale as the DEM map file is imported, and multiple maps can be imported and automatically merged. Once imported into RiverCAD, the DEM can be displayed as elevation contours at user-specified intervals. The ability to define contour ranges and intervals allows for the precise display of desired areas of topography for cross section generation.
Base maps: digital raster graphics
Perhaps the most recognised base map in use today is known as Digital Raster Graphics (DRG) maps. A DRG map is a raster image of a scanned topographic map georeferenced to the surface of the earth and fit to the Universal Transverse Mercator (UTM) projection to ensure horizontal and vertical accuracy. The DRG maps, scanned at a minimum resolution of 250 dots per inch, are generally complete with all full-colour base map information including topography, hydrography, and roadways.
An advantage to importing a DRG base map is having the opportunity to compare the generated contours of the DEM to the mapped contours of the original quadrangle. Ideally, the contours should match exactly. Differences can be caused by the accuracy of the DEM elevation point interval and spacing.
Once the base map overlay was set up for the Catskill and Delaware Watershed project, RiverCAD was used to digitally cut the cross sections. The user established the end points and any ‘bends’ in the cross section via on-screen digitisation using the contours generated from the DEM. The result is a 2D station/elevation cross section plot. RiverCAD preserved the geo-referenced accuracy of the DEM and base map to allow the user to pull DAMBRK top widths using RiverCAD’s distance measuring utilities.
After the DAMBRK model had been successfully completed, RiverCAD used the DEM as a basis for plotting the flood boundary. The program then interpolated the flood boundary between the cross sections. RiverCAD’s Floodplain Mapping Module interpolates the edge of water between cross sections. This allows users to see - in precise detail - which areas of the topographic map are flooded. RiverCAD is capable of plotting multiple flood boundaries to allow for the simultaneous display of fair weather and wet weather dam failure conditions. The program’s ability to manage, display, and format several layers of data facilitates the process - this key RiverCAD feature allowed for relative ease when editing, re-running, and producing final inundation maps of multiple dam failure scenarios.
Once the flood inundation limits had been plotted in RiverCAD, utilities could be used to apply finishing touches such as shading flood areas, formatting cross sections, etc. The finished product was a full-colour inundation map at a user-specified scale that fulfills guidelines for inundation map formatting.
One of the major advantages of using this digital mapping procedure is the ability to create full colour inundation maps using only RiverCAD. This simplified process increased the speed and efficiency of the mapping process, eliminating the need for antiquated hand-drawing of inundation boundaries, managing paper maps, and/or contracting an outside mapping company. Another advantage is the ability to produce a high quality, full colour final inundation map electronically. The electronic format of the map means making ‘last-minute’ or quick edits to the final map is greatly simplified.
RiverCAD also has the ability to export data as ESRI (Environmental Systems Research Institute) format data layers or shapefiles. ESRI format is synonymous with the ArcView/ArcGIS family of Geographic Information Systems software. ArcView is a geographic information systems (GIS) software application that is perhaps better suited than RiverCAD to handle geo-referenced data layers. GIS systems also offer the added ability to manage databases and merge information properties with graphic objects such as cross sections and flood boundaries.
Upcoming RiverCAD releases
The newest release of RiverCAD, RiverCAD XP, has been in development for over three years and is planned to be released within a couple of months. New features will include a more powerful CAD engine, integrated digital terrain modelling, a more sophisticated output viewer, and faster flood inundation mapping.
Also being released later this year is RiverCAD 2D, which can perform 2D dam failure analysis, 2D reservoir sedimentation modelling, and 2D river modelling. RiverCAD 2D can perform two-dimensional hydrodynamic modelling of a river system, allowing the engineer to route a complicated 2D dam failure flood wave downstream, accounting for the sedimentation and scour that also occurs during the event. Unlike with most models, the hydrodynamics of flow, sedimentation, and scour remain coupled during the simulation.
Boss International, 6300 University Avenue, Madison, WI 53562 US, http://www.bossintl.comTablesFigure 2