Introduction

The Surfacewater Modeling System (SMS) is a comprehensive graphical user environment for performing 2D hydrodynamic simulations and 1D step backwater profile computations. SMS is a graphical user interface intended to be used as a pre- and post-processor for a number of analysis codes (RMA2, SED2D-WES, RMA4, RMA10, HIVEL2D, FLO2DH (FESWMS), ADCIRC, CGWAVE, WSPRO, DAMBRK). The SMS interface was developed by the Engineering Computer Graphics Laboratory of Brigham Young University in partnership with the U.S. Army Corps of Engineers Waterways Experiment Station and the Federal Highway Administration.

SMS was designed as a comprehensive modeling environment. One dimensional step backwater models and two dimensional finite element models are currently supported. In addition, support is currently being added for three dimensional finite element and finite difference models. Facilities are provided to share information between different models and data types. Tools are provided for model conceptualization, cross section extraction, mesh generation, and post-processing. SMS includes a new suite of tools in the Map Module for creating high level representations of surfacewater models using GIS objects. These models will soon have the ability to be imported/exported between SMS and Arc/Info or ArcView.

Figure 1. A river junction modeled with SMS.

Conceptual Model Approach

With the current state of the art in surfacewater modeling, simulations are typically performed according to the following steps:

Develop conceptual model
Generate the model (cross sections, mesh, grid)
Assign model parameters
Calibrate the model
Make predictions

After developing an initial hydrodynamic model, the calibration effort usually requires several changes to the model. Traditional pre-processing software is designed to automate and enhance the work involved in steps 2-5 named above. Such software provides the user with tools to create the model and then to manipulate the model, especially during the calibration period.

A new approach to model development, called the conceptual model approach has been incorporated into SMS. The conceptual model is a high-level representation of the physical study area. With this approach, the user creates GIS objects to describe features of the study area. These objects are defined in a general purpose fashion. Boundary conditions and material properties are assigned to these objects. The numerical model is generated from these feature objects in a manner that fits or adapts to the definition of the conceptual model. Boundary conditions and material properties are extracted from the conceptual model and assigned to the appropriate entities of the numerical model.

The development of a conceptual model is the new key to economical, accurate numerical modeling. When changes in the model are desired, the feature objects are changed and the model can be regenerated.

Setting Up a 2D Conceptual Model

Conceptual models are constructed in the Map Module of SMS. A sample conceptual model is shown in Figure 2. The conceptual model has been constructed on top of a scanned USGS quad map which has been imported to SMS and registered to the correct world coordinates on the SMS desktop. The objects in the conceptual model consist of sets of points, arcs, and polygons organized into coverages (layers). The data model used in SMS for GIS objects is patterned after the Arc/Info data model. Currently, these objects are constructed only within SMS, but will soon be able to be imported/exported from either ArcView or Arc/Info.

After creating the GIS objects, attributes are assigned to them. For finite element meshes, arc attributes include flow rate, water surface elevation, and material zones. For one dimensional models, arc attributes include a centerline, cross sections, and flow lengths. In Figure 2, the yellow arc shows a definition of flow while the blue arc shows a definition of water surface elevation. For finite element meshes, polygons have attributes of a material type, meshing type for creating elements, and elevation function data. The elevation data can be defined by a set of scatter points or by an existing triangular network. The elevation of mesh nodes generated inside the polygon are interpolated from the elevation attribute of the polygon. The one dimensional models uses a land use coverage to determine section break points.

Figure 2. GIS Objects describing a 2D conceptual model.

Converting the Conceptual Model to a Mesh

Once the conceptual model is built, SMS uses the GIS objects to construct a mesh according to the parameters assigned (Figure 3). The finite element mesh is created and boundary conditions are assigned to nodestrings across the open boundaries. Material types are assigned to elements of the mesh. The only thing left to do is define the global parameters, such as time controls, special print options, and iteration options.

Figure 3. Finite Element Mesh Data Constructed From the Conceptual Model.

Running The 2D Model

After the conceptual model has been converted to a finite element mesh and the global parameters have been assigned, the 2D numerical model (rma2, flo2dh, hivel2d, adcirc, cgwave) can be launched from the SMS menu. The numerical model solution can be imported to SMS for plotting functions such as velocity vectors and magnitude (Figure 4).

Figure 4. Sample Velocity Contours and Vectors

One Dimensional Applications

The conceptual model GIS approach can also be used in SMS to help define one dimensional models. This is useful when bathymetric data exists at the desired site and cross sections need to be extracted from the data. One arc is set up as a centerline and cross sections are cut across it. SMS will generate one point on the cross section for each vertex in the cross section arc. To generate more points on a cross section, more verticies can be created in the GIS arcs. Figure 5 shows an example of cross sections extrapolated from a triangulated irregular network (TIN).

Figure 5. Sample Centerline and Cross Sections

Advantages of the Conceptual Model Approach

The conceptual model approach has numerous advantages over the traditional element by element approach for creating the finite element mesh. First, defining a model using GIS objects is much faster and much simpler than the traditional approach. Second, once a simulation is performed, changes to the model can be made by changing the GIS objects in the conceptual model and regenerating the mesh data. For example, suppose it is desired to refine the elements in one region of a model. This can be accomplished easily by redistributing the verticies in the arcs of that area and then regenerating the mesh with the finer distribution. The boundary conditions are reassigned and the model can be run with the new mesh.

More Information

More information about SMS can be obtained from the SMS web pages at:

http://www.ecgl.byu.edu/software/sms/

A demo version of SMS can be downloaded from this site. In addition, the complete SMS documentation is available in Adobe Acrobat format (*.pdf).

These materials may be used for study, research, and education, but please credit the authors and the Engineering Computer Graphics Laboratory, Brigham Young University. All commercial rights reserved. Copyright 1998 Engineering Computer Graphics Laboratory.

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