1. GIS and SMS in Numerical Modeling of Open Channel Flow
Ryan Murdock
November 28, 2000

2. SMS = Surface Water Modeling Modeling System
Graphical pre and post processor for numerical surface water models

3. Data Collection

4. Detailed Stream Elevation Data
DEMs not suitable
Small scale TIN needed
TIN representing Pecan Bayou SE of Brownwood, TX
Based on 2’ elevation contour data from aerial photogrammetry

5. TIN of Pecan Bayou SE of Brownwood, TX

6. Image Data Displayed in the background For on-screen digitizing
To enhance display of SMS model
For model placement (with registered images)

7. DRG of Brownwood, TX Quad Map

8. Flow Data for Pecan Bayou
USGS gaging station
27 mi downstream
Downloaded last 3
years of data
Apply max, mean,
and min flows to
SMS model

9. *More happened here than meets the eye
Data Processing
*More happened here than meets the eye

10. TIN Data Clip down data Need to convert to scatter point for SMS
Very large (>200 MB), hard to work with
Surface | Create Contours using Spatial Analyst
Clip contours using Geoprocessing Wizard
Recreate TIN using 3D Analyst
Now what?
Need to convert to scatter point for SMS
SMS could not read my TIN directly

11. TIN Data

12. Convert TIN to Grid Theme | Convert to Grid using Spatial Analyst
Grid extents based on a smaller theme
Specify cell size

13. Convert Grid to ASCII Points
Arc workstation — new name = gridascii(tingrid)
SMS — import ascii points as an arc view file (.arc)

14. Conceptual Model and Mesh Building in SMS

15. Conceptual Model Created using GIS objects (map module)
Constructed independently of the mesh
Description of the site
Geometric features (main channel and banks)
Boundary of domain to be modeled
Flow rates and wsels of boundary conditions
Material zones (Mannings n values, etc)

16. Conceptual Model
River boundary feature objects

17. Projection Challenges
Built conceptual model and mesh based on registered quad image
Elevation data (scatter points) based on TIN
Data in different projections
TIN- Albers Equal Area
Quad Image- UTM

18. Tracing channel in GIS using TIN

19. Import Shapefiles into SMS

20. Finish Conceptual Model
Redistribute vertices
For good element creation
Define polygons
Assign meshing parameters
For creating finite elements
Patch desirable when direction of flow known
Apply boundary conditions
Flowrate and head
Assign materials

21. Construction of Mesh Network
Convert feature objects to a mesh
Interpolating to the mesh
(scatter point module)
Renumber mesh (mesh module)
Organizes node and element ordering from specified boundary condition nodestring

22. Finite Element Mesh

23. Finite Element Modeling
Represent something physical with a mathematical equation
Want as few elements as possible, but still represent geometries accurately
Numerical model takes the conceptual model and gives results
SMS has capabilities for 1, 2, & 3 D models

24. 2D Work Mesh was set up to run FESWMS, a 2D hydrodynamic model
Equations based on continuity of mass and momentum
Depth-averaged flow (downstream & cross-stream)
Input model parameters (eddy viscosity, n, etc.)
Model crashed
Not a push button exercise

25. 1D Modeling Given position 1, find head and velocity at position 2
Balance energy at each cross section
Conservation of continuity & momentum
Cross-section averaged flow

26. Near Future Work Perform an advanced WSPRO analysis on the mesh
WSPRO is a one dimensional water surface profile computation model
Assumes flow normal to cross sections, steady state conditions, flat wsel across cross section
Examine results (depths and velocities) based on a few different characteristic flowrates at various cross sections
Refine roughness/land use estimates