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GIS and SMS in Numerical Modeling of Open Channel Flow

GIS and SMS in Numerical Modeling of Open Channel Flow. Ryan Murdock November 28, 2000. SMS = Surface Water Modeling Modeling System. Graphical pre and post processor for numerical surface water models. Data Collection. Detailed Stream Elevation Data. DEMs not suitable

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GIS and SMS in Numerical Modeling of Open Channel Flow

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  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. Data Processing *More happened here than meets the eye

  10. TIN Data • Clip down data • 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 andMesh 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

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