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 Small scale TIN needed TIN representing Pecan Bayou SE of Brownwood, TX Based on 2’ elevation contour data from aerial photogrammetry

TIN of Pecan Bayou SE of Brownwood, TX

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

DRG of Brownwood, TX Quad Map

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

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

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

TIN Data

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

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

Conceptual Model and Mesh Building in SMS

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)

Conceptual Model River boundary feature objects

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

Tracing channel in GIS using TIN

Import Shapefiles into SMS

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

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

Finite Element Mesh

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

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

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

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