SWMM5 transect.c Summary

 The transect.c file in SWMM 5 handles the geometry of irregular cross-section transects used in hydraulic modeling. It defines functions to process the geometry, create and validate transects, and compute related flow characteristics based on user-supplied parameters. These functions are especially crucial when modeling streets, channels, or other conveyances with irregular or custom shapes.

Key Components of transect.c:

1. Transect Creation and Deletion:

   • transect_create(): Allocates memory for multiple transects and initializes the necessary variables.
   • transect_delete(): Frees the memory associated with all transects when they are no longer needed.

2. Reading and Parsing Parameters:

   • transect_readParams(): Reads and processes parameters for each transect from input data, including Manning's roughness coefficients and station elevation data.
   • addStation(): Adds a new station (point along the transect) to the transect with its corresponding elevation and location.

3. Geometry Calculation:

   • createTables(): Creates tables of geometry for each transect, including the calculation of cross-sectional areas, widths, and wetted perimeters for various depths.
   • getGeometry(): Calculates and updates the geometry of a transect at a given depth.
   • getSliceGeom(): Computes the geometry (width, area, and wetted perimeter) of a transect slice between two stations.
   • getFlow(): Uses Manning's equation to calculate the flow for each transect section.

4. Manning's n and Section Factor:

   • setManning(): Assigns Manning's roughness values to the left, right, and channel sections of a transect.
   • setMaxSectionFactor(): Determines the maximum section factor for a transect, which is important for flow calculations.

5. Street Transects:

   • transect_createStreetTransect(): Creates a transect for a street cross-section, considering both the street’s geometry and the associated runoff characteristics. This function models a street as either a half or full section with potential backing, curb, gutter, and other features.

Purpose of transect.c:

• Geometry Representation: The primary function of transect.c is to represent the geometry of the drainage system, particularly for irregularly shaped cross-sections (e.g., streets, trapezoidal channels). It calculates the area, wetted perimeter, and flow characteristics at different depths to accurately simulate water flow.

• Manning’s Equation: The file applies Manning’s equation to calculate flow through cross-sections with different roughness values, adjusting for the geometry of the shape.

• Street Modeling: The file includes special handling for street cross-sections, modeling them as either half or full streets with various geometries (curb, gutter, backing, etc.), and calculates their respective flow and hydraulic characteristics.

• Hydraulic Calculations: By creating and validating transects, transect.c ensures that accurate hydraulic calculations are made, considering the channel’s geometry and roughness values, which directly impact flow routing in SWMM simulations.

Overall, transect.c is an essential part of the SWMM 5 engine for modeling and simulating runoff and water flow through channels, streets, and other irregularly shaped hydraulic structures.