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C

Compling rillgen.c

Rillgen2D is written in C

The code is compiled by the Python script when the program is run.

To compile the C code outside of python, you can use gcc in Linux or Mac OS X

gcc -Wall -shared -fPIC rillgen2d.c -o rillgen2d.so

To compile the C code outside of Python on Windows 10:

gcc -o rillgen2d.exe rillgen2d.c

Developer Documentation

Understanding the rillgen.c Code

The provided rillgen.c code implements the core logic of the Rillgen2d model, which simulates rill erosion processes on a digital elevation model (DEM). The code is quite complex and involves various algorithms and calculations. Here's a breakdown of its key components:

1. Data Structures and Initialization:

  • Grids and Variables: The code defines several 2D grids (matrices) to store information such as topography (topo), slope (slope), rainfall (rain), contributing area (area), discharge (discharge), depth (depth), incised depth (inciseddepth), erosion (eroded), shear stress (tau), maximum shear stress (maxtau), flow direction (angle), and various factors used in calculations.
  • Input Parameters: Parameters such as flags for different model options, grid dimensions (lattice_size_x, lattice_size_y), cell size (deltax), Manning's n (manningsn), and various coefficients are read from the input.txt file.
  • Neighboring Cells: The setupgridneighbors function defines arrays to efficiently access neighboring cells in the grid.

2. Hydrologic Correction (Priority-Flood):

  • priority_flood_epsilon Function: Implements a priority-flood algorithm to fill pits and flats in the DEM, ensuring proper drainage for subsequent calculations.
  • Priority Queue: The algorithm utilizes a priority queue to efficiently process cells based on their elevation.
  • Epsilon Filling: Cells identified as pits or flats are filled by incrementally raising their elevation (fillincrement) until they drain to a lower neighbor.

3. Slope Calculation and Smoothing:

  • calculateslope Function: Calculates the slope at each cell using a central difference scheme and determines the flow direction based on the steepest descent.
  • smoothslope Function: Optionally smooths the calculated slope using a moving window average to reduce the impact of noise or artifacts in the DEM.

4. Flow Routing:

  • Routing Options: The code supports three flow routing methods: Multiple Flow Direction (MFD), D-infinity, and a depth-based approach. The chosen method is determined by the flagforroutingmethod parameter.
  • MFD Routing:
    • mfdflowrouteorig, mfdroutefordischarge functions: Distribute flow from each cell to its downhill neighbors based on the steepest descent and a weighting factor determined by the elevation difference.
  • D-infinity Routing:
    • dinfflowrouteorig function: Determines the flow direction based on the steepest slope within eight possible directions and distributes flow accordingly.
  • Depth-Based Routing:
    • initialguessforrouting, calculatedischargefluxes, routing functions: Iteratively solve for flow depths and discharge using the Manning's equation and the MFD routing scheme, updating the topography until convergence is reached.

5. Rill Erosion and Shear Stress Calculation:

  • calculatedischarge Function: Calculates the discharge at each cell based on the chosen routing method and the contributing area.
  • Shear Stress: Calculates the shear stress exerted by the flow at each cell, considering the slope, discharge, and rill width.
  • Critical Shear Stress: Determines the critical shear stress for soil and rock armor layers based on input parameters and empirical equations.
  • Rill Erodibility: In the dynamic mode, the code simulates rill erosion over multiple time steps, calculating the incision depth and sediment yield based on the excess shear stress and rill erodibility parameters.

6. Output Generation:

  • f1.txt, f2.txt: Store the factor of safety against rill initiation and the ratio of rock thickness to flow depth, respectively.
  • tau.txt: Stores the maximum shear stress experienced at each cell.
  • rills.ppm: Generates a PPM image visualizing the spatial distribution of rill erosion potential.
  • inciseddepth.txt (Dynamic Mode): Stores the cumulative incision depth due to rill erosion at each cell.

In summary, the rillgen.c code implements a complex model for simulating rill erosion processes on a DEM. It involves hydrologic correction, slope analysis, flow routing, shear stress calculations, and erosion modeling to predict the locations and intensity of rill development.

Last update: 2024-05-01