Adding a Hydraulic erosion node

The Hydraulic erosion node creates realistic erosion and deposition effects caused by rainfall and river flows. This simulation follows three basic rules: when water flows over terrain, it can erode it (i.e. carve rivers or at least weather the slopes); as water flows downhill, it transports the eroded materials with it; as the water settles out, it releases the suspended soil particles, thus creating sediment depositions.

To add a Hydraulic erosion node, right click in the Graph and select Create Node  > Simulation  > Hydraulic erosion.

The connectors from top to bottom correspond to:

  • The eroded terrain
  • The sediment elevation
  • The water elevation
  • Water accumulation

Double click on the node to open its parameters:

Editing a Hydraulic erosion node

  • Number of iterations: Sets the number of iterations.
  • Hydraulic erosion:
    • Time increment: Time that elapses between iterations, in seconds. If this value is too high, the simulation may diverge and give incorrect results. The usual range of values is between 0.010 and 0.150 s (i.e. between 10 ms and 150 ms).
    • Quantity of rain: Quantity of falling water, in centimeters per second.
    • Viscosity: Change the fluid behavior and thus the erosion pattern.
    • Rain impact: Quantity of rock shattered by rain and transformed into sediment.
    • Flow erosion: The higher the value, the more terrain will be eroded by the flowing water.
  • Additional optional inputs:
    • Evaporation mask: Quantity of evaporated water, in percentage per iteration. Note that without masks, the evaporation rate should not be greater than the rain flux (or the water would not have the time to flow over the terrain before being evaporated).
    • Deposition mask: This mask act as a localized sediment sink, allowing the user to erode without sediment transport.
  • Additional information:
    • Show water: This option is checked by default. Uncheck the option to view erosion without displaying any water on your terrain.
    • Show sediment: This option is checked by default. Uncheck the option to view the node without displaying any sediment.

Exporting the flow map

In order to export the flow map, use a Mask from heights node on the Water accumulation optional connector. Configure the Mask from heights node as an automatic gradient.

Video tutorial

Watch our Hydraulic erosion node video tutorial (video of the Instant Terra beta version March 2018).


Parameters

Parameter Description
Presets Light, Balanced, Strata weathering, Diffuse weathering, Favor carving, Only carving, Only fluid simulation, Custom
Strength: Modifies globally the volume of water brought by the simulation.
Carving: Choose to favor carving over smooth weathering
Deposition: Allows the simulation to create sediment deposits at the bottom of valleys.
Erodability: Define the nature of the soil.
Stickyness: Modify the fluid behavior to make it more viscous.
Show water: Blue areas represent the places where water flows and affects the terrain.
Number of iterations: Sets the number of iterations.
Time increment: Time that elapses between iterations, in seconds.
Gravity: Gravity, in meters per second squared.
Limit flow velocity: A constraint used in the fluid simulation.
Diffusivity: Favor the weathering or the carving of terrain by forcing the water to diffuse over height.
Viscosity: Kinematic viscosity of the fluid in centistokes
Rain flux: Quantity of falling water, in centimeters per second.
Evaporation flux: Quantity of evaporated water, in centimeters per second.
Number of cycles: Numbers of rain episodes during the simulation.
Proportion of rain: Each rain cycle is divided in two parts: the rainy episode and a dry duration where only the evaporation act over the terrain.
Transport capacity: Ability of water to transport sediment.
Min terrain slope: The capacity of water to transport sediments is proportional to the slope of the terrain.
Max water height: The capacity of water to transport sediment (in meters).
Dissolution rate: The higher the value, the more the simulation erodes the terrain.
Deposition rate: The higher the value, the more sediment is deposited by the simulation.
Erosion depth: This value in meters reduces the erosion action when the eroded rock height begins to reach this limit.

Remark: Some combinations of the Advanced parameters may lead to a divergent simulation.


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