# Hydraulic

## **Overview**

The Hydraulic Erosion filter provides highly adjustable simulated erosion. The filter simulates water raining on the terrain, moving downhill according to the normal of the terrain, eroding and depositing sediment along the way. In addition, it provides thermal erosion simulation, which describes the movement of sediment downslope due to the freezing/melting of water and the resulting movement of sediment into large piles at the end of slopes.

## **Parameters**

<table><thead><tr><th width="199.7999267578125">Property</th><th>Description</th></tr></thead><tbody><tr><td><strong>Iterations</strong></td><td>The number of iterations the simulation will run for. A higher iteration count will result in a stronger effect</td></tr></tbody></table>

### Hydraulic Erosion

<table><thead><tr><th width="199.7999267578125">Property</th><th>Description</th></tr></thead><tbody><tr><td><strong>Viscosity</strong></td><td>The viscosity with which the rain will run down the terrain.</td></tr><tr><td><strong>Irregularity</strong></td><td>Adds a randomized strength to the erosion step to create a more organic result.</td></tr><tr><td><strong>Evaporation</strong></td><td>The amount of water that is lost every iteration in each droplet.</td></tr><tr><td><strong>Surface Erosion</strong></td><td>The strength of the erosion.</td></tr><tr><td><strong>Angle Dependence</strong></td><td>Makes the erosion dependent on a higher slope. This protects flat areas in the terrain.</td></tr><tr><td><strong>Level Erosion Multiplier</strong></td><td>Links the erosion strength to the level step.</td></tr><tr><td><strong>Max Erosion Depth</strong></td><td>The maximum amount of erosion that can happen per pixel.</td></tr></tbody></table>

### Rain

<table><thead><tr><th width="199.7999267578125">Property</th><th>Description</th></tr></thead><tbody><tr><td><strong>Rain Strength</strong></td><td>The amount of rain that is dropped at the start of the simulation.</td></tr><tr><td><strong>Rain Probability</strong></td><td>Assigns a spawning probability to each raindrop that is compared to a randomized value.</td></tr></tbody></table>

### Hydraulic Design

<table><thead><tr><th width="199.7999267578125">Property</th><th>Description</th></tr></thead><tbody><tr><td><strong>Angle Offset</strong></td><td>Changes the angle of the starting velocity.</td></tr><tr><td><strong>Sediment Loss</strong></td><td>Loses a constant amount of sediment in each step of the simulation.</td></tr><tr><td><strong>Sediment Deposit</strong></td><td>Controls the amount of sediment added to the terrain each step.</td></tr><tr><td><strong>Sediment Fill</strong></td><td>Controls the amount of sediment at the bottom of a slippage.</td></tr></tbody></table>

### Wind

<table><thead><tr><th width="199.7999267578125">Property</th><th>Description</th></tr></thead><tbody><tr><td><strong>Wind Direction</strong></td><td>Allows you to set a wind direction, which will influence a particle's movement direction.</td></tr><tr><td><strong>Wind Strength</strong></td><td>Controls how strongly droplets will be affected by the wind.</td></tr><tr><td><strong>Wind Randomness</strong></td><td>Allows you to add a random rotation to the wind direction to be applied in each iteration.</td></tr></tbody></table>

### Thermal Erosion

<table><thead><tr><th width="199.7999267578125">Property</th><th>Description</th></tr></thead><tbody><tr><td><strong>Speed</strong></td><td>The speed at which the thermal erosion takes place.</td></tr><tr><td><strong>Threshold</strong></td><td>A threshold value below which erosion does not occur.</td></tr><tr><td><strong>Smoothness</strong></td><td>Controls the smoothness of the resulting erosion.</td></tr><tr><td><strong>Max Thermal Depth</strong></td><td>Limits the amount of thermal erosion that can happen on each pixel based on a thickness value.</td></tr><tr><td><strong>Deposit</strong></td><td>Controls the amount of sediment added back onto the terrain after the thermal erosion process.</td></tr><tr><td><strong>Add Sub</strong></td><td>Adjusts the balance between adding and removing sediment from the terrain. Leave it at .5 to have a consistent amount of material in the scene.</td></tr><tr><td><strong>Type</strong></td><td>Switches between two different computation modes.</td></tr></tbody></table>

## **Results**

<div><figure><img src="https://2837684122-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FM6zsxw2jbMYEZbKqEwpa%2Fuploads%2FEwuGfX3PJQ9NRBENRSFJ%2Freference_filters_basicerosion_hydraulic_01.webp?alt=media&#x26;token=ecf2ab6c-ef31-4e83-9f65-f90ecf2d41ee" alt=""><figcaption></figcaption></figure> <figure><img src="https://2837684122-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FM6zsxw2jbMYEZbKqEwpa%2Fuploads%2FRxRvdnAsI27OZJF27gJs%2Freference_filters_basicerosion_hydraulic_02.webp?alt=media&#x26;token=5afc6239-7ad4-465d-90b1-c4221d48fc3e" alt=""><figcaption></figcaption></figure> <figure><img src="https://2837684122-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FM6zsxw2jbMYEZbKqEwpa%2Fuploads%2F8GRB7guBzRL6pTSpo05P%2Freference_filters_basicerosion_hydraulic_03.webp?alt=media&#x26;token=e88b9372-0b7a-4060-95fd-0ee89d289d90" alt=""><figcaption></figcaption></figure></div>