River simulation - different approaches than fluid simulation?

Question

I am in the middle of a project which needs to have a river flowing in it. (You may be familiar with my recent questions; they are all related.) Just for reference and imagination, here's a preview of the setting where the river should go.

As you can see, what I need to accomplish is:

1) something like an "ever-flowing river". It shouldn't start flowing from some point and expand from there. The final render (it is for a video) should be continuous and seamless.

2) a "caged" river. You should see it flowing as if we took a slice of it, (just like with the rest of the terrain)

I've been looking for tutorials, but the ones I've found tend to cover typical fluid simulations, which I'm not so sure can help me. I think I may need something more simple. Something like a cloth waving (for now it doesn't need to be realistic).

I ran into this video, and I was hoping for some hints on how the creator did that, because I don't understand... I can tell he used code... Maybe some of you can give me a kind introduction to code in Blender aiming to generate this kind of river.

I'm not interested by now in making something as realistic or detailed as the video, but it happens to fits my 2 initial requirements.

Answer 1

How to make a Procedural River

The Curve Modifier can deform an object so that it conforms to the shape of a curve object. Note that the curve object must be a curve, not a mesh.

1. For this technique, your river should be a long straight plane, about the width and length you want the river to be:
   SHIFTA -> Mesh -> Plane -> S -> X -> drag the mouse until the plane is as long as you want it to be

2. For this technique to be easy, don't move the river away from the 3D cursor

3. Make sure the location, rotation and scale of the river have been applied if they have been changed:
   
   • Select the river -> CTRLA -> Apply Location
   • CTRLA again -> Apply Rotation & Scale
4. Make sure the Origin of the river object is in it's middle. You can put the Origin there like this:
   Tools panel (T) -> Tools tab -> Edit section -> Set Origin -> Origin to Geometry
5. Now make sure the river mesh has enough subdivisions so that it can deform to the shape you want the river to be. If the river plane doesn't have enough subdivisions, it will not be able to bend to conform to the path we're going to create soon:
   Select the river -> Edit mode (TAB) -> Tools panel -> Tools tab -> Add section -> click Subdivide maybe 4 or 5 times -> exit Edit mode (TAB)
6. Now add a path curve:
   SHIFTA -> Curve -> Path
7. Scale (S) the path to be the length of the river
8. Select the path curve and go into Edit mode (TAB)
9. Make the path approximately the shape you want your river to be, then exit Edit mode (TAB)
10. Select the river object, then:
    Properties panel -> Modifiers -> Add Modifier -> Curve (under the Deform header)
11. Now on the Curve modifier's properties:
    Object -> select the path curve you made for the river (it will be called NurbsPath unless you changed it's name)
12. The river should now conform to the shape of the path curve
13. To change the position of the river along the path, translate/slide it along the X axis:
    Select river plane -> Grab (G) -> X -> drag
    Note: you can animate the position of the plane along the curve if you want
14. To position the river on your landscape, select both the river & the path curve and move them together. You MUST move them together at the same time otherwise they will get separated and behave oddly. If you accidentally get the plane and the path separated, do this:
    
    • Select the path -> SHIFTS -> Selection to cursor
    • Select the river plane -> SHIFTS -> Selection to cursor
15. If you want to change anything about the river's width or length, just select it, go into Edit mode and change it
16. If the river is not smooth enough, you can increase the number of subdivisions in Edit mode, as listed above

17. If you want to change the path of the river, select the path curve and edit it
    (Note: you can subdivide the path just like you subdivided the river plane:
    Select the path curve -> TAB -> Tools panel -> Tools tab -> Add section -> Subdivide)

18. To get the river to conform properly to your landscape, you can now edit the shape of the plane if you want, and then you can also edit the shape of the path

Answer 2

Make a Procedural River using the Ocean Modifier

This technique for creating a river allows the flow of the water to follow the path of the river easily. To do it, simply create an long, narrow Ocean object, then add a Curve Modifier to it.

1. Create a plane: SHIFTA -> Mesh -> Plane
   (NOTE: For this technique to be easy, DO NOT move the plane away from where it is created -- the 3D Cursor is where it is created)

2. Add an Ocean Modifier to the plane. You may want to scale down the resulting mesh.

   

3. Lengthen the Ocean object along the X axis by increasing the Repeat X value. This will be the river object:

   

4. Add a Path Curve: SHIFTA -> Curve -> Path
   (NOTE: Again, for this technique to be easy, DO NOT move the path away from where it is created -- the 3D Cursor is where it is created, so it will appear right on top of the river)

5. Scale the path so it is a little bit bigger than the river, then position it so it is in the middle of the river:

   • Scale: Select path -> S -> drag mouse

   • Move on X Axis: Select path -> G -> X -> drag mouse
     (NOTE: This is the one time you can move the path until you reach Step #10 below)

   

6. With the path selected, go into Edit mode and subdivide the path as many times as you have bends in the river. In your river, you have one bend, so just subdivide it one time:
   Select path -> TAB W -> Subdivide -> Exit Edit Mode (TAB)

   

7. Select the river and add a Curve Deform Modifier to it and set the Object to the path:

   

   This makes the river mesh conform to the shape of the path.

8. Now move the river so it is fully on the path:
   Select river -> G -> X -> drag mouse

   

9. Edit the path so it is the shape you want your river to be:

   

10. Position the river on your landscape. To do this, you MUST move both the path and river together, so select them both, then move them:
    Select path -> hold SHIFT while selecting the river -> G -> Position them

11. If you want to make the river narrower or wider in certain places, you can do that by select one of the vertices of the path and altering it with ALTS:
    Select path -> TAB -> select vertex -> ALTS -> drag mouse

    

Animating the River

To make the river flow, you now need to animate it's properties by setting keyframes for the Ocean Modifier's properties.