Engine: Unreal Engine 5.8.3
Plugin: WaterAdvanced (experimental), with Water and Niagara enabled
Problem: Adding a ShallowWaterRiver actor produces this warning in the Output Log:
“LogShallowWater: Warning: UShallowWaterRiverComponent::Rebuild() - no valid sinks, using the first source as a sink”
When Render State is set to LiveSim, the river water disappears from the viewport.
Setup: The level has one Water Body River (WaterBodyRiver) and a WaterZone.
Source River Water Bodies: WaterBodyRiver
Sink River Water Bodies: [name the actor you added as the sink, and its type]
What I’ve tried: [list what you changed, e.g. added a second Water Body River at the downstream end, cleared the log and forced a rebuild, restarted the editor]
Question: What makes a sink valid for ShallowWaterRiverComponent, and what should the sink be for a river that end
A sink counts only when it is a different Water Body the river can actually flow into, and the river spline’s last point sits inside that body’s water. One Water Body River with an empty sink list is exactly the warning you got: Rebuild() finds nothing and uses the first source as the sink, so the flow has no exit. Live Sim then has a degenerate velocity field and the surface drops out. The mesh is still there, which is why a non-live render state can still show it.
Do it in this order:
Put a Water Body Lake or Ocean at the downstream end. The last river spline point has to be inside that water, overlapped a little, not just nearby.
On the Shallow Water River, Source River Water Bodies is the river. Sink River Water Bodies is the lake or ocean. Do not point the sink at the same actor as the source.
The river and the sink have to be in the same Water Zone. A body in another zone is invisible to Rebuild(), so the warning stays.
Move a spline point or toggle the component so it rebuilds, then read the log again. The “no valid sinks” line should be gone before you switch Render State to Live Sim.
If the warning is gone and Live Sim is still invisible, the sim grid is coarser than the river, or the river depth is 0. Switch back to the non-live state to confirm the mesh, then lower the sim resolution on the Water Zone and give the river a real depth and velocity. A spline shorter than one cell sims to nothing.
The Drive link asks for a Google sign-in, so nobody else can see the video. A shot of the last spline point against the sink body is enough to tell whether the point is actually inside the water.