How to find the height of a mesh at any point (x,z)?

Hello, im trying to make a buoyancy model and for a flat plane it works well, however i want it to be able to react to waves and any water surface simulation so i need to find a way to find the height of the mesh at any point so that the volume is correctly calculated as well as the center of buoyancy.

I used perlin noise to modify the mesh quickly (just for testing). The collider stays flat while the mesh has been modified. so (unless there is a way to raycast agaisnt meshes) any raycasting wont work.

I could try use the y values for modifying the mesh to use in the calculations but i worry that this is too rigid and would have to be recoded for different surface simulations.

Any help would be much appreciated.

Thanks.