Rectangular shaped culverts

Please add the option to import or create rectangular or square culverts, since the shape of a culvert influences the throughput of water. This way, culverts can be more accurately modelled. Also, rectangular culverts can be used to model tunnels in the 3D world.

For more information, see:

https://support.tygron.com/wiki/Culvert_rectangular_height_(Water_Overlay)