Concave floorpans...

I've got all the interior stripped out for some repairs.It has hole beside n/s torsion bar end.I've noticed the floor is concave in front floorpans.Is this to allow for torsion bar fixings or is this damage by speedhumps etc.
Found a few areas of corrosion but impressed for a 20 yr old car kept in the country all its life.
Thanks for any help.....