At least Sembawang is quiet and peaceful. A few places you can go are:
1. Wak Hassan area - shoot lalang, macros, birds and can even catch couples making out in board daylight.
2. Sembawang Beach - kids at play, boats, ships and sometimes can see sailboat.
3. From Sembawang can go to SBWR, Lower Pierce res , upper Pierce res, Seletar res. These places are not very far away.
Sembawang may not offer much but its vicinity have lots of subjects to shoot. Not forgeting we have the only hot spring in singapore just nearby.