The floodplain of a river is the area most likely to naturally flood during heavy rains.
(The floodplain of a river; is; the area most likely to naturally flood during heavy rains) (the area most likely; to naturally flood; T:during heavy rains)
The floodplain of a river the area most likely
is to naturally flood
the area most likely to naturally flood during heavy rains
T:during heavy rains