Raise base of lead object containing flower (4)
I believe the answer is:
weir
'object containing flower' is the definition.
(a weir contains a river - something that flows)
I don't understand how the remainder of the clue works.
(Other definitions for weir that I've seen before include "River flow regulator" , "Structure for raising water level in river" , "Something that may be seen across river" , "fish may be trapped in this enclosure" , "Madagascan primate" .)