Answer:
Straight river is not a floodplain.
Step-by-step explanation:
Alluvium - It is a deposit of silt , clay and sand left by the flowing floodwater in the river valley or in the delta which typically produces a fertile soil.
Oxbow Lakes - An oxbow lake is the crescent-shaped lake which results through the meandering course of the river along the floodplain.
Natural levees - When the river occasionally floods and deposits the coarse alluvium such as the gravel onto the banks which slows down the flow of the river and the alluvial deposits settles down on the riverbed if the river does not flood and thereby raising the river level. Hence, the Natural levees raises the boundaries against rising water levels .
Straight river - Straight river is the typical river type present in the classifications in terms of their channel plain landforms . Hence is not a floodplain .