r&b: floodplains

floodplain

flat land that immediately surrounds a channel that is submerged at times of high discharge

when does incision occur on a floodplain?

when erosion is greater than deposition

when does aggradation occur on a floodplain?

when deposition is greater than erosion

what two ways are floodplain sediments deposited?

deposition of bedload as channel migrates; deposition of suspended load over the banks

when does a bedload floodplain occur?

as channel meanders across valley, bedload is deposited as point bars (typically a thin layer of suspended sediment is on top); repeated point bars make a scroll bar, which then cuts off into oxbow lake

what landforms are indicative of bedload floodplains?

scroll bars and oxbow lakes

when does a suspended load floodplain occur?

when natural levees form along a channel due to debris being left during floods, only suspended sediment later on is light enough to be carried by water over the levees during floods; once outside channel, suspended load is deposited cause of lower velocity, which leads to murky swamps

what landforms are indicative of suspended load floodplains?

buckswamps, splays, levees

splay

deposit of coarse material due to levee failure during a flood

what other landforms are found on floodplains?

alluvial fans and terraces

alluvial fan

fan-shaped deposit at mouth of gulley/valley; appear when streams encounter sudden gradient drop (such as when leaving a mountain)

bajad

structure formed when multiple alluvial fans join together

terraces

old floodplains that were abandoned due to base level change, sediment/water load changes, or uplift