floodplains

what is a floodplain

A flat area adjacent to the river carved out by rivers

why is it important to identify the location of a floodplain

- if you live in a floodplain you pay higher insurance rates

- building infrastructure: soil stability, soil erosion

hydrologic floodplain

every 1.5 yrs this area should experience flooding

Riparian zone

buffers formed b/w upland and aquatic zone

characteristics of a riparian zone

toe= organic rich

slope= fine grained

point bar

where active channel was, non horizontal

banks of flood plain act as

natural levees

levee

-highest elevation of floodplain

- sed. deposited near the channel edges

- restrict conductivity

first to be deposited when moving from high to low velocity

coarse grained

crevasse splay

- temporary delta when levee is breached

meander scrolls

former locations of the meander

oxbow lake

lake that forms in the bend of river where river no longer flows

Vertical accretion

-On top of floodplain deposits

- Can be colluvial or alluvial

-a Floodplain Process

Fluvial Terraces

abandoned floodplains formed when the river flowed at a higher level than at present; due to down-cuttings of river

Erosional terraces

- eroded down farther

- tread formed by lateral erosion

- when it occurs in Bedrock its called

• Bench, strath, or rock-cut terrace

depositional terraces

- River deposits build the river up

- Requires valley filling by something soft

-Subsequent incision

• Highest tread = highest elevation of valleyfloor

•

depositional terraces caused by

- Glacial outwash

- Climate change

- Change in sediment load, slope, or base level

Delta

A depositional plain where a stream enters a body of standing water

- The river supplies more sediment than can be redistributed

- have finer materials

- low gradient

-

fan

- Sediment eroded from the mountain is transported into a basin and deposited

- Coaser materials

- steeper

fan and delta similarities

- distributary channels

- fan shaped

- form by depositing sediments

What causes change in deltas?

- Sediment load

- Wave energy/turbulence

- Channel diversions through crevasses anddistributaries