Unit 7: streams and flood processes

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the regulatory floodplain is based on areas flooded during a

100 year floos

What is avulsion?

A flooding stream permanently leaves its old channel to form a new floodplain channel.

Delta

A landform made of sediment that is deposited where a river flows into an ocean or lake

Why does a stream bottom erode more deeply when its water level rises in a flood?

Its water level rises, so water velocity increases and it can carry more sediment.

recurrence interval flood formula

T=(n+1)/m n=number of years in flood record m=rank of flood in question

Floodplain

The area subject to flooding by a stream overflowing its levees

How does urbanization affect flooding?

Urbanization causes increased runoff because less water infiltrates the ground.

when a flood is classified as a 50 year flood it is understood that

a flood of thag size occurs on the average of once every 50 years

any surface water flowing through a channel under the influence of gravity is

a stream

difference between alluvial fan and delta

alluvial fans are in land deltas are in water

If a 100-year floodplain was flooded in 2003, when should we expect the next 100-year flood?

anytime

lowest depth a stream can erode its channel

base level

flood

excessive discharge

characteristic of a downstream regional flood

extended rise of river elevation for weeks large storm systems or extended rainfall floodplains covered in flood waters

as a result of the great floods along the mississippi river in 1993 the FIA now has chosen the 500 year flood level as the regulatory floodplain? true or false?

false

what can occur in upstream prt of a drainage basin during brief heavy rainfall

flash floods

people die from what natural disaster the most?

flash floods and flooding

With urbanization of the upstream drainage area, what changes can be expected in the height of the 100-year flood?

greater height

is the 100 year floosplain size a reliable indicator for future floods?

no

hydrograph

plot of stream stage or discharge vs time

dams are designed to reduce flooding by

providing storage for flood water

upstream part of a drainage basin when heavy rainfall occurs there may be

rapid runoff flash floods

how woukd a hydrograph for a stream change if major urban growthh occured

shorter lag time and higher peak discharge

channelization of streams reduces flooding by

speeding the passage of floodwaters

stream velocity

the distance the water travels in a given amount of time

discharge of a stream is

velocity times cross sectional area volumw of water flowing pasr a given point in a certain amount of time product of velocity times its width times the average depth at a particular point

stream gradient

vertical drop in elevation of the stream channel divided by the horizontal distance it travels

what leads to the failure of a river levee?

water overtopping the levee erosion of levee slumping of banks of levee into the river seepage through levee

why does stream level rise without water running into it

water seeping into the ground raises the water table

characteristics of a downstream channel

wide floodplain natural levees shallow gradiant

do natural levees created during flooding prevent later floods?

yes

do flash floods cause deaths?

yes bc hard to predict


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