11.11 From precipitation to discharge: hydrographs Flashcards
(19 cards)
Discharge def
Amount of water in a river channel at a given time
Peak rainfall def
The highest amount of rainfall per time unit (the highest bar)
Rising limb def
Shows how quickly discharge rises after a rain storm (the first part of the line graph)
Peak discharge def
The highest recorded discharge following a rainfall event (top of the line graph)
Lag time def
The time difference between the rainfall and the peak discharge
Falling limb
Shows the reduced discharge once the main effect of the runoff has passed
Because flow
The normal flow of a river when its water level is being sustained by groundwater flow
Bankfull discharge def
(Not always shown on hydrographs) will be drawn as a horizontal line marking the level of discharge above which flooding will occur as the river will burst its banks q
What are the two types of hydrographs
- long lag time (delayed) storm hydrographs
- short lag time (flashy) hydrographs
When do flashy hydrographs occur
When a river responds rapidly to a storm event and there is a flash flood
Flash flood def
A sudden, brief, dramatic flood event
What are 7 factors that will make a flashy hydrograph?
- high drainage density
- steep slopes
- impermeable rock
- thin soil
- moor land
- limited use of river
Why does high drainage density lead to a flash flood
More streams allows rain to reach river systems quickly
Why do steep slopes cause flash floods
Faster run-off takes water to river system quickly
Why does impermeable rock cause flash flooding q
Water passing through soil moves much slower than on the surface
Why does thin soil lead to flash floods
Deep soil can hold more water, slowing it down
Why does moor land lead to flush floods
Less vegetation means less interception and roots to absorb water
Why does urban land use lead to flash floods
Drains and tarmac increase speed of run-off
Why does limited use of river lead to flash floods
No control on a river (dam could have been built to control flow)
