Hydrographs Flashcards
What are hydrograph
Graphs which show river discharge over a GIVEN PERIOD OF TIME and show the RESPONSE OF A DRAINAGE BASIN AND ITS RIVER to a given period of rainfall
What is discharge measured in
Cumecs
What is discharge
The volume of water passing any one point at any given time
How is discharge calculated
Multiply the rivers cross sectional area by its velocity
What is a storm hydrograph
A graph that allows us to examine the relationship between a single rainfall event and discharge
What are the 3 labels on a storm hydrograph axis
River discharge (cumecs)
Rainfall (mm)
Time
What are the 8 labels on a storm hydrograph
Peak rain fall
Peak discharge
Lag time
Rising limb
Falling limb
Base flow
Storm flow
Bank full capacity
What is storm flow
Additional flow contributed by all the rivers discharge from a period of rain (area under the curve 1)
What is lag time and what is it measured in
The time taken between peak rainfall and peak discharge measured in minutes
What is the rising limb
The increasing curve on the hydrograph leading to peak discharge
How does the rising limb rise
Channel catch
Overland flow
Through flow
What is the falling limb and describe its appearance
The recession limb is when discharge decreases and the rivers discharge level falls.
It has a gentler gradient than the rising limb as most overland flow has been discharged and through flow and base flow are the main sub surface water transfers making up the river water
Two types of storm hydrograph
Flat
Flashy
Describe a flat storm hydrograph and it’s likeliness of flooding and why
Gentle limbs
Low peak discharge
Long lag time
Large base flow
Flooding unlikely due to permeable soil and rocks and forests
Describe the characterises of a flashy hydrograph and its likeliness to flood and why
Steep limbs
High peak discharge
Short lag time
Small base flow
Likely to flood due to impermeable soil and rock, urbanised surfaces and drain and guttering systems
What three factors make a flashy storm hydrograph
Prolonged rainfall: saturated ground and increased surface runoff
Intense storm: heavy rainfall intensity may be greater than infiltration capacity of the soil likely to cause flash floods
Snowfall: when snow melts there will be a great increase in surface runoff
6 factors affecting a drainage basin
Size of basin
Soil type
Rock type
Relief
Vegetation cover
Urbanisation agriculture
How to answer stores and transfers question 3 points
1 store
Describe change giving figures
What has changed
What effect does it have
2 transfer
Describe change giving figures
What has changed
What effect does it have
How to describe and explain with 2 characteristics
Describe with facts and figures
State characteristic and explain what it is and its impact and link back to question
How to describe and explain changes in land use
State change giving facts and river
Go through EACH land use change
Give full detail example
Why does relief affect hydrograph
Steep upland valleys increases surface runoff as the gravitational pull reduces infiltration and subsurface transfers which means water reaches the river channel more quickly, producing a storm hydrograph
Why does agriculture affect hydrographs
Crops create a higher potential of infiltration as crops take up water for photosynthesis and transpiration which means water is lost in the atmosphere and water reaching the channel is reduced
How does urban areas affect hydrographs
FLASHY HYDROGRAPH
increased exposure to flooding
Elaborate drainage due to drains and sewers which speed up water reaching the river via surface runoff
Construction of buildings replace permeable surfaces (grassland) with non permeable surfaces (tarmac and concrete) which means no sub surface transfers
What is an annual hydrograph
A graph which shows the variation in a rivers discharge over 1 year
October-September
