topic 4 : storm hydrographs

topic 4: the uk's evolving physical landscape

storm hydrographs

to measure a river's flow and show the change in river discharge over a short period of time after a storm

hydrograph

record of river discharge over a period of time

river discharge

cross sectional area x river mean (average) velocity

discharge

the amount of water in a river at any given point and time

what is discharge measured in?

cumecs (cubic metres per second)

velocity

speed of a river

what is velocity measured in?

m/s

lag time

the time taken between peak rainfall and peak discharge

rising limb

shows the increase in discharge on a hydrograph

falling limb

shows the return of discharge to normal / base flow on a hydrograph

peak rainfall

maximum rainfall (mm)

peak discharge

maximum discharge (cumecs)

base flow

normal discharge or flow of the river

list five factors influence the storm hydrograph

vegetation, urbanisation, intensity and duration of rain, saturated soil, climate, drainage basin size

why would vegetation influence the storm hydrograph?

influences the amount of rain intercepted more vegetation means more interception, so it takes longer/less water reaching the ground and therefore the river

why would urbanisation influence the storm hydrograph?

more impermeable surfaces so therefore there is no infiltration to rapid run-off which means the peak flow is achieved quickly

why would the intensity and duration of rain influence the storm hydrograph?

in a downpour the ground isn't able to abosorb the water quickly enough therefore the water reaches the river quickly

why would saturated soil influence the storm hydrograph?

this has absorbed as much water as it can therefore anymore water will run-off, reaching the water quickly

why would the climate influence the storm hydrograph?

extremes in weather e.g in winter the ground will freeze, so the water cannot infiltrate the ground causing rapid run-off

why would the drainage basin size influence the storm hydrograph?

if it's a large area it will have more land to drain and therefore more water

storm hydrograph