River Discharge

Question 1

what is river discharge

Answer 1

volume of water (in cubic metres m^3) that flows in a river per second
measured in cubic metres per second - m^3/s), or cumecs

Question 2

effect of… on river discharge:
precipitation
hot weather
removal of water

Answer 2

precip - more precip, higher discharge
higher the temp, the lower the discharge as rate of evaporation is higher
removal of water from river (abstraction) also reduces discharge

Question 3

what do hydropgraphs show

Answer 3

river discharge over a period of time

shows how the volume of water flowing at a certain point in a river changes over a period of time

Question 4

what do storm hydrographs show

Answer 4

river discharge around the time of a storm event

only cover a relatively short period (hours or days)

Question 5

what is peak discharge

Answer 5

highest point on the graph, where river discharge is at its greatest

Question 6

what is lag time

Answer 6

delay between peak rainfall and peak discharge
occurs as it takes time for the rainwater to flow into the river
shorter lag time can increase peak discharge as more water reaches the river during a shorter period of time

Question 7

what is the rising limb

Answer 7

part of the graph up to peak discharge
discharge is decreasing as less water is flowing into the river
shallow falling limb shows water is flowing in from stores long after its stopped raining

Question 8

what is bankfull discharge

Answer 8

point when water level reaches top of the river channel

Question 9

what is a flashy hydrograph

Answer 9

the graph has steep, roughly symmetrical rising and falling limbs

Question 10

physical factors affecting storm hydrographs (7)

Answer 10

1. drainage basin characteristics
   - large, steep-sided, circular, lots of streams
2. antecedant moisture (amount water present)
3. rock type
4. soil type
5. vegetation
6. precipitation
7. temperature

Question 11

how do drainage basin characteristics affect storm hydrograph

Answer 11

large drainage basins catch more precipitation, so have higher peak discharge
smaller basins have shorter lag times as precipitation has less distance to travel, so reaches main channel quicker
steep-sided DB have shorter lag times - water flows quickly downhill, can also increase peak discharge
circular basins more likely to have flashy hydrograph - all points on watershed are roughly same distance from point of discharge measurement - lots of water meets measuring point at same time, increasing PD
lots of streams (high drainage density) drain quickly, so shorter lag times

Question 12

how does antecedent moisture affect SH

Answer 12

if ground is waterlogged then infiltration is reduced and surface run off increases
surface runoff is faster than throughflow/baseflow so rainwater reaches the river more quickly, reducing lag time

Question 13

how does rock type affect SH

Answer 13

affects lag time /peak discharge
impermeable rocks dont store water or let water flow through them
this reduces infiltration and increases surface runoff, reducing lag time
peak discharge also increases as more water reaches the river in a shorter period

Question 14

how does soil type affect SH

Answer 14

sandy soils allow a lot of infiltration, but clay soils have very low infiltration rates
low infiltration rates increase surface runoff, reducing lag time and increasing peak discharge

Question 15

how does vegetation affect SH

Answer 15

affects lt/pd
intense storms will generate more precipitation and slows its movement to the river channel, increasing LT
interception is highest when theres lost of vegetation and deciduous trees have their leaves
more vegetation there is, more water is lost (through transpiration and evaporation) before it reaches the river channel, reducing PD

Question 16

how does temperature affect SH

Answer 16

affects lt/pd
hot, dry conditions and cold, freezing conditions result in hard ground
this reduces infiltration and increases surface run off - reducing LT and increasing PD
high temps can increase evapotranspiration, so less water reaches the channel - reducing PD

Question 17

how can human activity affect hydrographs (2)

Answer 17

in urban areas, much of the soil is covered with man -made impermeable materials like concrete
water cant infiltrate, which increases surface runoff, so water flows quickly into river - makes LT short and increases PD
man-made drainage basins can increase evapotranspiration, so less water reaches the river channel, reducing PD