River Dischange Flashcards
What is river discharge measured in?
Cumecs, cubic metres per second (m3/s)
What do storm hydrography show?
Shows the changes in river discharge around the time of a storm
What is the peak discharge?
The highest discharge in the redid of time you’re looking at
What is the lag time?
The delay between peak discharge and peak rainfall
What is the rising limb
The increase in river discharge as rainwater flows into the river
What is the falling limb
The decrease in the river discharge as the river return to its normal level
What is there a lag time between peak rainfall and peak discharge
Most rainwater doesn’t fall directly in the river channel and there is a delay as rainwater gets to the channel.
How does the rainwater enter the river channel
Flowing overland quickly (surface runoff), soaking into the ground (infiltration) or flowing slowly underground
How does surface runoff affect river discharge
The more water that flows as runoff, the shorter the lag time will be. This means the discharge will increase because more water gets to the channel in a shorter space of time
How does temperature affect discharge
Hot, dry condition and cold, freezing ones result in hard ground, which increase ps runoff so lag time is decreased so discharge increases
How does the amount and type of raindpfall affect river discharge
Lots of rain and short heavy periods of rainfall means increased runoff, lag time is decreased so discharge increases
How does previous weather conditions affect river discharge?
After lots of rain soil can become infiltrated
More rainwater cannot infiltrate so run of is increased
Lag time decreased so discharge increases
What is river discharge?
The volume of water that flows in a river per second
How does land use affect river discharge
Urban areas and they’re covered with impermeable materials like concrete, these increase surface runoff
lag time is decreased so discharge increased
How does relief affect river discharge
Lots of runoff occurs on steep slopes
Lag time is decreased so discharge increases
How does rock type affect river discharge
Water infiltrates through pore space in permeable rock and flows cracks in pervious rock, so there isn’t much runoff
Lag time is increased and discharge decreases
Water cannot infiltrate impermeable rock so there is lots of runoff lag time is decreased and discharge increases
When does flooding occur
When the level of the river gets so high it spills over its banks
What does the discharge mean in regards to river level
The river level increases when the discharge increases because a high discharge mean there is more water
Why may prolonged rainfall cause flooding
After a long period of rain, the soil becomes saturated. Any further rainfall can’t infiltrate which increases runoff into rivers. This increases discharge quickly, which can cause a flood
How may heavy rainfall cause flooding
Heavy raindpfall means there’s a lot of runoff this increases discharge quickly which can cause flooding
How may relief cause flooding
If a river has a steep sided valley, water will reach the river channel much quicker because water flows much quicker on steeper slopes. This increases discharge quickly which can cause a flood
How may snowmelt cause flooding
When a lot of snow melts it means that a lot of water goes into a river in a short space of time. This increases discharge quickly which can cause flooding
How may deforestation cause flooding
Trees intercept rainwater on their leaves which then evaporates. Trees also take up water from the ground and store it. This means cutting down trees increases the volume of water that reaches the river channel, which increases discharge and makes flooding more likely
How may urbanisation on the flood plain cause flooding
Buildings are made of impermeable substances such as concrete which increases surface runoff and drains quickly take runoff to rivers. This increases discharge quickly which can cause a flood
