River Regimes And Flood Hydrographs Flashcards
What is a river regime?
The annual variation in the discharge of a river, the amount of water that travels through a river and how this changes throughout the year
What might influence the river regime?
Urbanisation
Deforestation
Slope/ gradient
Intensity/type of weather event
Rock type
What is a perennial channel?
Continuous flow in parts of its bed all year round during years of normal rainfall
What is an intermittent channel?
Normally ceases flowing for weeks or months each year
What is an Ephemeral channel?
Only flows for hours or days following rainfall
What type of river regime is the river wye?
Perennial as it has continuous flow all year around
Where is the river wye drainage basin would you expect to find intermittent or ephemeral channels?
Some tributaries in the mountains of mid wales near the source of the Wye will be ephemeral because of the extreme variations in the mountain climate
What is common in hydrograph’s in areas with snow cover?
In the summer months there will be an increase in discharge because of snowmelt
In warmer climates around India what in the cause for an increase in rainfall in the summer months?
Monsoons
What is the main geology of the River Wye?
Predominantly characterised by old red sandstone
What are the characteristics of sandstone?
It is permeable
Which means it increases the lag time reducing the peak discharge
How does building new houses affect the river regime?
It creates impermeable surface and drainage systems with reduce lag time and increase peak discharge
How does damming affect the river regime?
Prevents the natural flow of the river so discharge/flow downstream in reduced
What are flood hydrographs?
Graphs that show how a drainage basin responds to a period of rainfall
What is peak discharge?
The highest recorded discharge following a rainfall event
What is peak rainfall?
The highest amount of rainfall per unit of time
What is the rising limb?
Shows how quickly the discharge rises after a rainstorm
What is lag time?
The time difference between peak rainfall and peak discharge
What is the falling limb?
Shows the reduced discharge once the main effect off run-off has passed
What is base flow?
The normal flow of the river when its water level is being sustained by ground water flow
What is the bank full discharge?
The level of discharge above which flooding will occur
What will the drainage basin of a flashy hydrograph be like?
Small circular basin as the water reaches the channel rapidly as it has a shorter distance to travel
Steep slopes
Impermeable surfaces
What will the basin size of a typical hydrograph be like?
A large basin that means water will take longer to reach the channel as it has a greater distance to travel
What will the basin shape be of a flashy hydrograph?
Circular basin will take less time for the water to reach channel as the extremities are equidistant
What will the basin shape of a flatter/ typical hydrograph be?
Elongated basin
Water will take longer to reach the channel format he extremities
What will the slopes be like for an area with a flashy hydrograph?
Steep slopes
Water flows down hill rapidly and reaches the channel quickly
What will the slopes be like in an area with a typical hydrograph?
Gentle slopes water can infiltrate into the ground and travel slowly to channel through soil/ rock.
What the hydrograph of an area with clay and thin soils look like?
Flashy hydrograph
As clay soil has a low porosity
So water infiltrates slowly
Thin soils are saturated easily
What will the hydrograph look like in an area with sandy soils and thick soils?
Flatter as sandy soils have a:
High porosity meaning water can infiltrate
Deep soils allow infiltration
What will the hydrograph look like in an area with impermeable rocks?
Flashy
Percolation wont occur
Increased surface run-off
What will a hydrograph look like in an area with permeable rock?
Flatter
Percolation can occur
What will the hydrograph look like in an area with a high drainage density?
Flashy
Many streams per km2 means water will reach the channel quicker
What will a hydrograph look like in an area with low drainage density?
Flatter
Small number of streams per km2 means water travels slowly back to the channel
What will a hydrograph look like in an area with thin grass?
Flashy
Little water intercepted
Little loss by evapotranspiration
More water reaches channel
What is a flashy hydrograph?
When there are sharp vertical increase sin river discharge
What will a hydrograph look like from an area with forest and woodland?
Flatter/ typical
More water intercepted
High evapotranspiration rates
Less reaches the channel and more slowly
What will the hydrograph look like in an urban area?
Flashy
More impermeable surfaces (road and drains) mean water gets to the channel quicker
What will a hydrograph in a rural area look like?
Vegetated surfaces intercept water and allow infiltration so water travels slowly to the channel
What will the hydrograph look like after high intensity rainfall?
Flashy
Rain falls faster then infiltration capacity so surface run-ff occurs water reaches the channel quicker
What will a hydrograph look like after low intensity rainfall?
Flatter/ typical
Water can infiltrate into soil where it travels slowly to river channel
What will a hydrograph look like after prolonged rainfall?
Flashy
Water table rises
Soil becomes saturated
Increased surface runoff
Water reaches channel faster
What will a hydrograph look like after short duration rainfall?
Flatter
Most water infiltrates into soil
Slower travelling through soil and rock
What will a hydrograph look like in an area with fast snowmelt?
Flashy
Water can’t infiltrate the frozen ground
Flows rapidly to channel
What will a hydrograph look like with slow snowmelt?
Flatter
Ground thaws is melt water can infiltrate into soil so moves slower to the channel
What will a hydrograph look like in an area with low evapotranspiration rates?
Flashy
Fewer losses from the drainage basin
Increased discharge
Hat will a hydrograph look like in a area with high evapotranspiration rates?
Flatter
Increased form drainage basin
Reduced discharge
