HYDROGRAPHS Flashcards
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Precipitation
In heavy rainstorms, rainfall is often far greater than the infiltration capacity of the soil, so there’s increased overland flow which means there are rapid rises in river levels.
If rainfall is prolonged, the ground may become saturated and overland flow increases
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Drainage density
High drainage density means there are lots of tributary rivers, and water can make its way to the main river more quickly, decreasing the amount and time it takes for water to reach the river, possibly causing flooding
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Basin shape
The more circular the shape of the basin, the shorter the lag time as all the water reaches the river at the same time, and the more likely the river is to flood
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Basin size
Smaller basins can have shorter lag time as the water will take less time to reach the river
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Vegetation
Flooding is more likely to occur in deforested areas as there’s less vegetation to intercept the water and absorb it
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Relief/steepness
Steep slopes means water will reach the river faster and so there’s less time for infiltration and percolation as overland flow speeds up with gravity , meaning there’s a steeper rising limb
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Geology/ underlying bedrock
Impermeable ground layers means water can not infiltrate and flow into the soil, so overland flow increases and water reaches the river faster e.g. granite is impermeable
Clay based soils have less pore spaces, meaning water flows over the land and cannot infiltrate
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Soil depth
The shallower the soil, the less water it can take and the easier it will become saturated, so water flows overland instead of through the soil, in a slower way
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Climate and season
During winter, not as much storage and interception will occur as the ground is frozen, which leads to rapid surface runoff as precipitation can’t infiltrate into the soil
There’s less vegetation to absorb water
SHORT LAG TIME AND HIGH PEAK DISCHARGE
Land use
Urban areas have impermeable surfaces, so less there’s infiltration and percolation and increased surface runoff. There’s also no soil for storage of water, and so water reaches the river more quickly and all at once, decreasing lag time
LONG LAG TIME AND LOW PEAK DISCHARGE
Precipitation
Steady rain fall means there is more time for rain to infiltrate into the soil
If there’s snow, steady melting may mean there’s a longer lag time as it takes longer for the snow to melt and reach the river
LONG LAG TIME AND LOW PEAK DISCHARGE
Drainage density
Low drainage density means there are less rivers that lead directly to the main river so water infiltrates into the soil and is forced to take longer routes into the river
LONG LAG TIME AND LOW PEAK DISCHARGE
Basin shape
Oval shape means water takes longer to reach the river as water has different distances to travel, so not all water reaches the river at the same time, giving the river more time to cope
LONG LAG TIME AND LOW PEAK DISCHARGE
Basin size
The bigger the basin, the more time it takes for water to reach the main river, so the less water will reach the river at once
LONG LAG TIME AND LOW PEAK DISCHARGE
Vegetation
Areas with significant vegetation intercept more water and absorb more water, storing it, as well as losing it to evapotranspiration
Plants also absorb water moving through the soil, reducing the through flow that reaches the river
