Hydrographs Flashcards
What is a river regime?
A graph showing changes in river discharge over the course of a year in responses to climactic change with the seasons e.g precipitation, temperature, evapotranspiration
What is discharge?
The amount of water in a river flowing past a particular point expressed in metres cubed per second (cumecs)
What do storm hydrographs show?
Changes in river discharge in response to a rainfall event - short term change
What is a hydrograph?
A graph that shows river discharge and rainfall over time
What is a flood?
When the capacity of a river to transport water is exceeded and water flows over its banks
What is base flow?
The base flow of the river represents the normal day to day discharge of the river and the consequence of groundwater seeping into the river channel
What is storm flow?
Storm runoff resulting from storm precipitation involving both surface and through flow
What is bankful discharge?
The maximum discharge that a particular river channel is capable of carrying without flooding
What is peak discharge?
The point on a flood hydrograph when river discharge is at its greatest
What is peak rainfall?
The point on a flood hydrograph when rainfall is at its greatest
What is lag time?
The period of time between the peak rainfall and peak discharge
What are the factors affecting the shape of a hydrograph? (4)
Size of drainage basin
Vegetation
Valley side steepness
Soil Type
How does the size of the drainage basin affect the hydrograph?
Small drainage basin = flashy
Large = subdued
How does the amount of vegetation affect the hydrograph?
Bare = flashy (deciduos in winter, low levels of interception, rapid movement through system)
Forest = subdued (deciduous in summer, high levels of interception and slower passage through the system: more water lost to evaporation from vegetation surfaces)
How does the valley steepness (relief) affect the hydrograph?
Steep valley = flashy (promote surface run-off)
Gentle sloped valley = subdued (allow infiltration + percolation)
How does soil type affect the hydrograph?
Impermeable = flashy
Permeable = subdued
What are the key physical aspects affecting a hydrograph? (8)
- Shape of drainage basin
- steepness of drainage basin
- high/ low density
- saturation
- impermeable/ permeable rock
- vegetation
- precipitation intensity
- large/ small drainage basins
What are the key human aspects affecting a hydrograph? (5)
- deforestation/ afforestation
- Agriculture
- Urban areas
- Growing population
- urbanisation
What are the characteristics of a flashy hydrograph? (3)
- short lag time
- high peak
- steep rising limb
What are the characteristics of a subdued hydrograph? (3)
- long lag time
- low peak
- gently sloping rising limb
How does drainage density impact hydrograph?
High = more streams + rivers/ unit area so water moves quickly to measuring point
LOw = few streams + rivers / unit so water more likely to enter ground and move slowly through basin
How does human activity impact hydrograph? (3)
- Urbanisation producing impermeable surfaces
- Deforestation reduces interception
- Arable land, downslope ploughing
How does little human activity impact storm hydrograph? (3)
Low population density, few artificial impermeable surfaces
Reforestation increases interception
Pastoral, moorland and forested land
How do pre-existing (antecedent) conditions impact hydrograph?
Basin already wet from previous rain, water table high, soil saturated, so low infiltration/percolation
Basin dry, low water table, unsaturated soils, so high infiltration/percolation
