Geography- drainage basin
- Created by: Gina5395
- Created on: 15-02-19 19:15
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- Processes that shape fluvial environments
- Drainage Basin as an open system
- 3 types of systems
- Isolated- If nothing transfers in or out across its boundaries eg. The Universe
- Closed- If only energy can enter or leave eg water (hydrological) cycle
- Open- Both material and energy can exit or enter them eg. Drainage Basin
- DEFINITION: The Drainage basin is an area of land drained by its river and all of its tributaries. The boundary is known as the watershed
- Inputs- precipitation stores- Interception, surface store, soil moisture store, groundwater store Transfers- stem flow, infiltration, percolation, overland flow, throughflow, groundwater flow Outputs- evaporation, transpiration, channel runoff
- 3 types of systems
- Storm and annual hydrographs
- Hydrograph- A graph that shows river discharge and precipitation over time
- Storm hydrographs show the change in discharge caused by a period of rainfall
- Features of FLASHY: Steep limbs short lag time high peak discharge flooding likely
- Features of FLAT: Gentle limbs long lag time low peak discharge flooding unlikely
- Annual hydrograph- shows the variation in river discharge over 12 months
- Factors that influence discharge and the storm hydrograph
- Nature of the storm- how long the storm lasts, how heavy it is, type of precipitation and direction and speed of rain can impact hydrograph
- Permanent features
- Basin size and shape
- Small Basin- rain gathered and transferred quickly= short lag time+ storm flow
- Large Basin- Precipitation could take days or weeks to flow through= longer lag time eg Nile/Congo
- Relief- Steep slopes will shed water more rapidly than gentle slopes = mountainous areas flash floods
- Soil type- Permeable soils with high sand content = infiltration+ throughflow. This decreases the vol. of surface runoff
- Geology- Permeable bedrock= percolation which reduces vol. of water stored in the soil + transferred via surface runoff
- Drainage density- On surface rain drains rapidly if reaches channel quickly. increased drainage density= more efficiently drained
- Basin size and shape
- Temporary features
- Previous conditions- state of basin just before storm. recent rainfall= saturated soil drought= depleted groundwater stores= high storage
- Vegetation Cover- high vegetation= increased evapotranspiration= reduced precipitation transferred by river. In summer, deciduous trees intercept + if it enters soil= taken by roots
- Land use- human factor
- Vegetation change- different farming will alter amount+ speed flowing through basin
- Urbanisation- Afforestation= less flashy Artificial surfaces= flashy replacement of vegetated soil= less permeable eg tarmac Urban areas are highly engineered. Drainage systems= rapid drainage
- Storm hydrographs show the change in discharge caused by a period of rainfall
- River Discharge is the volume of water passing a particular point at a particular time
- Discharge = width x depth x velocity
- Hydrograph- A graph that shows river discharge and precipitation over time
- Drainage Basin as an open system
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