5.2 drainage basin

• what are the three ways humans impact the drainage basin

  -deforestation/land use can accelerate processes

  -creating water stores (reservoirs)

  -abstracting water
• explain the general impacts of deforestation on the drainage basin

  -permanent drying- moisture regulation disrupted as lower evapotranspiration rates reduce amount of water returned to local atmosphere

  -climate increases as transpiration is cooling (3 warmer) can cause fires

  -destructive flood cycles as greater overland flow due to less interception
• why his evapotranspiration crucial in the rainforest

  because up to 80% of their water is recycled in their local atmosphere, so without it being retuned, there is a lack of rainfall
• what % of the rainforests water is recycled/ rains in their system

  80%
• how many degrees warmer can it get from reduced transpiration in the rainforest

  3
• how can changing land use affect drainage basins

  -deforestation often clears land for agriculture / mining

  -pastural land suffers from soil compaction which increases surface run off, thus speeding cycle up = destructive flood cycles
• is the El Nine phenomenon a physical or human impact

  physical
• why are hydroelectric dams being constructed in Brazil (human geography-superpowers)

  because becoming energy independent to escape exploitation of the periphery core model

  they are an emerging superpower so must have energy for increasing infrastructure, population. and economy, thus becoming a superpower
• which river is especially affected by the dams

  Madeira River
• fact to show the Madeira River being heavily affected by the dam construction in the Amazon

  at its lowest level in 60 years due to drastic changes in river flow
• explain the structure of dams and reservoirs


  dams built which creates a reservoir behind (upstream)

  it controls the flow of water downstream, generating hydroelectric power
• where are dams often built and why

  highland areas as the valleys contain the floods
• explain the physical impacts of dam construction upstream


  -massive areas of forest flooded, thus trees killed

  -reservoir becomes polluted as conditions favour methylation which produces mercury, thus reducing biodiversity (fish farms)
• why is the flooding causes by reservoirs even worse than deforestation

  because dead plant material anaerobically respires which produces methane swell as CO2, contributing even more to global warming
• what are the human implications of dam construction (downstream)

  -water insecurity

  -villages on the coastline vulnerable to erosion

  -farmer suicides
• explain the water insecurity as a result of dam construction

  disrupts natural flow of river, and limits inputs downstream which reduces channel flow
• explain why villages become vulnerable to erosion

  -villages built on coastlines due to optimum farming conditions

  -sediment inputs into the river make deposition a dominant process downstream, but the controlled channel flow limits the sediment input, thus erosion comes dominant process
• why is there a lack of sediment in the river due to dam construction

  sediment inputs of the river come from erosion upstream

  the sediment sinks to bottom of reservoir so much of it is prevented from moving downstream
• define a drainage basin

  an open system within the global hydrological cycle, where an area of land is drained by a river
• what is a drainage basin normally divided by


  a water shed- area of high land that diverts water down either side to create 2 drainage basins
• what is the input into a drainage basin

  precipitation
• what are the three types of precipitation

  convectional, frontal, orographic
• explain convectional rainfall


  solar energy heats the earths surface and the air directly above it, including the moisture for example of vegetation. this causes warm air to rise, cool and condense. it is not carried away by winds, thus rains in the same place.
• where is convectional most common and why

  tropical climates as it is very hot, however Britain can experience this in peak summer months
• explain frontal rainfall

  -where two air masses (warm air and cold air) meet, a depression is formed

  -the warm air is less dense and forced above cold air, causing it to cool and condense, thus precipitation is formed

  -at the warm front, warm air moves more quickly towards cool air, creating lighter but longer rain

  -at the cold front, cold air moves more quickly towards warm air, creating heavier but shorter rain
• what is the rain like at the warm front (frontal rainfall)

  lighter/drizzle, but lasts for longer
• what is the rain like at the cold front (frontal rainfall)

  heavy rain for short time periods
• in frontal rainfall, what two types of air meet

  warm air mass and cold air mass
• what happens to warm air in frontal rainfall and why

  rises above cool air as it is less dense
• explain orographic rainfall

  -where warm, moist air often travelling from sea onto land

  -the air meets high relief land thus forced to rise, cool and condense

  -this causes precipitation on the front side of the mountain

  -then dry air on the other side causes desert

  (rain shadow effect)
• what is another name for orographic rainfall

  rain shadow effect
• apart from types of precipitation, name .. features that can affect the drainage basin

  -seasonality

  -distribution

  -form

  -climate
• explain how seasonality affects the inputs of a drainage basin

  monsoon/ dry periods
• explain how distribution of precipitation affects the inputs of a drainage basin


  in larger drainage basins (eg) Nile, if in pits are only upstream (Ethiopia) then downstream (Egypt) will be starved of water
• explain how form of precipitation affects the inputs of a drainage basin

  different forms include rain, snow, sleet, hail

  -snow will cause delayed inputs whereas rainfall will be immediate
• explain how climate affects the inputs of a drainage basin

  at the equator it is low pressure, so rainfall much ,ore constant
• what is the pressure at the equator

  low pressure
• what are rainfall patterns like at low pressure

  constant
• what is a flow

  a process which transfers the precipitation into the drainage basin
• what is interception

  the direct intervention of vegetation which prevents precipitation reaching the ground. It can return it t the local atmosphere via evapotranspiration