rivers

• • The hydrological cycle is a closed system 
• • Stores are those places where water is held for a period of time. These include:
  • Water in the atmosphere in the form of water vapour or water droplets in clouds
  • Surface stores such as puddles, lakes, rivers and reservoirs
  • Interception is how precipitation is prevented from reaching the ground, usually by being caught on leaves or branches
  • Aquifers are permeable rocks such as limestone and sandstone which can hold water 
  • Ice and snow
  • Seas and oceans 
• Rivers flow from their source to their mouth. The course of a river may be affected by its gradient, the type of rock it passes through and human activity. Rivers have many uses including transporting goods, providing drinking water, generating electricity and supporting wildlife.
• • Transfers are the ways in which water is moved around the hydrological cycle. They include:
  • Evaporation
  • Condensation
  • Transpiration 
  • Evapotranspiration
  • Precipitation
  • Overland flow
  • Infiltration
  • Percolation
  • Through flow 
  • Groundwater flow
• Percolation is the transfer of water down into the rocks and aquifers
• through flow is the movement of water through the soil between the groundwater store ( water table ) and the surface
• groundwater flow is the flow of water through rock
• an aquifer is a layer of permeable rock that stores water underground
• Infiltration is the movement of water down from surface to soil
• Transpiration is the loss of water vapour from the stomata of a plant
• Evapotranspiration - The combined transfer of water vapour from the Earth's surface and plants.
• the drainage basin is the area of land drained by a river it is an open system
• features of drainage basins are - watershed , source , confluence , tributary , mouth
• a watershed is a boundary between two drainage basins, and is the point where two rivers meet
• a confluence is a point where two or more rivers meet and form a single river
• the mouth is where the river enters the sea or a lake
• the number of tributaries which connect to the main river channel is referred to as the drainage density. Lots of tributaries are a high drainage density. Drainage density is the result of the soil and rock under the surface , impermeable rock leads to high drainage density as the water cannot infiltrate so it flows over the soil.
• • The river regime is a record of the changes in discharge of a river over the period of a year
• a storm hydrograph

  • shows the changes in river discharge after a storm event
  • The graph shows a short period of time, usually 24 hours
• • The storm hydrograph has a number of features:
  • Base flow - normal level of discharge
  • Peak rainfall
  • Rising limb - shows an increase in river discharge
  • Peak discharge
  • Lag time - difference between peak rainfall and peak discharge
  • Recessional limb - discharge returning to normal (base flow)
• factors affecting river regimes are - climate , vegetation , land use , geology , soils , abstraction , dams , relief , drainage density
• how does climate affect a river regime

  Snow and ice melt leads to higher discharge - usually in the spring months

  High temperatures increase evaporation and reduce river discharge

  Higher rainfall in autumn and winter increases river discharge

  Convectional rainfall in summer or hot, moist climates increases river discharge
• how does vegetation effect a rivre regime

  Vegetation increases interception and infiltration leading to reduced overland flow and so lower river discharge

  Deciduous trees lose their leaves in winter decreasing interception, increasing overland flow and river discharge
• Land Use affecting river regime

  Concrete and tarmac in urban areas and built environments are impermeable leading to high overland flow - this is rapidly taken by drainage systems to the rivers/streams, increasing river discharge

  Geology affecting river regime

  Permeable rocks increase infiltration and percolation which reduces overland flow and decreases river discharge
• Soils affecting rr

  Soils which are compacted or frozen reduce infiltration, increasing overland flow and river discharge

  Abstraction affecting rr

  Water taken for irrigation and domestic use decreases the river discharge
• Dams affecting rr

  Dams control the flow of water, so can both increase and decrease river discharge

  Reservoirs experience higher levels of evaporation which can decrease river discharge

  Relief affecting rr

  Steep slopes increase overland flow which leads to increased river discharge

  Drainage Density affecting rr

  High drainage density leads to increased discharge, particularly after a rainfall ev
• Both fluvial and landscape processes shape the river and surrounding land in the drainage basin.
• • There are three types of weathering. These happen in-situ:
  • Physical - rock is broken down into smaller pieces. This occurs due to changes in temperature - such as freeze-thaw and exfoliation
  • Chemical rocks disintegrate and dissolve in slightly acidic rainwater 
  • Biological - rocks are broken apart by the roots of plants 
• The landscape processes of weathering and mass movement shape land surrounding the river channel.
• Fluvial processes shape the river channels and the landforms linked to them.
• The greater the discharge and velocity the more energy a river has.
• Fluvial processes include erosion, transportation, and deposition.
• Most (about 95%) of a river's energy is used to overcome friction.
• Energy in the river depends on the river discharge and velocity.
• The rest of the energy is used in erosion and transportation.
• There is more friction in the upper course of the river where it is shallow and narrow.
• • There are a number of types of mass movement where large-scale movement of material occurs
  • In river valleys there are two main types of mass movement:
  • Slumping where the slope is eroded by the river. This undercuts the slope causing large-scale movement of material down the slope
  • Soil creep the influence of gravity causes weathered material to slowly move down the slope towards the river
• Climate 

  In hot, wet climates, chemical and biological weathering are dominant

  Weather

  Heavy rain increases mass movement

  Slope

  Any slope over 5o experiences mass movement. The steeper the slope, the more mass movement there will be

  Geology

  Different rocks have different levels of resistance to weathering

  Altitude

  At higher altitudes, freeze-thaw weathering occurs frequently due to the low temperatures

  Aspect

  Physical weathering is more common on a colder, north-facing slope due to a higher likelihood of freeze-thaw

  Vegetation

  Roots bind the soil together which limits mass movement
• • Erosion is the wearing away of surfaces 
  • There are four erosion processes which change the shape of the river channel:
  • Hydraulic action - the force of water
  • Abrasion - when materials in the river scrape away banks and bed
  • Attrition - material hitting each other
  • Corrosion (solution) - acidic water dissolving rocks
• • Erosion can be mainly vertical or lateral: 
  • Vertical erosion is dominant in the upper course of rivers. It increases the depth of the river and valley, as the river erodes downwards
  • Lateral erosion is dominant in the middle and lower course of rivers. It increases the width of the river and valley as it erodes sideways