Hydrograph

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Factors affecting storm hydrographs

Intensity & duration of storm-If both high theyll produce steep rising limb as the infiltration capacity will be exceeded.

Temperature-High means evapotranspiration is higher reducing discharge. Cold may freeze the ground therefore preventing infiltration meaning water reaches the river quciker.

Vegetation-In the summer there are more leaves on trees meaning there is ore interception so less water reaches the river.

Slope angle-Steep sided uplan drainage basins the water reaches the channel much more quickly producing a shorter lag time and steeper rising limb.

Antedecent rainfall-If there has been heavy rain in the previous 2 days then soil may be saturated meaning there will be a steep rising limb.

Urbanisation-Main human impact. Reduces lag time and increas discharge. e.g. increased permeable surfaces, drains and sewers that transport water to rivers quickly.Water runs quicker over impermeable surfaces like caravan parks, lag time is reduced.

Size of drainage basin-Small usually means water will reach the river quicker, so greater risk of flooding. Rain reaches river quicker in a round drainage basin.

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Erosion

  • Abrasion-The scraping, scouring and rubbing actions of materials carried along by a river. Rvers carry fragments of rock and dratg them along the bed.
  • Hydraulic Action-Caused by the sheer power of the moving water. The movement of loose unconsolidated material due to frictional drag of moving water. As velocity increases the flow can lift a larger number of particles.
  • Attrition-Is the particles in the river banging into one another and becoming smaller, smoother and more rounded, Consequently particles become smaller downstream.
  • Corrosion-Active on rocks that contain carbonated such as limestone and chalk. The minerals in the rock are dissolved by weak acide in the river water and carried away.
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Transportation

Traction-Large stones and boulders are rolled along the river bed moving donstream. This only happens at times of high discharge.

Suspension-very small particles of sand and silt are carrie along the flow of the river. The material is not only carried but picked up too. This gives the brown appearance.

Saltation-Small stones bounce along the channel bed. This is associated with high energy conditions. As particles move they may dislodge other particles upwards.

Solution-Dissolved materials are transported in the water.

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The Hjulstrom Curve

  • Shows size of different loads of different materials and the velocity the river needs to be to transport the materials.
  • Shows the amount of particles that are eroded. The curve in this section is because it takes different velocities for different materials to be eroded.
  • Shows paricles deposited 
  • Shows particles transported
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