River Wye Case study

• River Wye


  5th longest river in the UK, passes through a series of towns in central Wales
• Rhayader


  First town the River Wye passes through
• Cleddon Falls


  Waterfall located in the Wye Valley, formed where there were different resistant rock types
• Formation of Cleddon Falls

  1. Horizontal bands of resistant rock positioned above bands of less resistant rock

  2. Less resistant rock eroded faster than more resistant cap rock due to hydraulic action

  3. Cap rock undercut by less resistant rock, forming an overhang

  4. Overhang collapsed as erosion by hydraulic action and abrasion continued

  5. Plunge pool developed and deepened by boulders scraping against river bed (abrasion)
• Rhayader Falls


  Waterfall formed in a similar way to Cleddon Falls
• Replacement of Rhayader Falls

  1. In 1780, town built a bridge over the river

  2. This led to a series of mini rapids

  3. Increased volume of water in the river

  4. Faster flowing water increased the erosive power of the River Wye to create waterfalls and gorges like Cleddon Falls
• Formation of Letton Lakes

  1. River valley widens at lower levels (towns like Hay-on-Wye), allowing for formation of meanders through lateral erosion
  2. Faster flowing water (thalweg) erodes outer bend through hydraulic action and abrasion to form river cliff
  3. Deposition occurs on inner bend where flow is slower, forming slip-off slope
  4. Continued erosion and deposition causes meander neck to narrow
  5. During periods of high discharge (flood), river cuts through to create a new, straighter channel, cutting off the meander loop
  6. Forms ox-bow lake like Letton Lakes near Hereford 
• Where is the River Wye’s source?

  Plynlimon Hills
• What type of erosion is dominant in the lower section of the River Wye?

  Lateral erosion
• What geographical feature is formed by the River Wye's meandering?

  Floodplain
• What is a floodplain?


  Wide, flat area on either side of river
• What happens when the river floods annually?

  Material is deposited as river loses speed and energy
• How does the deposition of material during floods affect the riverbanks?

  Forms raised banks from larger material first
• What happens to levees after many floods?

  They build up higher to carry more water
• Why have levees been structured near Hereford?


  To help manage flood waters
• What are the processes involved in the formation of floodplains and levees in Hereford?

  • River Wye flows from Plynlimon Hills
  • Lateral erosion dominates in lower river section
  • River meanders to form floodplain
  • Annual floods deposit material as river slows
  • Larger material deposited first, forming raised banks
  • Levees build up higher after many floods
  • Levees structured to manage flood waters
• How does geology in the upper course influence geomorphic processes on the river Wye?

  • The upper Wye is mountainous with impermeable landscapes
  • This increases surface runoff and allows more water to flow into the river
  • This increases it’s erosive power vertically which creates steep V-shaped valleys
• How does geology influence geomorphic processes in the middle and lower courses on the river Wye

  • Landscape is made of sandstone (softer rock)
  • The river’s increasing volume and energy mean that there’s lots of lateral erosion, widening the river channel and forming meanders and steep river cliffs
  • Limestone outcrops in the middle and lower courses and more resistant to erosion, creating features such as Symonds Yat
• How does temperature influence geomorphic processes on the river Wye?

  • Temperatures can be much colder on higher ground close to the Plynlimon Hills source
  • This causes the ground to freeze regularly, leading to freeze thaw weathering which breaks up areas of exposed rock on valley sides
  • Increases likelihood of sudden mass movement such as landslides as valley sides are weakened
  • Material from landslides is added to river load, increasing its power to erode by abrasion
• How does rainfall influence geomorphic processes on the river Wye?

  • Plynlimon receives one of the highest rainfall totals in the UK
  • Heavy rainfall can flow quickly into the River Wye, causing the volume of water to rapidly increase
  • High volume of water can increase transportation of material by the river which increases erosion by abrasion
• Flood risk on the River Wye


  • 9000 properties estimated to be at risk from flooding

  This is caused by the number of impermeable surfaces within towns, which decrease the rate of infiltration and increase surface runoff, leading to large amounts of water rapidly entering the river
• What management has been implemented to slow the rate of entry and reduce flooding?

  • Storage ponds such as Letton Lakes, built to store surplus water during storms
  • Planting trees in the upper course to increase interception and storage by vegetation
  • Removable flood walls
• How has floodplain zoning reduced flooding?

  • Restricts development in high-risk flood areas, such as the natural floodplain above Hereford
  • In Hereford and Ross-on-Wye, flood-prone zones are designated for agriculture or recreational use Ria their than residential or commercial development
  • Allowing these areas to flood naturally reduces the risk of flooding to properties further downstream thus minimising damage
• Soft engineering methods to reduce flooding

  • Afforestation in the upper catchment have reduced the speed of surface runoff by improving soil infiltration and vegetation cover
  • This has helped reduce the likelihood of flash flooding downstream
  • Risks of mass movement have reduced as the tree roots stabilise the soil surface