River Landscape Case Study (OCR GCSE Geography B)

River Case Study: The River Wye

• The Wye River is over 150 miles (120 km) long, it is the 5th longest river in the UK and descends over 700m along its course

• Both the Wye and Severn rise, within a few miles of each other, in the foothills of the Cambrian Mountains in Plynlimon, Wales 

• The Wye is a Site of Special Scientific Interest, a Special Area of Conservation and one of the most important rivers in the UK for nature conservation

• It is a relatively natural river, with minimal human activity along its course and is considered to be among one of the best rivers for large 'spring' salmon fishing in the UK 

• It flows through several towns including Rhayader, Builth Wells, Hay-on-Wye, Hereford (the only city), Ross-on-Wye, Symonds Yat, Monmouth and Tintern, and discharges (along with the River Severn) into the Bristol Channel just below Chepstow

Course of the River Wye

Upper course

• Landscape features are bog and heathland with underlying impermeable shale and gritstone, along with patches of limestone from past glaciation

• The river drops rapidly (approx. 600m over the first 50miles) and this generates enough energy to form steep-sided 'V' shaped valleys in places

• Sediment transportation is minimal and the river's bed is covered in stepped, large, angular rocks over which the river flows

• Rhayader (means 'waterfall on the Wye) is the first town the river passes through. The original waterfall was removed when the town's bridge was built, leaving a series of rapids (which are great for canoeists) but doesn’t absorb much water. This leads to higher volumes of water, faster flow rate and therefore, faster erosion by hydraulic action and creation of waterfalls and gorges at Cleddon Falls

• Above Builth Wells the river is about 27m wide, fast flowing and rocky and as it flows towards Hay-on-Wye 

Middle course

• Hay-on-Wye marks the point where the river passes into England

• It is a meandering river, more uniform in depth but with some very deep holes flowing onwards to Hereford

• The river has widened through lateral erosion

• Below the city of Hereford, the sweeping meanders cut laterally across the flat, valley floodplains

• The floodplains are formed from weak/permeable mudstone and sandstones, making the area particularly prone to flooding, but they are highly fertile through the deposition of fine sediments/alluvium

Lower course

• The Wye River floods annually and this helps with the formation of ox-bow lakes

• There are very few settlements close to the river between Ross on Wye and Symonds Yat due to the flood risk

• There are levees and floodplains due to deposition

• Symonds Yat has limestone outcrops rising over 120m above the river, forcing the river to wind around them, where several tributaries meet generating more erosive potential

• This is the start of the Wye Valley where the river has cut sheer-sided gorges, between broad valley reaches, with rounded hills and bluffs

• The geology is a mixture of more resistant limestone and less resistant sand and mudstone, which has produced the Wye gorge valley, running from Goodrich to Chepstow

• The river flows into the Severn Estuary where it mixes with saltwater 

Geomorphic processes

• Average rainfall in the Wye River basin is 725mm

• At Plynlimon it averages 2500 mm

• Much of the rainfall is in winter with little interception by vegetation, leading to rapid river flows and high rates of erosion

• Mass movement is dominant due to weathering and high rainfall

• Freeze-thaw is prevalent due to fluctuating temperatures in winter, which have created V-shaped valleys and interlocking spurs

Human activity

• Leisure and tourism including rock climbing, canoeing and kayaking

• Trees were cut down for shipbuilding, but have been replanted since WW2

• Limestone quarrying has changed the valley’s gradient

• Agriculture is dominant (90%), particularly chicken farming and water is used from the river for irrigation

Flood risk

• 9000 properties are 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 run-off, leading to large amounts of water rapidly entering the river 

• Management to slow the rate of entry and reduce flooding has included:

  • Storage ponds such as Letton Lakes that were built to store surplus water during storms

  • Planting trees in the upper course to increase interception and storage by vegetation

  • Removable flood walls 

Other management

• Strategies include:

  • Vegetation management to reduce rates of runoff by increasing surface cover and improving interception storage

    • The risk of landslides or other mass movement may be reduced by planting trees which also intercept rainfall and help bind the soil surface together

  • Afforestation has helped the River Wye, by stabilising the slopes which reduces the amount of mass movement

  • There have been positive and negative impacts of afforestation:

    • It has helped to reduce the height of floods by 20% through increased storage

    • However, the slower flow and deposition rate have decreased the natural formation of levees

  • Floodplain Zoning

    • Parts of the floodplain above Hereford are allowed to flood and this reduces the risk of flooding to properties further downstream

  • Improved slope stabilisation

    • This helps with flooding as more water can be held in the channel, although this has a knock-on effect downstream for deposition (lack of) and therefore, increased rates of erosion

    • It also can decrease the rate of natural levee formation