River Landscape Case Study (OCR GCSE Geography B)
Revision Note
Written by: Jacque Cartwright
Reviewed by: Bridgette Barrett
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
Worked Example
To what extent has the impact of human activity been greater than geomorphic processes, on the formation of landforms in your chosen river basin?'
(8 marks)
Answer
The river I have studied is The River Wye. At 150 miles long, the river Wye is the UK's 5th longest river and one of the UK's main rivers. Its source is in the foothills of the Cambrian Mountains in Plynlimon and flows through central east Wales into England and back into Wales to discharge into the Severn Estuary at Chepstow. I agree that humans impact a river's basin but not more so than geomorphic processes. Left alone, a river will naturally collect and discharge precipitation and return it to the water cycle. At Rhayader, the original waterfall was removed when the town's bridge was built, this left behind small rapids (which are great for canoeists) but doesn’t absorb much water or slow the rate of erosion. 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. Humans have built bridges at major points along the course of the river, which has further impacted the natural flow of the river. To reduce the risk of flooding, afforestation has been done towards the source and along the middle course vegetation has been planted to increase the rate of infiltration, particularly during periods of prolonged rainfall.
Before Hereford, the river is allowed to flood naturally to prevent flooding of homes south of Hereford due to the amount of impermeable surfaces within the city. These surfaces increase the rate of run-off, leading to larger amounts of water quickly entering the river's channel and increasing the likelihood of flooding. Other strategies such as removable flood walls have prevented flooding, but this moves the problem downstream and increases the rate of flooding elsewhere.
Geomorphic processes do shape the river, through creating waterfalls in the upper course of the river, meanders in the middle course and floodplains in the lower course. Erosion processes such as hydraulic action and abrasion help to form the plunge pool of a waterfall whilst lowering the gradient of the river's course. All the while the river is increasing in velocity, as tributaries from other parts of the basin, join the main channel. This helps to form meanders in the middle to lower course and deposit alluvium during floods. I believe that geomorphic processes have the biggest impact on river basins as they occur the whole length of the river whereas, human activity such as flood zoning only work on small sections of the river such as the middle course.
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