The River Tees

High rainfall and steep upper slopes

The source area near Cross Fell is one of the wettest and highest parts of England, so the young Tees carries plenty of water and flows down steep gradients. This gives it the energy for vertical erosion, cutting a deep V-shaped valley into the moorland through hydraulic action and abrasion.

Hard rock lying over soft rock

At High Force the river crosses the Whin Sill, a tough layer of dolerite sitting on weaker limestone and sandstone. The soft rock beneath erodes faster, undercutting the hard lip until blocks collapse into the plunge pool. The waterfall retreats upstream each time, leaving a steep sided gorge below it.

Lateral erosion in the middle course

As the gradient flattens near Yarm, the river swings sideways rather than cutting down. Faster flow on the outside of each bend erodes river cliffs while deposition on the inside builds slip off slopes, so meanders grow and migrate. When a loop is cut through in flood, it is abandoned as an oxbow lake.

Deposition near the mouth

In the lower course the Tees carries a heavy load of fine sediment across almost flat land. During floods the water spills over the banks, loses energy and drops its coarsest load first, building natural levees. In the sheltered estuary the finest material settles out as wide mudflats at Teesmouth.

Primary

• High Force drops 21 metres over the Whin Sill, the biggest waterfall in England, with a gorge stretching downstream.
• Large meanders and oxbow lakes have formed on the flat land near Yarm.
• The lower course has a wide floodplain with natural levees and an estuary of mudflats at Teesmouth.

Secondary

• The waterfall retreats slowly upstream as the soft rock beneath the dolerite lip is undercut.
• Fertile floodplain soils built from deposited silt support farmland in the middle and lower valley.
• Flat reclaimed land beside the estuary made space for ports and heavy industry.

Social

• High Force and the Pennine Way bring walkers and visitors into Upper Teesdale.
• The white water course at the Tees Barrage is used for canoeing and rafting.
• Towns such as Yarm, Stockton and Middlesbrough grew up along the river and its crossings.

Economic

• Tourism at High Force earns income for the surrounding estate and villages.
• The estuary supports port trade and chemical and steel related industry at Teesmouth.
• The £55 million Tees Barrage encouraged waterside development around Stockton by keeping the river level constant.

Environmental

• The mudflats at Teesmouth are feeding grounds for wading birds and home to seals.
• The barrage changed the river above it from tidal and muddy to a constant freshwater level.
• Upper Teesdale's valley is a protected landscape with rare plants growing on the sugar limestone.

Immediate

• The Environment Agency issues flood warnings for towns along the river.
• The barrage gates are operated to manage water levels through Stockton.
• Footpaths and viewing areas at High Force are maintained to keep visitors safe near the gorge.

Long term

• The Tees Barrage, opened in 1995 at a cost of around £55 million, permanently holds the river at a steady level above Stockton.
• The estuary has been dredged and land reclaimed over many decades to serve industry at Teesmouth.
• Upper Teesdale is managed as a National Nature Reserve to protect its geology and rare habitats.
• Nature reserves on the estuary, such as Teesmouth, protect the remaining mudflats alongside industry.