Background

The River Tees is 100 km in length and has its source in the moorlands of Cumbria. Altitude at the crest of the Pennines is 600 metres. Consequently annual rainfall is 1200 mm. The marshy land soaks up the rain and feeds the Tees tributaries. The land is often saturated and therefore, excess water creates streams.

River features

V-shaped valley

Just 100 metres downstream the river has a distinct V-Shaped valley, although it is still a narrow stream. It carries sediment in three ways:

• 1. Solute load: Material chemically dissolved in the water
• 2. Suspended load: the force of the water carries minute particles.
• 3. Bedload: Larger material is carried due to increased velocity (rock and boulders)

5 km from the source, the bedload has become smooth and rounded due to erosion

Highforce Waterfall - an erosional river landform

The downward gradient and high flow rate means that the river can carry large rocks and boulders. As a result, this part of the river has high erosion rates. The Tees has a flow rate of 20 cubic metres per second. The changing rock type forms Highforce waterfall. The waterfall contains Whinestone. The water flows over the hard layer of rock hitting the softer rock below. This means that erosion such as abrasion and hydraulic action takes place. The softer rock is eroded forming a plunge pool. This plunge pool gets larger over time. Consequently, the hard rock above is undercut and falls away. As a result, the waterfall retreats upstream. This also creates a gorge.

Meanders

95% of the water energy is lost due to friction. It declines as it moves further downstream. The river can no longer carry the large pieces of sediment that it could further upstream. Therefore, bedrock is smaller. Meanders are created as the gradient is reduced and the river begins to widen and slow. The faster flow on the outside of the bend and the slower flow on the inside encourage erosion and deposition respectively. Consequently, the river channel is constantly changing its appearance. Ox bow lakes develop as the river changes direction due to erosion and deposition.

At Stockton, the Victorians changed the natural course of the river by cutting off the meanders so that ships could navigate the stretch from the mouth. At this point of the river sediment is small die to the loss of power in the river.

D.Drake 2009