The River Tees, located in Northern England, flows from its source at Cross Fell in the Pennines travelling 130 km until it reaches its mouth at Teesside, where it meets the North Sea.
With a drainage basin spanning 1,800 km², the River Tees undergoes various processes that shape its course, influenced by both natural and human factors.
In the upper course of the River Tees (near its source), the landscape is characterised by mountains, hills and steep slopes.
There are V-shaped valleys in this region that form as the river descends rapidly through the moorlands. The force of the water erodes the rock, resulting in the formation of steep-sided valleys with a distinctive V-shape. Large rocks within the riverbed contribute to abrasion, which vertically erodes the riverbed.
A notable feature in the upper course is the High Force waterfall. This waterfall is formed by the interaction of a resistant igneous rock called dolerite, locally known as Whin Sill, with a softer rock called limestone.
The hydraulic action erodes the softer rock more rapidly, causing undercutting and leaving the harder rock to overhang. Over time, the unsupported hard rock collapses, causing the waterfall to move upstream and gradually leaving behind a gorge.
As the River Tees enters its middle section, adding tributaries increases its water volume, making the river wider and deeper.
Attrition in the upper section reduces large rocks to smaller pebbles. This reduces friction in the river, allowing it to flow faster. The increased energy from faster flow leads to more hydraulic action.
This process contributes to the formation of meanders, characterised by lateral erosion and the development of a floodplain. These features can be observed around Barnard Castle along the river’s course.
In the lower course of the River Tees, the meanders continue to grow, and the floodplain expands further.
This transformation is evident in the areas of Darlington and Yarm. In some locations, meanders may evolve into oxbow lakes.
Another feature present in the lower section is the formation of levees. Levees form when the river overflows during floods and deposits sediment along its banks. Over time, this repeated deposition builds up the levees, which help contain the river within its channel during future flood events.
Finally, the River Tees reaches its estuary, the point where it flows into the North Sea.
The estuary serves as a transition zone between the freshwater river and the sea’s saltwater, displaying unique ecological characteristics.