River Characteristics and Profiles

Following the River Tees from source to mouth

A river’s course is its route from its source to its mouth. The upper, middle and lower courses describe successive parts of that journey, rather than three sections of equal length.

The River Tees, in north-east England, begins at Cross Fell in the Pennines and flows towards the North Sea at Teesmouth. Its landscape changes from steep upland valleys to broad lowland floodplains. These changes involve both the river channel—the hollow containing the flowing water—and the much larger valley around it.

Two different views help us understand these changes. A long profile follows the river downstream and shows how its height and gradient change. A cross-profile cuts across it: a channel cross-profile shows the river’s width and depth, while a valley cross-profile includes the valley floor and surrounding slopes.

Three contrasting parts of the Tees

Near Cross Fell, the upper-course channel is narrow and shallow, with a rough, rocky bed. It lies within a steep-sided, V-shaped valley. The river has a steep gradient, but its discharge is relatively small because few tributaries have joined it. Large, angular pieces of sediment are common.

Around Barnard Castle, the middle-course channel is wider and deeper. The gradient is gentler, and the valley is wider, with gentler sides and areas of floodplain beside the river. Meanders become prominent. Discharge and average velocity have increased, and sediment is generally smaller and more rounded.

Towards Stockton-on-Tees and Middlesbrough, the lower-course channel is very wide and deep. The gradient is very gentle, and the valley has a broad, relatively flat floodplain. The river carries a large discharge and much fine sediment in suspension. It eventually reaches the estuary at Teesmouth.

These are overall patterns, not rules for every individual reach. A waterfall, a resistant rock outcrop or a particularly rough stretch can interrupt the downstream trend.

Why the channel and valley become larger

Discharge is the volume of water passing a point each second. As tributaries join the Tees, they add water, so discharge generally increases downstream. A wider and deeper channel can accommodate this larger flow.

Erosion also changes direction along the river. In the upper course, downward or vertical erosion deepens the channel. The surrounding slopes are weathered and material moves downhill, helping to produce the steep-sided valley.

Farther downstream, lateral erosion—erosion sideways—becomes increasingly important. It widens the channel and valley, particularly where the river bends. Over time, erosion and deposition help create a broad valley floor and floodplain. This explains why a lower-course valley is not simply a larger version of an upper-course V-shaped valley.

Why velocity can increase as gradient decreases

Gradient and velocity are different. Gradient describes the steepness of the river’s descent; velocity describes how quickly its water moves.

Although the upper Tees has a steep gradient, its shallow channel and rough bed create substantial friction. Rocks and irregularities obstruct the flow, and a large proportion of the water is close to the bed or banks.

Downstream, the channel becomes wider and deeper. A smaller proportion of its water is in direct contact with the bed and banks, so friction has less influence on the flow as a whole. Together with the increasing discharge, this helps average velocity increase despite the gentler gradient.

This does not mean every point in the lower course is faster than every point upstream. Rapids and waterfalls can have very fast local flow, and velocity also changes with water level.

Why sediment becomes smaller and rounder

Weathering supplies angular rock fragments to the upper river. As these fragments move downstream, they collide with one another. This process, attrition, chips off corners and breaks particles into smaller pieces, making the remaining fragments more rounded.

The material carried by the river also becomes sorted. Large particles are harder to move and may remain upstream or be deposited along the journey. Fine particles can travel farther in suspension. Consequently, the lower Tees carries much finer sediment than the upper course.

Size and shape are separate characteristics: a pebble can become both smaller and rounder. Very fine clay and silt are best described as fine sediment rather than as visibly rounded pebbles.

Reading the river’s long profile

Most river long profiles have an overall concave shape: steep near the source and progressively gentler towards the mouth. For the Tees, this connects the high Pennine source with the almost flat lower course.

On a long-profile graph, the horizontal axis represents distance downstream and the vertical axis represents height. A steep part of the line indicates a large fall in height over a short distance; a flatter part indicates a smaller fall over the same distance.

Local features can interrupt the smooth curve. At High Force, resistant Whin Sill rock lies above softer limestone. The contrast in resistance contributes to the waterfall and a sudden drop in the river’s profile. Geology therefore helps explain why a real river does not follow a perfectly smooth curve.

Constructing a valley cross-section from contours

An OS map shows relief using contour lines: each line joins places at the same height above sea level. The contour interval is the height difference between neighbouring contour levels. Check the map’s stated interval rather than assuming one.

Closely spaced contours show a steep slope because height changes quickly over a short horizontal distance. Widely spaced contours show a gentler slope. A broad area with few contours beside a river may indicate a relatively flat valley floor.

To construct a valley cross-section:

1. Choose a line across the valley, usually approximately perpendicular to the river. Label its ends A and B.
2. Place a strip of paper along A–B. Mark both ends, every contour crossing and the river’s position. Record the height of each contour.
3. Draw a horizontal axis the same length as the map transect so that the spacing of your paper-strip marks transfers directly. Use the map scale to label horizontal distances from A.
4. Check the highest and lowest heights along the line, then choose a suitable vertical scale. Label this axis as height above sea level in metres. Plot each contour crossing at its correct position and height.
5. Use a pencil to join the points with a smooth profile and mark the river. Between known heights, the line is an estimate of the land surface, not a precise measurement.

A constructed illustration: imagine a fictional map extract with a stated scale of 1 cm representing 100 m. Along a 6 cm line, selected contours occur at these positions:

Suppose a spot height at the river, 300 m from A, gives a valley-floor height of 130 m. On a horizontal axis preserving the map scale, the 140 m contour crossings go 2 cm and 4 cm from A, while the river goes 3 cm from A. Plot their heights on the vertical axis and join the points smoothly. The profile falls towards the river and rises on the opposite side. Each side falls 50 m over 300 m horizontally. If the same fall occurred over a shorter distance, the side would be steeper.

This illustration demonstrates the plotting method; it is not an OS extract or a measured Tees cross-section. On an authentic map, transfer every crossing and use its actual scale, contour interval and available heights. Contours show the valley’s land surface, not the depth of water or the submerged river bed. A cross-section with an enlarged vertical scale also makes slopes look steeper than they really are.

Linking profiles to BGS geology maps

A topographic map shows the shape and height of the land. A British Geological Survey (BGS) geology map shows the rocks and deposits beneath or at its surface. Comparing the two helps explain changes in a river’s profile.

The BGS Geology Viewer allows you to select a location to identify its bedrock and superficial geology. Its layer legend identifies the mapped formations, and its 3D terrain view allows geology to be compared with the shape of the landscape.

Use matching locations when making the comparison. First identify a feature on the river profile, such as a steep reach or sudden drop. Then identify the rocks at that location using the geological layer and legend. Finally, explain how their properties could contribute to the feature.

High Force provides a concrete example: the sudden drop is associated with resistant Whin Sill rock above softer limestone. The rock contrast helps explain a local interruption in the Tees’s otherwise gentler downstream profile.

For a comparison elsewhere, imagine a river crossing from a resistant rock formation into a less resistant one. If a steep step in its profile coincides with that boundary, differential erosion is a possible explanation. The useful evidence is the agreement between the location of the profile change and the geological boundary—not simply the presence of two colours on a map.

Keep bedrock and superficial deposits separate: loose material covering a valley floor is not necessarily the rock beneath it. A geological boundary alone also does not prove the cause of a landscape feature; rock properties and the river’s processes matter. Finally, zooming farther into the BGS viewer does not create finer geological detail: its underlying mapping has limits of resolution.

River Tees: source to mouth

Cross Fell, Pennines → Barnard Castle → Stockton-on-Tees and Middlesbrough → Teesmouth, North Sea.

• Upper: narrow, shallow channel; steep V-shaped valley; steep gradient; low discharge; generally lower ; large, angular .