Journey of a River

Most rivers begin high up on hills and mountains. If you’ve been walking in hills, you’ll know they can be surprisingly damp. That’s because the ground acts like a sponge soaking up rain.

Excess water flows downhill, pulled by gravity, first in trickles and then small streams called rivulets, which in turn join together to form larger streams. Finally, a stream becomes a river. We’re going to follow a river from start to finish: the River Forth, in central Scotland.

Heat from the Sun evaporates water from the loch surface. It rises into the air, condensing in the cooler temperature to form clouds. The clouds become denser with moisture until the cycle starts again with rainfall.

As a river tumbles down from high ground, it cuts through the earth. This part of a river is called the upper course. The rushing water erodes the landscape in different ways according to the kind of ground it passes over. 

This vertical erosion creates steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges. The water carries small parts of rock and earth eroded by the river, which then become part of the river, and contribute to erosion and deposition downstream.

In the upper course, water is pulled downwards by gravity. This can be seen most dramatically in waterfalls. Later, as the river levels off, the water is directed horizontally.

There are 22 lochs in the Loch Lomond & the Trossachs National Park in Scotland, constantly replenished with fresh water pouring down from Ben Lomond and the other mountains in the area. Loch Ard collects water from the surrounding hills and then feeds into the River Forth. 

A small outlet on the loch’s eastern side continues to flow eastwards, growing wider and fed by smaller rivers, across to Scotland’s east coast and into the North Sea.

Loch Ard is a freshwater lake, fed by rainwater and streams coming down from surrounding hills. In contrast to seawater, which is salty, freshwater can be treated for human consumption. Different kinds of fish can live in freshwater habitats than in saltwater habitats. 

The river is wider and deeper in the middle course. The water appears less turbulent than in the upper course and its gradient is gentler, but it is actually moving faster. The increased velocity and volume of the water gives it greater force to erode riverbanks. 

Sediment – small pieces of rock and earth – is carried along with the river, increasing its erosive power, and deposited as the river winds to create distinctive river features.

This is the view from the Wallace Monument on the summit of Abbey Craig, near Stirling. The monument commemorates Sir William Wallace, a 13th-century Scottish hero. 

From here, you can see the middle course of the Forth as it winds its way across the countryside. This bending path is typical of the middle course of a river.

Deposition happens where a river does not have enough energy to carry material further and deposits it instead. This happens in the middle course of a river, or on the inside of bends or meanders.

The Firth of Forth is where the river flows out to the North Sea. “Firth” means an estuary, which is where a river meets the sea. Estuaries are often home to many different forms of wildlife. Around a third of people in the UK live close to estuaries.

At estuaries, freshwater from rivers meets salty seawater, producing a mixture called brackish water or briny water. The mixing circulates sea nutrients and expels waste products, creating rich, dynamic ecosystems.