The valley of the Rhône also indicates that the river is in its upper course. Instead of flood plains and bluffs, there are steep valleys that are unstable. This shows that the principal erosion taking place is vertical erosion.
The channel’s irregular shape is compounded by the large amount of bed load present in the channel, proof that the Rhône is very powerful when the glacier is melting at a fast rate. The type of bed load carried also indicates the capacity and competence of the river. As there are mainly rocks and boulders in the river bed, this shows that the river has a high competence, but a low capacity for much of the year.
Further downstream, the river enters Lac Léman (Lake Geneva) at Montreux. The lake, which is three hundred metres deep, and seventy kilometres across, acts as a natural bottleneck for the river. It is estimated that water entering the lake stays there for fourteen years before leaving. During this time, any debris, such as sediment transported by the river, is deposited on the bed of the lake. Indeed, the river is depositing so much sediment, that in 200,000 years time, the lake will be full. As a consequence, water leaving the lake is much clearer than would typically be seen at this point in a river’s course.
After leaving Lac Léman, the river enters the Jura mountains in south-east France, and is stopped again, by the Genessiat dam. Although not a natural physical feature of the river, the one hundred metre high dam profoundly affects the river. The dam removes much of the river’s energy at this point, harnessing its power for hydroelectricity. The result is that in the remaining upper course to Lyons, the river is now a gently meandering river that is depositing sediment. The river now looks incongruous with its environment, hemmed in by the deep valleys that surround it.
At Lyons, the Rhône is joined by the Saône tributary, and marks the start of the river’s southward course. In many respects the Rhône is characteristic of rivers in their lower course. The river channel is more efficient, allowing a laminar flow with wide flood plains and bluffs around the Rhône, The river’s competence and capacity also change. The Rhône upstream was more suited to carrying large amounts of material occasionally, while the Rhône downstream is completely different. It competence has gone down, so that it is only capable of carrying material in suspension and solution, due to a decrease in the river’s peak energy. Yet, the actual amount of material carried has gone up drastically, because of the increase in the river’s discharge.
The erosion taking place has also changed, from being vertical to horizontal. Instead of steep-sided valleys being present, there are features more typical of a river downstream. First, the river has become meandering, since it is easier for the river to cut through sediment, than cut down into bed rock. The meandering nature of the river is caused by heli-coidal action, whereby small river currents colliding into the river bank This results in debris spinning off onto the other side of the river, and being deposited there. Over time, this cutting and deposition will result in natural river cliffs and meanders, and, ultimately ox-bow lakes. The reason why the channel is now more efficient is because of the land the river is cutting into. Previously, the upstream river had had to slowly erode its channel into very hard rock, where downstream, the task is easier, since the river is eroding into sediment.
There are however several anomalies with the Rhône at this stage in its course. For example, there are several river terraces present in the Rhône valley. This shows that the Rhône has been rejuvenated, which means that the river’s discharge has suddenly increased, leaving the previous floodplain ‘high and dry’, resulting in the formation of river terraces. Second, although at most times the river’s channel and surroundings are typical of most downstream rivers, these characteristics can suddenly change. At some times, the river channel can be very narrow, and in several valleys, the Rhône actually disappears. This occurs when the rock the Rhône cuts through has a band of softer rock beneath an outer layer of harder rock, causing the river to ‘tunnel’ under. The third anomaly occurs towards the end of the Rhône’s course, where it is joined by the Ardèche tributary. This river is fed by melt water from the Massif Central in central France, and is a very powerful and unpredictable tributary. As a consequence, the river becomes even more unpredictable, with floods determined by both the weather in the Swiss Alps, and in the Massif Central. After the Ardèche has joined the Rhône, the chance of flooding increases dramatically. For example, in May 1856 the Rhône flooded so much that over two hundred kilometres either side of the river were covered. This was the main stimulus for the taming of the Rhône by the French authorities.
At Arles, the river enters the final stage of its course: the delta, or ‘Camargue’. Here the river changes dramatically again, splitting up into the Grand and Petit Rhône. As sediment is being constantly deposited, the Camarge is forever expanding outwards into the Gulf of Lions. The delta itself is actuate, so that sediment is dumped before the river reaches the Mediterranean, since the river no longer has enough energy to continue carrying material.
In conclusion, it can be seen that the river Rhône is very different in character according to which stage of its course it is in. Whilst turbulent and small upstream, the river becomes a large, lazy, meandering river downstream, and a braided river at the Camargue. This shows that physical conditions, such as gradient and rock type, considerably affect the character of the Rhône, and rivers in general.
