River Characteristics HYDROSPHERE 3 River Characteristics

STUDYING RIVER VALLEYS HYDROSPHERE 3 STUDYING RIVER VALLEYS We will look at;- General characteristics of rivers. Upper stages- waterfalls. Middle stages- meanders Lower stages – ox-bow lakes, levees and deltas Rejuvenation

GENERAL CHARACTERISTICS HYDROSPHERE 3 GENERAL CHARACTERISTICS A river LONG PROFILE is a sideways look at a river valley from source to mouth. It can also be called a LONG SECTION. In an ideal river, it looks like this;-

Large sized material needs high energy. HYDROSPHERE 3 The key to understanding how a river creates its landforms is to look at the energy needed to move the material around it. Large sized material needs high energy. Large amounts of material needs high energy. Tiny particles need only low amounts of energy. Small amounts of material need little energy.

The volume of water, which varies with precipitation. HYDROSPHERE 3 Where does the energy come from? The volume of water, which varies with precipitation. The speed of the flow, which varies with gradient of the river bed.

HYDROSPHERE 3 So it is obvious that erosion is greatest in the upper stage and deposition in the lower stage. EROSION DEPOSITION SOURCE MOUTH

Transportation Suspension – very small particles can be carried along in the river. The faster the river = the more it can carry Traction – the largest boulders roll along the river bed at times of flood when the energy level in the river is high. Solution – some material may be dissolved by the river. Saltation – larger particles bounce along the river bed. These particles can cause other larger particles to become dislodged

Rivers can deepen and widen their valleys by: Corrasion – rivers use the stones and pebbles they carry (its load) to smash against the sides and bottom of the river. Hydraulic Action - the sheer force of the water causes the outer banks of the river to break up and collapse. It is most effective in times of flood. Solution - this is when rivers dissolve material Attrition - the stones and pebbles the river carries (its load) rub against each other. Over time the size of this load becomes smaller and more rounded.

Upper stage features: Waterfall HYDROSPHERE 3 Upper stage features: Waterfall

HYDROSPHERE 3 Waterfall and gorge

SINUOSITY WAVELENGTH Helicoidal flow HYDROSPHERE 3 MIDDLE STAGES- MEANDERS These are found initially in the middle stage, although they get well developed in the lower stage too. There are a few new terms about meanders for you to learn, beyond the Standard Grade ones. Read your textbook for definitions of these terms SINUOSITY WAVELENGTH Helicoidal flow

HYDROSPHERE 3 The first stages in the formation of meanders is believed to be the development of ‘riffles and pools’. These are zones of alternating deposition and erosion that cause the channel of the river to alter course, thus creating the meander.

Remind yourself how they do this- what are the PROCESSES? HYDROSPHERE 3 Remember that meanders are a developing feature, changing with time and moving both across the flood plain and down-stream! Remind yourself how they do this- what are the PROCESSES?

HYDROSPHERE 3 The photograph here and the diagram on the next slide shows the processes going on below the water. Notice how the inner bank is being built up into a point bar deposit /river beach/ slip-off slope, and the outer bank is being eroded into a river cliff.

HYDROSPHERE 3

The finale of the process is for an ox-bow lake to form. HYDROSPHERE 3 A The finale of the process is for an ox-bow lake to form. B This happens in the lower course of the river

An ox-bow lake on the Endrick valley floodplain. HYDROSPHERE 3 An ox-bow lake on the Endrick valley floodplain.

The meanders and ox-bow lakes of the Mississippi River from the air. HYDROSPHERE 3 The meanders and ox-bow lakes of the Mississippi River from the air.

HYDROSPHERE 3 The movement of the meanders create the wide floodplain and bluffs of the mature lower stage of the river.

HYDROSPHERE 3 LOWER STAGE Here the gradient is low and energy levels are also low. As a result……….. ……there is much deposition and high sinuosity; the flood plain is wide.

Levees are either natural or man-made raised banks. HYDROSPHERE 3 LEVEES Levees are either natural or man-made raised banks.

HYDROSPHERE 3

HYDROSPHERE 3 1. Increased discharge in the river will bring down more (and larger) load from upstream. 2. If the discharge drops quickly, reducing the volume in the channel, the material will be dropped in the bed. Sometimes debris remains long enough to be colonised with vegetation which stabilises it more! 3. The material is poorly consolidated and is likely to be re-eroded with further increased discharge.

1. Currents would wash away the deposits before they could gather. HYDROSPHERE 3 Deltas 1. Currents would wash away the deposits before they could gather. 2. As the material reaches the still water, the river flow almost stops. The heavier material drops and rolls down the slope offshore, and the medium particles fall on top of them. The lightest particles are carried further out to sea and deposited, to be covered much later by more heavy deposits. 3. Distributaries form as the water has trouble flowing over the deposited material. 4.The Rhine delta is in Netherlands at Rotterdam, and the Rhone delta is in France, beside Marseilles.

HYDROSPHERE 3 Summary-handouts

This is the name given to when a river gets a new rush of energy. HYDROSPHERE 3 REJUVENATION This is the name given to when a river gets a new rush of energy. This is due to ISOSTATIC UPLIFT- remember what that is? This is when the land rises up after the weight of the glaciers has been removed. It is seldom even across the land.

HYDROSPHERE 3 As the land rises, there is now more falling for the river to do to get to sea- level. It starts to flow faster with the renewed energy, and vertical erosion starts to increase. The results are the channel of the river eats downwards into the floodplain and creates river terraces and incised/ entrenched meanders.