Rivers

Key Definitions

A drainage basin is an area of high land where all water that falls on it will make its way to the river.

• Drainage basin — an area of high land where all water that falls on it will make its way to the river
• Deposition — the settling and dropping of moving sediment as a result of a change in energy and water speed
• Tributaries — a smaller river that flows into a larger river
• Confluence — the area where two tributaries meet
• Thalweg — the area of the fastest water flow in a river

Fluvial Processes

Erosional Processes

• Hydraulic action — where the force of water hits the river bed, causing cracks and erosion
• Abrasion — where rocks hit against the river bank and cliff surfaces like sandpaper
• Attrition — where rocks and sediment hit each other and break down into smaller pieces
• Solution — where chemicals in the water dissolve some rock

Transport Processes

• Traction — where big rocks are rolled around in the river bed
• Suspension — where smaller rocks are carried by the current
• Saltation — where medium sized rocks bounce along the river bed
• Solution — where particles and dissolved rock are carried in the river water

Courses of a River

Features of a River

Use keywords including the names of fluvial processes when describing formation.

Meanders

1. Found in lower courses.
2. An area of soft rock begins to erode.
3. The thalweg of the river changes, so it erodes quicker.
4. Deposition occurs where there is slower flow: the opposite side.
5. As more deposition occurs, more erosion occurs as hydraulic action erodes the opposite side of the river, causing zig-zag meanders.

Oxbow Lakes

1. Found in lower courses.
2. Repeat of steps 1-5 of meanders.
3. Eventually sediment continually deposits and closes off the meander.
4. A new main flow is created (new thalweg).
5. An oxbow lake is left at what was cut off.

Waterfalls

1. Found in upper courses.
2. The water erodes (hydraulic action) away at the soft rock faster than the hard rock, forming an undercut.
3. As the soft rock erodes, the overhang breaks off into the plunge pool.
4. The process continues.
5. This causes the waterfall to retreat and create a gorge.

Deltas

1. Found in the lower course.
2. The sea's waves slow the water velocity as it meets the sea.
3. Deposition occurs due to this slowing; the river splits into channels called distributaries.
4. The river winds around these landforms.
5. As sediment continues to create islands to the delta, vegetation begins to emerge, giving a delta its fan shape.

Interlocking Spurs

1. The high velocity water in the river vertically erodes the river by hydraulic action, causing a deep notch.
2. The river's bank is made of hard and soft rock layers.
3. As the soft rock erodes quicker than the hard rock, a zigzag pattern is formed.
4. The river flows around the areas of hard rock.
5. Interlocking spurs are formed.

Levees

1. During floods, water slows at the banks and deposits silts.
2. With each new flood, the bed continues to build up with sediment.
3. Water levels rise, whilst the river banks continue to raise in height.

Hazards and Opportunities of Living Near a River

Case Study: The Nile River

Key facts:

• 97% of Egyptian fresh water is from the Nile (overreliance as a domestic water source).
• 99% of Egypt's fast-growing population live in the Nile basin (settlements).
• Home to 275,000,000 people.
• The 4.3 billion dollar Grand Ethiopian Renaissance Dam (GERD — hydroelectric energy).

Flooding and Management

• Hard engineering — using man-made methods to stop flooding
• Soft engineering — using natural methods to mitigate the impact of flooding

Hydrographs

A hydrograph is a graph that shows the rate of flow in a river (the discharge) over time, usually after a rainfall event, to monitor flooding.

• Discharge — the volume of water flowing in a river per second (measured in cumecs)
• Width — the distance of the river from river bank to river bank
• Depth — the distance from the surface of the water to the river bed
• Lag time — the time between peak precipitation and peak discharge

Factors monitored by hydrographs:

1. Size of drainage basin
2. Vegetation
3. Relief
4. Soil type

Flooding Case Study: River Elbe (2013)