The Water Cycle
The River Basin
River Channel Characteristics
Here are some key stages to the water cycle:
- Evaporation - When water turns into water vapour.
- Transpiration - When excess moisture is released by plants and leaves.
- Precipitation - When rain/snow/sleet falls back down to the ground.
- Interception - When rainwater is caught by vegetation and doen't make it to the ground/soil.
- Infiltration - The process by which water enters the soil
- Percolation - The process of water moving down through the soil.
- Surface runoff - The process of water running along the soil into the river/stream.
- Stream flow - The process of movement of water within a river/stream.
A river/drainage basin is an area of land drained by a river and its tributaries. Here are some key features of a river/drainage basin:
- Watershed - Area of highland forming the edge of a river/drainage basin.
- Source - Where the river begins.
- Tributary - Stream or small river flowing into a main river.
- Channel - Where a river flows.
- Confluence - Place where a tributary joins the main river.
- Mouth - where a river flows into a lake or the sea.
Upper course of the river:
- Width - Narrower
- Depth - Shallower
- Cross-section area - Smaller
- Gradient - Steeper
- Velocity - Slow
- Valley - V-shaped valley
- Land-forms - Interlocking spurs, waterfalls, hills
- Erosion - Vertical erosion
- Discharge - Lower volume
- Width - Wider
- Depth - Deeper (sometimes becomes shallower towards mouth)
- Cross-section area - Bigger
- Gradient - Flatter
- Velocity - Faster flow
- Valley - U-shaped valley
- Land-forms - Mianders/ox-bow lakes, deltas, flood plains
- Erosion - Lateral erosion
- Discharge - Higher volume
There are 4 main types of erosion in rivers. Here they are:
- Hydraulic action - This is when the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and eventually wears it away.
- Abrasion - When rocks carried along by the river wear down the river bed and banks.
- Attrition - When rocks being carried by the river smash into each other and break down into smaller, smoother and rounder rocks.
- Solution - When dissolvable particles are dissolved into the river.
A waterfall occurs when a river meets a band of softer, less-resistant rock. Because of this, the underlying, softer rock is eroded away more quickly. Processes of erosion (ie: abrasion) cause undercutting, therefore, the more resistant rock is left unsupported and overhangs. Eventually, the more resistant rock collapses onto the river bed, causing abrasion on the river bed. Hydraulic action also helps to create a deep plunge pool. This process is repeated and causes the waterfall to retreat upstream. The retreat of the waterfall leaves behind a gorge.