Energy of a River

How is the energy of a river determined?

Speed of a river Volume of a water

Speed and Volume (High) Energy High

Speed and Volume (Low) Energy Low

What will the amount of energy in a river determine?

ErodeTransportDeposit Materials

Why does the energy of a river change?

GradientRoughnessWetted PerimeterSize of drainage basinPresence of vegetationPermeability of rocksClimate

Upper Course

Middle Course

Lower Course

Factors that affect the speed of a river

GradientRoughnessWetted Perimeter

Gradient of Channel

The Steeper the gradient is, the faster is the flow.

Water flowing down a steep slope has higher velocity than one which flows down a gentler gradient .

Gradient of Channel

(Steep) (Gentle)

Roughness of Channel

Rocks Boulders

Underwater Vegetation River Bed

Cause friction between the water and channel, the water has to overcome the friction and this lead to slow down of river flow and reduce of speed.

Roughness of Channel

Faster River Flow Slower River Flow

(Lesser Friction) (Higher Friction)

Wetted Perimeter

Refers to the extent to which water is in contact with its channel.

The Larger the wetted perimeter is, the river will have to overcome more friction and is slowed down.

Wetted Perimeter

Wetted perimeter is calculating by adding the length and the breadth of the channel in contact with water.

Factors that affect the volume of water in a river

Size of drainage basinPresence of vegetationPermeability of rocksClimate

Size of drainage basin

The larger the drainage basin= the more tributaries there are= the greater the volume of water

Resulting in a *higher surface runoff.

*Runoff that moves over the soil surface to the nearest surface stream.

Size of drainage basinA Larger

Drainage Basin

More

tributaries

Greater Volume of water

Higher surface runoff

B Smaller Drainage Basin

Lesser tributaries

Lower Volume of water

Lower surface runoff

Presence of vegetation

Intercepts the rain and enables the rain water to infiltrate into the ground.

Reduces surface run-off and so less water flows immediately into the river.

Presence of vegetation

Rain Rain

High Interception

Low Interception

High Infiltration

Low Infiltration

Low surface runoff

High surface runoff

Permeability of rocks

Determined by the size of the pores between the rock particles.

Rock has small pores, water cannot easily infiltrate into the rock

Rock is impermeable

Permeability of rocks

When water flows through an area of impermeable rock

Little water infiltrates the groundHigh surface runoff and leads to a high

volume of flow of water.

Climate

Precipitation Temperature

Climate

Dry Season Wet Season

Low Rainfall High Rainfall

High precipitation

Low precipitation

Low volume of flow

High Volume of flow

High Temperature

Low Temperature

More evaporation and transpiration

Lesser evaporation and transpiration

Lower amount of water

Higher amount of water

Precipitation Temperature

Climate

Low rainfall, lower volume of water

High rainfall, higher volume of water