geography - river

3 major stores where water on earth is held

atmosphere, ocean & land

water cycle

dendritic pattern

trellis pattern

source of river

where a river starts, normally high up in the mountains where rain collects or a spring is found

tributary

a small stream that flows into the main channel

confluence

where two streams meet

watershed

the boundary of a drainage basin. it is an imaginary line joining the high grounds (ridges & spurs) separating adjacent drainage basins

mouth of a river

where a river enters the sea

distributary

a stream that branches off and flows away from mainstream channel

1st order stream

river source, smallest stream, no tributaries

2nd order stream

when 2 1st order streams join together

3rd order stream

when 2 2nd order streams join together

drainage density

total channel length/total area of drainage basin

discharge calculation formula

stream width x average depth x river velocity

typical conditions for high drainage density

1. high annual rainfall

2. steep basin slope

3. impermeable rock layer at the surface

4. bare land surface

2 factors that affect the energy of a river

amount of channel water & speed of water flow

3 fluvial processes in a river channel

erosion, transportation, deposition

fluvial erosion

running water carrying load to remove fine particles from the river bank or beds

vertical erosion

deepens the river channel, occurs at upper course

lateral erosion

widens the river channel , occurs in middle and lower courses

headward erosion

lengthens the river, occurs at river source

4 types of fluvial erosion

1. solution

2. attrition

3. abrasion

4. hydraulic action

transportation

downstream movement of river load

how deforestation affects the rate of fluvial erosion

less vegetation cover → more overland flow → more rocks & stones washed into river → more tools for erosion

4 types of transportation

1. suspension

2. traction

3. saltation

4. solution

fluvial deposition

when a river loses energy, it drops its load. this load will be deposited on the river bed as sediment

v-shaped valley

vertical erosion is active at the upper course. over time, a narrow steep sided V-shaped valley is formed

interlocking spurs

continuing from the formation of v-shaped valleys, on the other hand, the river water is unable to remove the obstacles (spurs) and it flows side to side around the obstacles forming interlocking spurs

rapids

when a land of more resistant and less resistant rock lies horizontally, vertically, or obliquely across a river, erosion (abrasion) will be concentrated at the less resistant rock. small steps develop due to fluvial erosion, forming rapids

waterfall

when there is continuous erosion (abrasion) on less resistant rock, great differences are created in water level between the hard and soft rocks, forming a waterfall

gorges

the strong hydraulic action enlarges the notch at the back of the waterfall. without support, the overhanging rock collapses and when the process repeats overtime, the waterfall recedes. this forms a well-developed gorge, a valley with narrow, deep and very steep side channels

plunge pools

once waterfalls form, the force of running water can undercut the cracks at the base and back of the waterfall, forming a plunge pool by hydraulic action

example of gorges

sanxia in china

examples of plunge pools

bride’s pool in tai po

pot holes

when a river flows over an uneven surface, it causes turbulence in the water. the turbulence causes rocks or pebbles to drill holes on the river bed, forming potholes