Saturday, September 24, 2005
GEOG - RIVERS
Drainage basin (catchment area): area of land drained by a river & its tributaries
-source: beginning of river
-mouth: where water is emptied
River discharge: volume of water flowing through a particular point in the river in a given time
=area of cross section (m2) X velocity of flow (m/s)
Drainage density: average length or river/unit area
-length of all the streams in drainage basin added up divided by the area of the drainage basin
Drainage patterns: arrangement of a river & its tributaries in a drainage basin
1. dendritic pattern: tributaries flow into main river at acute angles (tree like branching)
-usually develops in area with homogenous rocks or rocks with similar resistance
2. radial pattern: rivers flow down in all directions form a central high point (conical hill / volcano)
3. trellised pattern: developed in area with alternate bands of rocks with different resistance
-tributaries flow along less resistant rock, joins main river at right angles
4. centripetal pattern: common in inland basins & desert regions: streams from various directions drain towards centre of a depression (lake, lowland basin)
Hydrological cycle: 1. infiltration: some water that reaches the ground soaks into the soil subsurface
-some flow sideways as throughflow
-some are absorbed by roots of trees & transpired back to atmosphere
2. percolation: some water moves further down into unsaturated underlying soil & rock layers
-results n large amt of underground water that collects on top of an impermeable rock layer
3. base flow (ground water flow): water that flows sideways frm water table
4.overland flow (surface runoff): when precipitation exceeds infiltration rate > high in urban areas
5. evapotranspiration: loss of moisture frm earth’s surface to atmosphere
-evaporation frm water bodies
- transpiration frm vegetation
Storm hydrograph: shows variations in river discharge at a particular point in a rive over a certain period of time
-river does not rise immediately aft storm starts
-river level rises quickly (steep rising limb) later when surface runoff & throughflow arrive
-peak discharge: river level at its highest
-lag time: difference in time between highest rainfall & peak discharge
-recession limb is not as steep as the rising limb as throughflow is still entering the river
-river is maintained by the base flow after water brought by the storm has drained away
Factors affecting shape of storm hydrograph: 1.basin size, shape, relief: smaller and more circular basin, steep sided: shorter lag time
2. types of precipitation: prolonged heavy rain, intense storms: saturated ground, more surface runoff
snow: water held in storage, river level drops; reaches river when temperature rises & snow melts
3. extreme hot or cold temperature restricts infiltration, increase surface runoff; high evapotranspiration rate, less water flows into river
4. landuse: vegetation intercepts rainfall, reduce throughflow; water cannot infiltrate concrtete, water is carried quickly to rivers via drains & gutters
5. rock type: permeable rocks allow rapid infiltration
6. soil type: sandy soil more porous, allow rapid infiltration; clays less porous, more surface runoff
7. drainage density: higher, greater chance of floods
Energy of river: mostly used to overcome friction with river bed & sides; erosion & transportation
-when energy is low, materials are deposited
-energy depends on velocity of flow & volume
Velocity of river: 1. gradient of land: steeper, faster
2. roughness of channel: rougher, slower
-more energy used to overcome friction
3. shape of channel cross section: more wetted perimeter (length of river sides & bed), more friction
-symmetrical channel: water flows faster mid stream, slower near sides & bed
-asymmetrical channel: water flows faster at concave bank, slower at convex bank due to shallower water
Volume of water: 1. size of drainage basin: larger basin, bigger volume (tributaries increase volume)
2. vegetation cover: thick cover, more interception, less runoff to river
3. rainfall: higher, greater volume
4. temperature: high temperature, high rate of evaporation, less volume
5. permeability of rocks & ground surface: more permeable, less surface runoff, less volume
River erosion: vertical & horizontal erosion
1. abrasion/corrasion: uses river load to grind sides & bed of channel
2. hydraulic action: swift flowing water breaks and loosens rocks
3. attrition: rocks in river load hit again one another, becoming smaller, smoother & more rounded
4. solution/corrosion: river dissolves minerals
River transportation: 1. solution: carries dissolved minerals (calcium & sodium)
2. suspension: fine particles carried (sand silt clay)
3. saltation: gravel, coarse sand bounce on river bed
4. traction: bigger pebbles & boulders rolled along
_saltation & traction loads form the bedload
River deposition: when volume & speed of water decreases; carry a greater load than it can support
Volume decreases when: 1. little or rain falls
2. flows across arid area with high evaporation rate
3. flows across permeable rocks
4. flood water brought by storm has drained away
Speed decreases when: 1. sudden change of gradient
2. river flows into another body of water
3. increase in wetted perimeter: more friction
4. water flowing in shallow section (convex bank of meander) encounters friction
5. obstructions (mounds of deposits & protruding rocks) roughen channel & increase friction
_heaviest materials are deposited first
Course of river: 1. upper: a. river channel: small, narrow rough, usually shallow
b. river valley: deep, narrow, steep sided, v shaped
c. work of river: most energy used to overcome friction of rough channel, little energy for erosion
-during heavy downpour, increased volume enables vertical erosion: bedload swirls in whirlpool
-headward erosion: throughflow reaches surface & undercuts the overlying rocks & soil
d. landforms: i. rapids: short & fast flowing turbulent falls of water along a river; water is quite shallow
-alternating bands of resistant & less resistant rocks: less resistant rocks are eroded faster
ii. waterfalls: sudden fall of water vertically+rapidly
_formed when river flows frm a band of resistant rock to less resistant rock (Niagara falls)
-resistant rock can be vertical (sill), horizontal or dip upstream (dyke)
-less resistant rock downstream erodes faster: causes change in gradient of river
_formed when faulting causes land to be displaced
-difference in height causes water to cascade down
-waterfall retreats upstream, gorge is formed at downstream part of waterfall (Victoria falls Africa)
iii. plunge pools: depression at foot of waterfall
-enlarge & deepened by hydraulic action of plunging water; rock debris swirled abt > abrasion
iv. gorge: deep narrow valley w very steep sides
-formed when waterfall retreats upstream
v. potholes: depressions in river bed
-formed by abrasion: pebbles trapped in slight hollows & swirled about in the currents & turbulence of fast flowing water; enlarge & deepen the holes
2. middle: a. river channel: wider & deeper; asymmetrical cross section; meanders; bigger volume of water; less gradient
b. river valley: more open v shape - lateral erosion
- weathering & mass wasting of river sides
c. work of river: gentler gradient less vertical erosion
-increased volume & load used for lateral erosion
-energy used to transport load
-deposition occurs on meander convex banks
d. landforms: meanders, river cliffs, slip off slopes
meanders: forms when river meets an obstacle; erode and undercuts concave banks at outer bends
-water moves in a spiral manner, fast at concave
-materials deposited at convex: slow due to friction
3. lower: a. river channel: widest & deepest, smooth channel floor; irregularities in bed filled w sediment
-largest volume due to tributaries
b. river valley: wide & flat bottomed: lateral erosion
c. work of river: lateral erosion on concave banks of meanders; to deposit the load it is transporting
d. landforms: i. flood plains: wide & low lying plain found on both sides of river; covered by deposition
levees: embankments found along banks, coarser
-during heavy rain water overflows, meets friction
-deposits coarse material first (levee)
-smaller & lighter material deposited further away
ii. ox bow lakes: horseshoe or crescent shaped lakes
-cut off from river when narrow neck separating 2 ends of a meander is broken by lateral erosion on the concave banks or strong currents during a flood
-the ends are sealed by deposits on convex bank
-lake may dry up due to evaporation & percolation
iii. deltas: flat depositional plain at river mouths
-formed if load removal is slower than deposition
-water enters sea at individual mouths
1. active erosion in upper cause: enhance load
2. presence of shallow sea at river mouth
3. presence of gentle shope near shore
4. sheltered bay where tides are calm & weak
5. absence of large lakes along river course that might reduce the load
Shapes: 1. arcuate: triangular or fan shaped; deposits evenly spread out (nile delta)
2. bird’s foot: irregular shape; deposits unloaded rapidly at river mouth (Mississippi delta)
3. compound delta: complex in shape
4. estuarine delta: formed by infilling of an estuary
Uses of rivers: 1. hydro electric power: dams
2. irrigation: impt in drought prone areas
3. fertile alluvial soil: rice growing
4. transport, ports, harbours: cheap (chang jiang)
5. domestic uses: food, water for drinking, cooking
6. tourist attractions & recreational
Problems caused: 1. flooding: damage & loss of property & lives (huang he)
2. pollution: not suitable for drinking
OMG SO MANY THGS TO RMB!!! >.< - lala
-source: beginning of river
-mouth: where water is emptied
River discharge: volume of water flowing through a particular point in the river in a given time
=area of cross section (m2) X velocity of flow (m/s)
Drainage density: average length or river/unit area
-length of all the streams in drainage basin added up divided by the area of the drainage basin
Drainage patterns: arrangement of a river & its tributaries in a drainage basin
1. dendritic pattern: tributaries flow into main river at acute angles (tree like branching)
-usually develops in area with homogenous rocks or rocks with similar resistance
2. radial pattern: rivers flow down in all directions form a central high point (conical hill / volcano)
3. trellised pattern: developed in area with alternate bands of rocks with different resistance
-tributaries flow along less resistant rock, joins main river at right angles
4. centripetal pattern: common in inland basins & desert regions: streams from various directions drain towards centre of a depression (lake, lowland basin)
Hydrological cycle: 1. infiltration: some water that reaches the ground soaks into the soil subsurface
-some flow sideways as throughflow
-some are absorbed by roots of trees & transpired back to atmosphere
2. percolation: some water moves further down into unsaturated underlying soil & rock layers
-results n large amt of underground water that collects on top of an impermeable rock layer
3. base flow (ground water flow): water that flows sideways frm water table
4.overland flow (surface runoff): when precipitation exceeds infiltration rate > high in urban areas
5. evapotranspiration: loss of moisture frm earth’s surface to atmosphere
-evaporation frm water bodies
- transpiration frm vegetation
Storm hydrograph: shows variations in river discharge at a particular point in a rive over a certain period of time
-river does not rise immediately aft storm starts
-river level rises quickly (steep rising limb) later when surface runoff & throughflow arrive
-peak discharge: river level at its highest
-lag time: difference in time between highest rainfall & peak discharge
-recession limb is not as steep as the rising limb as throughflow is still entering the river
-river is maintained by the base flow after water brought by the storm has drained away
Factors affecting shape of storm hydrograph: 1.basin size, shape, relief: smaller and more circular basin, steep sided: shorter lag time
2. types of precipitation: prolonged heavy rain, intense storms: saturated ground, more surface runoff
snow: water held in storage, river level drops; reaches river when temperature rises & snow melts
3. extreme hot or cold temperature restricts infiltration, increase surface runoff; high evapotranspiration rate, less water flows into river
4. landuse: vegetation intercepts rainfall, reduce throughflow; water cannot infiltrate concrtete, water is carried quickly to rivers via drains & gutters
5. rock type: permeable rocks allow rapid infiltration
6. soil type: sandy soil more porous, allow rapid infiltration; clays less porous, more surface runoff
7. drainage density: higher, greater chance of floods
Energy of river: mostly used to overcome friction with river bed & sides; erosion & transportation
-when energy is low, materials are deposited
-energy depends on velocity of flow & volume
Velocity of river: 1. gradient of land: steeper, faster
2. roughness of channel: rougher, slower
-more energy used to overcome friction
3. shape of channel cross section: more wetted perimeter (length of river sides & bed), more friction
-symmetrical channel: water flows faster mid stream, slower near sides & bed
-asymmetrical channel: water flows faster at concave bank, slower at convex bank due to shallower water
Volume of water: 1. size of drainage basin: larger basin, bigger volume (tributaries increase volume)
2. vegetation cover: thick cover, more interception, less runoff to river
3. rainfall: higher, greater volume
4. temperature: high temperature, high rate of evaporation, less volume
5. permeability of rocks & ground surface: more permeable, less surface runoff, less volume
River erosion: vertical & horizontal erosion
1. abrasion/corrasion: uses river load to grind sides & bed of channel
2. hydraulic action: swift flowing water breaks and loosens rocks
3. attrition: rocks in river load hit again one another, becoming smaller, smoother & more rounded
4. solution/corrosion: river dissolves minerals
River transportation: 1. solution: carries dissolved minerals (calcium & sodium)
2. suspension: fine particles carried (sand silt clay)
3. saltation: gravel, coarse sand bounce on river bed
4. traction: bigger pebbles & boulders rolled along
_saltation & traction loads form the bedload
River deposition: when volume & speed of water decreases; carry a greater load than it can support
Volume decreases when: 1. little or rain falls
2. flows across arid area with high evaporation rate
3. flows across permeable rocks
4. flood water brought by storm has drained away
Speed decreases when: 1. sudden change of gradient
2. river flows into another body of water
3. increase in wetted perimeter: more friction
4. water flowing in shallow section (convex bank of meander) encounters friction
5. obstructions (mounds of deposits & protruding rocks) roughen channel & increase friction
_heaviest materials are deposited first
Course of river: 1. upper: a. river channel: small, narrow rough, usually shallow
b. river valley: deep, narrow, steep sided, v shaped
c. work of river: most energy used to overcome friction of rough channel, little energy for erosion
-during heavy downpour, increased volume enables vertical erosion: bedload swirls in whirlpool
-headward erosion: throughflow reaches surface & undercuts the overlying rocks & soil
d. landforms: i. rapids: short & fast flowing turbulent falls of water along a river; water is quite shallow
-alternating bands of resistant & less resistant rocks: less resistant rocks are eroded faster
ii. waterfalls: sudden fall of water vertically+rapidly
_formed when river flows frm a band of resistant rock to less resistant rock (Niagara falls)
-resistant rock can be vertical (sill), horizontal or dip upstream (dyke)
-less resistant rock downstream erodes faster: causes change in gradient of river
_formed when faulting causes land to be displaced
-difference in height causes water to cascade down
-waterfall retreats upstream, gorge is formed at downstream part of waterfall (Victoria falls Africa)
iii. plunge pools: depression at foot of waterfall
-enlarge & deepened by hydraulic action of plunging water; rock debris swirled abt > abrasion
iv. gorge: deep narrow valley w very steep sides
-formed when waterfall retreats upstream
v. potholes: depressions in river bed
-formed by abrasion: pebbles trapped in slight hollows & swirled about in the currents & turbulence of fast flowing water; enlarge & deepen the holes
2. middle: a. river channel: wider & deeper; asymmetrical cross section; meanders; bigger volume of water; less gradient
b. river valley: more open v shape - lateral erosion
- weathering & mass wasting of river sides
c. work of river: gentler gradient less vertical erosion
-increased volume & load used for lateral erosion
-energy used to transport load
-deposition occurs on meander convex banks
d. landforms: meanders, river cliffs, slip off slopes
meanders: forms when river meets an obstacle; erode and undercuts concave banks at outer bends
-water moves in a spiral manner, fast at concave
-materials deposited at convex: slow due to friction
3. lower: a. river channel: widest & deepest, smooth channel floor; irregularities in bed filled w sediment
-largest volume due to tributaries
b. river valley: wide & flat bottomed: lateral erosion
c. work of river: lateral erosion on concave banks of meanders; to deposit the load it is transporting
d. landforms: i. flood plains: wide & low lying plain found on both sides of river; covered by deposition
levees: embankments found along banks, coarser
-during heavy rain water overflows, meets friction
-deposits coarse material first (levee)
-smaller & lighter material deposited further away
ii. ox bow lakes: horseshoe or crescent shaped lakes
-cut off from river when narrow neck separating 2 ends of a meander is broken by lateral erosion on the concave banks or strong currents during a flood
-the ends are sealed by deposits on convex bank
-lake may dry up due to evaporation & percolation
iii. deltas: flat depositional plain at river mouths
-formed if load removal is slower than deposition
-water enters sea at individual mouths
1. active erosion in upper cause: enhance load
2. presence of shallow sea at river mouth
3. presence of gentle shope near shore
4. sheltered bay where tides are calm & weak
5. absence of large lakes along river course that might reduce the load
Shapes: 1. arcuate: triangular or fan shaped; deposits evenly spread out (nile delta)
2. bird’s foot: irregular shape; deposits unloaded rapidly at river mouth (Mississippi delta)
3. compound delta: complex in shape
4. estuarine delta: formed by infilling of an estuary
Uses of rivers: 1. hydro electric power: dams
2. irrigation: impt in drought prone areas
3. fertile alluvial soil: rice growing
4. transport, ports, harbours: cheap (chang jiang)
5. domestic uses: food, water for drinking, cooking
6. tourist attractions & recreational
Problems caused: 1. flooding: damage & loss of property & lives (huang he)
2. pollution: not suitable for drinking
OMG SO MANY THGS TO RMB!!! >.< - lala
# we mugged! @ 12:44 PM 
