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River environments
| Question | Answer |
|---|---|
| list the processes of the hydrological cycle | evapotranspiration --> condensation --> precipitation -->surface run off |
| transpiration definition | the loss of moisture directly from rivers, lakes or seas |
| evaporation definition | loss of moisture directly from vegetation |
| what is a river contained in | drainage basin |
| parts of a drainage basin | watershed, source, tributaries, confluence, main channel, mouth |
| watershed definition | dividing line between neighbouring drainage basins, normally on a ridge of high land |
| source definition | marks the starting point of a river. it is normally found near the watershed in mountainous areas |
| tributary definition | smaller channel than meets the main river channel |
| confluence definition | where a tributary joins the main river channel |
| mouth definiton | where the river terminates at a sea or lake |
| describe what a drainage basin is | the area of land drained by a river and its tributaries. it is defined from other basins by the watershed |
| what is an open system and why is a drainage basin an open system | a drainage basin is an open system because material(water) both enters and leaves it |
| what are the inputs of a simple drainage basin system | precipitation |
| what is precipitation | any form of water- liquid or solid - falling from the sky. |
| what are the stores of a simple drainage basin system | interception, groundwater storage |
| what is interception | part of the rainfall that is intercepted by the earth's surface and which subsequently evaporates |
| what are the six transfers of a simple drainage basin | surface run-off, infiltration, throughflow, percolation, groundwater flow |
| what is surface run-off | water that is moving over the surface of the ground. its rate of flow depends on the degree of slope and other surface characteristics |
| what does the rate of flow of surface run-off depend on | the degree of slope and other surface characteristics |
| give five examples of precipitation | rain, snow, hail, sleet and drizzle |
| where is a source normally found | near the watershed in mountainous areas |
| what is infiltration | the movement of water from the surface down into soil |
| what is throughflow | downhill movement of water through the soil |
| what is percolation | downward vertical movement of water from the soil into groundwater storage area |
| what is the name given for the groundwater storage area | water table |
| what is groundwater flow | when water moves downhill through the rock of the drainage basin |
| what are the outputs of the simple drainage basin system | river discharge, evapotranspiration |
| what is river discharge | volume of water flowing past a particular point in the river at ny given time. |
| what is river discharge measured in | cumecs (cubic metres per second) |
| what is evapotranspiration | combination of the processes of transpiration and evaporation which both act together as outputs of water from the drainage basin system |
| how does most water reach the river | through surface run-off, infiltration and groundwater flow |
| what is the fastest way for water to reach the river (asides from direct precipitation), and what can it cause in doing so | surface run-off, flooding |
| two reason why water may never reach the river channel | percolation means water is stored underground for many years evaporation prevents water reaching the river as it stays in the clouds |
| what five things does a river undergo changes in, in its long profile | gradient, width, depth, discharge, load |
| what is the river's long profile | its journey from source to mouth |
| what is groundwater storage | water that is stored in the ground (within porous rock). the uppermost limit of groundwater is known as the water table |
| what are the three stages in a river's journey | uppercourse, middlecourse and lowercourse |
| describe uppercourse | in the mountains near the source |
| describe middlecourse | as the river enters an area of low land and the valley starts to broaden out |
| describe lowercourse | the river flows over a broad, flat floodplain into sea |
| what part of the river do these characteristics belong to: steep v-shaped valley narrow shallow channel high bedload interlocking spurs waterfalls gorges | uppercourse |
| what part of the river do these characteristics belong to: open, gentle sloping valley with floodplain wider deeper channel more suspended sediment meanders river cliffs slip off slopes | middlecourse |
| what part of the river do these characteristics belong to: open, gentle sloping valley with floodplain flat wide floodplain wide open valley very wide and very deep channel ox-bow lakes floodplains | lowercourse |
| describe width in a river | the distance from one bank to the other. the width increases down the long profile as the channel needs to have greater storage capacity for the extra water that tributaries bring |
| why does width increase down the long profile | the channel needs greater storage capacity for the extra water that tributaries bring |
| describe depth | average depth of the river, measured at equal intervals across it. like the width, it also increases as you move further downstream to hold the extra river discharge |
| describe discharge | volume of water passing a measuring point or gauging station in a river at any given time. discharge will increase with distance downstream as more tributaries join the main channel |
| how do we measure discharge | by multiplying the cross sectional area of the river by the velocity of the river |
| what is load | the material carried by the river ranging from small clay sixed sediment to large boulders |
| how do we measure load in a river | it is very hard to measure the size of the load in suspension so instead we concentrate on the load lying on the channel bed. this load is normally measured for size and roundness |
| what is the load on the channel bed called | bedload |
| why might a small at uppercourse sometimes be able to carry a much greater amount of water and more bedload | if precipitation increases in springtime, particularly due to melted snow from the mountains, the river volume will surge therefore producing a bigger force to carry large sediment |
| what index to we use to measure load roundness | Power's Roundness index |
| what does power's roundness index help us do | make more objective decisions on the degree of roundness or angularity of a piece of bedload |
| what are the six stages in the roundness index | very angular, angular, sub-angular, sub-rounded, rounded, well rounded |
| in the uppercourse where will most erosion be directed | vertically, wearing away the bed of the river |
| what does uppercourse erosion produce in the landscape | deep v-shaped valleys |
| where does most erosion direct itself in lowercourse | laterally, wearing away the banks |
| what does lowercourse erosion produce in the landscape | flat broad valley floors |
| what are the four types of erosion | abrasion, attrition, solution, hydraulic action |
| describe abrasion | sand and stones in the river scrape the bed and banks and wear them away |
| describe attrition | rocks and stones knock against each other, wearing each other away |
| describe solution | water dissolves soluble minerals from the bed and banks. this helps to break them up |
| describe hydraulic action | in a fast-flowing river water is forced into cracks in the bank. overtime it breaks up the bank |
| how can some soil and stones previously be carried to the river | rain and gravity |
| how can the material around the river already be loosened | by weathering |
| what are the four types of transportation | traction, saltation, suspension, solution |
| describe traction | rolling stones along the bed |
| describe saltation | sand-sized particles bounce along the bed in a 'leap frog' movement |
| describe suspension | silt and clay-sized particles are carried within the water flow |
| describe solution | some minerals dissolve in the water |
| which process of transportation requires the most energy | traction |
| which process of transportation requires the least energy | solution |
| why do rivers transport more load in winter than summer | in the wintertime the water evaporated in summer will fill the river higher through precipitation, meaning its energy and force will be increased and more load will be transported |
| in what four situations does deposition occur | when the river enters a lake or the sea, slowing its flow when there is an area of shallow water, slowing the river flow when the river floods onto its floodplain, where it flows very slowly when the load is increased suddenly |
| what is an example of when load could be suddenly increased | after a landslide |
| where do waterfalls occur | in uppercourse where the long profile is steep |
| how are waterfalls formed | when a more resistant rock (the capstone) overlies a softer rock. Specifically hydraulic action and abrasion will erode a deep plunge pool at the base of the waterfall |
| why does the waterfall move backwards | the waterfall becomes undercut and the hard cap rock above periodically collapses, resulting in the gradual movement o fthe waterfall upstream |
| what does a waterfall leave behind in its path | a gorge |
| which course of the river are meanders found in | middle and lower |
| what are slip-off sloped and river cliffs | if there is a difference in depth in the channel, water will flow to the deepest side of the river, meaning that more erosion will occur on that side, and more deposition will occur on the side that the river is avoiding. two landforms are formed through |
| where will the velocity be highest in a river meander | on the outside bend |
| why does water travel quicker on a deeper channel | there is less friction so the water moves faster |
| what are point bars | the old inside bends of the meander |
| how does a meander become an oxbow lake | in some cases the neck of the meander gets so thin through erosion that the river eventually cuts across it. deposition occurs on the old bank and the meander is sealed |
| what is a floodplain | a flat area of valley floor |
| which course of the river runs through a floodplain | middle and lower |
| how does a river turn a valley floor into a floodplain | as the meanders grow outwards, they also move position downstream, meaning erosion at the outside of the river cuts into higher land at either side of the floodplain floor, creating distinctive bluff lines. |
| how does a levee form | during a flood the water at the edge of the floodplain is barely moving and so does not have enough energy to transport large bits of bedload out at the edge. only fine sands and clays can make it there. the largest bedload pieces are deposited on the ban |
| what is the name of the floodplain floor beneath the levees | alluvium |
| what five reasons make rivers attractive for settlers | drinking water, irrigation, fish(food), sewage/hygiene, communications |
| what are the four physical causes of flooding | precipitation soil and underlying rock landuse/vegetation steepness of drainage basin |
| four human causes of flooding | deforestation urban growth river management global warming |
| how does precipitation cause a flood | *heavier rainfall *fills air spaces in soil *surface run-off caused *flash floods |
| what is a flash flood | during a period of drought, dry soil cannot infiltrate any precipitation, causing a flash flood |
| how does soil and underlying rock cause a flood | *different soil types different levels of infiltration capability *porous rocks let water through |
| how does landuse/vegetation cause a flood | *trees/plant roots intercept water through leaf/root system |
| how does the steepness of the drainage basin cause a flood | *large basin takes water long time to reach the bottom *however steep slopes increase flood risks |
| how can deforestation cause a flood | *lack of vegetation increases surface run-off *roots no longer hold soil structure together, increasing soil erosion and depositon *lack of space for water in channel |
| how can urban growth cause a flood | *farmland converted to concrete *water collected in drain pipes and channelled to river *less infiltration *less throughflow *common flooding cause |
| how can river management cause a flood | *changing river channel shape by narrowing or building a bridge can cause river capacity to reduce and increases flood risks |
| how can global warming increase flood risks | *more water released from glaciers/ice caps *rivers must cope with more water than used to |
Created by:
keo788
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