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16 Cards in this Set
- Front
- Back
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What is a drainage basin? |
An area of land drained by the river and its tributaries. |
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Define the boundaries of the drainage basin. |
It's watershed, known as raised pieces of land which bound the drainage basin, and the sea. All precipitation which falls within the boundaries of the watershed will make its way into the sea. |
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Describe the inputs and outputs of the drainage basin in terms of a systems theory. |
The inputs of the drainage basin would be solar energy (used for evapotranspiration) and precipitation. The outputs of the drainage basin consist of evapotranspiration, surface runoff / overland flow leading to the sea, and percolation of water into underlying rock strata. |
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List how water is stored in the drainage basin hydrological cycle. |
Puddles, rivers, lakes, groundwater storage, soil moisture, water stored on vegetation following precipitation. |
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Describe the dynamic equilibrium of rivers. |
This describes the constantly changing characteristics of a river which strive overtime to reach a state of 'balance' or 'equilibrium'. Changes in flow states and energy contribute to this. |
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What is systems theory, and give an example for each type of system. |
System's theory is a way of identifying relationships between the different components of a given system, particularly the inputs and outputs of that system. There are 3 different type of systems. Isolated - These are systems which have no overall input or output of energy or material - an example of this would be the universe. Closed - These are systems which have inputs and outputs of energy, but not matter. Open - These are systems which both receive inputs of energy and material, and also output energy and material. An example of this would deb the drainage basin hydrological cycle. |
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Contrast a negative feedback loop with a positive feedback loop in relation to systems theory. |
A negative feedback loop is changes which occur in a given system such as a river, which present new circumstances that cause the next set of changes to revert the system to its previous state. To contrast, a positive feedback loop is such that changes to the state of the system lead to further changes to the system that work towards leading the system further and further away from its original state. (Each change reinforces the next). |
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Describe the difference between the global hydrological cycle and a drainage basin hydrological cycle.
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The global hydrological cycle is a system which encompasses the entire global circulation of energy and moisture across the Earth, whereas the drainage basin hydrological cycle encompasses the characteristics of a singular drainage basin, not a network thereof. |
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Describe how the inputs and outputs of the hydrological cycle vary with progression through he seasons. |
During winter, inputs of the system are high due to higher levels of precipitation introducing water into the system. At such time, temperatures are low such that evapotranspiration rates are also low. This leads to increased surface runoff as soils are saturated, resulting in increased river discharge and river level. During summer, the outputs of the system succeed the inputs. Precipitation is low and outputs such as evapotranspiration have increased temperatures resulting in higher rates. Because there is little replenishment of the soil from precipitation, it means that the soil moisture may be used up in evapotranspiration, resulting in them becoming increasingly dry. This reduces surface run off and encourages lower levels of river discharge and lower river levels. |
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Why is it that discharge is not affected immediately after a subsequent precipitation event? |
This is because not all of the precipitation enters the river head on. Some of it lands on the basin and catchment area. Not all of the water enters the river, some is intercepted by vegetation, infiltrated, stored by soil moisture and slowed down in the process, meaning that it can take a while for the water to reach the river. The time it takes for the water to reach the river following a peak rainfall is known as the lag time. |
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Describe how River discharge may be affected. |
- Precipitation - Hot weather (evaporation) - Removal of water (evaporation/abstraction - animals, agriculture and so forth.) |
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Describe the drainage basin charactersistics that can affect river discharge. |
- The size of the drainage basin. If the catchment area is larger, it can catch more precipitaiton, leading to higher discharge than smaller areas. In contrast, lag time will be higher as the water needs to travel a larger distance than smaller basins to reach the river. - Basins with steep-sided slopes will have shorter lag times as the water will be able to travel to the river much quicker. Becuase more of the water is accumulating at once at the river, this can also lead to a higher peak discharge. - Circular drainage basins are much more 'flashy' since the distance that the water has to travel from each point along the circumference of the basin is roughly the same, meaning that the water reaches the river at the same time, reducing lag time and increasing the peak discharge significantly. - Drainage basins with lots of streams (high drainage density) will have shorter lag times as it can drain the water in very short time. SUMMARIZE: - Size of catchment area - Slope (water can move fast) - Circularity (water reaches at the same time) - Drainge density (does it have any streams?) |
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Describe other ways in which river discharge can be affected, related to precipiation. |
The amount of moisture in the soil is a significant factor. If the soil is already saturated, it reduced the infiltration of water through precipitation, and as such increases the rates of surface run off. Since surface run off is much quicker than throughflow and baseflow it means that the lag time is much shorter as the water can reach the river in a much shorter amount of time. - Rock type. This affects the lag time and the peak discharge. Rocks which are more permeable beneath the surface will allow for more water to be stored, increasing percolation and inflitration rates, thus reducing surface runoff, but also increasing throughflow and groundwater flow rates. Impermeable rock (can be introduced through urbanisation) will reduce the rates of infiltration as water cannot pass through the rock, less will be stored therefore, increasing the peak discharge as more water will make it to the river, and it will also increase surface run off as less water is infiltrated, reducing the lag time. - Soil type affects both lag time and discharge. sandy soils are more porous and allow for higher rates of infiltration than soils like clay. This would mean that there is less surface run off because more of the water is infiltrated, reducing the peak discharge and increasing lag time. - Vegetation affects both lag time and peak discharge. More vegetation allows for more interception, storage and infiltration. Also allows for more transpiration. This reduces peak discharge and increases the lag time. - Precipitation affects just the peak discharge. More water falling on the basin will result in a higher peak discharge. The type of precipitation can also affect the lag time. E.g. snow vs. rain. - Temperature can affect lag time and peak discharge. Hot dry, or cold, freezing conditions result in harder grounds, reducing infiltration, increasing runoff, decreasing lag time and increasing peak discharge. Higher temperatures also results in higher evapotranspiration which results in lower peak discharge. SUMMARIZE: - The amount of antecedent moisture pre-existing in the soil before the precipitation event. (Soil saturation > runoff > increased discharge.) - Rock Type. (permeable vs. non permeable) - Precipitation - Presence of vegetation - Temperature - Soil Type (Sandy vs. Clay). |
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Describe human factors which may affect discharge. |
- Urbanisation - Man made drainage systems reduce lag time as the water travels to the river in much shorter time. Increasing peak discharge and reducing lag time. |
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Describe 5 ways in which river erosion occurs. |
- Abrasion - large rocks scrape and rub against the bed and banks, removing material. (This causes most river erosion). - Hydraulic action - Pressure of water breaks rock particles away from bed and banks. - Solution - Often a byproduct of hydraulic action, the rock is dissolved into the water itself. - Attrition - small eroded rocks smash into each other and break off into smaller fragments, becoming less angular and rounded as this happens over time. This does not affect the bed and banks, but helps to round off river material over time. - Cavitation - air bubbles in turbulent stretches of water implode, causing shockwaves that break pieces of rock off the banks and bed. SUMMARIZE: - Abrasion - Attrition - Solution - Hydraulic Action - Cavitation |
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Describe 4 ways in which material is transporterd along the river. |
- Solution (material that has been dissolved and carried away by the flow of the river) - Suspension - larger particles that may not be soluble are light enough to not deposit on the bed, and are 'suspended' in the channel. They are also carried along by the river. - Saltation - heavier particles which are too heavy to be suspended or dissolved. They 'jump' and hop along the surface of the river bed as the force of water encourages them to. - Traction - larger particles such as rocks and boulders are too heavy to jump, and are instead rolled and scraped along the surface of the river. * Traction and saltation is bedload. |
