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1- The drainage basin hydrological cycle TB page 2Where slopes meet at the bottom of a valley, water is concentrated and forms a river channel. A drainage basin is an area of land drained by a river and its tributaries. Drainage basins are separated from each other by ridges of higher land called watershed. A drainage basin is an open system- a system where there are inputs and/or outputs of energy and matter- with inputs (water and energy) and outputs of water. The water enters the system as precipitation and leaves as stream flow or as evaporation or transpiration.Inputs: energy from the sun/precipitationStores such as glaciers, rivers, lakes and vegetationTransfers and flows move water through the system, such as infiltration. Outputs: moisture lost by evapotranspiration + runoff into the seaKey terms:1- Precipitation (input): All forms of rainfall, snow, frost, hail and dew. It is the transfer of moisture in the atmosphere to the land. 2- Evaporation + Transpiration=Evapotranspiration (output)Evaporation: The change of state from liquid to gas from exposed water surfacesTranspiration: The loss of water from the leaves of plantsEvapotranspiration: the combined losses3- Surface stores such as glaciers and lakes4- Interception (Storage): The process by which precipitation is trapped on the surface of vegetation. Interception loss (output): The proportion of water which evaporates from the surface of vegetation. After interception…transfers5- Stemflow : Intercepted precipitation which runs down the stems of plants to reach the ground. 6- Throughfall: The precipitation which falls straight through the vegetation (or drips off leaves) and reaches the ground.7- Overland flow/ surface runoff (transfers): Water that moves over the ground surface. Water moving as overland flow reaches the river channel much more quickly than water flowing through soil and rocks. The more overland flow that takes place, the faster the river level rises and the more likely flooding is to occur. Overland flow happens from a combination of the following reasons:- The ground surface is relatively impermeable and the water cannot infiltrate as a result of, foe example, urban development.- Vegetation cover has been removed, reducing the infiltration rates and the interception loss. The extra water runs over the ground surface.- When the soil store is already full of water, the term used is saturated overland flow. - The rainfall comes down faster than it can infiltrate the soil. This can occur with intense summer storms.8- Infiltration (Transfer): process by which water soaks into or is absorbed by the soil. It is a very important process, because water entering the soil will move slowly through the drainage basin to the river channel, whereas water which does not infiltrate will flow relatively quickly over the surface to a river as overland flow.Infiltration rate: refers to how much water IS passing through in a certain time.Infiltration capacity: is the maximum rate at which water CAN enter the soil in a particular case [measured in cubic millimetres per hour].

AQA AS Core section: Rivers

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9- Throughflow (Transfer): The downslope flow of water within the soil.10- Percolation (transfer): As water reaches the underlying soil or rock layers, which tend to be more compact, its progress is slowed. This slow movement , called percolation, creates groundwater storage. 11- Groundwater flow/baseflow (transfer): Groundwater refers to subsurface water. The upper layer of the permanently saturated zone is known as the water table and it varies seasonally. Groundwater flow is the slow movement of water through the underlying geology via cracks and joints below the water table and it varies seasonally. The slow flow through rock produces a steady input of water which varies relatively little in comparison with the discharge of the whole river. This explains why rivers can continue to flow even if it has not rained for weeks.