Selasa, 02 Mei 2017

discharge



hello this is the geographysical and today we're going to talk about river discharge. simply put it's the volume of water that flows in the river measured in cubic meters per second or cumecs.


discharge, discharge increases with precipitation and decreases as temperature and therefore evaporation increases or with the removal of water and known as abstraction


the changes in river discharge over time can be shown using a hydrograph and during a storm it can be shown the storm hydrograph which usually last a couple of hours or days first we have the approach segment which shows the discharge of the river prior to the storm and then peak rainfall in the midst and then there's a steep rising


limb due to rapid increase in water reaching the river followed by peak discharge being the maximum amount of both in the river during the storm. lag time is then used to measure the time it takes between peak rainfall and discharged. after peak discharge as a falling limb with less water flowing into the river at the bottom you can see


base flow which releases groundwater maintaining the rivers flow during periods of low precipitation and above is the runoff or storm flow. at the point of bank full discharge water level has reached the top of its channel and so any further increase will lead to flooding. the storm hydrograph can be affected by several physical factors; the


drainage basin, antecedent moisture, rock type, soil type, vegetation, precipitation, and temperature. a larger drainage basin can catch more precipitation, causing a higher peak discharge. the water has a large distance to travel however and so it will have a longer lag time than a smaller basin. steep-sided drainage basins though have a shorter lag time due


to the quicker flowing water. circular basins will have a much quicker hydrograph and higher peak discharge as all the water will reach the river at the same time. if the basin has lots of streams it will also drain quicker causing a shorter lag time antecedent moisture is the amount of water already present in the drainage basin. if the


ground is already waterlogged then infiltration will be reduced and surface run off will increase, causing water to reach the river more quickly and reducing lag time likewise if the rocks are impermeable water will be unable to infiltrate, reducing the lag time if the soil is sandy more water will infiltrate increasing lag time


but clay soils which have low infiltration rates will reduce it vegetation in the basin will intercept precipitation reducing the speed it reaches the river channel and increasing lag time. the more vegetation there is, the more water is lost through transpiration and evaporation reducing peak discharge. during intense storms


there will be a greater peak discharge the type of precipitation however will effect like time with slow taking longer to melt causing lag time to increase finally, hot dry conditions and cold freezing conditions harden the ground reducing infiltration and therefore lag time high temperatures also increase evapotranspiration reducing the peak


discharge as less water will reach the channel. human activity also affects the hydrograph, in urban areas houses and, roads intersect precipitation causing surface runoff to increase, reducing lag time in farmland areas grazing animals and


discharge

plowing compact the soil, reducing interception and therefore lag time and that is the end of todays video


thanks for listening!


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