Questions.
Please answer the following questions as comments.
1. How can hyrdrographs explain the magnitude., spatial extent and timing of floods?
2. Describe the differences between the urban and natural hydrographs shown in figure 5.16. Explain why the differences exist.
1. Hydrographs can illustrate the extent of discharge out of the river, after a period of rainfall. The peak on the graph shows the maximum discharge of any given flood, therefore, the magnitude and amount of flood.
Spatial extent can be determined using hydrographs for a number of different rivers in a similar area. The hydrographs of these different rivers can evidently show what rivers will have a larger effect on the surrounding area. An assumption can be made based on previous hydrographs, considering factors such as urbanisation has remained the same.
Timing can also be determined in a similar way, based on past events and floods. The previous graphs can show how long it will take for a river to flood and the extent to which it effects the surrounding area.
2. Rivers flowing in urban areas have a significantly higher discharge than those rivers flowing in natural areas. This is because in urbanised locations the land is generally blocked off to the water flow, and no absorption or assimilation into the land is possible in urban areas. Furthermore, in natural environments more trees and water requiring plants are present to absorb the water, hence the lower discharge.
1. If you have serval hydro-graphs then you can make an assumption from previous floods at each point of the river basin whether or not it is prone to flood. This works as long have not change the river basin upstream. Has it reached base flow from the previous flood.
1) If you have hydrographs of each point of a river in a drainage basin, it can visually show several flood events and their discharges separated by periods of low flow or base flow. It can also explain the timing of floods. By looking closely at the flood period, the total time of the rising and receding limbs, you can find out the flood frequencies.
1. In a drainage basin, if you can take several hydrographs you can see which river is more likely to flood. The ones with the longer lag times will have fewer floods of smaller magnitude. Larger basins will have more precipitation therefore have larger runoff. The larger size also means a longer lag time. Hydrographs with a taller peak indicates a larger magnitude. Timing and spacial extent can be taken as assumptions from previous floods as long as the area has not been changed by urbanisation or anything.
2. Urban hydrographs have a greater discharge because the new less impermeable surfaces such as concrete increase surface runoff. urban areas have less vegetation therefore less infiltration and more quickflow.
rural hydrographs will have less discharge because the vegetation will intercept the precipitation and allow for more evaporation to occur.
1. How can hydrographs explain the magnitude, spatial extent and timing of floods?
Previous hygrographs can demonstrate how prone the river or stream is to flood (how likely it is to flood). The longer than lag time, the less likely it is to flood and the shorter the lag time the more likely it is to flood. Previous hydrographs of the same part of the river can also help contribute the likeliness of flooding. However if the area has been change due to human influences such as urbanisation or building a dam upstream, the hydrograph will change drastically. It can either make it more easier/harder for the river to flood depending on amount of surface run off.
2. Describe the differences between the urban and natural hydrographs shown in figure 5.16. Explain why the differences exist.
Urbanisation changes the surface of land from natural soil to concrete. Concrete is impermeable and therefore increase volumes of surface run off, straight into the river. This is demonstrated by the short lag time on the graph.
1. How can hyrdrographs explain the magnitude., spatial extent and timing of floods?
1. Hydrographs can illustrate the extent of discharge out of the river, after a period of rainfall. The peak on the graph shows the maximum discharge of any given flood, therefore, the magnitude and amount of flood.
ReplyDeleteSpatial extent can be determined using hydrographs for a number of different rivers in a similar area. The hydrographs of these different rivers can evidently show what rivers will have a larger effect on the surrounding area. An assumption can be made based on previous hydrographs, considering factors such as urbanisation has remained the same.
Timing can also be determined in a similar way, based on past events and floods. The previous graphs can show how long it will take for a river to flood and the extent to which it effects the surrounding area.
2. Rivers flowing in urban areas have a significantly higher discharge than those rivers flowing in natural areas. This is because in urbanised locations the land is generally blocked off to the water flow, and no absorption or assimilation into the land is possible in urban areas. Furthermore, in natural environments more trees and water requiring plants are present to absorb the water, hence the lower discharge.
http://www.google.com/imgres?imgurl=https://www.meted.ucar.edu/hydro/basic/FlashFlood/media/graphics/urban_hydrograph.gif&imgrefurl=https://www.meted.ucar.edu/search/module_images.php?currentPage%3D3%26module_id%3D233&h=385&w=448&sz=18&tbnid=m2oD2zoK9HtXwM:&tbnh=90&tbnw=105&prev=/search%3Fq%3Dhydrograph%2Burban%26tbm%3Disch%26tbo%3Du&zoom=1&q=hydrograph+urban&usg=__57zEo-5E2bxy0QUoHFkm_YIhaGM=&docid=oxkRbwyzfRXC0M&hl=en&sa=X&ei=-FCHUZ2sBIWaiQfl34D4Dg&ved=0CC4Q9QEwAA&dur=250
Delete1. If you have serval hydro-graphs then you can make an assumption from previous floods at each point of the river basin whether or not it is prone to flood. This works as long have not change the river basin upstream. Has it reached base flow from the previous flood.
ReplyDelete1) If you have hydrographs of each point of a river in a drainage basin, it can visually show several flood events and their discharges separated by periods of low flow or base flow. It can also explain the timing of floods. By looking closely at the flood period, the total time of the rising and receding limbs, you can find out the flood frequencies.
ReplyDelete1. In a drainage basin, if you can take several hydrographs you can see which river is more likely to flood. The ones with the longer lag times will have fewer floods of smaller magnitude. Larger basins will have more precipitation therefore have larger runoff. The larger size also means a longer lag time. Hydrographs with a taller peak indicates a larger magnitude.
ReplyDeleteTiming and spacial extent can be taken as assumptions from previous floods as long as the area has not been changed by urbanisation or anything.
2. Urban hydrographs have a greater discharge because the new less impermeable surfaces such as concrete increase surface runoff. urban areas have less vegetation therefore less infiltration and more quickflow.
rural hydrographs will have less discharge because the vegetation will intercept the precipitation and allow for more evaporation to occur.
1. How can hydrographs explain the magnitude, spatial extent and timing of floods?
ReplyDeletePrevious hygrographs can demonstrate how prone the river or stream is to flood (how likely it is to flood). The longer than lag time, the less likely it is to flood and the shorter the lag time the more likely it is to flood. Previous hydrographs of the same part of the river can also help contribute the likeliness of flooding. However if the area has been change due to human influences such as urbanisation or building a dam upstream, the hydrograph will change drastically. It can either make it more easier/harder for the river to flood depending on amount of surface run off.
2. Describe the differences between the urban and natural hydrographs shown in figure 5.16. Explain why the differences exist.
Urbanisation changes the surface of land from natural soil to concrete. Concrete is impermeable and therefore increase volumes of surface run off, straight into the river. This is demonstrated by the short lag time on the graph.