Urbanised drainage basin has fewer trees and less grass, with more paved areas than natural catchment so there is less infiltration and more quickflow. When there is a fall of rain, the steam in urbanised catchment rises more quickly and is more likely to flood and therefore discharge increases more rapidly and has a higher peak. Also, since there is less ongoing seepage from groundwaer in urbanised catchment, steam is more likely to dry up so it has more rapid decrease of discharge.
Flood Period: The total time shown in the rising (increasing discharge towards peak) and receding (decreasing discharge ) limps of the flood hydrograph.
The graph above clearly shows the base flow level. The Flood period is the time it takes from the increase in discharge to recede back to the base flow level.
Peak Rainfall - the time of the highest rainfall Peak Discharge - the time when the river reaches its highest flow Lag Time - time taken for water to find its way into the river Base Flow - Normal flow of the river
The purple bar graph shows the rainfall happening within a period of time. The blue line represents the discharge of the river. It only rains from 0 to 12 hours and the peak rainfall is between 6-8 hours. However this is not when the highest discharge is. There is a time between peak discharge and peak rainfall. This would be the lag time.
As you can see, in the hydrograph the lag time is the time between peak rainfall and peak discharge, this is highest amount of rain to highest volume of water in a river after a rainy event
Streams that flow only after rain and do not have a permanent seepage source. In this graph as time moves on, there is no more discharge which means the stream is not flowing anymore.
Water has no capability to be absorbed into the land in the Urban areas. As the area becomes less urban and further into nature the waters ability to be absorbed increases, hence flooding decreases.
Rural hydrographs have a much longer lag time as the water that is needed to get to fill the river to its 'peak discharge' needs to go through the dense soil through the process of ground water flow and ground flow, to get into the river. This means that the rising limb of this hydrograph will be much longer than that of an urban area as it takes a longer time for the river to fill to its full capacity. The falling limbs will stay roughly the same.
In contrast, the urban hydrographs will have a much quicker lag time as the water that is needed to fill the river up to its 'peak discharge' can access it much quicker and easier as more surface run-off occurs from the urban areas being built out of impermeable cement or concrete buildings and roads. Also, as the water is sitting on the impermeable surfaces, more evaporation will occur and in turn this will cause more precipitation to happen, making the process in an urban area even faster than that of a rural one.
LAnd use: vegetation intercepts the precipitation and allows evaporation to take place directly into the atmosphere so it reduces the amount of water available for overland flow. vegetated areas reduce flood risk with a longer lag time
the large number of impermeable surfaces in urban areas such as concrete and tarmac encourages surface run off into gutters and drainage systems carrying water quickly to the nearest river. deforestation removes the trees so there is less interception
-Rural have a longer lag time as the water that is needed to get to fill the river to its 'peak discharge' needs to go through the dense soil through the process of ground water flow and ground flow, to get into the river.
A number of factors (known as drainage basin controls) influence the way in which a river responds to precipitation and have an effect on the shape of the hydrograph.
The size, shape and relief of the basin are important controls. Water takes longer to reach the trunk stream in a large, round basin than in does in a small, narrow one.
FAIRY MOMENT JEAR BEAR AND OLLIE 1. Learnt how to use blogger 2. Learnt how useful blogger sharing is as a study tool 3. Dictatorship is a successful lesson strategy 4. Discharge increases in urban areas 5. Bubbly love is happy
http://www.google.com/imgres?imgurl=http://serc.carleton.edu/images/introgeo/socratic/examples/Hydrograph.jpg&imgrefurl=http://serc.carleton.edu/sp/library/examples/hydrosphere.html&h=392&w=588&sz=28&tbnid=30bGXEPERNUfCM:&tbnh=81&tbnw=121&prev=/search%3Fq%3Dhydrograph%2Bgraph%2Bexamples%26tbm%3Disch%26tbo%3Du&zoom=1&q=hydrograph+graph+examples&usg=__d7lzBkjzfWevd5tiX6pZqZvRUIQ=&docid=Jy5LYMdDPKKWrM&hl=en&sa=X&ei=EUuHUdT_FMWViAeY44Fw&ved=0CDcQ9QEwAg&dur=32
ReplyDeleteUrbanised drainage basin has fewer trees and less grass, with more paved areas than natural catchment so there is less infiltration and more quickflow. When there is a fall of rain, the steam in urbanised catchment rises more quickly and is more likely to flood and therefore discharge increases more rapidly and has a higher peak. Also, since there is less ongoing seepage from groundwaer in urbanised catchment, steam is more likely to dry up so it has more rapid decrease of discharge.
DeleteFlood frequency is the number of times that a flood of a given magnitude will occur on average in a specified period. Second!
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteFlood Period: The total time shown in the rising (increasing discharge towards peak) and receding (decreasing discharge ) limps of the flood hydrograph.
ReplyDeletehttp://www.google.com/imgres?imgurl=http://www.bbc.co.uk/bitesize/higher/geography/images/hydro_01hydrograph.gif&imgrefurl=http://www.bbc.co.uk/bitesize/higher/geography/physical/hydrosphere/revision/1/&h=369&w=546&sz=11&tbnid=3R8jXK00cwMhdM:&tbnh=96&tbnw=142&prev=/search%3Fq%3Dhydrograph%26tbm%3Disch%26tbo%3Du&zoom=1&q=hydrograph&usg=__YUUeUJAgUUjYyGsmP-jfkVvnkxM=&docid=lASGV4GJUlrAgM&hl=en&sa=X&ei=kUyHUYmyEqqRigfE5IHACA&ved=0CDQQ9QEwAg&dur=329
DeleteThe graph above clearly shows the base flow level. The Flood period is the time it takes from the increase in discharge to recede back to the base flow level.
Peak Rainfall - the time of the highest rainfall
ReplyDeletePeak Discharge - the time when the river reaches its highest flow
Lag Time - time taken for water to find its way into the river
Base Flow - Normal flow of the river
http://www.bbc.co.uk/bitesize/higher/geography/images/hydro_01hydrograph.gif
DeleteThis hydrograph has been labelled.
http://ih-igcse-geography.wikispaces.com/file/view/1.3C_Storm_hydrograph1.png/78751469/615x382/1.3C_Storm_hydrograph1.png
DeleteThe purple bar graph shows the rainfall happening within a period of time. The blue line represents the discharge of the river. It only rains from 0 to 12 hours and the peak rainfall is between 6-8 hours. However this is not when the highest discharge is. There is a time between peak discharge and peak rainfall. This would be the lag time.
Hydrographs relate stream discharge to time. A typical flood hydrograph contains a rising limg, peak and a receding limb.
ReplyDeleteThe peak discharge shows the highest point on the hydrograph when the rate of discharge is highest. Here it is 50 cubic meters.
ReplyDeletehttp://www.bbc.co.uk/bitesize/higher/geography/physical/hydrosphere/revision/1/
Heavy rain for a shor period of time produces runoff that is concentrated into a short time span. The concentrated runoff is called a flood
ReplyDeletehttp://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes%20GCSE%20Blog%20Resources/Images/Rivers/Flood_Hydrograph.gif
ReplyDeleteAs you can see, in the hydrograph the lag time is the time between peak rainfall and peak discharge, this is highest amount of rain to highest volume of water in a river after a rainy event
https://www.google.com.hk/search?q=hydrographs&bav=on.2,or.&bvm=bv.45960087,d.aGc&biw=1366&bih=682&wrapid=tlif136782135521210&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=M0yHUYfnFYjxiAfW0oBQ#imgrc=3R8jXK00cwMhdM%3A%3BlASGV4GJUlrAgM%3Bhttp%253A%252F%252Fwww.bbc.co.uk%252Fbitesize%252Fhigher%252Fgeography%252Fimages%252Fhydro_01hydrograph.gif%3Bhttp%253A%252F%252Fwww.bbc.co.uk%252Fbitesize%252Fhigher%252Fgeography%252Fphysical%252Fhydrosphere%252Frevision%252F1%252F%3B546%3B369
ReplyDeleteThe pink area is the flood period (above the orange dotted line known as the 'base area'
http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes%20GCSE%20Blog%20Resources/Images/Rivers/Flood_Hydrograph.gif
ReplyDeleteFor this hydrograph it shows that the Lag Time is the time between Peak Rainfall and Peak Discharge
http://www.bbc.co.uk/scotland/education/int/geog/rivers/flash.shtml
ReplyDeleteEphemeral Stream:
ReplyDeletehttp://riverrestoration.wikispaces.com/file/view/hydrograph.jpg/323513992/hydrograph.jpg
Streams that flow only after rain and do not have a permanent seepage source. In this graph as time moves on, there is no more discharge which means the stream is not flowing anymore.
Perennial streams
ReplyDeletehttp://cals.arizona.edu/watershedsteward/resources/module/Stream/images/stream_proc_page11_clip_image001.gif
http://www.mdsg.umd.edu/images/uploads/siteimages/CQ/V07N2/urban_forest_hydrograph.jpg
ReplyDeleteThis graph compares both forested and urban
http://www.google.com/imgres?imgurl=http://www.meted.ucar.edu/hydro/basic_int/flash_flood/media/graphics/urban_hydrograph.gif&imgrefurl=http://www.meted.ucar.edu/hydro/basic_int/flash_flood/image_gallery.htm&h=385&w=448&sz=18&tbnid=m2oD2zoK9HtXwM:&tbnh=90&tbnw=105&prev=/search%3Fq%3Dhydrograph%2Burban%2Bvs%2Brural%26tbm%3Disch%26tbo%3Du&zoom=1&q=hydrograph+urban+vs+rural&usg=__TE3MRO9PzAXgo_VGW79ykn3T_2E=&docid=8kJMy5UeuC6SuM&hl=en&sa=X&ei=YVCHUfTqC6ybigesgYGQDA&sqi=2&ved=0CEEQ9QEwAw&dur=253
ReplyDeleteRURAL : SUBURBAN : URBAN HYDROGRAPHS
Water has no capability to be absorbed into the land in the Urban areas. As the area becomes less urban and further into nature the waters ability to be absorbed increases, hence flooding decreases.
DeleteThis comment has been removed by the author.
ReplyDeleteThis comment has been removed by the author.
ReplyDeletehttp://www.dwa.gov.za/Groundwater/Groundwater_Dictionary/introduction_hydrograph.htm
ReplyDeleteStream discharge can be controlled by flood-control reservoirs. This can be seen by the flat gradient on the yellow line.
DeleteRural hydrographs have a much longer lag time as the water that is needed to get to fill the river to its 'peak discharge' needs to go through the dense soil through the process of ground water flow and ground flow, to get into the river. This means that the rising limb of this hydrograph will be much longer than that of an urban area as it takes a longer time for the river to fill to its full capacity. The falling limbs will stay roughly the same.
ReplyDeleteIn contrast, the urban hydrographs will have a much quicker lag time as the water that is needed to fill the river up to its 'peak discharge' can access it much quicker and easier as more surface run-off occurs from the urban areas being built out of impermeable cement or concrete buildings and roads. Also, as the water is sitting on the impermeable surfaces, more evaporation will occur and in turn this will cause more precipitation to happen, making the process in an urban area even faster than that of a rural one.
http://www.bbc.co.uk/scotland/education/int/geog/rivers/images/hydrographs/hydro5.gif
ReplyDeleteLAnd use: vegetation intercepts the precipitation and allows evaporation to take place directly into the atmosphere so it reduces the amount of water available for overland flow. vegetated areas reduce flood risk with a longer lag time
the large number of impermeable surfaces in urban areas such as concrete and tarmac encourages surface run off into gutters and drainage systems carrying water quickly to the nearest river. deforestation removes the trees so there is less interception
Rural, urban hydrographs
ReplyDeletehttp://ei.cornell.edu/watersheds/Ditches/Ditch%20Images/Hydrograph_urban-rural.gif
-Rural have a longer lag time as the water that is needed to get to fill the river to its 'peak discharge' needs to go through the dense soil through the process of ground water flow and ground flow, to get into the river.
http://books.google.com.hk/books?id=LROqKvHaRyMC&pg=PA142&lpg=PA142&dq=hydrograph+perennial+stream&source=bl&ots=oiukKUh2UU&sig=lOlDADY1RzqIHFIE2XYcy0dH7_o&hl=en&sa=X&ei=-06HUb3EIMaaiQfDz4DIAw&ved=0CC0Q6AEwAQ#v=onepage&q&f=false
ReplyDeleteSO GOOD SCROLL DOWN PG 142
http://www.bbc.co.uk/scotland/education/int/geog/rivers/images/hydrographs/hydro2.gif
ReplyDeleteA number of factors (known as drainage basin controls) influence the way in which a river responds to precipitation and have an effect on the shape of the hydrograph.
The size, shape and relief of the basin are important controls. Water takes longer to reach the trunk stream in a large, round basin than in does in a small, narrow one.
This comment has been removed by the author.
ReplyDeleteFAIRY MOMENT JEAR BEAR AND OLLIE
ReplyDelete1. Learnt how to use blogger
2. Learnt how useful blogger sharing is as a study tool
3. Dictatorship is a successful lesson strategy
4. Discharge increases in urban areas
5. Bubbly love is happy
I learnt about hydrographs as I did not know much about them, and how they can vary. I also learned that Jeremy Engel's middle name is Bubbly_Love.
ReplyDeletefairy moment: this blog comment string is pretty useful
ReplyDeleteMy reign as a dictator has come to an end. I learn more about the individual details of the hydrograph.
ReplyDeleteI have learnt about the contrast of hydrographs in different situations, e.g. urban vs rural hydrographs, forested and deforested areas whooop whooop
ReplyDelete