Rivers Revision. SDME preparation Jan 2012 A Damming report- why are some strategies for flood management more sustainable than others?. The outline- 14 lessons till exams.
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A Damming report- why are some strategies for flood management more sustainable than others?
Surface run off
Soil moisture storage
normal (base) flow
I = Lagtime
Write a definition of lagtime.
Calculate the lagtime shown on this hydrograph.
Hydrographs are graphs which show river discharge (the amount of water in a river) over a given period of time and show the response of a drainage basin and its river to a period of rainfall.
Discharge is measured in cumecs (cubic metres per second). This can be calculated by multiplying river velocity by channel volume at a given point and time.
The shape of a hydrograph is determined by the speed in which flood waters are able to reach the river. The nature of the drainage basin therefore has a great influence on the way a river responds to a river as it will determine the types and speeds of the flow of water to the river.
Geology and soil
Gradient of the valley sides
What affects the shape of a hydrograph?
Type and amount of precipitation
trees intercept the rain
evapotranspiration reduces the amount of water that reaches the river
water is taken through the roots and so less enters the river
The hydrographs ‘a’ and ‘b’ have been produced from the same storm event but from different drainage basins.
What could cause 2 peaks in a hydrograph?
Compare these two hydrographs.
Which one has the largest lag time? Explain your answer.