4 Match the label to the correct letter WatershedcConfluenceTributarybSourceda
5 What affects the shape of a hydrograph? HydrographsHydrographs are graphs which show discharge (the amount of water passing a particular point in a river at a particular time).Geology and soilGradient of the valley sidesWhat affects the shape of a hydrograph?Type and amount of precipitationLand use
6 How do trees reduce flooding? trees intercept the rainevapotranspiration reduces the amount of water that reaches the riverwater is taken through the roots and so less enters the river
8 Hydrographs Rising limb Falling limb 1) What type of flow (choose from surface runoff, throughflow and groundwater flow) causes the rising limb?2) Which is the last type of flow to reach the river?3) What is the lag time?
9 HydrographsbaThe hydrographs ‘a’ and ‘b’ have been produced from the same storm event but from different drainage basins.Which of the following river basin descriptions are more likely to have produced hydrograph ‘a’ and which are more likely to produced hydrograph ‘b’?Chalk bedrockImpermeable bedrockUrban areaClay soilDeforested river basinRural areaGentle valley gradients
10 Hydrographs Compare these two hydrographs. Which one has the largest lag time? Explain your answer.
11 HydrographsImagine that these two areas have had the same amount of rain over a 24-hour period. Draw a possible hydrograph for each of these areas.AB
13 In some drainage basins the discharge of a river can rise slowly or quickly in response to a period of rainfall. This can be shown on the Flood Hydrograph. When a storm begins, discharge does not rise immediately as only a little of the rain will fall directly into the channel. The shape of the hydrograph will very much depend on a number of factors.Key: Definitions:Discharge-Amount of water passing a given point at a given time.Lag Time- The difference between peak rainfall and Peak dischargeRising Limb – Discharge rising in the river (i.e. water level rises)Falling Limb – Water level falls in the river.
15 Which conditions give a Flashy Hydrograph Which conditions give a Flashy Hydrograph? Which will give a lower, later peak discharge?
16 Heavy storms Well distributed rainfall Permeable Rock Impermeable RockDense Vegetation Little VegetationLong & thin Basin Short & round BasinSteep slopes Gentle slopesFlood control scheme No river managementRural area Urban area