2 Learning objectives What is a drainage basin? How does the drainage basin system operate?What is a flood hydrograph?What factors influence the shape of a flood hydrograph?Learning objectives
3 What is a drainage basin? TributaryA river which joins a larger river.MouthWhere the river flows into the sea, or sometimes a lake.CatchmentThe area from which water drains into a particular drainage basin.WatershedThe boundary dividing one drainage basin from another- a ridge of high land.SourceThe upland area where the river begins.ConfluenceThe point at which two rivers join.
7 Match the label to the correct letter WatershedcConfluenceTributarybSourceda
8 Sketch the river showing its catchment Add the following labels – Watershed, Confluence, Tributary
9 Learning objectives What is a drainage basin? How does the drainage basin system operate?What is a flood hydrograph?What factors influence the shape of a flood hydrograph?Learning objectives
10 How does the drainage basin system operate? A drainage basin system is a part of the world’s hydrological (water) cycle:The hydrological cycle is a closed system.The drainage basin is an open system.You should be able to explain why once you have seen the following slides!
15 Drainage basin system inputs precipitation stores and flows interceptionsurface runoffsurface water storagesoil water storagegroundwater storageinfiltrationgroundwater flowthroughflowpercolationoutputsriver runoffevaporationtranspiration
20 Hydrographs I = Lagtime Write a definition of lagtime. Peak dischargeFalling limbRising limbstorm flownormal (base) flowI = LagtimePeak rainfallWrite a definition of lagtime.Calculate the lagtime shown on this hydrograph.
21 Learning objectives What is a drainage basin? How does the drainage basin system operate?What is a flood hydrograph?What factors influence the shape of a flood hydrograph?Learning objectives
22 What affects the shape of a hydrograph? HydrographsGeology and soilGradient of the valley sidesWhat affects the shape of a hydrograph?Land useDrainage densityType and amount of precipitation
23 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
24 What factors influence the shape of a hydrograph? The hydrographs ‘a’ and ‘b’ have been produced from the same storm event but from different drainage basins.
25 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
26 HydrographsWhat could cause 2 peaks in a hydrograph?
27 Hydrographs Compare these two hydrographs. Which one has the largest lag time? Explain your answer.
29 Key ideasA drainage basin is an area of land drained by a main river and its tributaries.The hydrological (water) cycle is the global circulation of water. It is a closed system.A drainage basin system is one part of the hydrological cycle. It is an open system as it has inputs and outputs.A flood hydrograph shows how a river’s discharge changes in response to a rainfall event.The shape of a flood hydrograph is influenced by a range of physical and human factors.