Drainage Basins
Definitions Drainage basin: An area of land drained by a single river. Also called the catchment area of a river. Watershed: The dividing line between two drainage basins. Drainage Density: The total length of streams / area of basin.
Drainage Basins Source Watershed Confluence point – where tributary meets main river Tributary Main river Catchment Area
Drainage Basins Write a definition of the major features of a river Watershed, source, tributary, confluence, mouth You must also be able to explain the drainage basin system with reference to: Inputs Outputs Transfers Stores
Hydrosphere: River Basins
Types of Drainage Patterns
Stream Order
Write the questions and answers: The drainage basin What is the area drained by a river called? What is the line around this that encircles the whole system? Stream ordering Draw a diagram to show stream ordering and explain what it is used to show. Drainage density Write out the formula for working out drainage density of a river system. What factors can affect the drainage density of an area? What major risk does a high drainage density exacerbate?
Hydrosphere Drainage basin as a system Explain why the river system is an open system. Make a copy of Fig 3.5 p.41, ensuring to colour code in the key. What is evapotranspiration? What is interception? Name the different ways in which water can be transferred through the system. What is groundwater and how can it be stored? Why is baseflow important to stream and rivers during the dry weather? Describe 2 ways in which runoff occurs.
Flows and storm hydrographs Make a list of the factors that can have a bearing on the discharge of a river. Define the term discharge. What is a hydrograph and how and where is the data for it’s construction collected? Make a copy of fig 3.8. What is lag time? Why does it happen? What can be said about the base flow lag time? Why is this? If this rising limb of the graph is steep, what does this mean? Why do you think that the recessional limb falls less steeply than the rising limb? What will happen if the bankful discharge level is exceeded? What becomes the source of water in a river after the storm flow has finished?