002 - River Discharge and Hydrographs

Geographic Knowledge and Understanding

River discharge and its relationship to stream flow, channel characteristics and hydraulic radius.

From sub-section 2: Hydrograph characteristics (lag time, peak discharge, base flow) and natural

influences on hydrographs, including geology and seasonality.

Key Concepts

Many physical processes are involved in influencing river discharge and challenge characteristics.

The relative power of each of these processes will dictate their influence.  

Aims

Key Terminology

There are lots of terms for this section of the syllabus! Many of them are listed above but the list is not exhaustive, we will try and define most of them as we go along during the lesson. If there are any that are not defined or just want to review what they mean use the links in the 'Useful Resources' box below.


If you are lucky we may even do a cut and stick exercise for the different terms.

Activity One - Watch

Before we look at the different factors which impact the amount of water that can be found in a river (discharge) we need to know something about discharge and what can be found within a river. Watch the following clip and answer the following questions:


Activity Two - Turbulent and Laminar Flow

It is often believed that a river is flowing faster when the water is turbulent and looks white. This turbulent flow is often found in the upper course of the river and you have have experienced this flow of water when you have been white water rafting or kayaking. Turbulent flow is exciting but not efficient and therefore the velocity of the water is slower when there is water. Look at the two diagrams below and answer the following questions:



Activity Three - Describe - Efficiency

The shape of the river will effect its efficiency. The more the water is in contact with the river bed and numerous obstacles the less efficient the river will be. Rivers are often dredged to remove uneven beds to make the river more efficient. When discussing flood management techniques efficiency is important as the greater the velocity of the river the faster the flood event will pass through key areas such as towns. The efficiency of the river is measured by calculating its hydraulic radius. 


           

Definition 

Hydraulic radius - This is the ratio between the length of the wetted perimeter and the cross section of the river (the higher the number the greater the efficiency of the river).


Image Five

Activity Four - Models - The Bradshaw Model

The Bradshaw Model illustrates the changing characteristics of a river through its three courses; upper, middle and lower. You will be using this model to help justify your hypotheses for the Internal Assessment. While this does not directly link to the geographic knowledge and understanding it is important to know what key characteristics change as you travel downstream, they can impact the discharge of a river.


Useful Resources

Slide Share - geographyalltheway

Activity Five - Hydrographs

Hydrographs helpto show the discharge of a river at a given point in space and time. They are important in helping plan for flooding and monitoring change. Go through the following slide show and answer the following questions to give you a basic understanding of what a hydrograph is and how it can be interpreted.


Taken From: http://www.bbc.co.uk/bitesize/higher/geography/physical/hydrosphere/revision/1/

Image Seven - A Hydrograph

From the BBC - Hydrograph

Construction and Analysis of Hydrographs

Images to help you with Question 5

Image Nine - Length of Precipitation Event

Exam Style Question

Explain the relationship between stream flow and channel shape. (6 marks)

This lesson was development in collaboration with Richard Allaway from geographyalltheway. For more resources please visit www.geographyalltheway.com