Expression Session Summarise “stream discharge” and “river load” using diagrams to assist your answer.

Learning Goal Define stream discharge. Examine its relationship to stream flow and channel shape.

Key Words Bed: The bottom of the river channel Bank: The sides of the river channel. Channel: The confines of the river, encompassing the bed and two banks. Wetted Perimeter: The total length of the bed and the banks in contact with the river. Cross-sectional area: The width of the river multiplied by the depth of the river. Because the depth of the river will vary across its width, an average depth reading is normally taken. The cross sectional area is normally given in m2. Velocity: This is the speed that the water in a river is travelling at. The unit of measurement is normally metres a second (m/s). River velocity can be measured using a flowmeter (pictured right), or more commonly by timing a floating object over a set distance (pictured left). Velocity is then calculated by dividing the time (seconds) by the distance (metres). Discharge: This is the amount of water in a river at a given point. Discharge is normally measured in cumecs (cubic metres a second). It is calculated by multiplying the cross-sectional area by the velocity. As you move from the source to the mouth, both the discharge and velocity of a river increases.

I DO What is Bradshaw Model? Discharge = the volume of water passing a particular point over a given period of time Increases as the distance increases due to added input from tributaries. I DO

I DO What is Bradshaw Model? Occupied Channel Width = distance from one side of the stream to the other Increases due to increases in discharge which means more erosion. I DO

I DO What is Bradshaw Model? Channel Depth = depth from the water surface to the sea bed Increases due to increases in discharge which means more erosion. I DO

I DO What is Bradshaw Model? Average velocity = speed of the river flow Increases steadily as you go downstream. How can this be with less of a gradient downstream? Less roughness of the riverbed = more efficiency I DO

I DO What is Bradshaw Model? Load quantity = total load of the river including all sizes Increases with the discharge and velocity. So wouldn’t this add to the friction and affect the average velocity downstream??? I DO

I DO What is Bradshaw Model? Load Particle Size = The actual size of the load particles Decreases as you head downstream. Therefore, the riverbed and wetted perimeter becomes more smooth and adds to the average velocity downstream. I DO

I DO What is Bradshaw Model? Channel Bed roughness = how rough the stream’s bed is Decreases as you head downstream as there are fewer stones and more sand. I DO

I DO What is Bradshaw Model? Slope angle = how steep the slope the river lies on is Decreases as you get further from the mountains and water source. I DO

Longitudinal Section Task Your Job – create an annotated longitudinal section of a river to help explain how it’s features and dynamics change throughout its different stages using the Bradshaw model. Use the GeoFact Sheet to assist you. WE DO

Task 1 a - Outline the role played by friction in the flow of water b - Define the two types of water flow.  c - Copy figure 3.15 (laminar flow) into your work book and label appropriately.  d - What is the relationship between velocity and turbulence?  e - Copy figure 3.15 (turbulent flow) into your work book and label appropriately.  ​ f - Outline and sketch the three main influences on river velocity. This will include diagrams 3.16, 3.17, 3.19 & 3.20.  Task 2 - Copy & Complete the following sentences, deleting as appropriate •A river in a deep, broad channel, often with a gentle gradient and small bedload, will have a greater/lesser velocity than a river in a shallow, narrow, rock filled channel – even if the gradient of the latter is steeper. •The velocity of the river increases/decreases as it nears the sea •The velocity increases/decreases as the depth, width and discharge of a river all increase. •As the roughness increases/decreases, so does turbulance and the ability of a river to pick up and transport sediment YOU DO I use Integrated Approach (Waugh) for this section of the work page 68-70.