We have been looking at how the valley changes downstream

SUMMARY – Valley Long profile changes downstream Long profile refers to the changes in altitude (height above sea level) from the source to the mouth 1. In general the long profile is smoothly concave with the gradient being steeper in the upper course and becoming progressively gentler towards the mouth 2. The idea that over a long period of time a smooth concave shape of the long profile will occur. 3. This smooth profile – known as the graded profile - will occur as irregularities in the underlying geology are eventually eroded by the river. 4. The graded profile represents a balance between erosion and deposition. 5. Changes in sea level can also effect the long profile. We will study this later.

SUMMARY – Valley cross profile changes downstream The valley cross profile is the view of the valley from one side to another. 1. The area valley profiles can be divided into 3 sections 2. The Upper Course. A narrow steep-sided valley where the river occupies all of the valley floor. This is a result of vertical erosion 3. The Middle Course. A wider valley with distinct valley bluffs and a flat floodplain. More U shaped. This is a result of lateral erosion. 4. The Lower Course. A very wide flat floodplain in which the valley sides are difficult to locate. Large scale deposition

Downstream changes in velocity and discharge 1.To understand changes to velocity downstream 2.To understand changes to discharge downstream

Where is the water moving faster? DISCHARGE and VELOCITY increase downstream!!! Where is there more water? Why did you think that this water was faster? Energy from the river is lost due to friction!

Why does velocity and discharge increase downstream? 1.The reduction in gradient downstream is more than offset by an increase in the mass of water, as more smaller tributaries join the main river – Amount of water is responsible for an increase in velocity 2.The roughness of the river channel also decreases downstream. – In the upper stretches boulders and rocks create a rough river bed. This leads to turbulent flow – Downstream finer sediment is deposited and the riverbed is less rough. This allows a less disturbed laminar flow – which is faster COPY THE DIAGRAM ON PAGE 26 OF YOUR BOOKS

Why does velocity and discharge increase downstream? 3. The channel down stream is more semi- circular, compared to a wide shallow shape. – This semi-circular shape is more efficient at transferring water because less energy is lost overcoming friction with the riverbed.

Challenge…. 3 teams 4 questions to answer Each time your hear the music move to the next question. Try to fill in as much information on the sheet as possible in the time given.