GCSE Geography Enquiry 25% of the final grade Topic area – Investigate how features of a river change over distance. Content • 2000 Words maximum • Introduction and methods – 800 words – in CLASSROOM CONDITIONS • Data presentation (tables graphs etc) – in CLASSROOM CONDITIONS • Analysis, conclusions and evaluation – 1200 words – in CONTROLLED CONDITIONS
Brainstorm – Which river features could changeover distance? Why? Now read pages 10 and 11.
The Bradshaw Model Velocity Stone size Discharge Gradient/slope Wetted perimeter Friction or turbulence Depth Width Source Mouth
The theory – Drainage basins • A drainage basin is the area of land drained by a river and its tributaries (small rivers that contribute water to the main river). The areas furthest upstream near to the hills are called the source areas. Where the river ends up is called the mouth. • A good example is the Tyne basin. The area between 2 drainage basins is called a drainage divide or WATERSHED. Where a tributary meets the main river we get a confluence.
The Theory – changes in width, depth and velocity • You are going to have to measure a river and see if its characteristics match that of the theory. • Generally as rivers progress downstream they undergo a series of changes. Tributaries contribute water to the main stream so the volume of water and the width and depth all tend to INCREASE. • In the upper reaches of a typical drainage basin there is very little water in the river or stream. Width and depth tend to be small and Velocity (in Metres per second is slow. Velocity is slow because in comparison to the amount of water in the stream there is a lot of friction from the bed and the banks. Velocity is also slower at the surface of the water because of frictional drag from the atmosphere (air). As you move downstream more water is added to the river and the proportion of water in comparison to the frictional force increases, so velocity increases.
The Theory – Gradient and Discharge • The fact that velocity increases with distance downstream often puzzles people because the gradient (slope of the land) is higher in the source areas. Friction simply has more of an impact on a river’s velocity than gradient does. • Gradient changes with distance downstream because the river starts to erode laterally in the middle course rather than vertically (as it does at the source). This means that the river snakes (meanders) across flood plains and does not decrease in height as quickly as it does in the source areas. • Cross sectional area – this is the width times the depth, it should increase with distance downstream. • Discharge is the volume of water passing an area per second. It is calculated using Discharge (m3 per second) = Cross sectional area (m2) X Velocity (m per second)
The Theory - Bedload • Bedload (the stones and sediment on the rivers bed) will generally get smaller and rounder as you move from source to mouth. • This is because of the erosion processes of Hydraulic action, Attrition, Corrasion (Abrasion) and Corrosion. • Lighter sediments are easier to erode, boulders are harder to move.
Where will we study? The river Breamish basin is here.
Tasks – Introducing your study. • Think of a title question and write it down. This should be a general question about rivers and their changes. • Write a paragraph on why you are doing the study. (To help use Who? What? Why? When? And Where) • Break your title question into 5 questions you want to answer? • Locate the study area with maps and paragraph. • You need to talk in depth about the theory behind the topic.