Explain the formation of a meander.

Explaining the formation of a meander is a common question at both GCSE and A-Level. The answer given below is for an A-Level response.Answering this question may also involve drawing a small annotated sketch of a meander as well as a substantial paragraph of explanation.The formation of a meander can often be explained in a series of key steps (remember that geographical terms are very important here):1. Due to banks of sediment at the bottom of the river (which are deposited at times of low flow, that is, a low velocity and low discharge, meaning deposition increases), the river weaves around these alternating shallow and deeper sections (riffles and pools) on what was an initially straight channel.2. This movement targets one bank of the section after the riffle, subsequently leading to erosion (carried out by hydraulic action and abrasion) – this becomes the outside bend of the meander.3. This leads to the formation of a river cliff on the outside bend. The material eroded further upstream is deposited on the opposite bank (inside bend) on the slip off slope. This is due to a corkscrew movement in the river (helicoidal flow) which results in water levels on the outside of a meander bend to be elevated, giving a faster velocity (the Thalweg line is located here). The deposition on the inside bend gives an asymmetrical cross section of the channel. The Thalweg line is the line of maximum water velocity down the path of the river.4. Erosion and deposition continues which leads to the meanders becoming more curved. This eventually results in ‘meander migration’ – i.e. these processes shift downstream and are not static in one particular location.