sampling

• a stratified system was used when deciding which sites along the river holford to use
• at least one site was used in the upper, middle and lower course of the river, to ensure a representative sample
• the other sites were chosen to represent specific changes, such as after a confluence of another river, as this will influence velocity
• at the village of holford itself, there is a change in the geology of the area, leading to a steep change in the gradient
• at each site, systematic sampling was used to measure velocity and depth, the width was divided into 6 so that 5 measurements were taken in the central part of the channel, and not to the very edge
• systematic sampling is necessary to get a representative velocity and depth across the whole river channel, as the widths will be different this was the fairest way to achieve results and the way to avoid errors