With a flow meter it is possible to obtain a measure of velocity in the field – if you do not have access to a flow meter you can take some measurements using a float and calculate velocity using the formula `"Velocity" = "Distance"/"Time"` Dog biscuits make good floats as they are not too easily moved by wind and break down in the water if swept away.
The easiest way to accurately record the locations of your sampling sites is to use a GPS – there are many different Smartphone apps that will allow you to do this.
Meander bend in the middle and lower course of the river (can result in the formation of ox bow lakes) River Cliff the outside bend of a meander the cliff is steep as this is where erosion has taken place.
Slip – off – slope the gentle slope on the inside of the meander where depostion has taken place.
In situations where access is more limited you may have to take a more opportunistic approach to sampling – however in this case it is sensible to get as close as possible to a systematic sample as possible.
An alternative approach would be to base your sampling on areas where you might expect significant changes in river discharge – By choosing sampling sites immediately downstream of confluences you may be able to identify the significant changes in discharge and consider the impact of stream order.
The accessibility of your chosen site will have an influence on your approach to sampling – for a question investigating downstream changes it is ideal to gather data from points progressively further downstream.
A systematic sampling strategy as illustrated – with sampling sites at equal intervals downstream – will help remove bias in site selection, whilst ensuring that your data best illustrates any changes downstream.
For the collection of your qualitative data it is not necessary (or practical!
) to measure all parts of the river – you will need to take a sample.