Stuck on GeographyWatch
Are you collecting objective or subjective data? Lets suggest a question of the level of erosion in a river.. You could measure this by sampling the smoothness of rocks along the length of your river.. there would be several ways of gatheting this data such as measuring the number of 'corners' greater than 90* on each rock - an in-accurate yet subjective measure that will give you a good idea if you collect enough samples - while this measure won't distinguish between rough rocks with no 90* corners and a perfectly spehical rocks - it will give you a more reliable result than if you were to 'feel' the rocks by hand and and record the smoothnes on an arbitrary sacle between -2 (very rough) and +2 (very smooth) - it will be difficult to keep your preception of 'rock smoothness' consistent throughout the field exercise and could lead to unreliable results.
A much more accurate way to measure the erosion might be to measure the surface area of the rock vs the weight, giving you a definite measure that you can perform statistic analysis on later, making the results much more useful for data presentation and analysis.
I didn't do rivers fieldwork so I'm guessing here, apologies if I got it completely wrong