A second problem is bifurcation. This means that the position statement contains more than one argument. Bifurcation is a particularly acute problem with short papers such as the one assigned for this course. The case above is again an example. The second statement above appears to diverge into several topics.
Few equations work.
The Bagnold equation is best. The Bagnold equation has limited use in gravel-bed rivers. This example is of course severe. A position statement for a short paper such as yours should clearly address one central idea. There is not sufficient space to develop more.