Agravel bar in a river is an example of a landform created by

Because the author of the article did not do an experiment to draw his own conclusions and issue his own information, but he did a bibliographic review of the work of other authors to write his own article.

Explanation:

The article presented in the question above was done through a bibliography search and not through an experiment. This means that the author did not test the hypotheses through a scientific experiment, but formulated the conclusions of his article, based on the works of other authors, which makes this article not the best option to be considered as a reference article.