FIELD INVESTIGATION ON STEP-POOL MORPHOLOGY AND PROCESSES IN STEEP MOUNTAIN STREAMS

Main objective of this paper is to compare the field data measured on a few step-pool reaches of the Aneva River in the Northern Apennines with a reference database including a large number of fields and laboratory data derived from the wide literature on step-pool streams in order to contribute to describe their geomorphology and to understand their generating processes. A field experiment with painted particles is carried out on the Aneva River to investigate the entrainment threshold conditions for particle as large as those making up the steps, and, consequently, for the formation of new or removal of old steps. Theories about the factors controlling the development of these coarse-grained bedforms are tested against the data sets available and the antidune hypothesis is investigated and discusses as well. The reference database and the Aneva data confirm the keystone hypothesis as the most likely to account for the development of step-pool sequence.