Gully development on large dam reservoir shores: dynamics, interaction, and mechanisms

The shores of the Bratsk reservoir are widely affected by bank gullies. We monitored the short- and medium-term gully dynamics at three key sites. The interaction of karst-erosional, aeolian-erosional, and gully and shore erosion processes were determined and presented as conceptual models. Gully and shore erosion were the dominating processes in the Rassvet site in the period of heavy rainfall and the maximum shore edge retreat at high water level stand (2009-2010). During 2011-2013 aeolian process prevailed over erosion due to small rainfall and low water-level stand, and aeolian material accumulated in the gullies. A high water-level period at the Ulei site resulted in shore edge retreat, hanging of gully mouths, formation of wave-cut holes in the shore scarp, and rejuvenation of retrogressive erosion in gully thalwegs. The combined action of karst and gully erosion processes led to a maximum increment in gully size (4486.34 m(3)), recorded at the Khadakhan site in 2004-2008 (at periods of reservoir water-level lowering following water saturation of shore massif at high water levels). This case study shows that the dynamics of the processes, their interactions, and environmental changes are characterized by a certain cyclicity corresponding to water-level changes.