Summary:

The most important factors causing deep erosion in the river side arm include positive bedload balance and hindered ice progress in the main river bed. Another factor is formation of near-bank channels along high banks or banks covered with high and dense vegetation. Those factors also lead to partial destruction of dams and washing out of silted material. Thus, access of predators to an island is restricted. That provides favourable conditions for natural development and for establishing nature reserves in regulated rivers.