Evaluating the incision rates of the river channel with the approach of dendrogeomorphology (case study: Lavij stream, Iran)

Abstract

One of the changes affecting the channel morphology is the bed channel changes. In general, the factors affecting incision can be divided into two natural and human groups. Incision can cause many problems for the river ecosystem.The study area was located in the downstream of the Lavij stream catchment (Mazandaran, Iran), where three sites were selected to study incision and avulsion channel. The channel changes were obtained using a tree ring analysis, which was used to determine the age of tree establishment and, therefore, date fluvial surfaces colonized by arboreal vegetation. In this study, two dendrochronological methods, including age measurement from 23 cores prepared from alder trees and an age determination method based on tree diameter, were used to assess the channel’s incision rate. The abandonment time of the abandoned channel was evaluated using dendrogeomorphological techniques. The analysis revealed that the erosion rate of the active channel bed, in relation to the abandoned channel, indicated a riverbed lowering of approximately 4.35–5.2 cm per year in the examined sections. The research highlights the significant role that large and rare floods have played in shaping river morphology. Specifically, it indicates that an incision in the riverbed can be attributed to historical flooding events characterized by a discharge of 175 m³/s, which has a return period of approximately 100 years.Also the Alnus glutinosa tree can be used as a suitable species in dendrogeomorphology due to its abundance in the region, its fast growth and the presence of annual rings. The limitation of using the Alnus glutinosa tree in the study area is that the average life of the tree in the area is about 50 years.