عنوان مقاله [English]
River terraces are important components of natural landscape, and among the key elements in the study of geomorphic features of river phenomena in regional and local scale as well as trend of river power changes in relation to different factors in the course of time. These phenomena, as river forms, represent the level of flowing waters in the past and river performance in response to changes in the characteristics of several factors. Regarding the activity of processes. and influenced by changes and disturbances in conditions, the river sometimes has to cut its bed and create benches parallel with its longitudinal profile.
The river terraces, which provide successive changes in beds of river flows, are in fact considered the best means for surveying the past history of regions in terms of the type of changes and rivers’ reaction to such changes in different times. Considering such an important feature, these phenomena are among the topics discussed in different sciences of the earth, especially geomorphology and soil science. For soil sciences, the terraces are: smooth surfaces with mild slopes formed by heterogeneous pebbles whose presence along the rivers provides a relatively stable place for soil formation.
For geomorphology, river terraces, as the most important geomorphologic forms, are results of the operation of water flows which have been formed by fluctuations and changes in various factors, such as changes in the energy of morphodynamic factors.
River terraces formed and developed by alternation of the processes of destruction and sequestration in the rivers are usually seen as slope cuts on either side of the rivers’ banks or only on one side of them.
Generally, it can be said that the formation of terraces around the bed of rivers suggests adjustments and changes in longitudinal profile of rivers in response to changes in the type and amount of exchanges related to the location, special time and evolution of longitudinal profile of river in order to adapt to the new conditions.
Despite the importance and major influence of tectonic activities on river alluvia and formation of terraces, research in this area has been very trivial. The difference in the shape of channels and variation in the response of rivers to such activities (due to difference in flow rate, type and amount of bed load) have possibly been the main reasons for complexity of the subject and, as a result, a decrease in the number of studies in this field.