Driving factors of short-term channel changes in a semi-arid area (Sahand Mountain, northwestern Iran)

Rivers change through time in response to upstream and downstream controls and may change over very short time periods (i.e., few years), in particular when human impact affects fluvial systems. In the Lighvan River catchment, a semi-arid mountainous area in northwestern Iran, remarkable changes in the fluvial environment and channel morphology have taken place over the last few years. The aim of this paper is to explain driving factors of channel changes along the Lighvan River, in a 16-km-long reach, over the period 2000–2012. Data and methods used include maps and field survey to quantify channel changes; analysis of hydrological data (precipitation and discharges); Landsat images for land-use classification and then evaluation of possible changes in flood peak discharge by SCS method; and calculation of unit stream power changes. In general, the channel underwent incision (up to 1 m) and narrowing (up to 18 m), although aggradation occurred in few cross sections in the upstream part of the study reach and widening in few cross sections in the downstream part. Investigation of causes of these changes showed that magnitude of annual peak discharges increased over the period 1991–2012, and it can be suggested that such increase is related to natural causes (i.e., increase of precipitation) and human impact so that both human and natural factors had a role in the recent evolution of the Lighvan River. Channelization and increase of peak discharges (due to an increase of precipitation and land-use changes) have been the main drivers of channel evolution.