Investigation of human role on morphological channel changes of Lighvan Chai River

Human role alter the amount of water and sediment inputs to rivers, directly and indirectly and leading to changes in channel geometry, such as changing the width and depth of the river. In this study was investigated channel morphology changes of Lighvan river by using surveys and field studies of Lighvan River, HEC-RAS model and changing river morphology of Lighvan and the human role in it were studied. Results show that there are not any systematic trends between morphological parameters and distance from downstream of river so that width, depth, width/depth ratio, bankfull area and discharge have not increased systematically towards downstream that shows beside of natural factors, unnatural factors such as human interventions were important in channel morphology changes. Changes of width and depth of the river in different cross- sections varies so that the number of changes in the channel width is visible by channelization (eg in sections 2, 6, 8 and 12) also changes of channel width and depth in other cross-sections such as cross-sections 4 and 5 is due to increasing agriculture lands and housing in river front. Also channel morphological changes during the past decade indicate that the dominant process in the studied reach was incision and narrowing of the channel. Only in some sections, aggradation occurred in upstream and in other sections, incision is the dominant process. In general, incision (over 1 m) and narrowing (over 18 meters) are dominate in Lighvan Chai river, though the channel has been widening at some sections such as 9 and 10 and little aggradation in sections 1, 2, 3, 5 and 7. All these changes indicate that, along with the natural factors (increasing the maximum discharge), the role of human factors (channelization and riverfront land use changes) has a significant impact in the Lighvan river channel changes.