Evaluating the hydromorphological condition of Tajan river using HMQI method

Abstract

Over the last two decades, the need to restore rivers to the natural and near-natural state has become noticeable. One of the most important tools to achieve this goal is to assess the hydromorphological changes of the river due to human intervention. In the present study, in order to evaluate the hydromorphological conditions of the Tajan River along the middle to lower parts (city of Sari) the morphological quality index (MQI) and hydromorphological quality index (HMQI) has been used. Seven reaches in 50 m Riparian buffer width were selected and three quality main indicators including Geomorphological, artificial, and channel adjustment were studied using satellite images of Landsat 4 in 1975 and Landsat 8 in 2019, aerial photos in 1960 and 2006, hydrological data, and data collected during the field surveys. The results show that the studied reaches of Tajan River mainly classified as the moderate-quality class for the morphological quality index (MQI), while it is classified as one quality class lower for hydromorphological quality index (HMQI), mainly as the poor-quality class. The main reason is that all the studied reaches (except reaches 1 and 7), located downstream of the Shahid Rajaee dam, within the 30 km, which change considerably the river discharge and sediment transfer, also the extreme human impact and anthropogenic stresses in the catchment, such as land-use change. The results also showed that the method, which was used in this study, is effective, in general, index-based assessment, diagnosis of the hydromorphological problems, and an exact comprehensive realization of the response to the mentioned stresses.