Hydrological Impact Assessment of Land Use Change on Annual Surface Runoff at the Gharasoo Catchment by Using L-THIA Model

Catchment land use changing in an area is one of the most important factors in hydrology. As a model, L-THIA was designed to assess the long-term impacts on the hydrology of a catchment for researchers who wanted to determine the relative changes in the runoffs from one land-use condition to another. In this regard, upstream section of Gharasoo catchment in Ardabil province has been evaluated in this study in terms of land use change (1987-2012) and the impacts on runoff production. To accomplish this end the research has used daily precipitation data from four stations, Landsat Satellite images (TM and ETM sensor), L-THIA extension software and Arc Map software. Modeling results indicate that during the 25 years, the land use change has caused an average of 1.8 mm increase in the runoff in this catchment. Land use changes mainly increase the expansion of residential areas, and loss of woodland and pastures. In some areas, such as Ardabil plain, due to conversion of pastures into farmland, land use changes have operated in a positive direction increasing the permeability of the ground and have mutually reduced runoff in this part of the catchment. Due to its capabilities in providing a zonation map, the volume and depth of the runoff, the model used in this study has the required ability to show the hydrologic impacts of land use change and demonstrate susceptible areas and flooding in the basin.