Investigation of Land Use Effects by Using a Hydrodynamic Model for Ankara Stream Watershed

Abstract

Water resources, their protection and regulation are essential to meet drinking water demand and to prevent hazards, e.g. flood events. Therefore, exploring and evaluating the results of human activities with direct influence on water resources and hazardous events is of concern for researchers in the hydrology area. Especially, new developments interfering with the amount of drinking water and hazard risk are major interests as these strongly depend on the increase in population which in turn is influential for water resources. As a result of urbanization, changes in concentration time, amount of infiltrated water, and overflow rates are expected to occur. Therefore, the impact of urbanization on water resources and hazards should be investigated to avoid present and future problems such as floods, droughts, and pollution. In this study, Ankara Stream Watershed located in Ankara is selected as the study site. Ankara Stream Watershed has 7,140 km2 of drainage area and the stream length is 140 km. It flows through the residential areas and into Sakarya River. The watershed contains forest, agricultural, residential, and industrial regions. Moreover, there is a tendency of increase in the residential area due to the great potential of population growth. Ankara Stream Watershed has experienced a land use/cover change especially during the last two decades and these changes are expected to continue in the future because of population affecting land use dynamics.

The aim of this study is to investigate the impact of land use change on surface runoff and flood events in Ankara Stream Watershed by employing a hydrodynamic model according to the various land use scenarios. For this purpose, first, a hydrodynamic model based on Environmental Protection Agency Storm Water Management Model (EPA SWMM) was developed for the watershed. EPA SWMM is a dynamic simulation model for the surface runoff developing on a watershed during a rainfall event and it calculates the quantity and quality of surface runoff on each subcatchment, i.e. the flow rate, depth and concentration in each conduit and junction. Next, we simulated the flow developed on the watershed under typical rainfall events with the hydrodynamic model. Finally, we selected several land use types and investigated their influence on runoff and flood occurrence by means of different scenarios, e.g. high urbanization, low forest and agricultural area, and vice versa. Thus, we observed the possible effects of human activities on surface runoff and flood risk in Ankara Stream Watershed.