Impacts of Urbanization on Flood and Soil Erosion Hazards in Istanbul, Turkey

Due to the inappropriate planning and explosive population growth in urban areas, especially in developing countries, sustainable and disaster-safe urbanization has become the most important challenge for governments. Urbanization presents benefits in different ways but has led simultaneously to changes in land use/land cover (LULC), impacting soil quality, runoff, surface temperature, water quality, and promoting climate change. The environmental implications of LULC changes cannot be understood well enough to take precautions without the knowledge of LULC change. This reality is the driving force behind my research, which focuses on impacts of urbanization on flood and soil erosion hazards in Istanbul, Turkey. Istanbul is the biggest city in Turkey with its almost 15.000.000 population. In 1999 the Marmara earthquake destroyed the city especially the newly developed zones. Every year Istanbul suffers also from flood damages. Istanbul has been experiencing uncontrolled migration, chiefly from rural areas, since the economic reform policies took place in the second half of the 20th century. These policies forced the city to expand towards the agricultural land and to the coastal areas. Istanbul has been faced with illegal housing and uncontrolled development since then. This development has produced significant decreases inproductive agricultural lands and created more impervious areas. Infrastructure development has not matched the rate of the population increase and uncontrolled urbanization, making the city vulnerable increasingly to natural disasters. This dissertation aims to understand the impacts of urbanization on flood and erosion hazards in Istanbul by examining changes in the city using remote sensing (RS) and geographical information systems (GIS) methods. LULC was examined first: Two change detection methods were applied to choose the best performer for Istanbul. The post-classification comparison (PCC) method produced better results than the principal component analysis (PCA). PCC utilized 1984, 1997, 2001, 2007 and 2010 Landsat images of the study area. These Landsat images were corrected atmospherically and radiometrically using COST Model (Markham and Barker, 1986). After the corrections geometric rectification was performed with the help of 1987 topographic map, 1995 orthophotos, 2005 GPS data. Location and nature of the change were derived for the time periods. Results show that since 1984, agricultural land have been replaced increasingly by urbanization. Flooding and related soil erosion are both natural events. Yet these events can be hazardous; they can harm/destroy lives and property. In recent years these events have become disasters for Istanbul. We investigated the role of urban growth in such disasters. To understand the urbanization and flood relation better, flood events for each time period were examined using LULC change, runoff information and watershed analysis. Soil erosion events occur slowly and in Istanbul they do not happen frequently (yearly) as with flooding. But some of the locations of erosion that occurred in the past are now urbanized areas. It is thus important to understand how the built environment affects soil erosion. We applied the Revised Universal Soil Loss Equation (RUSLE) method for each year in the time series. Prior erosion locations digitized from General Directorate of Mineral Research and Exploration were compared to predicted locations. The resultant maps indicates that European side of Istanbul is more prone to erosion than Anatolian side