© by PSP Volume 17 – No 11b. 2008 Fresenius Environmental Bulletin 1964 DETERMINATION OF FLOOD RISK IN SAKARYA SUB-BASIN USING REMOTELY SENSED DATA AND GIS Orkan Ozcan 1* , Nebiye Musaoglu 2 , Dursun Zafer Seker 2 and Aysegul Tanık 3 1 ITU, Informatics Institute, Satellite Communication and Remote Sensing Programme, 34469 Maslak, Istanbul/ Turkey 2 ITU, Faculty of Civil Engineering, Geodesy and Photogrammetry Department, 34469 Maslak, Istanbul/Turkey 3 ITU, Faculty of Civil Engineering, Environmental Engineering Department, 34469 Maslak, Istanbul/Turkey Presented at the 14 th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region (MESAEP), Sevilla, Spain, 10 – 14 Oct. 2007 ABSTRACT Between 1970-2005, 936 floods occurred, 17664393 ha agricultural land was damaged, and 604 people lost their lives, in Turkey. The floods have been mostly recorded in the Sakarya basin, selected as study area. In order to ana- lyze all kinds of changes in the study area, SPOT XS (20 m) and SPOT PAN (10 m) satellite sensor images within the years of 1999 and 2006 were used. Land-use/cover of the region was evaluated from satellite images. Ob- tained classification results were verified by the field study. Topography and the drainage qualities of the land were ana- lyzed by DTM, produced from topographic maps of scale 1:25 000. In addition, meteorological data were collected and included as inputs to the system. The parameters of the basin were modeled with the Hydrologic Engineering Centers River Analysis System (HEC-RAS) software. At the end of the modeling, areas under flood risk in the study area and land-use/cover were calculated to be 39.5 km 2 . When the results were examined, 6.2 km 2 of the risky areas were evaluated as residential, and the rest as agricul- tural areas. KEYWORDS: Remote Sensing, flood, Sakarya, HEC-RAS. INTRODUCTION Floods are among the most serious natural disasters that engender loss of life and property. It is impossible to prevent flood disasters only due to meteorological phenom- ena. Especially in the developing countries like Turkey being still on the way to economical development, urbani- zation, triggered by industrialization and sector diversity, greatly increases the variety and intensity of human activi- ties in several fragments of river basins. This fact annihi- lates the hydrological stability in the entire basins leading to devastating floods, resulting in vast amounts of life and property losses. The land-use changes observed by the con- struction of new residential areas, and transportation net- work extending in the river basins, are important outcomes of rapid and uncontrolled urbanization, which also drasti- cally destroys meadows and forests. Such activities, together with the intensive use of improper agricultural methods, accelerate intensity and damage of floods. Natural disasters can nowadays be evaluated and con- tingency plans and mitigation programs can be prepared, prior to a new event by means of Remote Sensing (RS) tech- nology utilizing satellite images via extracting necessary data and executing necessary risk analysis. RS provides a reli- able and cost-effective way for field data collection, allow- ing for continuous and large-area coverage of many vari- ables. For the last two decades, advancement in the field of RS and Geographic Information System (GIS) have greatly facilitated the operation of flood mapping and flood risk assessment [1]. The main advantage of using GIS for flood management is that it not only generates a visualization of flooding, but also creates potential to further analyze this product to estimate probable damage due to floods [2, 3]. The aim of this study is to evaluate the flood risk analysis (an important issue) in Sakarya sub-basin using RS and GIS. In the study area, a hydrological model is developed on the possible areas under flood risk, and related environ- mental effects were analyzed. THE STUDY AREA Sakarya is one of the 81 provinces of Turkey located in the Marmara region. Between 1970-2005, 114 floods occurred in this basin, 8 644 ha of agricultural land was