Hidro-CBS ile sel afeti etki analizi
Flood disaster impact analysis with hydro-GIS
Yazar: EMİRAY KAHYA
Danışman: DOÇ. DR. CANER GÜNEY
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Geomatik Mühendisliği Ana Bilim Dalı / Geomatik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Jeodezi ve Fotogrametri = Geodesy and Photogrammetry

Özet:
İklim değişikliğinin etkisi gün geçtikçe kendini daha fazla hissettirmektedir. İklim değişikliği sürecinde artan küresel sıcaklıklar aşırı yağışlara neden olmaktadır. Bu etki, sel afetlerini daha sık ve daha şiddetli gerçekleşmesine yol açmaktadır. Gerçekleşen sel afetleri can kayıplarına ve ekonomik hasara sebep olmaktadır. Bu durumda, iyi planlanmış afet yönetimi süreçlerine olan gereksinim artmaktadır. Afet yönetiminin özellikle planlama aşaması, artan afet sıklığının ve şiddetinin verebileceği zararı azaltmaktadır. Bu bağlamda, sel felaketlerinin sosyal etkilerini azaltmak, fiziksel hasarları en aza indirmek ve afet yönetimi hazırlık aşamasında planlama faaliyetlerini desteklemek için etkili önleyici yapısal çözümler geliştirmek büyük önem taşımaktadır. 
Bu çalışmada, sel felaketlerinden etkilenebilecek yapıları ve alanları belirlemek için CBS teknolojisi ve hidrolojik analiz araçlarını bir arada kullanılabilen bir yöntem geliştirilmiştir. Hidroloji bilimi, suyun fiziksel davranışının modellenmesine olanak sağlar. CBS teknolojisi, sel riski taşıyan bölgeleri belirlemek ve bu bölgelerdeki yapıları ve alanları incelemek için etkili bir araç olarak kullanılmaktadır. Çalışma kapsamında, hidroloji bilimi ve CBS teknolojisi araştırılarak sel tehlikesinin önlenmesi için uygulamalar incelenmiştir. Bu çalışmada, sel tehlikesini belirlemek için iki ana olgunun birlikte kullanıldığı bir yöntem geliştirilmiştir. Geliştirilen yöntem, seçilen bir çalışma alanında sınanmıştır. Çalışma alanında topografik koşulların neden olabileceği su akışının yönü, yükseklik ve eğim verileri kullanılarak belirlenmiştir. Suyun birikebileceği alanlar modellenerek olası taşkın alanlarının yerleri belirlenmiştir. Akış yollarının ve su seviyelerinin etkisinin modellenmesiyle sel riski taşıyan alanlar SWAT ve HEC-RAS gibi hidrolojik analiz araçlarıyla irdelenmiştir. Şiddetli yağışlarda debi hızı değişimleri, iki boyutlu değişken akış modeliyle hesaplanmıştır. Bu bölgelerdeki debi hızı değişikliği sonucunda sel havzasında suyun yayılması modellenmiştir. Modelleme sonrasında, sel felaketinden etkilenebilecek alanlar ile taşkın yayılma alanları mekansal olarak karşılaştırılmasını gösteren ve yapıların sel felaketinden etkilenme düzeylerini sınıflandırılmış biçimde gösteren bir sel afeti etki haritası üretilmiştir.  Gerçek ve tahmin sonuçları karşılaştırıldığında, tahmin sonuçlarının SRTM yükseklik verisiyle %65, ALOS PALSAR yükseklik verisiyle %70 oranında gerçek verilerle tutarlılık gösterdiği görülmüştür. Bu tutarlık oranı, sel felaketleri için yağış ve topografik verilerin birlikte kullanılarak kullanılmasıyla geliştirilecek mekânsal modellerin başarılı olacağını ve karar vericiler tarafından kullanılabileceğini göstermektedir. 
Çalışma sonucunda CBS teknolojisi ve hidroloji araçları kullanılarak sel felaketlerinden etkilenebilecek yapılarla ilgili karar destek süreçlerinin  etkili biçimde gerçekleştirilmesinin mümkün olduğu görülmüştür. Gelecekte yaşanabilecek  sel felaketleriyle başa çıkmak için bu tür bir karar destek sisteminin oluşturulması afetler gerçekleşmeden önlem alınabilmesine katkı verecektir.

Abstract:
Throughout human history, there has been a constant state of change. These changes can include climatic events as well. In the past, natural events have caused changes in the climate. During this process, humanity has experienced ice ages at certain times when the average temperatures dropped. After the Industrial Revolution, human-induced changes were added to these natural changes. These human-induced changes have affected the world order. Due to the effects of the Industrial Revolution, greenhouse gases such as CO2, methane, and nitrous oxide began to accumulate in the atmosphere, trapping long-wave radiation. As a result, average surface temperatures are rising. These changes affect meteorological events. As we approach the present day, we see that the pace of change has accelerated. 
The frequency of extreme heatwaves is increasing, and changes in precipitation patterns are being observed in our living environment. In this context, scientists are continuously conducting research and development to better understand climate change and determine what measures need to be taken against it. Those who conduct these studies are referred to as climatologists. Climatologists use numerical models to try to predict future changes based on current data. Around the world, national leaders are also investigating what needs to be done to address this issue. Therefore, the IPCC has been established. This organization strives to implement scientific policies to combat climate change.
The issue of climate change, which is addressed globally, naturally affects Türkiye as well. Due to its geographical location and the diversity in its topographical characteristics, Türkiye has a climate structure that varies across different regions. Therefore, when looking at the impacts that climate change can cause, Türkiye is one of the sensitive areas. In Türkiye, there is an institution under the Ministry of Environment, Urbanization and Climate Change, called the General Directorate of Meteorology (MGM), which produces and provides data related to meteorology and climatology. MGM continuously collects weather data through meteorological stations located in various regions of Türkiye and analyzes this data to provide weather forecasts to the public and relevant institutions. In climate change reports published annually by MGM, attention is drawn to increasing temperatures and meteorological disasters in Türkiye.
Meteorological disasters can include floods and flash floods. Various rivers and streams are located within Türkiye's geography. Sudden precipitation increases the flow rates of these water bodies, leading to flood and flash flood events. The establishment of settlements near rivers, the insufficiency of rehabilitation efforts, and the lack of preventative measures such as flood walls result in these flood events reaching disaster levels, causing loss of life and property. Preventing these losses can be achieved through effective planning processes within the framework of disaster management.
In the planning and preparation process of disaster management, hazard maps are of great importance. Maps that can be produced using hydrology and GIS technology can reduce the loss of life and property. Therefore, it is first necessary to understand the capabilities of hydrology. Hydrology is the science that studies and models the circulation, distribution, properties, and movements of water on Earth. Hydrology is used to better understand flood and flash flood events by analyzing flow rates. In this context, measuring the flow rate of a river is a primary condition for understanding flood and flash flood events. The highest instantaneous flow observed during a water year is called the Annual Instantaneous Peak Flow. Peak flow is a critical parameter used by hydrologists and engineers to evaluate flood risk and plan water management strategies. There are two main methods for calculating this flow. If historical records of precipitation and flow rates for the study area are available, statistical methods can be used. If there are difficulties in obtaining data, various calculations can be made with the help of hydrology. The methods used for such calculations are called deterministic methods. The obtained peak flow values are used as input data for running hydrological numerical models.
Numerical models are tools that simulate physical systems using mathematical equations and computational techniques. HEC-RAS is one of the most preferred tools for flood and flash flood simulation. GIS technology is also utilized in running numerical models. In the framework of modeling water flow, the use of DEM data in hydrodynamic models is a prerequisite. The behavior of water on the terrain can be simulated using elevation and slope information obtained from DEM.
The integration of hydrology and GIS technology can be utilized in disaster management. This integration can provide decision support capabilities for planning, mitigating the impacts of, and managing flood and flash flood disasters, which are among meteorological disasters. The integration of hydrology and GIS technology also makes significant contributions to urban planning. It helps urban planners manage water resources more efficiently, optimize water supply infrastructure, and be prepared for potential water crises.
Increased extreme and sudden precipitation due to climate change leads to flood and flash flood disasters, resulting in loss of life and property. One of the challenges for decision-makers is responding to the increasing disasters due to deficiencies in the planning stages of disaster management. Settlements spreading into floodplains are also among the factors increasing the risk. Therefore, incorrect urban planning can exacerbate potential damage. The main aim of this thesis is to identify the impact of potential flood disasters. Another objective of the study is to demonstrate that significant information can be obtained against flood disasters by using hydrology and GIS technology together. Furthermore, interpreting the outputs and visualizing them on maps lay the groundwork for understandable and effective solutions. Similar methodologies could be developed to demonstrate that the necessary information for the planning stage of disaster management can be obtained through such studies.
In this study, the Bozkurt district of Kastamonu, which experienced a major flood disaster in July 2021, was selected as the study area. Using elevation and slope data, were determined potential water flow directions due to topographic conditions in the study area. Floodplains were identified by modeling water accumulation in two dimensions. Hydrological analysis tools such as SWAT and HEC-RAS were used to classify areas at risk of flooding by modeling flow paths and water levels. The flood that could be caused by changes in flow rate due to heavy precipitation was calculated using a two-dimensional variable flow model. As a result of flow changes in these areas, the spread of water in the floodplain was determined through modeling. Areas susceptible to flooding were spatially overlaid with flood inundation areas, and classes of building vulnerability to flood disasters were determined.
As a result of this methodology, structures susceptible to flood disasters can be identified. When comparing the actual and predicted results, it was observed that the predicted results showed a consistency of 65% with the SRTM elevation data and 70% with the ALOS PALSAR elevation data. Higher consistency determinations may be possible with high-resolution spatial data such as DEM data.
In this information, a methodology for conducting flood disaster simulations and identifying affected buildings has been developed. In this methodology, developed using hydrology and GIS technology, an estimation of the buildings that could be affected has been made. Upon reviewing the results, a consistency rate of 65% was determined. To achieve higher consistency, higher spatial resolution DEM data is required. It has been observed that such studies have a certain level of consistency compared to open-source and free data. By conducting flood simulations with hydrology and GIS, vulnerable artificial structures can be identified. Applying this approach to water sources near settlements could provide a prediction to prevent loss of life and property during periods of increased flood disasters. Determining flood risk and emphasizing it statistically can contribute to the working processes of the insurance and banking sectors. It can also assist decision-making bodies in decision support systems.