Dogal Afetler ve Cevre Dergisi

16-38

Authors: Melek DALKES; Mehmet Seren KORKMAZ

Landslides are one of the leading natural disasters in the Black Sea Region of Türkiye. Trabzon is the province where the most landslides occurred in the country. Landslide susceptibility maps should be prepared in order to predetermine the areas with high landslide susceptibility in order to minimize the losses due to landslides. In this study, landslide susceptibility analysis is performed, and landslide susceptibility maps are produced to reveal the areas with high landslide susceptibility within the boundaries of Akçaabat and Düzköy districts of Trabzon province using Analytical Hierarchy Process (AHP) and Frequency Ratio (FR) methods. ArcGIS for Desktop, one of the Geographic Information Systems (GIS) platforms, is used for landslide susceptibility analysis. Geographical data are obtained from public institutions and open access online sources. The data are spatially organized according to the study area and purpose by various GIS tools. A total of 13 criteria which are respectively; slope, curvature, lithology, precipitation, aspect, topographic wetness index (TWI), distance to rivers, distance to highways, distance to fault lines, land use, soil type, elevation and normalized difference vegetation index (NDVI) for landslide susceptibility are evaluated as effective to cause landslides as a result of the literature review. Pairwise comparisons are made to determine the importance of the effects of each criterion on landslide formation and the weights between the criteria by using the AHP method. Then a landslide susceptibility map is produced according to the AHP method. In addition, a landslide susceptibility map was produced according to the FR method using the landslide inventory records obtained from responsible institutes of the country. It is noticed that the FR method produced more realistic results than the AHP method in terms of determining the locations of the landslides observed in the study area when the maps produced by both methods are compared.

58-70

Authors: Ahu KÖMEÇ MUTLU; Ülgen MERT TUĞSAL; Musavver CAMBAZ

The earthquake (Mw 6.9) that occurred in the northern part of Samos Island and Doğanbey-İzmir offshore in the Aegean Sea at 14:51 local time on October 30, 2020 was felt in İzmir, Samos Island and many surrounding cities and settlements. Considering the earthquake intensity map, contrary to what is expected, the highest impact occurred in Bayraklı district, which is 70 km away from the epicenter, and caused not only severe structural damage but also fatalities in the region. When the structural damages are evaluated, determining the local soil properties has an important place in the studies to predict the effects of a possible earthquake. The HVSR (Horizontal Vertical Spectral Ratio) method provides an advantage in determining the soil fundamental frequency and the soil amplification factor in the event of an earthquake, in that it can be widely used even in the seismically in-active regions. In this study, it is not only aimed to analyze the earthquake and ambient noise data obtained from the accelerometer and velocity stations but also to compare the results obtained by using HVSR method utilizing different softwares. Furthermore, response spectra were obtained for different local soil classes by using the data of the same stations and they are given in comparison with the design spectra included in the earthquake code. As a result of the study, it has been observed that the results obtained by the HVSR method are in good correlation with the soil effects in the region and the consequential structural damages. These examples illustrate HVSRpy’s commitment to exactly reproduce the results of GEOPSY, wherever the processing parameters and functionality of HVSRpy and GEOPSY overlap. This was done to allow users to check HVSRpy and to encourage standardization in HVSR processing.

81-89

Authors: Şerife Pınar GÜVEL; Mehmet Ali AKGÜL; Mehveş Feyza AKKOYUNLU

The mass movement towards stream beds and their accumulation there may cause flood events as a result of landslide events. In this study, Devrek Landslide, which occurred in 2015, was investigated by using a remote sensing technique. The Çomaklar stream is located at the lower elevations of this landslide region. Çomaklar stream and surrounding settlements are at risk of flooding due to the probability of preventing the water flow in the stream because of the effects of the landslide. Devrek district is located in Zonguldak in the northern part of Turkey. LANDSAT-8 satellite images between the dates 27 January 2015 and 22 July 2015 were used to investigate the location and size of the Devrek district landslide. Satellite-derived remote sensing data have been widely used in recent years to monitor changes on the earth's surface and to provide information. In this study, the Spectral Angle Difference method was used to compare the images before and after the landslide event. A change detection analysis was conducted between pre-landslide and post-landslide images to investigate the area affected by the disaster. As a result, the landslide was determined as 1050 meters in length and 110 meters in width, and the landslide area was calculated as 10.87 ha.

101-111

Authors: Bülent TURGUT

Wetlands are invaluable ecosystems as they provide important services, but these areas are rapidly degrading due to anthropogenic pressures and natural changes/transformations. It is thought that this negative change will increase in the upcoming period due to the climate change and the rising demand for soil and water. Determining the changes in wetlands is very important in terms of management planning of these areas. NDWI (Normalized Difference Water Index) is a widely used method for determining the hydrological characteristics of wetlands. This study was carried out to determine the temporal variability of wetlands in the Batumi Delta and the relationship of this change with basic climate parameters such as average temperature and total precipitation. For this purpose, the average temperature and total precipitation amount of the months of April, May, June, July, August, and September in the period between 2016-2021 of the study area and the NDWI values of these time periods were determined. Green and NIR bands of Sentinel2 satellite images were used to determine NDWI values. QGIS software was used to process satellite images, and ArcGIS software was used to determine and map NDWI values. As a result of the study, it was seen that NDWI values changed by months and years, and the temperature was more effective than precipitation on this change.

125-135

Authors: Betül METE; Sinan NACAR; Adem BAYRAM; Osman Tuğrul BAKİ

In this study considering total suspended solids (TSS) parameter monitored in a stream watershed, the predictability of upstream values from downstream data was investigated using regression analysis, which were applied to linear, power, exponential, and quadratic functions, and artificial neural networks (ANNs) method. The data were obtained within the scope of sampling studies carried out 40 times between June 2019 and March 2020 at eight monitoring stations selected in the Sera Stream Watershed (Trabzon). The monitoring stations were divided into two groups as upstream, the first four, and downstream, the last four, stations. Half of downstream data (two stations) was used for training, a quarter (one station) for validation, and the rest (one station) for testing. Two models with different combinations of independent variables were established. In the first model (M1), only the TSS values, and in the other model (M2), the month and week information of the sampling dates were digitized and used as independent variables, in addition to the TSS values. Root mean square error, mean absolute error, and Nash-Sutcliffe (NS) efficiency coefficient statistics were used to evaluate the model and method performances. Compared to other functions, the power one had the best estimation results in the regression analysis. On the other hand, the ANNs method gave better results than the regression analysis. In both methods, M2 performed better overall. In the ANNs method, the NS efficiency coefficients obtained from M1 and M2 were calculated as 0.980 and 0.997, respectively, for the training, and 0.978 and 0.978, respectively, for the testing data sets. Considering the efficiency values, it has been understood that the use of date information as an independent variable will positively affect the model performance in the stream TSS modeling studies. Within the scope of this study, it has been concluded that upstream TSS values can be successfully estimated from downstream TSS data in stream watersheds.

152-167

Authors: Onur AKSOY; Elif ALTAŞ; Kamil ERKEN

There are many possible impacts of global climate change such as loss of vegetation in urban and rural areas, deterioration in agricultural patterns, heat island effects. One of these effects is floods due to the deterioration of the precipitation regime. Floods threaten ecosystems and human life in urban and rural areas in many ways. In this context, many methods have been developed in the last century to combat flood risk. Landscape architecture discipline with the structural and vegetative measures it has taken also plays an active role in reducing the impact of the floods that will occur. With the ecological landscape design approach that came to the fore in the 20th century, the possible effects of flood can be decreased. This study covers the center of Kemer, which is the district of Antalya, and its nearby neighborhoods. Kemer district was selected as the study area because it faces with flood disasters at different times of the year. The study mainly consisted of 3 stages. In the first stage, literature research was made. In the area determined in line with the data examined in the second stage; the slope, aspect, land use, soil, precipitation and distance to stream maps were graded according to the multi-criteria decision making method on the Geographical Information Systems platform and then flood susceptibility analysis was performed in the ArcGIS environment. According to the results of the analysis, in a possible flood event, it was concluded that 893 ha of agricultural land and 2/3 of the residential areas in the study area will be affected by the flood. As a result of the study, ecological landscape design proposals have been developed in areas with high flood susceptibility. In case of suggestions are implemented, it is expected that besides economic and social benefits, ecological benefits will be gained as well as. The aim of this study is to develop ecological landscape design applications that are less costly and less harmful to the environment than structural engineering-based applications in areas where flood susceptibility is high. With the proposed ecological landscape design approaches, the water flow will be regulated with plant-based applications, while the groundwater will be fed by increasing open green areas and permeable areas.

181-190

Authors: Hakkı Oral ÖZHAN

Geosynthetic clay liner (GCL) can be used as a lining material in freshwater reservoirs due to its very low hydraulic conductivity. The high amount of water that can be collected on top of a GCL might force the bentonite in the GCL to be extruded out of the geotextiles and as a result, the sudden increase in the hydraulic conductivity might cause the GCL to loose its hydraulic capability. This interaction is defined as internal erosion. In this study, triaxial permeability tests were conducted on chitosan and Na carboxymethyl cellulose-added GCLs. These two biopolymers were added to the bentonite component of the GCLs with a content of 0.25, 0.5, 1, 2, 5 and 10% by dry weight respectively. Na and Ca bentonites were used in the GCLs and the GCLs that were placed over a rounded coarse gravel with a grain size of 37.5 mm, were tested at high hydraulic heads in order to observe internal erosion. This condition represents one of the worst-case scenarios. Test results indicated that all of the GCLs experienced internal erosion at a hydraulic head of 10 m. Furthermore, the permittivity values of the GCLs just before internal erosion, were measured and the effects of the biopolymers on the GCL’s hydraulic performance were investigated. According to the test results, 1% chitosan and 2% Na carboxymethyl cellulose addition to the bentonite component of the GCLs resulted in more than 2 orders of magnitude decrease in permittivity. Due to the results of this study, the usage of two different biopolymers that are environmentally friendly organic additives can be encouraged to be used as barriers in geoenvironmental application by decreasing the hydraulic conductivity of the lining material.