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GIS-based coastal area suitability assessment of geo-environmental factors in Laoshan district, Qingdao

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Nat. Hazards Earth Syst. Sci., 2, 43 50, doi:0.594/nhess Author(s) 202. CC Attribution 3.0 License. Natural Hazards and Earth System Sciences GIS-based
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Nat. Hazards Earth Syst. Sci., 2, 43 50, doi:0.594/nhess Author(s) 202. CC Attribution 3.0 License. Natural Hazards and Earth System Sciences GIS-based coastal area suitability assessment of geo-environmental factors in Laoshan district, Qingdao C. Y. Ju, Y. G. Jia,2, H. X. Shan,2, C. W. Tang 3, and W. J. Ma College of Environmental Science and Engineering, Ocean University of China, Qingdao 26600, China 2 Key Lab. of Marine Environment & Ecology, Ministry of Education (Ocean University of China), Qingdao 26600, China 3 Qingdao Geotechnical Investigation and Surveying Research Institute, Qingdao 26600, China Correspondence to: Y. G. Jia Received: 29 June 20 Revised: 6 November 20 Accepted: 7 November 20 Published: 7 January 202 Abstract. With increasing urbanization, particularly in the coastal regions of developing countries, the development of disaster management schemes is needed as the losses from a single event can destroy decades of development and threaten local populations, buildings and infrastructure. Geoenvironmental suitability is often evaluated systematically in order to assess the nature of hazards and their potential damage to human life, land, buildings and other property. A suitability assessment will indicate the priorities for geological and environmental hazard management. This paper presents a geological environment suitability assessment that aims to identify grading in a current seaside urban development and develop practices to aid in the identification of hidden geological and environmental hazards. The Laoshan area in the city of Qingdao was used as a case study because it constitutes a good example of a developing city with geological and environmental threats. Also, urban plans have been drawn up here with insufficient or absent information on losses from potential natural hazards. Introduction An increasing proportion of the world s population is based in coastal cities because of the beneficial services they provide (McGranahan et al., 2007). However, the rapid expansion of urban areas and accelerated growth in population has resulted in increasing environmental problems, particularly geo-environmental issues that are the product of natural and human activities (Dai et al., 200). By comparing geo-environmental factors with impact factors to assess a complex geo-environmental system, it is possible to determine whether the natural and human environments have been utilized optimally. If not, the established system can be refined and improved through the use of such tools as a geo-environmental suitability assessment. The ultimate goal of a geo-environmental assessment is to divide the study area into homogeneous units that can show the differential suitability for engineering land use. The results of a suitability assessment can be professionally mapped to show diverse areas with different suitability levels. The differentiation among the areas is, however, attribute-specific, because the kinds of graphs used only show a relative suitability grade for certain areas compared to others and do not represent absolute values. A geographical information system (GIS) is a powerful tool for geo-environmental evaluation in urban planning and designing. The spatial analysis power of GIS has been widely used to assess land use suitability by mapping and analysis (McHarg, 969; Hopkins, 977; Brail and Klosterman, 200; Collins et al., 200; Malczewski, 2004), and geologic hazards and vulnerability (e.g., Atkinson et al., 998; Carrara et al., 99; Hiscock, 995; Dai et al., 200). However, related studies that address geo-environmental evaluations for urban planning have been limited (Dai et al., 200). This paper analyzes the suitability of a geo-environmental system for the coastal city of Qingdao, China, using an Analytical Hierarchy Process (AHP). There are two main aims of this paper: (i) to outline the geo-environmental characteristics of this coastal city study area and the techniques required for GIS-based geo-environmental suitability mapping, and (ii) to identify the challenges and prospects of GIS-based land-use suitability analysis in the Laoshan District of Qingdao. Published by Copernicus Publications on behalf of the European Geosciences Union. landform terraces and marine landforms; diluvial fans are developed along the river. Groundwater distribution is strictly controlled by geological structures, stratal lithologies and landforms. Laoshan District is also a region of Quaternary accumulation, where material of 44 C. Y. Ju et al.: GIS-based coastal area suitability assessment varied thicknesses has accumulated on some of the ranges since the Cenozoic era (Kusky et al., 20). Fig.. Map showing the location of the city of Qingdao in China (left); the study area is the Fig.. Map showing thelaoshan location District of the (right). city of Qingdao in China (left); the study area is the Laoshan District (right). 2 Study area and materials 2. Study area The Laoshan District is located along the southeastern part of the Shandong Peninsula on the Yellow Sea coast of China, and includes four blocks (Zhonghan, Shazikou, Beizhai and Wanggezhuang). This area lies between and N and and E, covering km 2 (Fig. ). This study deals with the geo-environmental characteristics of this region. The Laoshan District has an extremely varied topography as a result of geological and geomorphologic processes. Most of the land area in the district is mountainous. The topography of Laoshan District is higher in the middle and lower at the edges. Mt. Laoshan, reaching an elevation of 33 m above sea level, is the second highest mountain in Shandong Province after Mt. Taishan, and is the highest mountain along China s km long coastline. Mountain ridges are the source of several streams that are controlled mainly by topography and geomorphology. The exposed strata of Laoshan District are Proterozoic metamorphic rocks, Mesozoic (primarily Cretaceous) clastic rocks, and loose Cenozoic (mainly Quaternary) deposits. Structural patterns are mainly aligned with NE-SW or NW- SE strikes. A range of geomorphic types have formed in Laoshan District, controlled by underlying geological structures, stratal lithologies, and exogenic geological processes. The main geomorphic features are fluvial landform terraces and marine landforms; diluvial fans have developed along the river. Groundwater distribution is strictly controlled by geological structures, stratal lithologies and landforms. Laoshan District is also a region of Quaternary accumulation, where material of varied thicknesses has accumulated on some of the ranges since the Cenozoic era (Kusky et al., 20). Historically, urban development has been limited primarily to lowlands or low slope areas within mountainous regions. However, in recent years, development has spread 3 rapidly upslope and also into small narrow valleys. As a result, disasters triggered by slope instabilities caused by human activities have become increasingly common. Potential hazards are particularly apparent along mountain roads. Local experts (Jinbo et al., 2006) have proved that the probability of geohazards in mountainous areas is higher than in neighboring regions. Simultaneously, pre-existing hazards (Fig. 2), even those that had been in a dormant or intermittent state, can be destabilized by heavy rainstorms, seismic activity, other hazards (debris, rockfall and landslide) and human activities. It is obvious that impact factors arising from human activities are more of a concern in an urban development. The scarcity of stable land for urban development exposes an increasing population to geological hazard and risk. The local geological setting of the Laoshan District has resulted in high ground stress that is stored in rock slopes giving rise to universal slope deformation in this area. Numerous landslides with the potential to develop new slope instabilities have been identified, including some in tourist areas next to a highway, that have a high level of hazard to passersby and to infrastructure lower down on the hillslope (Jinbo et al., 2006). Most of the landslides are small in scale, but a few of them are mid-sized, which suggests that these landslides cannot be ignored, particularly because records link the instigation of these slides to human activity, for example those occurring beside roads. In recent decades, records documenting unstable slope and collapse shows that eight collapses have happened around the Laoshan District, and a total of 8 potential hazard points are mapped along roadsides in tourism areas. In the documented case, most slope collapses were triggered by excavation, but the geomorphology, lithology and structure of the rock slopes may also have contributed to the slope collapses. Unstable slopes have been found with tensile fissures, some of which have caused damage to houses. In addition, abundant quantities of limestone have been randomly excavated around urban areas, particularly on roadsides, which has also caused unstable slopes. Such unstable slopes threaten the safety of inhabitants and passersby. Excavation scars the natural landscape and changes the shot-period stress distribution of the slope. This sometimes gives rise to landslides, collapses and debris flows. Furthermore, excavation causes floating dust that pollutes the air, destroys vegetation, and causes water loss and soil erosion Two debris flows have been recorded in the region, along with five potential hazard points. The initiation of debris flows is mainly caused by heavy rainfall or loosened solid materials. 2.2 Materials In urban geo-environmental assessment research, the Earth s surface can be categorized based on factors related to topography, geography and other physical factors. We have used Nat. Hazards Earth Syst. Sci., 2, 43 50, 202 Two debris flows have been recorded in the region, along with five potential hazard points. C. Y. Ju et al.: GIS-based coastal area suitability assessment 45 The initiation of debris flows is mainly caused by heavy rainfall or loosened solid materials. 2.2 Materials Fig. 2. Photographs of landslides, debris flows and collapse (as labeled). Fig. 2. Photographs of landslides, debris flows and collapse (as labeled) (Chunyan et al., 200). topography, geomorphology, rock and soil-type, geological structure and hydrogeology for our assessments. Topographic and geological data and maps were collected for each category and compiled in structured spatial databases using GIS software. These databases contained vector data. Additionally, polygons corresponding to identifiable units within the urban geo-environment were extracted using geological maps produced in 990 by the Bureau of Geology and Mineral Resources. Here, the urban geo-environment was considered to include areas defined by their geomorphology, rocks and soil, geological structure and hydrogeology. These include most of the Laoshan District covered by the study area. Topographic maps were developed from digital elevation model (DEM) data produced by professional bodies. In urban geo-environmental assessment research, the Earth s surface can be categorized based on factors related to topography, geography and other physical factors. We have used topography, geomorphology, rock and soil-type, geological structure and hydrogeology for our assessments. 3 Assessment of geo-environmental suitability 3. Methods and procedure 3.. An overview of methods The analytical hierarchy process (AHP), proposed by Saaty in the early 970s, is a comprehensive, logical and structural system, which allows a better understanding of complex decisions by decomposing the problem into a hierarchical structure (Saaty, 977; Saaty and Vargas, 99). Topographic and geological data and maps were collected Basically, AHP for each involves category building aand hierarchy compiled (a ranking) structured spatial databases using GIS software. These databases contained vector data. of decision elements, and then employing a pair-wise comparison procedure to arrive at a scale of preference among a set of alternatives. In the construction of a pair-wise com- Additionally, polygons corresponding to identifiable parisonunits matrix, within each factor theisurban rated against geo-environment every other factor by assigning a relative dominant same scale value. The sum of the components of the eigenvector will be unity. Thus we obtain a vector of weights, which reflects the relative were extracted using geological maps produced in 990 by the Bureau of Geology and Mineral Resources. Here, the urban geo-environment was considered to include areas defined Nat. Hazards Earth Syst. Sci., 2, 43 50, 202 by their geomorphology, rocks and soil, geological structure and hydrogeology. These include 46 C. Y. Ju et al.: GIS-based coastal area suitability assessment 3..2 Assessment variables and procedures Fig. 3. Methodological framework for this study. 7 (p.6, Section 3. 2, Fig.4.) Answer: importance Is the of the following various graph factorssuitable? from the matrix of paired comparisons (Dai et al., 200). The AHP method is based on: () decomposition of the decision problem, (2) comparative judgment of the elements, and (3) synthesis of the priorities. In the process of synthesis, an index of consistency known as the consistency ratio (CR) is used to indicate the likelihood that the matrix judgments were generated randomly (Saaty, 977; Dai et al., 200). CR = CI RI where the random index (RI) is the average of the resulting consistency index that depends on the order of the matrix 8 given (p.7, by Section Saaty (977), 3. 2, Fig.5.) and the consistency index (CI) can be Answer: expressedis asthe following graph suitable? RI = (λ max n) n () (2) A comprehensive analysis of the primary-level physical settings within Laoshan District revealed five major geoenvironmental variables for assessment. Each of these variables or categories has a number of sub-variables at the secondary level. () Landscape is important because it directly affects the nature of coastal urban development and engineering activities. (2) Terrain is important for maintaining slope stability and is critical to the distribution of other localscale variables. (3) Rock type and the Quaternary deposits relate to slope stability and play major roles in construction and engineering. (4) Geological structures affect the security of engineering activities. (5) The distribution and characteristics of hydrogeological regimes in a study area determine the amount of water available for population growth and the development of infrastructure. Geologic hazards are also an important geo-environmental consideration. The geoenvironmental roles of each of these factors varies from region to region. Therefore, due to the change in dominance in different areas, the same geo-environmental factor could have dissimilar influences at a different location. The aforementioned information was considered to be pertinent for defining the geo-environmental characteristics of the study areas (Fig. 3). The related geological factor maps were digitized using GIS software, and then a homogenous polygon was considered as a unit for any given factor. All influential factors were standardized and weighted, and then combined for each urban suitable geo-environmental category (Yan-Suil et al., 2006). During the geo-environmental evaluation process, a most important step is to be certain of a standardized measurement system for all factors (Dai et al., 200). The collection of basic data needs to be standardized to a uniform suitability rating scale. The value that each factor contributes to the decision is based on a set of rules that are governed by the shape of the threshold value for each factor (Table 2). 3.2 Results of geo-environmental suitability analysis where λ max is the largest or principal eigenvalue of the matrix, and n is the order of the matrix. A consistency ratio In this study, the first step was the analysis of geoenvironmental maps and factors from map attribute tables, (CR) on the order of 0.0 or less is reasonable (Saaty, 977). The introduction of cartographic modeling and map algebra techniques into computer-assisted mapping was an imculates the relative weights for each determinant based on a where the data were converted into vector format. AHP calportant advancement in the application of land-use suitability questionnaire; these weights then are used to generate a comparison matrix (e.g., Table 3 for main criteria). Then, a GIS 9 methods (p.7, Section (Tomlin, 3. 2, 990; column Malczewski,, line 3) 2004). urban development, Computerassisted overlay techniques, especially the spatial over- statistical package was used to calculate the values of factors even though the construction of seaside dwellings lay techniques here is of popular. geographic Field checks information confirmed systems that the (GIS) results are andconsistent correlate among with the the actual affected map layers. In this process, environment. (Steinitz et al., Some 976; tenses Collins have et al., been 200), changed are very for the effective sake of cohesion coefficients with were the rest estimated of the text using - the maximum likelihood please for processes check if involving OK for you vector overlap because of their advantages in terms of time, cost, and labor consumption. GIS A suitability assessment was then formed using a multiple method. The final results are shown in Table 2. Answer:That is OK for changed tenses. has been used in this study to overlap various factor maps criteria evaluation to combine and optimize a set of criteria and obtain suitable final maps faster and more efficiently. from a specific category. In this study, factors are combined 0 (p.7, Section 3. 2, column 2, line 0) This scheme encourages understanding of the geological Nat. Hazards Earth Syst. Sci., 2, 43 50, 202 C. Y. Ju et al.: GIS-based coastal area suitability assessment 47 Table. Scale of preference between two elements (Saaty, 998, 200; Hafeez et al., 2002). Preference weights/ Definition Explanation level of importance Equally Two activities contribute equally to the objective 3 Moderately 5 Strongly 7 Very strongly 9 Extremely 2,4,6,8 Intermediates values Reciprocals Experience and judgment slightly favor one activity over another Experience and judgment strongly or essentially favor one activity over another An activity is strongly favored over another and its dominance demonstrated in practice The evidence favoring one activity over another is affirmed to the highest degree possible Used to represent compromise between the preferences listed above Reciprocals for inverse comparison Table 2. Evaluation of five variables and sub-variables with evaluation scores for suitability in the Laoshan District. STAGE STAGE 2 STAGE 3 STAGE 4 Main criteria Weight *CR Criteria Weight *CR Sub-criteria Weight *CR Weight Topography Slope gradient Elevation Relief type Hill tectonic denudation lower mountain flood plain, terrace, the edge of foothill gently sloping field coastal plain Engineering geology Type of hard intrusive rocks Type of hard and semi hard rocks type of semi hard rocks Type of Intermontane valley loose (soft) Coastal soft (loose) Hydrological geology 0.46 Bedrock fissure water Loose rock pore water Clastic rock pore and fissure water Geologic hazard Area of occurrence probability No Hardly Low Middle High Proximity to beach 0.0 distance from beach (m) m 000 m Nat. Hazards Earth Syst. Sci., 2, 43 50, 202 48 C. Y. Ju et al.: GIS-based coastal area suitability assessment Table 3. Comparison matrix for main criteria. Topography Engineering geology Hydrological geology Geologic hazard Proximity to beach Topography Engineering geology Hydrological geology Geologic hazard Proximity to beach /5 /5 /5 /3 /8 /7 /7 8 7 /5 7 5 CR=0.827 Fig. 4. Landform maps. (a): slope map; (b): elevation map; (c): relief map. in weighted linear combinations (Easstma
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