Geo-spatial Analysis for Prediction of River Floods

Transcription

1 Geo-spatial Analysis for Prediction of River Floods Abstract. Due to the serious climate change, severe weather conditions constantly change the environment s phenomena. Floods turned out to be one of the most devastating catastrophes for Europe's population, economy and environment during the past decades. In this paper we are using geographic information systems (GIS) as a modeling tool for the prediction and prevention of such effects. We provide an emulation of geographic processes or phenomena of the real world problems by employing the geo-spatial analysis for two-dimensional models. The developed data model depicts spatial variations of the expectations about the analyzed data. Because the input is of a fine quality, the result, the representation model provides helpful information for interpretation and forecasting the behavior of natural phenomena. The intention of this paper was to develop two-dimensional model for the rivers water flow. With the spatial modeling of the hydrologic system we reconnect the systems dynamics modeling, modular simulation, data processing and visualization. Our hydrologic model uses ESRI ArcMap data model for water resources in ArcGIS as a core platform. The hydrologic process modeled for the purpose of this paper was the flooding of the areas around the drainage of river Brajcinska. These floods are simulated by the increase of the river flow above the boundary level of Q=15m 3 /s and by the additional demand that the delineation of the land surface terrain is less than 0.03%. With the developed model, the sections of the river flow with highest probability of flooding can be selected, and also the probable flooding terrain around the river flow can be predicted. Keywords: geo-spatial analysis, modeling, geographic information systems (GIS), river floods, waterflow. 1 Introduction Spatial analyses of models generated by the geographic information systems (GIS) provide an emulation of geographic processes or phenomena of the real world problems. The specific data model depicts spatial variations of the expectations about the analyzed data. If this input is of a fine quality than the result, the representation model provides helpful information for interpretation and forecasting the behavior of natural phenomena. 1.1 GIS On December 22, 2000, the Water Framework Directive [WFD] was established as a new challenge in the European water policy [1]. The Directive establishes a

2 framework for the protection of all waters (river basins, inland surface waters, transitional waters, coastal waters and groundwater) in preventing further deterioration of water resources as well as progressive reduction of pollution and preventing pollution in the future. Overall, the Directive aims at achieving good water status for all waters. A working group has been created for dealing specifically with issues related to the implementation of a Geographical Information System (GIS). This working group was named GIS-WG, and its main objective was the development of guidance document for supporting the implementation of the GIS elements of the Water Framework Directive [1], [2], [3], [4], [5], [6]. The guidance document of the GIS-WG gives a precise Data Model for designing of the database. This serves as a base from which the GIS will be built. The GIS-WG uses a restricted subset of static structure diagrams for representation of the Data Model, and we will use it in the paper for representing our specific Data Model. The Data Model should be created in such a manner as to satisfy the requirements defined in the Directive. In order to enforce the standardization the model is composed of logically divided and related features. According to the GIS-WG recommendation the features given on the map (containing explicit geometry) are presented as classes. Geographic Information Systems are technologies who integrate cartography and computer science. Its software is used for gathering, processing and analyzing of spatial/geographic information. GIS technologies is modern, computer method for creating databases for spatial objects, for digital analysis, creating digital maps, visualization of measured data or data from the models etc. [3] [5] [7]. Every GIS is composed from hardware and specialized software for GIS, geographic data, attribute bases and users. Sources of the information which are used in GIS can be satellite images or maps, or can be manually gathered data. Using the data gathered from the monitoring system and the ESRI software (ARC/INFO, ArcView spatial analyzer and ArcView analyzer) we provide the modeling and visualization of the flooding region around the river flow of river Brajcinska. Lots of benefits from GIS are applied for spatial analysis and modeling, such as: management of data (input/output databases, temporary datasets and metadata), data integration and transformation, fine range of modeling capabilities, model specification and execution, customization, scripting and interfacing, visualization and mapping, and medium for knowledge dissemination [6]. All of the above mentioned benefits are well combined and exploited in order for the first time to create an effective hydrologic model of river Brajcinska. 1.2 Hydrologic Modeling The hydrologic modeling and its integration with ArcGIS aims towards visual simulation of four basic types of water phenomena, such as: droughts, floods, water

3 pollution and extinction of aquatic eco-systems. All of the hydrologic models convey these two steps: description of the physical environment that surrounds the water flow and simulation of the water flow. For the first step, GIS helps in defining the shape and slope of the land surface terrain, watershed, decrease in the water flow system, description of soils, land-cover properties, and three-dimensional depiction of watershed and floodplain morphology. The second step is used for simulation of water velocity, depth, discharge, and quality throughout the domain of interest [5]. For the purpose of this paper we applied the first step for spatial analysis of river Brajcinska. 1.3 Surface Water Flow Model All the water streams follow the hydrologic cycle (Fig. 1). The water surface flow runs into streams and rivers, part soaks into the soil and part is stored into lake basins. The second part flows back into the sea or ocean, evaporates from the ocean or land surface, falls back on the terrain as a part of an atmospheric circulation, and continues with the cycle. Fig. 1. The hydrologic water cycle In this circular motion, the water is characterized by the following flows: surface water, atmospheric water, subsurface water, and ground water. Hydrologic models for all these types of water flows differ from each other and therefore should be treated within separate spatial analysis. The developed hydrologic model of river Brajcinska is used as a surface water flow model. The domain of this hydrologic model is defined by a watershed boundary delineated along the drainage

4 that separates flow draining into the stream network of interest from that draining away from those streams. 1.4 Graphical Representation River networks are represented in GIS by connected sets of line segments, while watershed by sets of polygons. Stream flow measuring stations and sites for monitoring water quality are represented as points, and the water flow and the water quality data measured at these measurements are stored as tables. Soils and surface terrain data are represented as raster or polygon features. 1.5 Data Flow The obtained hydrologic model is analyzed by the River Analysis System (RAS) that transforms the stream flow into water surface elevations along the river system, and therefore helps in prediction and prevention of river floods. Furthermore, because the efficient interface data model is obtained besides the Hydrologic Modeling System (HMS) and the RAS, it is feasible to obtain a communication between the hydrologic model and the geo-database, and also between RAS and HMS (Fig. 2). Fig. 2. The RAS-HMS communication

5 2 Geo-spatial Analysis Using Two-Dimensional Visualization Two-dimensional (2D) visualization of the natural phenomena is used for prediction of some problems or events that are forecasted on the bases of measurement values of the same phenomena during a time period. Analyzing 2D models facilitates identification of certain patterns of appearance of phenomena s features. This case study analyzes the impact and sensitiveness of the parameters such as stream flow capacity and delineation of the land surface terrain of the river Brajcinska for its flooding conditions. 2.1 Software Analysis For the purpose of 2D modeling of the surface waterflow of river Brajcinska we used ESRI ArcMap data model for water resources as a core platform. As fundaments of this modeling strategy we employed the functionalities of the digital elevation model (DEM) of the Prespa region terrain. This model describes the shape of the land surface terrain that will be analyzed to define the drainage area boundaries. Analytical methods were used to delineate stream network and drainage basins from DEM. For a better perspective of the flooding problem we additionally implemented hillshade characteristic and ArcGIS Model builder. The first one adds to the visual effects of the reality by applying shadows and shades on the region of interest. The second one is a useful functionality that creates a diagram of processes integrated in the model of the phenomena (Fig. 3). This allows the model-developer to easily adopt this model for different input data, information, characteristics and operational parameters and therefore obtain the results without extensive data management and remodeling. 2.2 Organization and Interpretation of the Data for 2D Hydrological Model In order to develop an effective 2D model of the surface water flow of river Brajcinska, several phases of data management should be completed. Design of the Database. All of the measurements for inundation of the river Brajcinska are organized in a scheme of the diagram and documents that portray the structure of the database and correlation among its elements. Each record in the database ESRI represents as a single characteristic of the phenomena. All of the data for river Brajcinska are stored in data tables in which attributes such as the water level and capacity of the river flow appear.

6 Interpretation of the Spatial Data. Before the spatial modeling and visualization is done a good model for representation of the spatial data is needed. The basis of the 2D analysis of river Brajcinska is the DEM of the region surrounding the lake Prespa (Fig. 3). This is the most important source for a precise model for drainage river network. The existing analytical methods help in delineation of stream networks and drainage river basin from the DEM. For the purpose of our DEM the gauging points differed from each other by 80 meters of length. Fig. 3. DEM for Prespa region Interpretation of the Attribute Series. An attribute of a feature is defined as a data for the geographic feature associated with the time series. In our case study, the attribute series are used as information for the quality and capacity of the phenomena. In the database, the attribute series are organized in tables (Fig. 4). The connectivity of the tables is accomplished by the unique ID key of each of the associated tables in the database. Fig. 4. The attributes series for river Brajcinska

7 The data attributes for the capacity of the river flow and its water level were used as attributes for the analysis of the river Brajcinska. The system of the database stores different formats of files for the spatial, time series, attribute series, raster series etc. Our system doesn t use the organization of the data in the centralized database possibly accessible by remote and different users. Therefore, this type of organization of the database is more suitable for smaller systems and limited number of users. 2.3 Designing 2D Hydrologic Model as Prediction Analysis for Floods The hydrologic 2D model of river Brajcinska facilitates identification of the predicted flooding area by its parameter such as the stream flow capacity. From the measurements for the river drainage system of river Brajcinska, the floods appear when the increase of the river flow is above the boundary level of Q=15m 3 /s. The first flooding effect targets the region surrounding the drainage system where the delineation of the land surface terrain has a smallest value. To decide what the critical value is, we designed the appropriate 2D model. Because river Brajcinska belongs to the water basin of Lake Prespa, first a DEM of Prespa region is created. The surface image analysis [8] [9] and the hillshade effect is applied (Fig. 5). Fig. 5. The hillshade analysis For a better visibility of the phenomena from the color ramp 50 % of transparency is selected. The generated view of the terrain after the first analysis is shown on Fig. 6.

8 Fig. 6. The DEM of the terrain after the first analysis The next step of designing the 2D hydrologic model is analyzing the DEM with the Model Builder. All of the processes employed for modeling the river floods, along the data for the boundary capacity of the waterflow, the attributes and the terrain of area of interest create a diagram of processes for modeling the river flood. The result from the intersection of the buffered region and the area from the smallest delineation of the land surface terrain along the river drainage show that the floods appear when the delineation of the land surface terrain belongs to the interval [0%, 0.03%]. The selected polygon (Fig. 7) is the area where the floods are predicted to appear with highest probability for the given input parameters of the river Brajcinska. Fig. 7. The polygon of flooding area of river Brajcinska

9 Furthermore, the graphic on Fig. 8, shows the correlation between the river gauging point (stage) and river waterflow. This stage-waterflow relation is employed to correlate the water level to an associated waterflow. Fig. 8. The stage-waterflow correlation This graphic obtains all the waterflow s characteristics for specific river locations. The waterflow measurements are gauged at many different river stages to define and maintain a stage-waterflow relation. These waterflow measurements and their corresponding stages are then plotted on a graph. Continuous waterflow throughout the year can be determined from the graph and the record of river stage. The graph is crucial because it allows the use of river stage, which is usually easily determined, to estimate the corresponding waterflow at virtually any stream stage. The slope of the line-graph frequently shifts due to changes in the factors that determine the relation between the river stage and the waterflow. The following are the factors that should be taken in consideration: slope of the river drainage roughness of the surface of the channel surrounding area of the channel at each river stage changes of river banks the drainage pattern the drainage water direction and etc.

10 3 Conclusion The environmental problems, situations, or phenomena are stated and analyzed from a hydrological point of view, while GIS provides effective tools for their representation. This paper integrates the hydrologic analysis and GIS technology and proves that all of the modeling for hydrologic phenomena is simply achievable. However, the quality and accuracy of the flood patterns and derived flood parameters always depends on the scale and the geometric precision of the original data as well as on the classification accuracy of the derived data products. The incorporation of auxiliary information such as elevation data can help to improve the plausibility and reliability of the derived flood patterns as well as higher level products. Due to the obtained experience from this case study, we will continue the environmental research in a way of extension of this generated model in order to compute and help predict a feature series of floods along the entire river flow. It is not prudent to create flooding maps for a lengthy period of time because of the nowadays rapid change of the intensity of the environmental phenomena and characteristics, but the enhancement of the GIS technology leads towards the near real-time mapping of the river floods as the severe whether conditions pass over the region of interest. This shows that 2D visualization of hydrologic models is a good predictive utility and quality in the geo-processing environment. References 1. Water GIS Working Group, Guidance Document on Implementing the GIS Elements of the Framework Directive [WFD], Mitreski K., Stevkovski S., Davcev D., 3-D Visualization and Standardization of GIS Elements for Pollution Monitoring of Water Resources, BALWOIS, Ohrid, Harmon J., Anderson S., The design and implementation of Geographic Information Systems, John Wiley & Sons, Abdul-Rahman A., Pilouk M., Spatial Data Modeling for 3D GIS, Springer, Maguire D., Batty M., Goodchild M., GIS Spatial Analysis and Modeling, ESRI Press, Goodchild&Longley, The future of GIS and spatial analysis, Geographical information systems: Principles, techniques, management and applications, ed. Longley, Goodchild, Maguire, and Rhind, Hoboken:John Wiley and Sons, Zwenzner, H. and Voigt, S.: Improved estimation of flood parameters by combining space based SAR data with very high resolution digital elevation data, Hydrol. Earth Syst. Sci., 13, , Veleva Sanja: Fractal image analysis based on the theory of iterative and contractive transformations, master thesis, FEIT, February Veleva, S., Kocic, Lj., Estimating box-dimension by sign counting, 28th International Conference on Information Technology Interfaces Volume, 2006 Page(s): , Cavtat-Dubrobnik, 2006.