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Poster Session
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Flood risk forecsting and disaster countermeasures
information system in the Dongting Lake region
Design of DLIS
DLIS is project supported by the central and local governments as well as sponsored by the International Development Research Centre (IDRC) of Canada. The development of the System aims at providing information to the decision making departments in charge of flood control and disaster relief in a speedy, accurate and timely way, effective processing and utilization of the provided information, application of the GIS methods to the process of decision making through the development of analysis models, meanwhile, exploration of the function, role and potentialities of GIS as well as appraisal of its application effect. Accordingly, the experience gained from the design and establishment of the system will be extended to the regions with similar geographical environments in China and Southeast Asia.
- Regional Features: The relief of the Region is shaped like the centre of a palm, and the Lake gathers water and sand from all sides with the exception of the northeastern Chenglingji where the Lake pours into the Changjiang River. The Region has a crisscrossed network of water body with small lakes scattered all over like stars in the sky; and through the links among the streams and lakes an network system of water body has resulted. The Dongting Plain is an alluvial and littoral deposit plain formed by the Four Rivers and the Four Distributaries. On the Plain the landscape feature is characterized by the overall flatness mixed with local unevenness. As a result of frequent dyke braking and flood inundation, the sand spits closed in to form land with the dish-like depressions appearing everywhere. In particular, with the agricultural development , the DSAs have emerged for the purpose of reducing the flood threats from either the rivers or the lakes, thus forming the micro-geomorphology of which the land plots with dykes intersect with one another and the dish-like depressions, big and small, overlap, from which it can be seen that Region exhibits the characteristics of special spatial structure with the intermixed overlapping of island like dykes with the river system.
- System Design: With relation to the special spatial structure which features the combination of multi-layer island-like data with net-like data, the System can be divided into three sections in accordance with the application targets of the System, i.e. the database system, database updating system and model base system. The interface between the first two systems is responsible for providing timely useful information to the database system and the continuous updating of the database so as to ensure the current ness of the database ; while the one between the database system and the model base system is responsible for providing the required data and the feedback of the valuable results of computation or the updating information to the database.
Establishment of the database system
- Composition of the Database: The main target for the establishment of the database system rests with providing basic data for the estimation of the flood inundation losses, simulation
and dynamic display of flood process, the synthetic analysis of the formation, developing conditions and dynamic process of flood risk and the and the estimation of the benefits of flood preventive projects. The database system so established to meet these targets is composed of the six sections as follows: 1) Environmental background database, which includes traffic network, distribution of the settlements, existing landuse, etc. ; 2) Database of flood preventive projects, which includes dyke types, distribution f the spots of potential danger, arrangement of hydrologic stations, distribution of the storehouses with materials and equipment used for flood control and disaster relief ;3) Database of DEM, for which the entire Region employs the unified geographic coordinates, the sizes of which are rated as 25X25 m, 50X50 m and 60X60 m; 4) Place name base, which includes place names, kilometer network coordinates, longitude -latitude coordinates , etc.;5) Socio-economic statistic database, which consists of to subdatabases representing the database with the DSA as statistic units and the one with the natural villages as the statistic units respectively , both covering population, number of households, output values of industry and agriculture, annual profits and taxes, etc. ; 6) Hydrologic Database, which mainly includes water stages, discharges, sand contents, etc.
- Spatial Structure of Graphic Data: The basic graphic components are points, lines and areas. The structure of graphic data generally employs the grid structure or the polygon structure. As to the ARC/INFO software which we use, its basic data structure belongs to topological structure of ARC/INFO software which carries out effective storage in terms of the structural grid of line segments and arcs exhibited by the administrative boundaries or geographic elements themselves. In addition to the recording of the recording of the characteristic codes of the elements, it will digitize all the points and arcs and then store them into the database, make topological definitions of the points and arcs and define the polygons by means of the arcs composing the boundaries and internal marking points . Using this kind of data structure of arc-nodal points can rather accurately express their profiles, locations, interrelationship between different geographic elements, being capable of overlaying, jointing and mapping and simple arithmetic operation, resulting in clear indication of retrieving. If complex statistic operation, appraisal and analyses as well as database updating using the remote sensing data are to be performed, it is possible to proceed with the conversion of the data formats so that vector data can be converted into grid data so as to facilitate computation. This makes the system flexible and practical.
- Logic Structure of Attribute Data: All the data of statistics and investigation are expressed in such units as the points, lines and polygons. The relational data model of the INFO relational database expresses the data in the form of a series of logic tables, the links of which are established through a common item possessed by every table. The tables are the sets of various attributes of the similar entities. One table forms one file; and the method of data expression is unified, simple and easy for expansion, adjustment and reorganization at that.
- Spatial Logic Structure of the Data Base System: Owing to the complexity of spatial data structure, the great amount of data and the always limited availability of economic but efficient computer resources, the design of the data base's spatial logic structure becomes the key to the success or failure of GIS. Starting from the effectiveness of the system, we separate the study Region into some DSAs and a river network so as to facilitate the storage of the related information; that is to say, the spatial logic structure of the database is mainly the combination of the data related to the island-like DSA with those of the river system.
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