Background

As flash flood disaster prevention is a difficult and weak aspect of China's flood control and disaster reduction, the CPC Central Committee and the State Council made important decisions and plans for flash flood disaster management. In 2010, the national flash flood disaster prevention project was launched on all fronts for the first time, which encompasses the investigation and assessment of flash flood disasters and the development of monitoring and early warning system. The study, an important component of the project, develops the base map, data collection software and data review and compilation software for investigation and assessment based on the collection and production of basic data. After reviewing and compiling the provincial results, the study establishes a national database and map of flash flood disaster investigation and assessment results and produces a unified map for the national investigation, assessment, monitoring and early warning platform.

Contents

    · Designing a technical system and the technical specifications for national flash flood disaster investigation and assessment, and clarifying the technical requirements for basic data processing, on-site data collection, investigation and assessment of various types of objects;

    · Performing fine division and attribute extraction of small river basins in a large scope, analyzing the runoff production characteristics of underlying surfaces, and developing the base map and software tools;

    · Proposing the solutions to core technical problems of investigation and assessment, and developing the software for data collection, data review and compilation, and disaster analysis and assessment; and

    · Reviewing and compilation of the 100-TB investigation and assessment results, implementing data modeling and quality control, and providing services for result management and application.

Achievements

    · A technical system with technical standards has been established for flash flood disaster investigation and assessment, facilitating the design of the overall technical roadmap, contents, objects, methods and processes, and the formulation of 22 specifications;

    · A technical system has been constructed for division standardization and attribute analysis of watersheds in a large scope, which divides 530,000 small watersheds and extracts the basic attributes and 15 sets of unit hydrographs. Further, the coding system and topological relationship of watershed system has been built, the underlying surface conditions and rainfall-runoff characteristics has been systematic analyzed, and the method of accurately identifying flash flood risk using the flood peak modulus of small watersheds has been proposed;

    · A systematic method and technique has been adapted to large-scale differentiated investigation (factors and indicators) and rapid risk assessment of flash floods in mountainous areas, including methods for housing and property survey based on classification statistics, for water-related engineering investigation, and for inference of critical rainfall from critical water level, and the three-factor double-line comparison method for hazard zone classification; and

    · A dualistic data model that takes into account of administrative subordination and watershed topological relationship has been introduced, a quality control method and indicator system constructed based on data model and spatial analysis, and a national database and map of investigation and assessment results formed.

Application

The achievements have been fully applied in the investigation and assessment of flash flood disasters in China by over 120,000 people from the State Flood Control and Drought Relief Headquarters Office, administrative agencies for 7 major river basins, and 30 provincial and 2138 county-level headquarters for flood control and drought relief. In addition, the national early warning information on flash flood disasters has been released on CCTV since 2015. The achievements provide strong data and technical support for monitoring, early warning and preparedness plan for flash flood disaster prevention, as well as the related disaster prevention and mitigation industries.

Fig. Division of small watersheds and extraction of rainfall-runoff characteristics in China

Distribution of flood peak modulus of national small watersheds

Flash flood disaster monitoring and early warning system of Qiubei County

Fig. National flash flood prevention areas

Fig. Distribution of historical flash flood disasters (1949-2015)

Flash flood disaster prevention benefit comparison chart (before and after control project implementation)