Study on the method of establishment of normal water extent database for flood monitoring using remote sensing

Floods occur in many countries every year and often cause great losses. How to monitor and assess them is becoming a key problem for flood mitigation and control. With the development of remote sensing technology, scientists have been able to monitor floods on a large scale. However, there is no standard for flood assessment. One promising approach is to establish the standard of assessment according to each flooding area. To solve this problem, a "normal water extent" concept is proposed for special areas around rivers, lakes, reservoirs and dykes, which often suffer during the flood season. The objective of our research is to study the methodology for identifying normal water extent and for setting up a database, which can be used as a standard for monitoring and assessing floods. The procedure can be generalized as two steps. The first one is to identify the normal water extent by automatic extraction or human-computer interactive interpretation using Landsat 5 TM and NOAA/AVHRR images. The second step is to integrate the normal water extent for each flooding area into a database, with some related spatial data and remote sensing images. In our study, a database for normal water extent of seven large river basins in China was set up for monitoring the floods in China since 1999. The assessment results were utilized in several government ministries of China, such as the State Planning Committee, the Civil Administration Ministries, etc. The application shows that the normal water extent database can help to improve the efficiency of flood assessment and the accuracy of flood information, unifying the criteria of its assessment. It can be used as a feasible standard for assessment of occurring floods. In this paper, we show how to set up a normal water extent database and how to use it to monitor a flood.