The enhancement of geomorphologic measurement using GIS

This study presents a methodology for using aerial photographs to improve the accuracy of the topographic survey data which are used to calculate water volumes in urban streams. First, a geographical information system spatial interpolation technique such as inverse distance weight and kriging was applied to construct the terrain morphology for sand-bars and grassed areas using cross-sectional survey data, and validation point data was used to estimate the accuracy of the created topographic data. The minimum distance method using aerial photographs was applied to efficiently extract sand-bar and grassed areas located within the river boundary, and the elevation value of extracted layers was allocated to the water level point value. Water volumes from topographic data derived from aerial photographs show an accuracy of 13% (in the sand-bar segment) and 12% (in the grass segment), compared with the water volume based on the original terrain data. Therefore, the river terrain analysis method using aerial photos is efficient in monitoring the sand-bar and grassed areas located, for example, downstream of dams during the flooding season, and also it can be applied in efficiently calculating water volumes.