Keywords: landslide, digital photogrammetry, digital terrain model (DTM).
abstract
After the serious 921-Tsau-Lin Earthquake, it's necessary and urgent to know the landslide condition and to handle the effectiveness of the silted earth mass on its upper and lower stream channel. Those data have been urgently concerned about engineering field. To integrate the aerial photogrammetric photograph, GIS and image processing software, and modeling 3-D image, drown range delineation, the overtopping height calculation and the storage water volume etc., we can finish the preprocessing operation. Next, to create the 10m*10m resolution DTM of the site before and after the earthquake. Finally, to overlap that coverage's we have finished, we can get the reliable volume of landslide.The purpose of this article is to make a complete introduce the results and some important procedures how we utilized the scientific technique of aerial photogrammetry, image processing and geographic information system etc. Finally, we made a real and complete record about the important digital information of Tsau-Lin landslide.
1.Introduction
A largest earthquake of this century in Taiwan occurred on September 21, 1999 and caused deaths of more than 2,000 human lives and loss of billions dollars worth in houses, buildings, roads, bridges and dams. This disastrous earthquake also induced 2,365 landslides and soil mass movements with total area of 14,000 ha. After the serious earthquake of central Taiwan, the biggest one, landslide dammed the Chin-Shui-Chi River and formed Tsau-Lin reservoir, it's necessary and urgent to know the landslide condition and to handle the effectiveness of the silted earth mass on its upper and lower stream channel and the mud disaster that may caused owing to the silted earth mass. Those data have been urgently concerned about by both research institute and engineering field such as: the location, area and the volume of the silted earth mass, the drown range of water, the over flow height, and the storage water volume. To integrate the aerial photogrammetric photograph, GIS and image processing software, and modeling 3-D image, drown range delineation, the over flow height calculation and the storage water volume etc., we can finish the preprocessing operation. Next, to create the 10m*10m resolution DTM of the site before and after the earthquake. Finally, to overlap that coverage's we have finished, we can get the reliable volume of silted earth mass.
The purpose of this article is to make a complete introduce the results and some important procedure how we utilized the scientific technique of aerial photogrammetry, image processing and geographic information system etc. and quickly to handle the field situation and processed the relative digital data. Finally, we made a real and complete record about the important digital information of Tsau-Lin landslide. The emergency treatment project to reduce the disaster can be determined helpfully and rapidly.
2.The history of Tsao-Ling landslide.
According to the documents, the Tsao-Ling landslides were decided by seismic and intense rainfall factors, the another factors were topography, soil, geology, and active fault zones.
An unusual series of events illustrating the formation and destruction of a landslide dam has been documented for the Tsao-Ling landslide in central Taiwan. This case demonstrates just how complex natural dam processes can be. In June 6,1862, a major earthquake triggered a landslide that dammed the Chin-Shui-Chi River. In 1898, the natural dam failed for unknown reasons. In December 17, 1941, a major earthquake formed another landslide dam, 140 m high, at the same location. In August 10, 1942, heavy rainfall caused reactivation of the landslide and the natural dam increased in height form 140 to 217 m. In May 1951, several days of intense rainfall led to the overtopping and failure of the natural dam. In the subsequent flood, 154 people were killed and 564 homes damaged. On August 15,1979, heavy rainfall again activated the landslide, which dammed the river with a natural barrier 90 m high. Heavy precipitation continued, and 9 days later, the landslide dam was overtopped and failed, causing severe flooding (Costa and Schuster 1988).
In September 21,1999, Richter scale 7.3 earthquake formed landslide dam again, the detailed landslide data were gathered rapidly by integrating aerial photogrammetry and GIS. The main data of Tsao-Ling Landslide are shown follow :
a. Deposit Height of Upstream:50m (EL.539.6m),
b. Area of Upstream Watershed:162Km
2 ,
c. Landslide Area:620ha,
d. Deposit Distance:5Km,
e. Landslide Volume:126 million M
3(Cut) and 150 million M
3(Fill),
f. Lake Volume:46 million M
3 ,
g. Overtopping Elevation:EL.539.6m,
h. Second pond volume:4.99 million M
3 for EL.520.4 overtopping, 3.4 million M
3 for EL.515 overtopping.
3. Processing of created DTM of before and after landslide
In order to compare the surface deformation before and after landslide, it's
rapid method to create the high resolution Images and DTM of the site, before and after the earthquake. We can compare, overlap, and calculate with these digital data conveniently and precisely. The detailed flow chat is shown as figure 1.
