On May 12th

2008

a magnitude of Richter 8.0 earthquake attacked Wenchuan in Sichuan Province

China

which caused fatal death and millions of people homeless.The landslides caused by earthquake damed some riverways in the mountainous areas

forming tens of quake lakes

among which the Tangjiashan Quake Lake was the largest one and the most dangerous to threaten the downriver residents.Therefore

it is urgent to find solutions to solve the problem of the quake lake for government.Fast and precisely calculation of quake lake water capacity is a key issue for solving the threat of it.Traditional capacity calculation methods

taking the water surface as a plane with a given water level

just consider the static capacity in which the water level is required to be monitored for a long time.Complex hydrodynamic model and complicated model inputs

which highly demand the computing resource and are compute-intensive

must be taken into consideration when calculating dynamic capacity.It cannot satisfy a fast process dealing with the emergence.In this paper

a pixel-based curved water surface method is proposed to calculate the total capacity including dynamic capacity with a natural curved water surface

and the technologies of Geographic Information System（GIS） and remote sensing are integrated in this method.The backwater area is extracted from a corrected geometrically SPOT-5 image

and then the riverway DEM is intersected to obtain the boundary of water body consisting of a set of points.A 3D curved water surface

which depicts the large ratio of slope for water surface in mountainous areas

can be draw out by interpolating these concrete points.Finally

capacity calculation is carried out based on a calculation model after interpolating the point boundary to a curved water surface.The model takes the space between the pixels on water surface and the riverway DEM as an underside-squared prism.The volume composed of riverway DEM and water surface are divided into many small prisms to calculate the capacity respectively.The total water capacity of the quake lake is obtained by summing up these volumes.Considering the calculation efficiency of this method

an improved

pixel-based river segmentation algorithm is proposed in this study.It is fully considered the rationality of pixel-based curved water surface method and the efficiency of the traditional static capacity calculation method.An experiment is carried out to implement these algorithms.At last

a comparison

among the ArcGIS method

the proposed methods including the pixel based curved water surface method and the improved pixel-based river segmentation method

is conducted to prove that the improved method is more acceptable for its calculation speed and accuracy.And it can be used for daily operation for monitoring the capacity of a lake or reservoir.