High velocity of flow channel in the bottom mat, mat extended length according to the cage height and maximum scour depth to determine.

This paper is based on the investigation of the fore people, makes use of 3s technologies, analyzes the bottom mat changed from the city expansion, which causes the fall of groundwater level.

A function expansion method as in Liu et al (2007) is used to formulate the mat-type VLFS floating on the wave surface over uneven sea bottom.