A particular porosity method named "slot method" is implemented in a depth-integrated shallow water flow model (DIVAST) to simulate wetting and drying processes. Discussed is the relationship between the shape factors of the "slot" and the preset depth used in "wetting-drying" algorithm. Two typical tests are conducted to examine the performance of the method with the effect of the shape factors of the "slot" being checked in detail in the first test. Numerical results demonstrate that: 1) no additional effort to improve the finite difference scheme is needed to implement "slot method" in DIVAST, and 2) "slot method" will simulate wetting and drying processes correctly if the shape factors of the "slot" being selected properly.