Section 166(2)(a) in West Bengal Municipal (Building) Rules, 2007
(a)Proper slopes, not less than 1 : 60 shall be maintained all around a building for quick drainage of the entire plot as provided in this rule. Note.The possibilities of erosion or ground failure through ingress and percolation of water into soft ground or through joints and fissures in the soil crust shall be prevented by suitable surface protection measures such as surface grouting, stone pitching, planting of small plants and grass, so as to protect and make the surface impervious in accordance with the provisions of the BIS Codes, specially the minimum distance from provision required to be maintained for planting trees;